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@c ===========================================================================
@c
@c This file was generated with po4a. Translate the source file.
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@c -*-texinfo-*-

@c %**start of header
@setfilename guix.zh_CN.info
@documentencoding UTF-8
@settitle GNU Guix 参考手册
@c %**end of header

@include version-zh_CN.texi

@c Identifier of the OpenPGP key used to sign tarballs and such.
@set OPENPGP-SIGNING-KEY-ID 27D586A4F8900854329FF09F1260E46482E63562
@set OPENPGP-SIGNING-KEY-URL https://sv.gnu.org/people/viewgpg.php?user_id=127547

@c Base URL for downloads.
@set BASE-URL https://ftp.gnu.org/gnu/guix

@c The official substitute server used by default.
@set SUBSTITUTE-SERVER ci.guix.gnu.org
@set SUBSTITUTE-URL https://@value{SUBSTITUTE-SERVER}

@copying
Copyright @copyright{} 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020,
2021 Ludovic Courtès@* Copyright @copyright{} 2013, 2014, 2016 Andreas
Enge@* Copyright @copyright{} 2013 Nikita Karetnikov@* Copyright
@copyright{} 2014, 2015, 2016 Alex Kost@* Copyright @copyright{} 2015, 2016
Mathieu Lirzin@* Copyright @copyright{} 2014 Pierre-Antoine Rault@*
Copyright @copyright{} 2015 Taylan Ulrich Bayırlı/Kammer@* Copyright
@copyright{} 2015, 2016, 2017, 2019, 2020, 2021 Leo Famulari@* Copyright
@copyright{} 2015, 2016, 2017, 2018, 2019, 2020 Ricardo Wurmus@* Copyright
@copyright{} 2016 Ben Woodcroft@* Copyright @copyright{} 2016, 2017, 2018,
2021 Chris Marusich@* Copyright @copyright{} 2016, 2017, 2018, 2019, 2020,
2021 Efraim Flashner@* Copyright @copyright{} 2016 John Darrington@*
Copyright @copyright{} 2016, 2017 Nikita Gillmann@* Copyright @copyright{}
2016, 2017, 2018, 2019, 2020 Jan Nieuwenhuizen@* Copyright @copyright{}
2016, 2017, 2018, 2019, 2020 Julien Lepiller@* Copyright @copyright{} 2016
Alex ter Weele@* Copyright @copyright{} 2016, 2017, 2018, 2019, 2020, 2021
Christopher Baines@* Copyright @copyright{} 2017, 2018, 2019 Clément
Lassieur@* Copyright @copyright{} 2017, 2018, 2020, 2021 Mathieu Othacehe@*
Copyright @copyright{} 2017 Federico Beffa@* Copyright @copyright{} 2017,
2018 Carlo Zancanaro@* Copyright @copyright{} 2017 Thomas Danckaert@*
Copyright @copyright{} 2017 humanitiesNerd@* Copyright @copyright{} 2017,
2021 Christopher Lemmer Webber@* Copyright @copyright{} 2017, 2018, 2019,
2020 Marius Bakke@* Copyright @copyright{} 2017, 2019, 2020 Hartmut Goebel@*
Copyright @copyright{} 2017, 2019, 2020, 2021 Maxim Cournoyer@* Copyright
@copyright{} 2017, 2018, 2019, 2020, 2021 Tobias Geerinckx-Rice@* Copyright
@copyright{} 2017 George Clemmer@* Copyright @copyright{} 2017 Andy Wingo@*
Copyright @copyright{} 2017, 2018, 2019, 2020 Arun Isaac@* Copyright
@copyright{} 2017 nee@* Copyright @copyright{} 2018 Rutger Helling@*
Copyright @copyright{} 2018, 2021 Oleg Pykhalov@* Copyright @copyright{}
2018 Mike Gerwitz@* Copyright @copyright{} 2018 Pierre-Antoine Rouby@*
Copyright @copyright{} 2018, 2019 Gábor Boskovits@* Copyright @copyright{}
2018, 2019, 2020 Florian Pelz@* Copyright @copyright{} 2018 Laura Lazzati@*
Copyright @copyright{} 2018 Alex Vong@* Copyright @copyright{} 2019 Josh
Holland@* Copyright @copyright{} 2019, 2020 Diego Nicola Barbato@* Copyright
@copyright{} 2019 Ivan Petkov@* Copyright @copyright{} 2019 Jakob
L. Kreuze@* Copyright @copyright{} 2019 Kyle Andrews@* Copyright
@copyright{} 2019 Alex Griffin@* Copyright @copyright{} 2019, 2020 Guillaume
Le Vaillant@* Copyright @copyright{} 2020 Leo Prikler@* Copyright
@copyright{} 2019, 2020 Simon Tournier@* Copyright @copyright{} 2020 Wiktor
Żelazny@* Copyright @copyright{} 2020 Damien Cassou@* Copyright @copyright{}
2020 Jakub Kądziołka@* Copyright @copyright{} 2020 Jack Hill@* Copyright
@copyright{} 2020 Naga Malleswari@* Copyright @copyright{} 2020 Brice
Waegeneire@* Copyright @copyright{} 2020 R Veera Kumar@* Copyright
@copyright{} 2020 Pierre Langlois@* Copyright @copyright{} 2020 pinoaffe@*
Copyright @copyright{} 2020 André Batista@* Copyright @copyright{} 2020,
2021 Alexandru-Sergiu Marton@* Copyright @copyright{} 2020 raingloom@*
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@copyright{} 2020 Edgar Vincent@* Copyright @copyright{} 2021 Maxime Devos@*

Permission is granted to copy, distribute and/or modify this document under
the terms of the GNU Free Documentation License, Version 1.3 or any later
version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the
license is included in the section entitled ``GNU Free Documentation
License''.
@end copying

@dircategory 系统管理
@direntry
* Guix：（guix）.         管理安装的软件和系统配置。
* guix package：调用guix package.  安装、删除和升级软件包。
* guix gc：调用guix gc.   回收不使用的硬盘空间。
* guix pull：调用guix pull.  更新可用的软件包列表。
* guix system：调用guix system.  管理操作系统配置。
* guix deploy: (guix)Invoking guix deploy.  Manage operating system 
                                              configurations for remote hosts.
@end direntry

@dircategory 软件开发
@direntry
* guix environment：调用guix environment.  用Guix构建开发环境。
* guix build：（guix）调用guix build.  构建软件包。
* guix pack：（guix）调用guix pack.  创建二进制bundle。
@end direntry

@titlepage
@title GNU Guix 参考手册
@subtitle 使用GNU Guix函数式包管理器
@author GNU Guix开发者

@page
@vskip 0pt plus 1filll
版本@value{EDITION} @* @value{UPDATED} @*

@insertcopying
@end titlepage

@contents

@c *********************************************************************
@node Top
@top GNU Guix

这份文档介绍GNU Guix版本@value{VERSION}，一个为GNU系统编写的函数式包管理器。

@c TRANSLATORS: You can replace the following paragraph with information on
@c how to join your own translation team and how to report issues with the
@c translation.
This manual is also available in Simplified Chinese (@pxref{Top,,,
guix.zh_CN, GNU Guix参考手册}), French (@pxref{Top,,, guix.fr, Manuel de
référence de GNU Guix}), German (@pxref{Top,,, guix.de, Referenzhandbuch zu
GNU Guix}), Spanish (@pxref{Top,,, guix.es, Manual de referencia de GNU
Guix}), and Russian (@pxref{Top,,, guix.ru, Руководство GNU Guix}).  If you
would like to translate it in your native language, consider joining
@uref{https://translate.fedoraproject.org/projects/guix/documentation-manual,
Weblate}.

@menu
* 介绍::                   Guix是关于什么的？
* 安装::                   安装Guix。
* 系统安装::             安装整个操作系统。
* 入门::                   Your first steps.
* 软件包管理::          软件包安装、升级等。
* 通道::                   定制软件包集合。
* 开发::                   Guix辅助的软件开发。
* 编程接口::             在Scheme里使用Guix。
* 工具::                   软件包管理命令。
* 系统配置::             配置操作系统。
* 文档::                   浏览软件用户手册。
* 安装调试文件::       为调试工具提供输入。
* 安全更新::             快速部署安全补丁。
* 引导::                   从头开始构建GNU/Linux。
* 移植::                   以别的平台或内核为目标。
* 贡献::                   你需要帮助！

* 致谢::                   感谢！
* GNU自由文档许可证::  这个用户手册的许可证。
* 概念索引::             概念。
* 编程索引::             数据类型、函数和变量。

@detailmenu
 －－－详细的章节列表－－－



介绍



* 以Guix的方式管理软件::  特殊的地方。
* GNU发行版::             软件包和工具。

安装



* 二进制文件安装::    立刻运行Guix！
* 需求::                   构建和运行Guix需要的软件。
* 运行测试套件::       测试Guix。
* 设置后台进程::       准备“构建后台进程”的环境。
* 调用guix-daemon::        运行“构建后台进程”
* 设置应用程序::       应用程序相关的设置。
* Upgrading Guix::           升级 Guix 及其构建守护进程。

设置后台进程



* 设置构建环境::       准备隔离的构建环境。
* 下发工作给后台进程的设置::  下发构建工作给远程的机器。
* SELinux的支持::         为后台进程使用SELinux规则。

系统安装



* 限制::                   你可以期待什么。
* 硬件的考虑::          支持的硬件。
* U盘和DVD安装::         准备安装介质。
* 准备安装::             网络、分区等。
* 指导的图形安装::    简单的图形安装。
* 手动安装::             适合巫师的手动安装。
* 系统安装之后::       当安装成功后。
* 在虚拟机里安装 Guix::  Guix系统游乐场。
* 构建安装镜像::       这是怎样实现的。

手动安装



* 键盘布局、网络和分区::  初始设置。
* 继续安装步骤::       安装。

软件包管理



* 功能::                   Guix怎样让你的生活更美好。
* 调用guix package::       软件包安装，移除等。
* substitutes::              下载构建好的二进制文件。
* 有多个输出的软件包::  单个输入多个输出的软件包。
* 调用guix gc::            运行垃圾回收器。
* 调用guix pull::          获取最新的Guix和发行版。
* Invoking guix time-machine::  Running an older revision of Guix.
* Inferiors::                和其它版本的Guix交互。
* 调用guix describe::      显示你的Guix版本信息。
* 调用guix archive::       导出和导入仓库文件。

substitutes



* 官方的substitute服务器::  substitute的一个特殊来源。
* 授权substitute服务器。::  怎么开启或关闭substitute。
* Getting Substitutes from Other Servers::  Substitute diversity.
* 验证substitute::         Guix怎样验证substitute。
* 代理设置::             怎样通过代理获取substitute。
* substitute失败::         当substitute失败时会发生什么。
* 关于信任二进制文件::  你怎么能信任二进制的 blob 呢？

通道



* Specifying Additional Channels::  拓展软件包集合。
* Using a Custom Guix Channel::  Using a customized Guix.
* Replicating Guix::         Running the @emph{exact same} Guix.
* Channel Authentication::   How Guix verifies what it fetches.
* Channels with Substitutes::  Using channels with available substitutes.
* 创建一个频道::       How to write your custom channel.
* Package Modules in a Sub-directory::  Specifying the channel's package 
                                          modules location.
* Declaring Channel Dependencies::  How to depend on other channels.
* Specifying Channel Authorizations::  Defining channel authors 
                                         authorizations.
* Primary URL::              Distinguishing mirror to original.
* Writing Channel News::     Communicating information to channel's users.

开发



* 调用guix environment::   设置开发环境。
* 调用guix pack::          创建软件bundle。
* The GCC toolchain::        Working with languages supported by GCC.
* Invoking guix git authenticate::  Authenticating Git repositories.

编程接口



* 软件包模块::          从程序员的角度看软件包。
* 定义软件包::          定义新软件包。
* Defining Package Variants::  Customizing packages.
* 构建系统::             指定如何构建软件包。
* Build Phases::             Phases of the build process of a package.
* Build Utilities::          Helpers for your package definitions and more.
* 仓库::                   操纵软件包仓库。
* Derivations::              软件包derivation的底层接口。
* 仓库monad::              仓库的纯函数式接口。
* G-表达式::              操纵构建表达式。
* 调用guix repl::          Programming Guix in Guile.

定义软件包



* 软件包引用::          软件包数据类型。
* origin参考手册::       origin数据类型。

工具



* 调用guix build::         用命令行构建软件包。
* 调用guix edit。::       编辑软件包定义。
* 调用guix download::      下载一个文件并打印它的hash。
* 调用guix hash::          计算一个文件的密码学hash。
* 调用guix import::        导入软件包定义。
* 调用guix refresh::       更新软件包定义。
* 调用guix lint::          从软件包定义里寻找错误。
* 调用guix size::          分析硬盘使用情况。
* 调用guix graph::         展示软件包的关系图。
* 调用guix publish::       分享substitute。
* 调用guix challenge::     挑战subtitute服务器。
* 调用guix copy::          复制到远程的仓库，或从远程的仓库复制。
* 调用guix container::     进程隔离。
* 调用guix weather::       评估substitute的可用性。
* 调用guix processes::     列出客户端进程。

调用@command{guix build}



* 普通的构建选项::    大部分命令的构建选项。
* 软件包变换选项。::  创建软件包的变体。
* 额外的构建选项::    只属于'guix build'的选项。
* 调试构建错误::       真实的打包经验。

系统配置



* 使用配置系统::       定制你的GNU系统。
* 操作系统参考::       操作系统声明详情。
* 文件系统::             设置文件系统挂载。
* 映射的设备::          块设备额外的处理。
* 用户帐号::             指定用户帐号。
* 键盘布局::             系统怎样理解按键。
* 区域::                   语言和文化惯例设置。
* 服务::                   指定系统服务。
* setuid程序::             以root权限运行的程序。
* X.509证书::              认证HTTPS服务器。
* Name Service Switch::      设置libc的name service switch。
* 初始的内存虚拟硬盘::  Linux-Libre引导。
* 引导设置::             设置引导程序。
* 调用guix system::        实例化一个系统配置。
* 调用 guix deploy::       Deploying a system configuration to a remote 
                               host.
* 在虚拟机里运行Guix::  怎样在虚拟机里运行Guix。
* 定义服务::             添加新的服务定义。

服务



* 基础服务::             必要的系统服务。
* 执行计划任务::       mcron服务。
* 日志轮替::             rottlog服务。
* 网络服务::             网络设置，SSH后台进程，等
* Unattended Upgrades::      Automated system upgrades.
* X窗口::                  图形显示器。
* 打印服务::             本地和远程打印机的支持。
* 桌面服务::             D-Bus和桌面服务。
* 声音服务::             ALSA和Pulseaudio服务。
* 数据库服务::          SQL数据库，键值仓库，等
* 邮件服务::             IMAP，POP3，SMTP，等
* 消息服务::             消息服务。
* 电话服务::             电话服务。
* 监控服务::             监控服务。
* Kerberos服务::           Kerberos服务。
* LDAP Services::            LDAP services.
* Web服务::                Web服务。
* 证书服务::             Let's Encrypt TLS证书。
* DNS服务::                DNS后台进程。
* VPN服务::                VPN后台进程。
* 网络文件系统::       网络文件系统相关的服务。
* 持续集成::             Cuirass and Laminar services.
* 电源管理服务::       延长电池寿命。
* 音频服务::             MPD。
* 虚拟化服务::          虚拟化服务。
* 版本控制服务::       远程访问Git仓库。
* 游戏服务::             游戏服务器。
* PAM Mount Service::        Service to mount volumes when logging in.
* Guix Services::            Services relating specifically to Guix.
* Linux Services::           Services tied to the Linux kernel.
* Hurd Services::            Services specific for a Hurd System.
* 其它各种服务::       其它服务。

定义服务



* 合成服务::             服务合成的模型。
* 服务类型和服务::    类型和服务。
* 服务参考::             API参考。
* Shepherd服务::           一种特别的服务。

安装调试文件



* Separate Debug Info::      Installing 'debug' outputs.
* Rebuilding Debug Info::    Building missing debug info.

引导



* Reduced Binary Seed Bootstrap::  A Bootstrap worthy of GNU.
* Preparing to Use the Bootstrap Binaries::  Building that what matters 
                                               most.

@end detailmenu
@end menu

@c *********************************************************************
@node 介绍
@chapter 介绍

@cindex 目的
GNU
Guix@footnote{``Guix''读做``geeks''，或``ɡiːks''（国际音标）}是GNU系统的包管理器和发行版。Guix让无特权的用户可以轻松地安装，升级，或删除软件包，回滚到前一个软件包集合，从源代码构建软件包，及辅助软件环境的创建和维护。

@cindex Guix系统
@cindex GuixSD，现在称为Guix系统
@cindex Guix系统发行版，现在称为Guix系统
你可以在现有的GNU/Linux发行版上安装GNU@tie{}Guix（@pxref{安装}），Guix可以补充已有的工具，并且不会和它们产生冲突。或者你可以把它当作独立的操作系统发行版（@dfn{Guix@tie{}系统}@footnote{我们以前把Guix系统称为``Guix系统发行版''或``GuixSD''。我们现在觉得把一切都统一在``Guix''的旗帜下更合理，因为，毕竟即使在别的发行版上你也可以随时通过@command{guix
system}命令获得Guix系统}）。@xref{GNU发行版}.

@menu
* 以Guix的方式管理软件::  特殊的地方。
* GNU发行版::             软件包和工具。
@end menu

@node 以Guix的方式管理软件
@section 以Guix的方式管理软件

@cindex 用户界面
Guix provides a command-line package management interface (@pxref{软件包管理}), tools to help with software development (@pxref{开发}),
command-line utilities for more advanced usage (@pxref{工具}), as well
as Scheme programming interfaces (@pxref{编程接口}).
@cindex 构建后台进程
@dfn{构建后台进程}为用户构建软件包（@pxref{设置后台进程}），及从授权的源（@pxref{substitutes}）下载预构建的二进制文件。

@cindex 发行版的扩展性
@cindex 定制软件包
Guix包含很多GNU和非GNU的软件包定义，所有的这些软件包都@uref{https://www.gnu.org/philosophy/free-sw.html,
尊重用户的自由}。它是@emph{可扩展的}：用户可以编写自己的软件包定义（@pxref{定义软件包}），并且把它们作为独立的软件包模块@pxref{软件包模块}。它也是@emph{可定制的}：用户可以从现有的软件包定义衍生出特殊的软件包，包括从命令行（@pxref{软件包变换选项。}）。

@cindex 函数式包管理器
@cindex 隔离
在底层，Guix实现了由Nix（@pxref{致谢}）开创的@dfn{函数式包管理器}。在Guix里，软件包构建和安装过程被视为数学意义上的@emph{函数}。函数获取输入，如构建脚本、编译器和库，并且返回一个安装好的软件包。作为一个纯函数，它的结果只取决于它的输入－－例如，它不能引用没有作为显式输入传入的软件和脚本。当传入特定的输入时，一个构建函数总是得到相同的结果。它不能以任何方式修改运行系统的环境，例如，它不能创建，修改，或删除构建和安装环境之外的文件夹。这是通过在隔离的环境（@dfn{容器}）里运行构建进程实现的，在这个环境里只能访问到显式的输入。

@cindex 仓库
软件包构建函数的结果被@dfn{缓存}在文件系统里的一个叫做@dfn{仓库}（@pxref{仓库}）的特殊文件夹内。每个软件包都被安装在仓库（默认在@file{/gnu/store}）里的一个独立的文件夹内。这个文件夹的名字含有用于构建这个软件包的所有输入的hash，所以，修改输入会得到一个不同的文件夹名。

这种手段是实现Guix的突出功能的基础：对事务型软件包升级和回滚的支持，每个用户独立的安装，软件包垃圾回收@pxref{功能}。


@node GNU发行版
@section GNU发行版

@cindex Guix系统
Guix提供了一个GNU系统发行版，这个发新版只包含自由软件@footnote{这里的“自由”指的是@url{https://www.gnu.org/philosophy/free-sw.html,软件提供给用户的自由}。}。这个发行版可以独立安装（@pxref{系统安装}），但是把Guix安装为一个已经安装好的GNU/Linux系统的包管理器也是可行的（@pxref{安装}）。当我们需要区分这两者时，我们把独立的发行版称为“Guix系统”。

这个发行版提供了GNU核心软件包，如libc、gcc和Binutils，以及很多GNU和非GNU应用程序。可用的软件包的完整列表可以在@url{https://www.gnu.org/software/guix/packages,on-line}浏览，或者通过运行@command{guix
package}（@pxref{调用guix package}）获得：

@example
guix package --list-available
@end example

我们的目标是提供一个基于Linux和其它GNU变体的可用的100%自由的软件发行版，我们的重点是推广和紧密集成GNU组件，以及强调帮助用户行使那些自由的程序和工具。

目前这些平台提供软件包：

@table @code

@item x86_64-linux
Intel/AMD @code{x86_64} 架构，Linux-Libre 内核。

@item i686-linux
Intel 32 位架构（IA32)，Linux-Libre 内核。

@item armhf-linux
ARMv7-A架构，带硬件浮点数、Thumb-2和NEON扩展，EABI硬件浮点数应用二进制接口（ABI），和Linux-Libre内核。

@item aarch64-linux
little-endian 64-bit ARMv8-A processors, Linux-Libre kernel.

@item i586-gnu
@uref{https://hurd.gnu.org, GNU/Hurd} on the Intel 32-bit architecture
(IA32).

This configuration is experimental and under development.  The easiest way
for you to give it a try is by setting up an instance of
@code{hurd-vm-service-type} on your GNU/Linux machine
(@pxref{transparent-emulation-qemu, @code{hurd-vm-service-type}}).
@xref{贡献}, on how to help!

@item mips64el-linux (deprecated)
little-endian 64-bit MIPS processors, specifically the Loongson series, n32
ABI, and Linux-Libre kernel.  This configuration is no longer fully
supported; in particular, there is no ongoing work to ensure that this
architecture still works.  Should someone decide they wish to revive this
architecture then the code is still available.

@item powerpc64le-linux
little-endian 64-bit Power ISA processors, Linux-Libre kernel.  This
includes POWER9 systems such as the
@uref{https://www.fsf.org/news/talos-ii-mainboard-and-talos-ii-lite-mainboard-now-fsf-certified-to-respect-your-freedom,
RYF Talos II mainboard}. This platform is available as a "technology
preview": although it is supported, substitutes are not yet available from
the build farm (@pxref{substitutes}), and some packages may fail to build
(@pxref{Tracking Bugs and Patches}).  That said, the Guix community is
actively working on improving this support, and now is a great time to try
it and get involved!

@end table

在Guix系统里，你@emph{声明}操作系统所有方面的配置，然后Guix以事务型的，可重复的，和无状态的方式解决实例化配置的问题（@pxref{系统配置}）。Guix系统使用Linux-Libre内核，Shepherd初始化系统@pxref{介绍,,,
shepherd, GNU Shepherd用户手册}，知名的GNU工具和工具链，以及你可选的图形界面环境和系统服务。

Guix System is available on all the above platforms except
@code{mips64el-linux} and @code{powerpc64le-linux}.

@noindent
关于移植到其它架构或内核的信息，@pxref{移植}。

构建这个发行版需要努力合作，欢迎你加入！关于你可以怎样提供帮助的信息，@xref{贡献}。


@c *********************************************************************
@node 安装
@chapter 安装

@cindex 安装Guix

@quotation 注
我们推荐使用@uref{https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh,
shell安装脚本}在已有的GNU/Linux系统（即@dfn{foreign
distro}）上安装Guix。@footnote{这个小节是关于安装包管理器的，可以在GNU/Linux系统上完成。如果你想安装完整的GNU操作系统，@pxref{系统安装}。}这个脚本自动下载、安装并且初始化Guix，它需要以root用户身份运行。
@end quotation

@cindex 别的发行版
@cindex 和foreign distro相关的文件夹
在foreign
distro上安装时，GNU@tie{}Guix可以在不引起冲突的前提下补充现有的工具。它的数据只存放在两个文件夹里，通常是@file{/gnu/store}和@file{/var/guix}；系统上的其它文件，如@file{/etc}，不会被修改。

一旦安装好了，可以通过运行@command{guix pull}升级Guix（@pxref{调用guix pull}）。

如果你希望手动执行安装步骤，或者想改变安装步骤，接下来这些小节会很有用。它们介绍Guix的软件依赖，以及如何手动安装和使用Guix。

@menu
* 二进制文件安装::    立刻运行Guix！
* 需求::                   构建和运行Guix需要的软件。
* 运行测试套件::       测试Guix。
* 设置后台进程::       准备“构建后台进程”的环境。
* 调用guix-daemon::        运行“构建后台进程”
* 设置应用程序::       应用程序相关的设置。
* Upgrading Guix::           升级 Guix 及其构建守护进程。
@end menu

@node 二进制文件安装
@section 二进制文件安装

@cindex 用二进制文件安装Guix
@cindex 安装脚本
这个小节介绍如何在任意的系统上用独立的Guix二进制文件包安装Guix和它的依赖。这通常比从源代码安装更快，下一小节会介绍如何从源代码安装。唯一的需求是有GNU@tie{}tar和Xz。

@c Note duplicated from the ``Installation'' node.
@quotation 注
We recommend the use of this
@uref{https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh,
shell installer script}.  The script automates the download, installation,
and initial configuration steps described below.  It should be run as the
root user.  As root, you can thus run this:

@example
cd /tmp
wget https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh
chmod +x guix-install.sh
./guix-install.sh
@end example

When you're done, @pxref{设置应用程序} for extra configuration you
might need, and @ref{入门} for your first steps!
@end quotation

安装步骤如下：

@enumerate
@item
@cindex 下载Guix二进制文件
Download the binary tarball from
@indicateurl{@value{BASE-URL}/guix-binary-@value{VERSION}.x86_64-linux.tar.xz},
where @code{x86_64-linux} can be replaced with @code{i686-linux} for an
@code{i686} (32-bits) machine already running the kernel Linux, and so on
(@pxref{GNU发行版}).

@c The following is somewhat duplicated in ``System Installation''.
请确保下载相关的@file{.sig}文件，并且用它验证文件包的可靠性，方法如下：

@example
$ wget @value{BASE-URL}/guix-binary-@value{VERSION}.x86_64-linux.tar.xz.sig
$ gpg --verify guix-binary-@value{VERSION}.x86_64-linux.tar.xz.sig
@end example

如果那个命令因为缺少所需的公钥而失败了，那么用这个命令导入它：

@example
$ wget '@value{OPENPGP-SIGNING-KEY-URL}' \
      -qO - | gpg --import -
@end example

@noindent
再次运行@code{gpg --verify}命令。

Take note that a warning like ``This key is not certified with a trusted
signature!'' is normal.

@c end authentication part

@item
现在你需要成为@code{root}用户。基于你的发行版，你可能需要执行@code{su -}或@code{sudo
-i}。以@code{root}用户身份，执行：

@example
# cd /tmp
# tar --warning=no-timestamp -xf \
     /path/to/guix-binary-@value{VERSION}.x86_64-linux.tar.xz
# mv var/guix /var/ && mv gnu /
@end example

This creates @file{/gnu/store} (@pxref{仓库}) and @file{/var/guix}.
The latter contains a ready-to-use profile for @code{root} (see next step).

@emph{不要}在一个正常的Guix系统上解压这个文件包，因为那会把现有的重要的文件覆盖。

The @option{--warning=no-timestamp} option makes sure GNU@tie{}tar does not
emit warnings about ``implausibly old time stamps'' (such warnings were
triggered by GNU@tie{}tar 1.26 and older; recent versions are fine).  They
stem from the fact that all the files in the archive have their modification
time set to 1 (which means January 1st, 1970).  This is done on purpose to
make sure the archive content is independent of its creation time, thus
making it reproducible.

@item
使profile出现在@file{~root/.config/guix/current}，这是@command{guix
pull}安装更新的位置（@pxref{调用guix pull}）：

@example
# mkdir -p ~root/.config/guix
# ln -sf /var/guix/profiles/per-user/root/current-guix \
         ~root/.config/guix/current
@end example

Source @file{etc/profile} to augment @env{PATH} and other relevant
environment variables:

@example
# GUIX_PROFILE="`echo ~root`/.config/guix/current" ; \
  source $GUIX_PROFILE/etc/profile
@end example

@item
像下面解释的那样为“构建用户”创建用户组和用户（@pxref{设置构建环境}）。

@item
运行后台进程，并设置为开机自启动。

如果你的主机的发行版使用systemd init系统，可以用这些命令：

@c Versions of systemd that supported symlinked service files are not
@c yet widely deployed, so we should suggest that users copy the service
@c files into place.
@c
@c See this thread for more information:
@c https://lists.gnu.org/archive/html/guix-devel/2017-01/msg01199.html

@example
# cp ~root/.config/guix/current/lib/systemd/system/gnu-store.mount \
     ~root/.config/guix/current/lib/systemd/system/guix-daemon.service \
     /etc/systemd/system/
# systemctl enable --now gnu-store.mount guix-daemon
@end example

如果你的主机的发行版使用Upstart init系统：

@example
# initctl reload-configuration
# cp ~root/.config/guix/current/lib/upstart/system/guix-daemon.conf \
     /etc/init/
# start guix-daemon
@end example

此外，你可以手动启动后台进程：

@example
# ~root/.config/guix/current/bin/guix-daemon \
       --build-users-group=guixbuild
@end example

@item
使机器上的其他用户也可以使用@command{guix}命令：

@example
# mkdir -p /usr/local/bin
# cd /usr/local/bin
# ln -s /var/guix/profiles/per-user/root/current-guix/bin/guix
@end example

最好让这个用户手册的Info版也可以被访问：

@example
# mkdir -p /usr/local/share/info
# cd /usr/local/share/info
# for i in /var/guix/profiles/per-user/root/current-guix/share/info/* ;
  do ln -s $i ; done
@end example

That way, assuming @file{/usr/local/share/info} is in the search path,
running @command{info guix} will open this manual (@pxref{Other Info
Directories,,, texinfo, GNU Texinfo}, for more details on changing the Info
search path).

@item
@cindex substitutes，对其授权
为了使用@code{@value{SUBSTITUTE-SERVER}}或其镜像的substitute（@pxref{substitutes}），对其授权：

@example
# guix archive --authorize < \
     ~root/.config/guix/current/share/guix/@value{SUBSTITUTE-SERVER}.pub
@end example

@item
每个用户可能需要执行一些额外的步骤以使各自的Guix环境可用，@pxref{设置应用程序}。
@end enumerate

瞧，安装完成了！

你可以通过给root profile安装一个软件包来确认Guix可以正常工作。

@example
# guix install hello
@end example

二进制安装包可以通过在Guix源代码树里运行下面这些命令来重现和验证：

@example
make guix-binary.@var{系统}.tar.xz
@end example

@noindent
...@: 这个命令会执行：

@example
guix pack -s @var{系统} --localstatedir \
  --profile-name=current-guix guix
@end example

@xref{调用guix pack}，了解这个方便的工具。

@node 需求
@section 需求

这个小节列举了从源代码构建Guix的需求。构建Guix的步骤和其它GNU软件相同，这里不介绍。请阅读Guix源代码树里的@file{README}和@file{INSTALL}文件以了解更多的信息。

@cindex 官方网站
GNU Guix可以从它的网站下载@url{https://www.gnu.org/software/guix/}。

GNU Guix依赖这些软件包：

@itemize
@item @url{https://gnu.org/software/guile/, GNU Guile}, version 3.0.x or
2.2.x;
@item @url{https://notabug.org/cwebber/guile-gcrypt, Guile-Gcrypt}，版本
0.1.0或更新；
@item
@uref{https://gnutls.org/, GnuTLS}，特别是它的Guile接口（@pxref{Guile Preparations,
怎样为Guile安装GnuTLS接口,, gnutls-guile, GnuTLS-Guile}）；
@item
@uref{https://notabug.org/guile-sqlite3/guile-sqlite3,
Guile-SQLite3}，版本0.1.0或更新；
@item @uref{https://notabug.org/guile-zlib/guile-zlib, Guile-zlib},
version 0.1.0 or later;
@item @uref{https://notabug.org/guile-lzlib/guile-lzlib, Guile-lzlib};
@item @uref{https://www.nongnu.org/guile-avahi/, Guile-Avahi};
@item
@c FIXME: We need the #:fetch-options parameter of 'submodule-update',
@c which appeared in 0.5.0.  Change below after string freeze.
@uref{https://gitlab.com/guile-git/guile-git, Guile-Git}, version 0.3.0 or
later;
@item @uref{https://savannah.nongnu.org/projects/guile-json/, Guile-JSON}
4.3.0 or later;
@item @url{https://www.gnu.org/software/make/, GNU Make}。
@end itemize

这些依赖是可选的：

@itemize
@item
@c Note: We need at least 0.13.0 for #:nodelay.
Support for build offloading (@pxref{下发工作给后台进程的设置}) and
@command{guix copy} (@pxref{调用guix copy}) depends on
@uref{https://github.com/artyom-poptsov/guile-ssh, Guile-SSH}, version
0.13.0 or later.

@item
@uref{https://notabug.org/guile-zstd/guile-zstd, Guile-zstd}, for zstd
compression and decompression in @command{guix publish} and for substitutes
(@pxref{调用guix publish}).

@item
@uref{https://ngyro.com/software/guile-semver.html, Guile-Semver} for the
@code{crate} importer (@pxref{调用guix import}).

@item
@uref{https://www.nongnu.org/guile-lib/doc/ref/htmlprag/, Guile-Lib} for the
@code{go} importer (@pxref{调用guix import}) and for some of the
``updaters'' (@pxref{调用guix refresh}).

@item
当@url{http://www.bzip.org, libbz2}存在时，@command{guix-daemon}可以用它压缩构建日志。
@end itemize

Unless @option{--disable-daemon} was passed to @command{configure}, the
following packages are also needed:

@itemize
@item @url{https://gnupg.org/, GNU libgcrypt}；
@item @url{https://sqlite.org, SQLite 3}；
@item @url{https://gcc.gnu.org, GCC's g++}，支持
C++11标准。
@end itemize

@cindex 状态文件夹
When configuring Guix on a system that already has a Guix installation, be
sure to specify the same state directory as the existing installation using
the @option{--localstatedir} option of the @command{configure} script
(@pxref{Directory Variables, @code{localstatedir},, standards, GNU Coding
Standards}).  Usually, this @var{localstatedir} option is set to the value
@file{/var}.  The @command{configure} script protects against unintended
misconfiguration of @var{localstatedir} so you do not inadvertently corrupt
your store (@pxref{仓库}).

@node 运行测试套件
@section 运行测试套件

@cindex 测试套件
成功执行@command{configure}和@code{make}之后，最好运行测试套件。它可以帮助查找设置和环境的错误，或者是Guix自身的bug－－并且，报告测试错误是帮助改进软件的好方法。输入下面的命令以执行测试套件。

@example
make check
@end example

测试用例可以并行运行：你可以用GNU@tie{}make的@code{-j}参数来加速运行。才一台较新的机器上第一次运行可能会花几分钟，后续的运行会更快，因为为测试创建的仓库已经包含了各种缓存。

你还可以通过定义makefile的@code{TESTS}变量只运行测试的一个子集：

@example
make check TESTS="tests/store.scm tests/cpio.scm"
@end example

默认情况下，测试结果只展示到文件层级。为了看每个独立的测试用例的详情，可以像这样定义@code{SCM_LOG_DRIVER_FLAGS}
makefile变量：

@example
make check TESTS="tests/base64.scm" SCM_LOG_DRIVER_FLAGS="--brief=no"
@end example

The underlying SRFI 64 custom Automake test driver used for the 'check' test
suite (located at @file{build-aux/test-driver.scm}) also allows selecting
which test cases to run at a finer level, via its @option{--select} and
@option{--exclude} options.  Here's an example, to run all the test cases
from the @file{tests/packages.scm} test file whose names start with
``transaction-upgrade-entry'':

@example
export SCM_LOG_DRIVER_FLAGS="--select=^transaction-upgrade-entry"
make check TESTS="tests/packages.scm"
@end example

Those wishing to inspect the results of failed tests directly from the
command line can add the @option{--errors-only=yes} option to the
@code{SCM_LOG_DRIVER_FLAGS} makefile variable and set the @code{VERBOSE}
Automake makefile variable, as in:

@example
make check SCM_LOG_DRIVER_FLAGS="--brief=no --errors-only=yes" VERBOSE=1
@end example

The @option{--show-duration=yes} option can be used to print the duration of
the individual test cases, when used in combination with
@option{--brief=no}:

@example
make check SCM_LOG_DRIVER_FLAGS="--brief=no --show-duration=yes"
@end example

@xref{Parallel Test Harness,,,automake,GNU Automake} for more information
about the Automake Parallel Test Harness.

遇到错误时，请给@email{bug-guix@@gnu.org}发邮件，并附带@file{test-suite.log}文件。请在消息里说明使用的Guix的版本信息和依赖（@pxref{需求}）的版本信息。

Guix还附带了一个可以测试整个Guix系统实例的全系统测试套件。它只能在已经安装Guix的系统上运行：

@example
make check-system
@end example

@noindent
或者，同样的，通过定义@code{TESTS}只运行测试的一个子集：

@example
make check-system TESTS="basic mcron"
@end example

这些系统测试是在@code{(gnu tests
@dots{})}模块里定义的。它们在虚拟机（VM）里运行轻量的指令。它们的计算量可能很多也可能很少，这取决于它们依赖的substitute（@pxref{substitutes}）是否已经存在。它们之中有些需要很多存储空间以保存虚拟机硬盘。

再重复一遍，如果遇到测试错误，请给@email{bug-guix@@gnu.org}发邮件，并附带详细的说明。

@node 设置后台进程
@section 设置后台进程

@cindex 后台进程
构建软件包或运行垃圾回收器之类的操作都是由一个特殊的进程代替客户执行的，即@dfn{构建后台进程}。只有这个进程可以访问仓库和相关的数据库。因此，所有修改仓库的操作都通过这个后台进程执行。例如，@command{guix
package}和@command{guix build}之类的命令行工具通过和这个后台进程通信（@i{通过}远程过程调用）来指示它该做什么。

接下来的几个小节介绍如何准备“构建后台进程”的环境。参考@ref{substitutes}，了解怎样允许这个后台进程下载预构建好的二进制文件。

@menu
* 设置构建环境::       准备隔离的构建环境。
* 下发工作给后台进程的设置::  下发构建工作给远程的机器。
* SELinux的支持::         为后台进程使用SELinux规则。
@end menu

@node 设置构建环境
@subsection 设置构建环境

@cindex 构建环境
在一个标准的多用户设置里，Guix和它的后台进程--@command{guix-daemon}程序--是由@code{root}用户安装的，并且@command{guix-daemon}以@code{root}用户身份运行。无特权的用户可以用Guix的工具构建软件包或访问仓库，这个后台进程会代替用户进行这些操作，以确保仓库保持一致的状态，并且允许构建好的软件包可以在不同用户间共享。

@cindex 构建用户
当@command{guix-daemon}以@code{root}用户身份运行时，由于安全方面的考虑，你可能不希望软件包构建进程也以@code{root}用户身份运行。为了避免那样，我们需要创建一个@dfn{构建用户}池，以供后台进程启动的构建进程使用。这些构建用户不需要拥有shell和家目录：他们只会在后台进程为构建进程剥夺@code{root}特权时使用。拥有多个这类用户使后台进程可以以不同的UID启动不同的构建进程，这保证它们不会互相干扰--这是一个重要的功能，因为构建被视为纯函数（@pxref{介绍}）。

在一个GNU/Linux系统上，可以这样创建一个构建用户池（用bash语法和@code{shadow}命令）：

@c See https://lists.gnu.org/archive/html/bug-guix/2013-01/msg00239.html
@c for why `-G' is needed.
@example
# groupadd --system guixbuild
# for i in $(seq -w 1 10);
  do
    useradd -g guixbuild -G guixbuild           \
            -d /var/empty -s $(which nologin)   \
            -c "Guix build user $i" --system    \
            guixbuilder$i;
  done
@end example

@noindent
构建用户的数量决定了有多少个构建任务可以并行执行，即@option{--max-jobs}参数(@pxref{调用guix-daemon,
@option{--max-jobs}})。为了使用@command{guix system
vm}和相关的命令，你需要把构建用户添加到@code{kvm}用户组，以使它们访问@file{/dev/kvm}。为此，把@code{-G
guixbuild}替换成@code{-G guixbuild,kvm}（@pxref{调用guix system}）。

之后以@code{root}身份用下面的命令运行@code{guix-daemon}程序command@footnote{如果你的机器使用systemd
init系统，把@file{@var{prefix}/lib/systemd/system/guix-daemon.service}文件复制到@file{/etc/systemd/system}文件夹里可以使@command{guix-daemon}自启动。类似的，如果你的机器使用Upstart
init系统，把@file{@var{prefix}/lib/upstart/system/guix-daemon.conf}文件复制到@file{/etc/init}文件夹里}：

@example
# guix-daemon --build-users-group=guixbuild
@end example

@cindex chroot
@noindent
这样，后台进程在一个chroot环境里，以一个@code{guixbuilder}用户组成员的身份启动构建进程。在GNU/Linux上，默认的，这个chroot环境仅包含这些东西：

@c Keep this list in sync with libstore/build.cc! -----------------------
@itemize
@item
一个和主机@code{/dev}独立的@footnote{大致这样，因为虽然chroot环境里的@code{/dev}包含的文件是固定的，大部分这些文件只有在主机有对应的文件时才能创建。}，最小的@code{/dev}文件夹；

@item
@code{/proc}文件夹；它只含有当前容器的进程，因为用了一个独立的进程PID命名空间；

@item
@file{/etc/passwd}，仅包含当前用户和@file{nobody}；

@item
@file{/etc/group}，包含用户的组；

@item
@file{/etc/hosts}，包含@code{localhost}映射到@code{127.0.0.1}的条目；

@item
一个可写的@file{/tmp}文件夹。
@end itemize

You can influence the directory where the daemon stores build trees @i{via}
the @env{TMPDIR} environment variable.  However, the build tree within the
chroot is always called @file{/tmp/guix-build-@var{name}.drv-0}, where
@var{name} is the derivation name---e.g., @code{coreutils-8.24}.  This way,
the value of @env{TMPDIR} does not leak inside build environments, which
avoids discrepancies in cases where build processes capture the name of
their build tree.

@vindex http_proxy
@vindex https_proxy
The daemon also honors the @env{http_proxy} and @env{https_proxy}
environment variables for HTTP and HTTPS downloads it performs, be it for
fixed-output derivations (@pxref{Derivations}) or for substitutes
(@pxref{substitutes}).

If you are installing Guix as an unprivileged user, it is still possible to
run @command{guix-daemon} provided you pass @option{--disable-chroot}.
However, build processes will not be isolated from one another, and not from
the rest of the system.  Thus, build processes may interfere with each
other, and may access programs, libraries, and other files available on the
system---making it much harder to view them as @emph{pure} functions.


@node 下发工作给后台进程的设置
@subsection 使用任务下发设施

@cindex 下发
@cindex 构建钩子
When desired, the build daemon can @dfn{offload} derivation builds to other
machines running Guix, using the @code{offload} @dfn{build
hook}@footnote{This feature is available only when
@uref{https://github.com/artyom-poptsov/guile-ssh, Guile-SSH} is present.}.
When that feature is enabled, a list of user-specified build machines is
read from @file{/etc/guix/machines.scm}; every time a build is requested,
for instance via @code{guix build}, the daemon attempts to offload it to one
of the machines that satisfy the constraints of the derivation, in
particular its system types---e.g., @code{x86_64-linux}.  A single machine
can have multiple system types, either because its architecture natively
supports it, via emulation (@pxref{transparent-emulation-qemu, Transparent
Emulation with QEMU}), or both.  Missing prerequisites for the build are
copied over SSH to the target machine, which then proceeds with the build;
upon success the output(s) of the build are copied back to the initial
machine.  The offload facility comes with a basic scheduler that attempts to
select the best machine.  The best machine is chosen among the available
machines based on criteria such as:

@enumerate
@item
The availability of a build slot.  A build machine can have as many build
slots (connections) as the value of the @code{parallel-builds} field of its
@code{build-machine} object.

@item
Its relative speed, as defined via the @code{speed} field of its
@code{build-machine} object.

@item
Its load.  The normalized machine load must be lower than a threshold value,
configurable via the @code{overload-threshold} field of its
@code{build-machine} object.

@item
Disk space availability.  More than a 100 MiB must be available.
@end enumerate

@file{/etc/guix/machines.scm}文件通常是这样的：

@lisp
(list (build-machine
        (name "eightysix.example.org")
        (systems (list "x86_64-linux" "i686-linux"))
        (host-key "ssh-ed25519 AAAAC3Nza@dots{}")
        (user "bob")
        (speed 2.))     ;incredibly fast!

      (build-machine
        (name "armeight.example.org")
        (systems (list "aarch64-linux"))
        (host-key "ssh-rsa AAAAB3Nza@dots{}")
        (user "alice")
        (private-key
         (string-append (getenv "HOME")
                        "/.ssh/identity-for-guix"))))
@end lisp

@noindent
In the example above we specify a list of two build machines, one for the
@code{x86_64} and @code{i686} architectures and one for the @code{aarch64}
architecture.

事实上，这个文件--并不意外地--是一个Scheme文件，当@code{下发}钩子被启动时执行。它的返回值必须是一个包含@code{build-machine}对象的列表。虽然这个例子展示的是一个固定的列表，你可以想象，使用DNS-SD来返回一个包含从局域网内发现的构建机器的列表，@pxref{介绍,
Guile-Avahi,, guile-avahi, 在Guile
Scheme程序里使用Avahi}。@code{build-machine}数据类型的详细信息如下。

@deftp {数据类型} build-machine
这个数据类型表示后台进程可以下发构建任务的构建机器。重要的项有：

@table @code

@item 名字
远程机器的主机名。

@item systems
The system types the remote machine supports---e.g., @code{(list
"x86_64-linux" "i686-linux")}.

@item 用户
通过SSH连接远程机器时使用的用户帐号。注意，SSH密钥@emph{不}能被密码保护，以支持无交互的登录。

@item 主机公钥
这必须是机器的OpenSSH格式的SSH@dfn{公钥}。这是用来在连接机器时认证身份的。它是一个像这样的长字符串：

@example
ssh-ed25519 AAAAC3NzaC@dots{}mde+UhL hint@@example.org
@end example

如果这个机器正在运行OpenSSH后台进程，@command{sshd}，那么主机公钥可以在@file{/etc/ssh/ssh_host_ed25519_key.pub}找到。

如果这个机器正在运行GNU@tie{}lsh，@command{lshd}，那么主机公钥可以在@file{/etc/lsh/host-key.pub}或类似的位置找到。它可以通过@command{lsh-export-key}命令转换成OpenSSH格式（@pxref{Converting
keys,,, lsh, LSH用户手册}）：

@example
$ lsh-export-key --openssh < /etc/lsh/host-key.pub
ssh-rsa AAAAB3NzaC1yc2EAAAAEOp8FoQAAAQEAs1eB46LV@dots{}
@end example

@end table

一些可选的项：

@table @asis

@item @code{port}（默认值：@code{22}）
机器上的SSH服务器的端口号。

@item @code{private-key}（默认值：@file{~root/.ssh/id_rsa}）
连接机器时使用的SSH私钥，OpenSSH格式。这个私钥不能被密码保护。

注意，默认值是@emph{root帐号}的私钥。使用默认值时请确保它存在。

@item @code{compression}（默认值：@code{"zlib@@openssh.com,zlib"}）
@itemx @code{compression-level}（默认值：@code{3}）
SSH压缩算法和压缩级别。

下发任务依赖SSH压缩来减少传输文件到构建机器时使用的带宽。

@item @code{daemon-socket}（默认值：@code{"/var/guix/daemon-socket/socket"}）
那台机器上的@command{guix-daemon}监听的Unix套接字文件名。

@item @code{overload-threshold} (default: @code{0.6})
The load threshold above which a potential offload machine is disregarded by
the offload scheduler.  The value roughly translates to the total processor
usage of the build machine, ranging from 0.0 (0%) to 1.0 (100%).  It can
also be disabled by setting @code{overload-threshold} to @code{#f}.

@item @code{parallel-builds}（默认值：@code{1}）
那台机器上可以并行运行的构建任务数量。

@item @code{speed}（默认值：@code{1.0}）
一个相对的速度值。下发调度器会偏好速度更快的机器。

@item @code{features} （@code{'()}）
一个表示机器支持的功能的字符串列表。例如，@code{"kvm"}表示机器有KVM
Linux模块和相关的硬件支持。Derivation可以通过名字请求需要的功能，然后被分发到匹配的机器的任务队列里。

@end table
@end deftp

@command{guix}命令必须在构建机器的搜素路径里。你可以通过这个命令检查：

@example
ssh build-machine guix repl --version
@end example

@file{machines.scm}到位后，还有一件要做的事。如上所述，下发任务时会在机器的仓库之间传输文件。为此，你需要在每台机器上生成一个密钥对，以使后台进程可以从仓库导出签名后的文件包（@pxref{调用guix archive}）：

@example
# guix archive --generate-key
@end example

@noindent
每台构建机器都必须认证主机器的公钥，从而接收从主机器接收的仓库文件：

@example
# guix archive --authorize < master-public-key.txt
@end example

@noindent
类似的，主机器必须认证每台构建机器的公钥：

所有这些有关公钥的繁琐事宜都是为了表达主服务器和构建服务器之间成对的互相信任关系。具体地，当主机器从构建机器接收文件时（反之亦然），它的构建后台进程可以确保文件是原样的，没有被篡改，并且被认证的公钥签名过。

@cindex 下发测试
为了测试你的设置是否能正常工作，在主节点上运行这个命令：

@example
# guix offload test
@end example

This will attempt to connect to each of the build machines specified in
@file{/etc/guix/machines.scm}, make sure Guix is available on each machine,
attempt to export to the machine and import from it, and report any error in
the process.

如果你希望用别的文件测试，只需要在命令行指定它：

@example
# guix offload test machines-qualif.scm
@end example

最后，你可以像这样只测试机器列表里名字匹配某个正则表达式的子集：

@example
# guix offload test machines.scm '\.gnu\.org$'
@end example

@cindex 下发状态
若想展示所有构建主机的当前负载，在主节点上运行这个命令：

@example
# guix offload status
@end example


@node SELinux的支持
@subsection SELinux的支持

@cindex SELinux，后台进程策略
@cindex 强制访问控制，SELinux
@cindex 安全，guix-daemon
Guix附带一个SELinux策略文件，位置在@file{etc/guix-daemon.cil}，它可以在启用SELinux的系统上安装，为Guix的文件添加标签及指定后台进程的期望行为。由于Guix系统不提供SELinux基础策略，这个后台进程策略不能在Guix系统上使用。

@subsubsection 安装SELinux策略
@cindex SELinux，安装策略
用root用户执行这个命令以安装策略：

@example
semodule -i etc/guix-daemon.cil
@end example

用@code{restorecon}或者你的系统提供的其它机制重新给文件系统打标签。

一旦安装好策略，为文件系统重新打好标签，并且重启了后台进程，它应该在@code{guix_daemon_t}环境里运行。你可以用下面这个命令确认：

@example
ps -Zax | grep guix-daemon
@end example

运行@code{guix build hello}之类的命令并监控SELinux日志以说服你自己SELinux允许所有的操作。

@subsubsection 限制
@cindex SELinux，限制

这个策略不是完美的。这里有一个关于限制和缺陷的列表，当为Guix后台进程部署提供的SELinux策略时该认真考虑。

@enumerate
@item
@code{guix_daemon_socket_t} isn’t actually used.  None of the socket
operations involve contexts that have anything to do with
@code{guix_daemon_socket_t}.  It doesn’t hurt to have this unused label, but
it would be preferable to define socket rules for only this label.

@item
@code{guix
gc}不可以任意访问指向profile的链接。由于设计的原因，符号链接的目标的文件标签和符号链接本身的文件标签是不同的。尽管$localstatedir里的所有profile都被打上了标签，指向这些profile的符号链接继承它们所在的文件夹的标签。对于普通用户的家目录里的链接，标签是@code{user_home_t}。但是对于root用户的家目录，或@file{/tmp}，或HTTP服务器的工作目录等文件夹里的链接不是这样。@code{guix
gc}会被阻止读取和跟随这些链接。

@item
后台进程监听TCP连接的功能不再可用。这可能需要额外的规则，因为SELinux区别对待网络套接字和文件。

@item
目前，所有匹配正则表达式@code{/gnu/store/.+-(guix-.+|profile)/bin/guix-daemon}的文件都被赋予@code{guix_daemon_exec_t}标签；这意味着@emph{任何}profile里的任何有这样名字的的文件都会被允许在@code{guix_daemon_t}域里执行。这不够理想。一个攻击者可以构建提供这个可执行程序的软件包，并说服一个用户安装、运行它，以此进入@code{guix_daemon_t}域。那时，SELinux无法阻止它访问所在域的进程可以访问的文件。

You will need to relabel the store directory after all upgrades to
@file{guix-daemon}, such as after running @code{guix pull}.  Assuming the
store is in @file{/gnu}, you can do this with @code{restorecon -vR /gnu}, or
by other means provided by your operating system.

我们可以在安装时生成一个更严格的策略，仅当前安装的@code{guix-daemon}的@emph{精确的}的文件名会被打上@code{guix_daemon_exec_t}标签，而不是用一个宽泛的正则表达式。这样的缺点是root必须在每次安装提供@code{guix-daemon}的Guix软件包时安装或升级策略。
@end enumerate

@node 调用guix-daemon
@section 调用@command{guix-daemon}

@command{guix-daemon}程序实现了所有访问仓库的功能。包括启动构建进程，运行垃圾回收器，查询构建结果，等。它通常以@code{root}身份运行：

@example
# guix-daemon --build-users-group=guixbuild
@end example

@noindent
关于如何设置它，@pxref{设置后台进程}。

@cindex chroot
@cindex 容器，构建环境
@cindex 构建环境
@cindex 可复现的构建
By default, @command{guix-daemon} launches build processes under different
UIDs, taken from the build group specified with
@option{--build-users-group}.  In addition, each build process is run in a
chroot environment that only contains the subset of the store that the build
process depends on, as specified by its derivation (@pxref{编程接口, derivation}), plus a set of specific system directories.  By
default, the latter contains @file{/dev} and @file{/dev/pts}.  Furthermore,
on GNU/Linux, the build environment is a @dfn{container}: in addition to
having its own file system tree, it has a separate mount name space, its own
PID name space, network name space, etc.  This helps achieve reproducible
builds (@pxref{功能}).

When the daemon performs a build on behalf of the user, it creates a build
directory under @file{/tmp} or under the directory specified by its
@env{TMPDIR} environment variable.  This directory is shared with the
container for the duration of the build, though within the container, the
build tree is always called @file{/tmp/guix-build-@var{name}.drv-0}.

The build directory is automatically deleted upon completion, unless the
build failed and the client specified @option{--keep-failed} (@pxref{普通的构建选项, @option{--keep-failed}}).

The daemon listens for connections and spawns one sub-process for each
session started by a client (one of the @command{guix} sub-commands).  The
@command{guix processes} command allows you to get an overview of the
activity on your system by viewing each of the active sessions and clients.
@xref{调用guix processes}, for more information.

下面这些命令行选项受支持：

@table @code
@item --build-users-group=@var{用户组}
这会从@var{用户组}里选取用户，以运行构建进程（@pxref{设置后台进程,构建用户}）。

@item --no-substitutes
@cindex substitutes
不要为构建商品使用substitute。即，总是在本地构建，而不是下载预构建的二进制文件（@pxref{substitutes}）。

When the daemon runs with @option{--no-substitutes}, clients can still
explicitly enable substitution @i{via} the @code{set-build-options} remote
procedure call (@pxref{仓库}).

@anchor{daemon-substitute-urls}
@item --substitute-urls=@var{urls}
@var{urls}是用空格分隔的substitute源URL列表。当这个选项被省略时，默认使用@indicateurl{https://@value{SUBSTITUTE-SERVER}}。

这意味着可以从@var{urls}下载substitute，只要它们的签名可信（@pxref{substitutes}）。

@xref{Getting Substitutes from Other Servers}, for more information on how
to configure the daemon to get substitutes from other servers.

@cindex 下发
@item --no-offload
Do not use offload builds to other machines (@pxref{下发工作给后台进程的设置}).
That is, always build things locally instead of offloading builds to remote
machines.

@item --cache-failures
缓存失败的构建。默认地，只缓存成功的构建。

当这个选项被使用时，可以用@command{guix gc --list-failures}查询被标记为失败的仓库文件；@command{guix gc
--clear-failures}从仓库里删除失败的缓存。@xref{调用guix gc}。

@item --cores=@var{n}
@itemx -c @var{n}
用@var{n}个CPU核来构建每个derivation；@code{0}表示有多少就用多少。

The default value is @code{0}, but it may be overridden by clients, such as
the @option{--cores} option of @command{guix build} (@pxref{调用guix build}).

The effect is to define the @env{NIX_BUILD_CORES} environment variable in
the build process, which can then use it to exploit internal
parallelism---for instance, by running @code{make -j$NIX_BUILD_CORES}.

@item --max-jobs=@var{n}
@itemx -M @var{n}
最多允许@var{n}个并行的构建任务。默认值是@code{1}。设置为@code{0}表示不在本地执行构建；而是下发构建任务（@pxref{下发工作给后台进程的设置}），或者直接失败。

@item --max-silent-time=@var{seconds}
当构建或substitution进程超过@var{seconds}秒仍然保持静默，就把它结束掉并报告构建失败。

默认值是@code{0}，表示关闭超时。

The value specified here can be overridden by clients (@pxref{普通的构建选项, @option{--max-silent-time}}).

@item --timeout=@var{seconds}
类似地，当构建或substitution进程执行超过@var{seconds}秒，就把它结束掉并报告构建失败。

默认值是@code{0}，表示关闭超时。

The value specified here can be overridden by clients (@pxref{普通的构建选项, @option{--timeout}}).

@item --rounds=@var{N}
为每个derivation构建@var{n}次，如果连续的构建结果不是每个比特都相同就报告错误。这个设置可以被@command{guix
build}之类的客户端覆盖（@pxref{调用guix build}）。

当和@option{--keep-failed}一起使用时，不同的输出保存在@file{/gnu/store/@dots{}-check}。这让检查两个结果的区别更容易。

@item --debug
生成调试输出。

This is useful to debug daemon start-up issues, but then it may be
overridden by clients, for example the @option{--verbosity} option of
@command{guix build} (@pxref{调用guix build}).

@item --chroot-directory=@var{dir}
把@var{dir}添加到构建的chroot。

这么做可能会改变构建进程的结果--例如，如果它们使用了在@var{dir}里发现的可选依赖。因此，建议不要这么做，而是确保每个derivation声明所需的全部输入。

@item --disable-chroot
关闭chroot构建。

不建议使用这个选项，因为它会允许构建进程访问到没被声明的依赖。但是，当@command{guix-daemon}以没有特权的用户身份运行时，这个选项是必须的。

@item --log-compression=@var{type}
以@var{type}方式压缩构建日志，可选的值：@code{gzip}，@code{bzip2}，@code{none}。

Unless @option{--lose-logs} is used, all the build logs are kept in the
@var{localstatedir}.  To save space, the daemon automatically compresses
them with Bzip2 by default.

@item --discover[=yes|no]
Whether to discover substitute servers on the local network using mDNS and
DNS-SD.

This feature is still experimental.  However, here are a few considerations.

@enumerate
@item
It might be faster/less expensive than fetching from remote servers;
@item
There are no security risks, only genuine substitutes will be used
(@pxref{验证substitute});
@item
An attacker advertising @command{guix publish} on your LAN cannot serve you
malicious binaries, but they can learn what software you’re installing;
@item
Servers may serve substitute over HTTP, unencrypted, so anyone on the LAN
can see what software you’re installing.
@end enumerate

It is also possible to enable or disable substitute server discovery at
run-time by running:

@example
herd discover guix-daemon on
herd discover guix-daemon off
@end example

@item --disable-deduplication
@cindex 去重
关闭自动对仓库文件“去重”。

默认地，添加到仓库的文件会被自动“去重”：如果新添加的文件和仓库里找到的某个文件完全相同，后台进程把这个新文件变成另一个文件的硬链接。这可以明显地减少硬盘使用，代价是构建结束后轻微地增加输入／输出负载。这个选项关闭这个优化。

@item --gc-keep-outputs[=yes|no]
垃圾收集器（GC）是否必须保留存活的derivation的输出。

@cindex GC根
@cindex 垃圾收集的根
When set to @code{yes}, the GC will keep the outputs of any live derivation
available in the store---the @file{.drv} files.  The default is @code{no},
meaning that derivation outputs are kept only if they are reachable from a
GC root.  @xref{调用guix gc}, for more on GC roots.

@item --gc-keep-derivations[=yes|no]
垃圾收集器（GC）是否必须保留和存活的输出相关的derivation。

When set to @code{yes}, as is the case by default, the GC keeps
derivations---i.e., @file{.drv} files---as long as at least one of their
outputs is live.  This allows users to keep track of the origins of items in
their store.  Setting it to @code{no} saves a bit of disk space.

In this way, setting @option{--gc-keep-derivations} to @code{yes} causes
liveness to flow from outputs to derivations, and setting
@option{--gc-keep-outputs} to @code{yes} causes liveness to flow from
derivations to outputs.  When both are set to @code{yes}, the effect is to
keep all the build prerequisites (the sources, compiler, libraries, and
other build-time tools) of live objects in the store, regardless of whether
these prerequisites are reachable from a GC root.  This is convenient for
developers since it saves rebuilds or downloads.

@item --impersonate-linux-2.6
On Linux-based systems, impersonate Linux 2.6.  This means that the kernel's
@command{uname} system call will report 2.6 as the release number.

这可能会有助于构建那些（通常是错误地）依赖内核版本号的程序。

@item --lose-logs
Do not keep build logs.  By default they are kept under
@file{@var{localstatedir}/guix/log}.

@item --system=@var{system}
假设@var{system}是当前的系统类型。默认值是configure时发现的架构／内核元组，如@code{x86_64-linux}。

@item --listen=@var{endpoint}
Listen for connections on @var{endpoint}.  @var{endpoint} is interpreted as
the file name of a Unix-domain socket if it starts with @code{/} (slash
sign).  Otherwise, @var{endpoint} is interpreted as a host name or host name
and port to listen to.  Here are a few examples:

@table @code
@item --listen=/gnu/var/daemon
Listen for connections on the @file{/gnu/var/daemon} Unix-domain socket,
creating it if needed.

@item --listen=localhost
@cindex daemon, remote access
@cindex remote access to the daemon
@cindex daemon, cluster setup
@cindex clusters, daemon setup
Listen for TCP connections on the network interface corresponding to
@code{localhost}, on port 44146.

@item --listen=128.0.0.42:1234
Listen for TCP connections on the network interface corresponding to
@code{128.0.0.42}, on port 1234.
@end table

This option can be repeated multiple times, in which case
@command{guix-daemon} accepts connections on all the specified endpoints.
Users can tell client commands what endpoint to connect to by setting the
@env{GUIX_DAEMON_SOCKET} environment variable (@pxref{仓库,
@env{GUIX_DAEMON_SOCKET}}).

@quotation 注
The daemon protocol is @emph{unauthenticated and unencrypted}.  Using
@option{--listen=@var{host}} is suitable on local networks, such as
clusters, where only trusted nodes may connect to the build daemon.  In
other cases where remote access to the daemon is needed, we recommend using
Unix-domain sockets along with SSH.
@end quotation

When @option{--listen} is omitted, @command{guix-daemon} listens for
connections on the Unix-domain socket located at
@file{@var{localstatedir}/guix/daemon-socket/socket}.
@end table


@node 设置应用程序
@section 设置应用程序

@cindex 别的发行版
When using Guix on top of GNU/Linux distribution other than Guix System---a
so-called @dfn{foreign distro}---a few additional steps are needed to get
everything in place.  Here are some of them.

@subsection 区域

@anchor{locales-and-locpath}
@cindex locales, when not on Guix System
@vindex LOCPATH
@vindex GUIX_LOCPATH
Packages installed @i{via} Guix will not use the locale data of the host
system.  Instead, you must first install one of the locale packages
available with Guix and then define the @env{GUIX_LOCPATH} environment
variable:

@example
$ guix install glibc-locales
$ export GUIX_LOCPATH=$HOME/.guix-profile/lib/locale
@end example

Note that the @code{glibc-locales} package contains data for all the locales
supported by the GNU@tie{}libc and weighs in at around 917@tie{}MiB@.
Alternatively, the @code{glibc-utf8-locales} is smaller but limited to a few
UTF-8 locales.

The @env{GUIX_LOCPATH} variable plays a role similar to @env{LOCPATH}
(@pxref{Locale Names, @env{LOCPATH},, libc, The GNU C Library Reference
Manual}).  There are two important differences though:

@enumerate
@item
@env{GUIX_LOCPATH} is honored only by the libc in Guix, and not by the libc
provided by foreign distros.  Thus, using @env{GUIX_LOCPATH} allows you to
make sure the programs of the foreign distro will not end up loading
incompatible locale data.

@item
libc suffixes each entry of @env{GUIX_LOCPATH} with @code{/X.Y}, where
@code{X.Y} is the libc version---e.g., @code{2.22}.  This means that, should
your Guix profile contain a mixture of programs linked against different
libc version, each libc version will only try to load locale data in the
right format.
@end enumerate

This is important because the locale data format used by different libc
versions may be incompatible.

@subsection Name Service Switch

@cindex name service switch, glibc
@cindex NSS (name service switch), glibc
@cindex nscd (name service caching daemon)
@cindex name service caching daemon (nscd)
When using Guix on a foreign distro, we @emph{strongly recommend} that the
system run the GNU C library's @dfn{name service cache daemon},
@command{nscd}, which should be listening on the @file{/var/run/nscd/socket}
socket.  Failing to do that, applications installed with Guix may fail to
look up host names or user accounts, or may even crash.  The next paragraphs
explain why.

@cindex @file{nsswitch.conf}
The GNU C library implements a @dfn{name service switch} (NSS), which is an
extensible mechanism for ``name lookups'' in general: host name resolution,
user accounts, and more (@pxref{Name Service Switch,,, libc, The GNU C
Library Reference Manual}).

@cindex Network information service (NIS)
@cindex NIS (Network information service)
Being extensible, the NSS supports @dfn{plugins}, which provide new name
lookup implementations: for example, the @code{nss-mdns} plugin allow
resolution of @code{.local} host names, the @code{nis} plugin allows user
account lookup using the Network information service (NIS), and so on.
These extra ``lookup services'' are configured system-wide in
@file{/etc/nsswitch.conf}, and all the programs running on the system honor
those settings (@pxref{NSS Configuration File,,, libc, The GNU C Reference
Manual}).

When they perform a name lookup---for instance by calling the
@code{getaddrinfo} function in C---applications first try to connect to the
nscd; on success, nscd performs name lookups on their behalf.  If the nscd
is not running, then they perform the name lookup by themselves, by loading
the name lookup services into their own address space and running it.  These
name lookup services---the @file{libnss_*.so} files---are @code{dlopen}'d,
but they may come from the host system's C library, rather than from the C
library the application is linked against (the C library coming from Guix).

And this is where the problem is: if your application is linked against
Guix's C library (say, glibc 2.24) and tries to load NSS plugins from
another C library (say, @code{libnss_mdns.so} for glibc 2.22), it will
likely crash or have its name lookups fail unexpectedly.

Running @command{nscd} on the system, among other advantages, eliminates
this binary incompatibility problem because those @code{libnss_*.so} files
are loaded in the @command{nscd} process, not in applications themselves.

@subsection X11 Fonts

@cindex 字体
The majority of graphical applications use Fontconfig to locate and load
fonts and perform X11-client-side rendering.  The @code{fontconfig} package
in Guix looks for fonts in @file{$HOME/.guix-profile} by default.  Thus, to
allow graphical applications installed with Guix to display fonts, you have
to install fonts with Guix as well.  Essential font packages include
@code{gs-fonts}, @code{font-dejavu}, and @code{font-gnu-freefont}.

@cindex @code{fc-cache}
@cindex font cache
Once you have installed or removed fonts, or when you notice an application
that does not find fonts, you may need to install Fontconfig and to force an
update of its font cache by running:

@example
guix install fontconfig
fc-cache -rv
@end example

To display text written in Chinese languages, Japanese, or Korean in
graphical applications, consider installing
@code{font-adobe-source-han-sans} or @code{font-wqy-zenhei}.  The former has
multiple outputs, one per language family (@pxref{有多个输出的软件包}).  For instance, the following command installs fonts for Chinese
languages:

@example
guix install font-adobe-source-han-sans:cn
@end example

@cindex @code{xterm}
Older programs such as @command{xterm} do not use Fontconfig and instead
rely on server-side font rendering.  Such programs require to specify a full
name of a font using XLFD (X Logical Font Description), like this:

@example
-*-dejavu sans-medium-r-normal-*-*-100-*-*-*-*-*-1
@end example

To be able to use such full names for the TrueType fonts installed in your
Guix profile, you need to extend the font path of the X server:

@c Note: 'xset' does not accept symlinks so the trick below arranges to
@c get at the real directory.  See <https://bugs.gnu.org/30655>.
@example
xset +fp $(dirname $(readlink -f ~/.guix-profile/share/fonts/truetype/fonts.dir))
@end example

@cindex @code{xlsfonts}
After that, you can run @code{xlsfonts} (from @code{xlsfonts} package)  to
make sure your TrueType fonts are listed there.


@subsection X.509证书

@cindex @code{nss-certs}
The @code{nss-certs} package provides X.509 certificates, which allow
programs to authenticate Web servers accessed over HTTPS.

When using Guix on a foreign distro, you can install this package and define
the relevant environment variables so that packages know where to look for
certificates.  @xref{X.509证书}, for detailed information.

@subsection Emacs Packages

@cindex @code{emacs}
When you install Emacs packages with Guix, the Elisp files are placed under
the @file{share/emacs/site-lisp/} directory of the profile in which they are
installed.  The Elisp libraries are made available to Emacs through the
@env{EMACSLOADPATH} environment variable, which is set when installing Emacs
itself.

Additionally, autoload definitions are automatically evaluated at the
initialization of Emacs, by the Guix-specific
@code{guix-emacs-autoload-packages} procedure.  If, for some reason, you
want to avoid auto-loading the Emacs packages installed with Guix, you can
do so by running Emacs with the @option{--no-site-file} option (@pxref{Init
File,,, emacs, The GNU Emacs Manual}).


@node Upgrading Guix
@section Upgrading Guix

@cindex Upgrading Guix, on a foreign distro

To upgrade Guix, run:

@example
guix pull
@end example

@xref{调用guix pull}, for more information.

@cindex upgrading Guix for the root user, on a foreign distro
@cindex upgrading the Guix daemon, on a foreign distro
@cindex @command{guix pull} for the root user, on a foreign distro

On a foreign distro, you can upgrade the build daemon by running:

@example
sudo -i guix pull
@end example

@noindent
followed by (assuming your distro uses the systemd service management tool):

@example
systemctl restart guix-daemon.service
@end example

On Guix System, upgrading the daemon is achieved by reconfiguring the system
(@pxref{调用guix system, @code{guix system reconfigure}}).

@c TODO What else?

@c *********************************************************************
@node 系统安装
@chapter 系统安装

@cindex installing Guix System
@cindex Guix System, installation
This section explains how to install Guix System on a machine.  Guix, as a
package manager, can also be installed on top of a running GNU/Linux system,
@pxref{安装}.

@ifinfo
@quotation 注
@c This paragraph is for people reading this from tty2 of the
@c installation image.
You are reading this documentation with an Info reader.  For details on how
to use it, hit the @key{RET} key (``return'' or ``enter'') on the link that
follows: @pxref{Top, Info reader,, info-stnd, Stand-alone GNU Info}.  Hit
@kbd{l} afterwards to come back here.

Alternatively, run @command{info info} in another tty to keep the manual
available.
@end quotation
@end ifinfo

@menu
* 限制::                   你可以期待什么。
* 硬件的考虑::          支持的硬件。
* U盘和DVD安装::         准备安装介质。
* 准备安装::             网络、分区等。
* 指导的图形安装::    简单的图形安装。
* 手动安装::             适合巫师的手动安装。
* 系统安装之后::       当安装成功后。
* 在虚拟机里安装 Guix::  Guix系统游乐场。
* 构建安装镜像::       这是怎样实现的。
@end menu

@node 限制
@section 限制

We consider Guix System to be ready for a wide range of ``desktop'' and
server use cases.  The reliability guarantees it provides---transactional
upgrades and rollbacks, reproducibility---make it a solid foundation.

Nevertheless, before you proceed with the installation, be aware of the
following noteworthy limitations applicable to version @value{VERSION}:

@itemize
@item
More and more system services are provided (@pxref{服务}), but some may
be missing.

@item
GNOME, Xfce, LXDE, and Enlightenment are available (@pxref{桌面服务}), as well as a number of X11 window managers.  However, KDE is
currently missing.
@end itemize

More than a disclaimer, this is an invitation to report issues (and success
stories!), and to join us in improving it.  @xref{贡献}, for more
info.


@node 硬件的考虑
@section 硬件的考虑

@cindex hardware support on Guix System
GNU@tie{}Guix focuses on respecting the user's computing freedom.  It builds
around the kernel Linux-libre, which means that only hardware for which free
software drivers and firmware exist is supported.  Nowadays, a wide range of
off-the-shelf hardware is supported on GNU/Linux-libre---from keyboards to
graphics cards to scanners and Ethernet controllers.  Unfortunately, there
are still areas where hardware vendors deny users control over their own
computing, and such hardware is not supported on Guix System.

@cindex WiFi, hardware support
One of the main areas where free drivers or firmware are lacking is WiFi
devices.  WiFi devices known to work include those using Atheros chips
(AR9271 and AR7010), which corresponds to the @code{ath9k} Linux-libre
driver, and those using Broadcom/AirForce chips (BCM43xx with Wireless-Core
Revision 5), which corresponds to the @code{b43-open} Linux-libre driver.
Free firmware exists for both and is available out-of-the-box on Guix
System, as part of @code{%base-firmware} (@pxref{操作系统参考,
@code{firmware}}).

@cindex RYF, Respects Your Freedom
The @uref{https://www.fsf.org/, Free Software Foundation} runs
@uref{https://www.fsf.org/ryf, @dfn{Respects Your Freedom}} (RYF), a
certification program for hardware products that respect your freedom and
your privacy and ensure that you have control over your device.  We
encourage you to check the list of RYF-certified devices.

Another useful resource is the @uref{https://www.h-node.org/, H-Node} web
site.  It contains a catalog of hardware devices with information about
their support in GNU/Linux.


@node U盘和DVD安装
@section U盘和DVD安装

An ISO-9660 installation image that can be written to a USB stick or burnt
to a DVD can be downloaded from
@indicateurl{@value{BASE-URL}/guix-system-install-@value{VERSION}.x86_64-linux.iso},
where you can replace @code{x86_64-linux} with one of:

@table @code
@item x86_64-linux
for a GNU/Linux system on Intel/AMD-compatible 64-bit CPUs;

@item i686-linux
for a 32-bit GNU/Linux system on Intel-compatible CPUs.
@end table

@c start duplication of authentication part from ``Binary Installation''
Make sure to download the associated @file{.sig} file and to verify the
authenticity of the image against it, along these lines:

@example
$ wget @value{BASE-URL}/guix-system-install-@value{VERSION}.@var{系统}.iso.sig
$ gpg --verify guix-system-install-@value{VERSION}.@var{系统}.iso.sig
@end example

如果那个命令因为缺少所需的公钥而失败了，那么用这个命令导入它：

@example
$ wget @value{OPENPGP-SIGNING-KEY-URL} \
      -qO - | gpg --import -
@end example

@noindent
再次运行@code{gpg --verify}命令。

Take note that a warning like ``This key is not certified with a trusted
signature!'' is normal.

@c end duplication

This image contains the tools necessary for an installation.  It is meant to
be copied @emph{as is} to a large-enough USB stick or DVD.

@unnumberedsubsec Copying to a USB Stick

Insert a USB stick of 1@tie{}GiB or more into your machine, and determine
its device name.  Assuming that the USB stick is known as @file{/dev/sdX},
copy the image with:

@example
dd if=guix-system-install-@value{VERSION}.x86_64-linux.iso of=/dev/sdX status=progress
sync
@end example

Access to @file{/dev/sdX} usually requires root privileges.

@unnumberedsubsec Burning on a DVD

Insert a blank DVD into your machine, and determine its device name.
Assuming that the DVD drive is known as @file{/dev/srX}, copy the image
with:

@example
growisofs -dvd-compat -Z /dev/srX=guix-system-install-@value{VERSION}.x86_64-linux.iso
@end example

Access to @file{/dev/srX} usually requires root privileges.

@unnumberedsubsec Booting

Once this is done, you should be able to reboot the system and boot from the
USB stick or DVD@.  The latter usually requires you to get in the BIOS or
UEFI boot menu, where you can choose to boot from the USB stick.  In order
to boot from Libreboot, switch to the command mode by pressing the @kbd{c}
key and type @command{search_grub usb}.

@xref{在虚拟机里安装 Guix}, if, instead, you would like to install Guix
System in a virtual machine (VM).


@node 准备安装
@section 准备安装

Once you have booted, you can use the guided graphical installer, which
makes it easy to get started (@pxref{指导的图形安装}).
Alternatively, if you are already familiar with GNU/Linux and if you want
more control than what the graphical installer provides, you can choose the
``manual'' installation process (@pxref{手动安装}).

The graphical installer is available on TTY1.  You can obtain root shells on
TTYs 3 to 6 by hitting @kbd{ctrl-alt-f3}, @kbd{ctrl-alt-f4}, etc.  TTY2
shows this documentation and you can reach it with @kbd{ctrl-alt-f2}.
Documentation is browsable using the Info reader commands (@pxref{Top,,,
info-stnd, Stand-alone GNU Info}).  The installation system runs the GPM
mouse daemon, which allows you to select text with the left mouse button and
to paste it with the middle button.

@quotation 注
Installation requires access to the Internet so that any missing
dependencies of your system configuration can be downloaded.  See the
``Networking'' section below.
@end quotation

@node 指导的图形安装
@section 指导的图形安装

The graphical installer is a text-based user interface.  It will guide you,
with dialog boxes, through the steps needed to install GNU@tie{}Guix System.

The first dialog boxes allow you to set up the system as you use it during
the installation: you can choose the language, keyboard layout, and set up
networking, which will be used during the installation.  The image below
shows the networking dialog.

@image{images/installer-network,5in,, networking setup with the graphical
installer}

Later steps allow you to partition your hard disk, as shown in the image
below, to choose whether or not to use encrypted file systems, to enter the
host name and root password, and to create an additional account, among
other things.

@image{images/installer-partitions,5in,, partitioning with the graphical
installer}

Note that, at any time, the installer allows you to exit the current
installation step and resume at a previous step, as show in the image below.

@image{images/installer-resume,5in,, resuming the installation process}

Once you're done, the installer produces an operating system configuration
and displays it (@pxref{使用配置系统}).  At that point you
can hit ``OK'' and installation will proceed.  On success, you can reboot
into the new system and enjoy.  @xref{系统安装之后}, for what's
next!


@node 手动安装
@section 手动安装

This section describes how you would ``manually'' install GNU@tie{}Guix
System on your machine.  This option requires familiarity with GNU/Linux,
with the shell, and with common administration tools.  If you think this is
not for you, consider using the guided graphical installer (@pxref{指导的图形安装}).

The installation system provides root shells on TTYs 3 to 6; press
@kbd{ctrl-alt-f3}, @kbd{ctrl-alt-f4}, and so on to reach them.  It includes
many common tools needed to install the system.  But it is also a full-blown
Guix System, which means that you can install additional packages, should
you need it, using @command{guix package} (@pxref{调用guix package}).

@menu
* 键盘布局、网络和分区::  初始设置。
* 继续安装步骤::       安装。
@end menu

@node 键盘布局、网络和分区
@subsection Keyboard Layout, Networking, and Partitioning

Before you can install the system, you may want to adjust the keyboard
layout, set up networking, and partition your target hard disk.  This
section will guide you through this.

@subsubsection 键盘布局

@cindex keyboard layout
安装镜像使用的是美国的 qwerty 键盘布局，如果想更改，可以使用 @command{loadkeys} 命令。 例如，用以下命令选择 Dvorak
键盘布局：

@example
loadkeys dvorak
@end example

See the files under @file{/run/current-system/profile/share/keymaps} for a
list of available keyboard layouts.  Run @command{man loadkeys} for more
information.

@subsubsection Networking

运行以下命令查看你的网络接口的名称：

@example
ifconfig -a
@end example

@noindent
@dots{} 或者，使用 GNU/Linux 特有的 @command{ip} 命令：

@example
ip address
@end example

@c https://cgit.freedesktop.org/systemd/systemd/tree/src/udev/udev-builtin-net_id.c#n20
Wired interfaces have a name starting with @samp{e}; for example, the
interface corresponding to the first on-board Ethernet controller is called
@samp{eno1}.  Wireless interfaces have a name starting with @samp{w}, like
@samp{w1p2s0}.

@table @asis
@item 有线连接
To configure a wired network run the following command, substituting
@var{interface} with the name of the wired interface you want to use.

@example
ifconfig @var{interface} up
@end example

@noindent
@dots{} 或者，使用 GNU/Linux 特有的 @command{ip} 命令：

@example
ip link set @var{interface} up
@end example

@item 无线连接
@cindex wireless
@cindex WiFi
To configure wireless networking, you can create a configuration file for
the @command{wpa_supplicant} configuration tool (its location is not
important) using one of the available text editors such as @command{nano}:

@example
nano wpa_supplicant.conf
@end example

As an example, the following stanza can go to this file and will work for
many wireless networks, provided you give the actual SSID and passphrase for
the network you are connecting to:

@example
network=@{
  ssid="@var{my-ssid}"
  key_mgmt=WPA-PSK
  psk="the network's secret passphrase"
@}
@end example

Start the wireless service and run it in the background with the following
command (substitute @var{interface} with the name of the network interface
you want to use):

@example
wpa_supplicant -c wpa_supplicant.conf -i @var{interface} -B
@end example

Run @command{man wpa_supplicant} for more information.
@end table

@cindex DHCP
At this point, you need to acquire an IP address.  On a network where IP
addresses are automatically assigned @i{via} DHCP, you can run:

@example
dhclient -v @var{interface}
@end example

Try to ping a server to see if networking is up and running:

@example
ping -c 3 gnu.org
@end example

Setting up network access is almost always a requirement because the image
does not contain all the software and tools that may be needed.

@cindex proxy, during system installation
If you need HTTP and HTTPS access to go through a proxy, run the following
command:

@example
herd set-http-proxy guix-daemon @var{URL}
@end example

@noindent
where @var{URL} is the proxy URL, for example
@code{http://example.org:8118}.

@cindex installing over SSH
If you want to, you can continue the installation remotely by starting an
SSH server:

@example
herd start ssh-daemon
@end example

Make sure to either set a password with @command{passwd}, or configure
OpenSSH public key authentication before logging in.

@subsubsection 磁盘分区

Unless this has already been done, the next step is to partition, and then
format the target partition(s).

The installation image includes several partitioning tools, including Parted
(@pxref{Overview,,, parted, GNU Parted User Manual}), @command{fdisk}, and
@command{cfdisk}.  Run it and set up your disk with the partition layout you
want:

@example
cfdisk
@end example

If your disk uses the GUID Partition Table (GPT) format and you plan to
install BIOS-based GRUB (which is the default), make sure a BIOS Boot
Partition is available (@pxref{BIOS installation,,, grub, GNU GRUB manual}).

@cindex EFI, installation
@cindex UEFI, installation
@cindex ESP, EFI system partition
If you instead wish to use EFI-based GRUB, a FAT32 @dfn{EFI System
Partition} (ESP) is required.  This partition can be mounted at
@file{/boot/efi} for instance and must have the @code{esp} flag set.  E.g.,
for @command{parted}:

@example
parted /dev/sda set 1 esp on
@end example

@quotation 注
@vindex grub-bootloader
@vindex grub-efi-bootloader
Unsure whether to use EFI- or BIOS-based GRUB? If the directory
@file{/sys/firmware/efi} exists in the installation image, then you should
probably perform an EFI installation, using @code{grub-efi-bootloader}.
Otherwise you should use the BIOS-based GRUB, known as
@code{grub-bootloader}.  @xref{引导设置}, for more info on
bootloaders.
@end quotation

Once you are done partitioning the target hard disk drive, you have to
create a file system on the relevant partition(s)@footnote{Currently Guix
System only supports ext4, btrfs, JFS, and F2FS file systems.  In
particular, code that reads file system UUIDs and labels only works for
these file system types.}.  For the ESP, if you have one and assuming it is
@file{/dev/sda1}, run:

@example
mkfs.fat -F32 /dev/sda1
@end example

For the root file system, ext4 is the most widely used format.  Other file
systems, such as Btrfs, support compression, which is reported to nicely
complement file deduplication that the daemon performs independently of the
file system (@pxref{调用guix-daemon, deduplication}).

Preferably, assign file systems a label so that you can easily and reliably
refer to them in @code{file-system} declarations (@pxref{文件系统}).
This is typically done using the @code{-L} option of @command{mkfs.ext4} and
related commands.  So, assuming the target root partition lives at
@file{/dev/sda2}, a file system with the label @code{my-root} can be created
with:

@example
mkfs.ext4 -L my-root /dev/sda2
@end example

@cindex encrypted disk
If you are instead planning to encrypt the root partition, you can use the
Cryptsetup/LUKS utilities to do that (see @inlinefmtifelse{html,
@uref{https://linux.die.net/man/8/cryptsetup, @code{man cryptsetup}},
@code{man cryptsetup}} for more information).  Assuming you want to store
the root partition on @file{/dev/sda2}, the command sequence would be along
these lines:

@example
cryptsetup luksFormat /dev/sda2
cryptsetup open --type luks /dev/sda2 my-partition
mkfs.ext4 -L my-root /dev/mapper/my-partition
@end example

Once that is done, mount the target file system under @file{/mnt} with a
command like (again, assuming @code{my-root} is the label of the root file
system):

@example
mount LABEL=my-root /mnt
@end example

Also mount any other file systems you would like to use on the target system
relative to this path.  If you have opted for @file{/boot/efi} as an EFI
mount point for example, mount it at @file{/mnt/boot/efi} now so it is found
by @code{guix system init} afterwards.

Finally, if you plan to use one or more swap partitions (@pxref{Memory
Concepts, swap space,, libc, The GNU C Library Reference Manual}), make sure
to initialize them with @command{mkswap}.  Assuming you have one swap
partition on @file{/dev/sda3}, you would run:

@example
mkswap /dev/sda3
swapon /dev/sda3
@end example

Alternatively, you may use a swap file.  For example, assuming that in the
new system you want to use the file @file{/swapfile} as a swap file, you
would run@footnote{This example will work for many types of file systems
(e.g., ext4).  However, for copy-on-write file systems (e.g., btrfs), the
required steps may be different.  For details, see the manual pages for
@command{mkswap} and @command{swapon}.}:

@example
# This is 10 GiB of swap space.  Adjust "count" to change the size.
dd if=/dev/zero of=/mnt/swapfile bs=1MiB count=10240
# For security, make the file readable and writable only by root.
chmod 600 /mnt/swapfile
mkswap /mnt/swapfile
swapon /mnt/swapfile
@end example

Note that if you have encrypted the root partition and created a swap file
in its file system as described above, then the encryption also protects the
swap file, just like any other file in that file system.

@node 继续安装步骤
@subsection 继续安装步骤

With the target partitions ready and the target root mounted on @file{/mnt},
we're ready to go.  First, run:

@example
herd start cow-store /mnt
@end example

This makes @file{/gnu/store} copy-on-write, such that packages added to it
during the installation phase are written to the target disk on @file{/mnt}
rather than kept in memory.  This is necessary because the first phase of
the @command{guix system init} command (see below) entails downloads or
builds to @file{/gnu/store} which, initially, is an in-memory file system.

Next, you have to edit a file and provide the declaration of the operating
system to be installed.  To that end, the installation system comes with
three text editors.  We recommend GNU nano (@pxref{Top,,, nano, GNU nano
Manual}), which supports syntax highlighting and parentheses matching; other
editors include GNU Zile (an Emacs clone), and nvi (a clone of the original
BSD @command{vi} editor).  We strongly recommend storing that file on the
target root file system, say, as @file{/mnt/etc/config.scm}.  Failing to do
that, you will have lost your configuration file once you have rebooted into
the newly-installed system.

@xref{使用配置系统}, for an overview of the configuration
file.  The example configurations discussed in that section are available
under @file{/etc/configuration} in the installation image.  Thus, to get
started with a system configuration providing a graphical display server (a
``desktop'' system), you can run something along these lines:

@example
# mkdir /mnt/etc
# cp /etc/configuration/desktop.scm /mnt/etc/config.scm
# nano /mnt/etc/config.scm
@end example

You should pay attention to what your configuration file contains, and in
particular:

@itemize
@item
Make sure the @code{bootloader-configuration} form refers to the target you
want to install GRUB on.  It should mention @code{grub-bootloader} if you
are installing GRUB in the legacy way, or @code{grub-efi-bootloader} for
newer UEFI systems.  For legacy systems, the @code{target} field names a
device, like @code{/dev/sda}; for UEFI systems it names a path to a mounted
EFI partition, like @code{/boot/efi}; do make sure the path is currently
mounted and a @code{file-system} entry is specified in your configuration.

@item
Be sure that your file system labels match the value of their respective
@code{device} fields in your @code{file-system} configuration, assuming your
@code{file-system} configuration uses the @code{file-system-label} procedure
in its @code{device} field.

@item
If there are encrypted or RAID partitions, make sure to add a
@code{mapped-devices} field to describe them (@pxref{映射的设备}).
@end itemize

Once you are done preparing the configuration file, the new system must be
initialized (remember that the target root file system is mounted under
@file{/mnt}):

@example
guix system init /mnt/etc/config.scm /mnt
@end example

@noindent
This copies all the necessary files and installs GRUB on @file{/dev/sdX},
unless you pass the @option{--no-bootloader} option.  For more information,
@pxref{调用guix system}.  This command may trigger downloads or builds
of missing packages, which can take some time.

Once that command has completed---and hopefully succeeded!---you can run
@command{reboot} and boot into the new system.  The @code{root} password in
the new system is initially empty; other users' passwords need to be
initialized by running the @command{passwd} command as @code{root}, unless
your configuration specifies otherwise (@pxref{user-account-password, user
account passwords}).  @xref{系统安装之后}, for what's next!


@node 系统安装之后
@section 系统安装之后

Success, you've now booted into Guix System! From then on, you can update
the system whenever you want by running, say:

@example
guix pull
sudo guix system reconfigure /etc/config.scm
@end example

@noindent
This builds a new system generation with the latest packages and services
(@pxref{调用guix system}).  We recommend doing that regularly so that
your system includes the latest security updates (@pxref{安全更新}).

@c See <https://lists.gnu.org/archive/html/guix-devel/2019-01/msg00268.html>.
@quotation 注
@cindex sudo vs. @command{guix pull}
Note that @command{sudo guix} runs your user's @command{guix} command and
@emph{not} root's, because @command{sudo} leaves @env{PATH} unchanged.  To
explicitly run root's @command{guix}, type @command{sudo -i guix @dots{}}.

The difference matters here, because @command{guix pull} updates the
@command{guix} command and package definitions only for the user it is run
as.  This means that if you choose to use @command{guix system reconfigure}
in root's login shell, you'll need to @command{guix pull} separately.
@end quotation

Now, @pxref{入门}, and join us on @code{#guix} on the Freenode
IRC network or on @email{guix-devel@@gnu.org} to share your experience!


@node 在虚拟机里安装 Guix
@section Installing Guix in a Virtual Machine

@cindex virtual machine, Guix System installation
@cindex virtual private server (VPS)
@cindex VPS (virtual private server)
If you'd like to install Guix System in a virtual machine (VM) or on a
virtual private server (VPS) rather than on your beloved machine, this
section is for you.

To boot a @uref{https://qemu.org/,QEMU} VM for installing Guix System in a
disk image, follow these steps:

@enumerate
@item
First, retrieve and decompress the Guix system installation image as
described previously (@pxref{U盘和DVD安装}).

@item
Create a disk image that will hold the installed system.  To make a
qcow2-formatted disk image, use the @command{qemu-img} command:

@example
qemu-img create -f qcow2 guix-system.img 50G
@end example

The resulting file will be much smaller than 50 GB (typically less than 1
MB), but it will grow as the virtualized storage device is filled up.

@item
Boot the USB installation image in an VM:

@example
qemu-system-x86_64 -m 1024 -smp 1 -enable-kvm \
  -nic user,model=virtio-net-pci -boot menu=on,order=d \
  -drive file=guix-system.img \
  -drive media=cdrom,file=guix-system-install-@value{VERSION}.@var{system}.iso
@end example

@code{-enable-kvm} is optional, but significantly improves performance,
@pxref{在虚拟机里运行Guix}.

@item
You're now root in the VM, proceed with the installation process.
@xref{准备安装}, and follow the instructions.
@end enumerate

Once installation is complete, you can boot the system that's on your
@file{guix-system.img} image.  @xref{在虚拟机里运行Guix}, for how to do
that.

@node 构建安装镜像
@section 构建安装镜像

@cindex installation image
The installation image described above was built using the @command{guix
system} command, specifically:

@example
guix system image -t iso9660 gnu/system/install.scm
@end example

Have a look at @file{gnu/system/install.scm} in the source tree, and see
also @ref{调用guix system} for more information about the installation
image.

@section Building the Installation Image for ARM Boards

Many ARM boards require a specific variant of the
@uref{https://www.denx.de/wiki/U-Boot/, U-Boot} bootloader.

If you build a disk image and the bootloader is not available otherwise (on
another boot drive etc), it's advisable to build an image that includes the
bootloader, specifically:

@example
guix system image --system=armhf-linux -e '((@@ (gnu system install) os-with-u-boot) (@@ (gnu system install) installation-os) "A20-OLinuXino-Lime2")'
@end example

@code{A20-OLinuXino-Lime2} is the name of the board.  If you specify an
invalid board, a list of possible boards will be printed.

@c *********************************************************************
@node 入门
@chapter 入门

Presumably, you've reached this section because either you have installed
Guix on top of another distribution (@pxref{安装}), or you've
installed the standalone Guix System (@pxref{系统安装}).  It's
time for you to get started using Guix and this section aims to help you do
that and give you a feel of what it's like.

Guix is about installing software, so probably the first thing you'll want
to do is to actually look for software.  Let's say you're looking for a text
editor, you can run:

@example
guix search text editor
@end example

This command shows you a number of matching @dfn{packages}, each time
showing the package's name, version, a description, and additional info.
Once you've found out the one you want to use, let's say Emacs (ah ha!), you
can go ahead and install it (run this command as a regular user, @emph{no
need for root privileges}!):

@example
guix install emacs
@end example

@cindex profile
You've installed your first package, congrats! The package is now visible in
your default @dfn{profile}, @file{$HOME/.guix-profile}---a profile is a
directory containing installed packages.  In the process, you've probably
noticed that Guix downloaded pre-built binaries; or, if you explicitly chose
to @emph{not} use pre-built binaries, then probably Guix is still building
software (@pxref{substitutes}, for more info).

Unless you're using Guix System, the @command{guix install} command must
have printed this hint:

@example
hint: Consider setting the necessary environment variables by running:

     GUIX_PROFILE="$HOME/.guix-profile"
     . "$GUIX_PROFILE/etc/profile"

Alternately, see `guix package --search-paths -p "$HOME/.guix-profile"'.
@end example

Indeed, you must now tell your shell where @command{emacs} and other
programs installed with Guix are to be found.  Pasting the two lines above
will do just that: it will add @code{$HOME/.guix-profile/bin}---which is
where the installed package is---to the @code{PATH} environment variable.
You can paste these two lines in your shell so they take effect right away,
but more importantly you should add them to @file{~/.bash_profile} (or
equivalent file if you do not use Bash) so that environment variables are
set next time you spawn a shell.  You only need to do this once and other
search paths environment variables will be taken care of similarly---e.g.,
if you eventually install @code{python} and Python libraries,
@code{PYTHONPATH} will be defined.

You can go on installing packages at your will.  To list installed packages,
run:

@example
guix package --list-installed
@end example

To remove a package, you would unsurprisingly run @command{guix remove}.  A
distinguishing feature is the ability to @dfn{roll back} any operation you
made---installation, removal, upgrade---by simply typing:

@example
guix package --roll-back
@end example

This is because each operation is in fact a @dfn{transaction} that creates a
new @dfn{generation}.  These generations and the difference between them can
be displayed by running:

@example
guix package --list-generations
@end example

现在你知道包管理的基本知识了吧！

@quotation Going further
@xref{软件包管理}, for more about package management.  You may like
@dfn{declarative} package management with @command{guix package --manifest},
managing separate @dfn{profiles} with @option{--profile}, deleting old
generations, collecting garbage, and other nifty features that will come in
handy as you become more familiar with Guix.  If you are a developer,
@pxref{开发} for additional tools.  And if you're curious,
@pxref{功能}, to peek under the hood.
@end quotation

Once you've installed a set of packages, you will want to periodically
@emph{upgrade} them to the latest and greatest version.  To do that, you
will first pull the latest revision of Guix and its package collection:

@example
guix pull
@end example

The end result is a new @command{guix} command, under
@file{~/.config/guix/current/bin}.  Unless you're on Guix System, the first
time you run @command{guix pull}, be sure to follow the hint that the
command prints and, similar to what we saw above, paste these two lines in
your terminal and @file{.bash_profile}:

@example
GUIX_PROFILE="$HOME/.config/guix/current"
. "$GUIX_PROFILE/etc/profile"
@end example

@noindent
You must also instruct your shell to point to this new @command{guix}:

@example
hash guix
@end example

At this point, you're running a brand new Guix.  You can thus go ahead and
actually upgrade all the packages you previously installed:

@example
guix upgrade
@end example

As you run this command, you will see that binaries are downloaded (or
perhaps some packages are built), and eventually you end up with the
upgraded packages.  Should one of these upgraded packages not be to your
liking, remember you can always roll back!

You can display the exact revision of Guix you're currently using by
running:

@example
guix describe
@end example

The information it displays is @emph{all it takes to reproduce the exact
same Guix}, be it at a different point in time or on a different machine.

@quotation Going further
@xref{调用guix pull}, for more information.  @xref{通道}, on how to
specify additional @dfn{channels} to pull packages from, how to replicate
Guix, and more.  You may also find @command{time-machine} handy
(@pxref{调用guix archive}).
@end quotation

If you installed Guix System, one of the first things you'll want to do is
to upgrade your system.  Once you've run @command{guix pull} to get the
latest Guix, you can upgrade the system like this:

@example
sudo guix system reconfigure /etc/config.scm
@end example

Upon completion, the system runs the latest versions of its software
packages.  When you eventually reboot, you'll notice a sub-menu in the
bootloader that reads ``Old system generations'': it's what allows you to
boot @emph{an older generation of your system}, should the latest generation
be ``broken'' or otherwise unsatisfying.  Just like for packages, you can
always @emph{roll back} to a previous generation @emph{of the whole system}:

@example
sudo guix system roll-back
@end example

There are many things you'll probably want to tweak on your system: adding
new user accounts, adding new system services, fiddling with the
configuration of those services, etc.  The system configuration is
@emph{entirely} described in the @file{/etc/config.scm} file.  @xref{使用配置系统}, to learn how to change it.

Now you know enough to get started!

@quotation Resources
The rest of this manual provides a reference for all things Guix.  Here are
some additional resources you may find useful:

@itemize
@item
@xref{Top,,, guix-cookbook, The GNU Guix Cookbook}, for a list of ``how-to''
style of recipes for a variety of applications.

@item
The @uref{https://guix.gnu.org/guix-refcard.pdf, GNU Guix Reference Card}
lists in two pages most of the commands and options you'll ever need.

@item
The web site contains @uref{https://guix.gnu.org/en/videos/, instructional
videos} covering topics such as everyday use of Guix, how to get help, and
how to become a contributor.

@item
@xref{文档}, to learn how to access documentation on your computer.
@end itemize

We hope you will enjoy Guix as much as the community enjoys building it!
@end quotation

@c *********************************************************************
@node 软件包管理
@chapter 软件包管理

@cindex packages
The purpose of GNU Guix is to allow users to easily install, upgrade, and
remove software packages, without having to know about their build
procedures or dependencies.  Guix also goes beyond this obvious set of
features.

This chapter describes the main features of Guix, as well as the package
management tools it provides.  Along with the command-line interface
described below (@pxref{调用guix package, @code{guix package}}), you
may also use the Emacs-Guix interface (@pxref{Top,,, emacs-guix, The
Emacs-Guix Reference Manual}), after installing @code{emacs-guix} package
(run @kbd{M-x guix-help} command to start with it):

@example
guix install emacs-guix
@end example

@menu
* 功能::                   Guix怎样让你的生活更美好。
* 调用guix package::       软件包安装，移除等。
* substitutes::              下载构建好的二进制文件。
* 有多个输出的软件包::  单个输入多个输出的软件包。
* 调用guix gc::            运行垃圾回收器。
* 调用guix pull::          获取最新的Guix和发行版。
* Invoking guix time-machine::  Running an older revision of Guix.
* Inferiors::                和其它版本的Guix交互。
* 调用guix describe::      显示你的Guix版本信息。
* 调用guix archive::       导出和导入仓库文件。
@end menu

@node 功能
@section 功能

Here we assume you've already made your first steps with Guix
(@pxref{入门}) and would like to get an overview about what's
going on under the hood.

When using Guix, each package ends up in the @dfn{package store}, in its own
directory---something that resembles @file{/gnu/store/xxx-package-1.2},
where @code{xxx} is a base32 string.

Instead of referring to these directories, users have their own
@dfn{profile}, which points to the packages that they actually want to use.
These profiles are stored within each user's home directory, at
@code{$HOME/.guix-profile}.

For example, @code{alice} installs GCC 4.7.2.  As a result,
@file{/home/alice/.guix-profile/bin/gcc} points to
@file{/gnu/store/@dots{}-gcc-4.7.2/bin/gcc}.  Now, on the same machine,
@code{bob} had already installed GCC 4.8.0.  The profile of @code{bob}
simply continues to point to
@file{/gnu/store/@dots{}-gcc-4.8.0/bin/gcc}---i.e., both versions of GCC
coexist on the same system without any interference.

The @command{guix package} command is the central tool to manage packages
(@pxref{调用guix package}).  It operates on the per-user profiles, and
can be used @emph{with normal user privileges}.

@cindex transactions
The command provides the obvious install, remove, and upgrade operations.
Each invocation is actually a @emph{transaction}: either the specified
operation succeeds, or nothing happens.  Thus, if the @command{guix package}
process is terminated during the transaction, or if a power outage occurs
during the transaction, then the user's profile remains in its previous
state, and remains usable.

In addition, any package transaction may be @emph{rolled back}.  So, if, for
example, an upgrade installs a new version of a package that turns out to
have a serious bug, users may roll back to the previous instance of their
profile, which was known to work well.  Similarly, the global system
configuration on Guix is subject to transactional upgrades and roll-back
(@pxref{使用配置系统}).

All packages in the package store may be @emph{garbage-collected}.  Guix can
determine which packages are still referenced by user profiles, and remove
those that are provably no longer referenced (@pxref{调用guix gc}).
Users may also explicitly remove old generations of their profile so that
the packages they refer to can be collected.

@cindex reproducibility
@cindex 可复现的构建
Guix takes a @dfn{purely functional} approach to package management, as
described in the introduction (@pxref{介绍}).  Each
@file{/gnu/store} package directory name contains a hash of all the inputs
that were used to build that package---compiler, libraries, build scripts,
etc.  This direct correspondence allows users to make sure a given package
installation matches the current state of their distribution.  It also helps
maximize @dfn{build reproducibility}: thanks to the isolated build
environments that are used, a given build is likely to yield bit-identical
files when performed on different machines (@pxref{调用guix-daemon,
container}).

@cindex substitutes
This foundation allows Guix to support @dfn{transparent binary/source
deployment}.  When a pre-built binary for a @file{/gnu/store} item is
available from an external source---a @dfn{substitute}, Guix just downloads
it and unpacks it; otherwise, it builds the package from source, locally
(@pxref{substitutes}).  Because build results are usually bit-for-bit
reproducible, users do not have to trust servers that provide substitutes:
they can force a local build and @emph{challenge} providers (@pxref{调用guix challenge}).

Control over the build environment is a feature that is also useful for
developers.  The @command{guix environment} command allows developers of a
package to quickly set up the right development environment for their
package, without having to manually install the dependencies of the package
into their profile (@pxref{调用guix environment}).

@cindex replication, of software environments
@cindex provenance tracking, of software artifacts
All of Guix and its package definitions is version-controlled, and
@command{guix pull} allows you to ``travel in time'' on the history of Guix
itself (@pxref{调用guix pull}).  This makes it possible to replicate a
Guix instance on a different machine or at a later point in time, which in
turn allows you to @emph{replicate complete software environments}, while
retaining precise @dfn{provenance tracking} of the software.

@node 调用guix package
@section Invoking @command{guix package}

@cindex installing packages
@cindex removing packages
@cindex package installation
@cindex package removal
@cindex profile
The @command{guix package} command is the tool that allows users to install,
upgrade, and remove packages, as well as rolling back to previous
configurations.  These operations work on a user @dfn{profile}---a directory
of installed packages.  Each user has a default profile in
@file{$HOME/.guix-profile}.  The command operates only on the user's own
profile, and works with normal user privileges (@pxref{功能}).  Its
syntax is:

@example
guix package @var{options}
@end example

@cindex transactions
Primarily, @var{options} specifies the operations to be performed during the
transaction.  Upon completion, a new profile is created, but previous
@dfn{generations} of the profile remain available, should the user want to
roll back.

For example, to remove @code{lua} and install @code{guile} and
@code{guile-cairo} in a single transaction:

@example
guix package -r lua -i guile guile-cairo
@end example

@cindex aliases, for @command{guix package}
For your convenience, we also provide the following aliases:

@itemize
@item
@command{guix search} is an alias for @command{guix package -s},
@item
@command{guix install} is an alias for @command{guix package -i},
@item
@command{guix remove} is an alias for @command{guix package -r},
@item
@command{guix upgrade} is an alias for @command{guix package -u},
@item
and @command{guix show} is an alias for @command{guix package --show=}.
@end itemize

These aliases are less expressive than @command{guix package} and provide
fewer options, so in some cases you'll probably want to use @command{guix
package} directly.

@command{guix package} also supports a @dfn{declarative approach} whereby
the user specifies the exact set of packages to be available and passes it
@i{via} the @option{--manifest} option (@pxref{profile-manifest,
@option{--manifest}}).

@cindex profile
For each user, a symlink to the user's default profile is automatically
created in @file{$HOME/.guix-profile}.  This symlink always points to the
current generation of the user's default profile.  Thus, users can add
@file{$HOME/.guix-profile/bin} to their @env{PATH} environment variable, and
so on.
@cindex search paths
If you are not using Guix System, consider adding the following lines to
your @file{~/.bash_profile} (@pxref{Bash Startup Files,,, bash, The GNU Bash
Reference Manual}) so that newly-spawned shells get all the right
environment variable definitions:

@example
GUIX_PROFILE="$HOME/.guix-profile" ; \
source "$GUIX_PROFILE/etc/profile"
@end example

In a multi-user setup, user profiles are stored in a place registered as a
@dfn{garbage-collector root}, which @file{$HOME/.guix-profile} points to
(@pxref{调用guix gc}).  That directory is normally
@code{@var{localstatedir}/guix/profiles/per-user/@var{user}}, where
@var{localstatedir} is the value passed to @code{configure} as
@option{--localstatedir}, and @var{user} is the user name.  The
@file{per-user} directory is created when @command{guix-daemon} is started,
and the @var{user} sub-directory is created by @command{guix package}.

The @var{options} can be among the following:

@table @code

@item --install=@var{package} @dots{}
@itemx -i @var{package} @dots{}
Install the specified @var{package}s.

Each @var{package} may specify either a simple package name, such as
@code{guile}, or a package name followed by an at-sign and version number,
such as @code{guile@@1.8.8} or simply @code{guile@@1.8} (in the latter case,
the newest version prefixed by @code{1.8} is selected).

If no version number is specified, the newest available version will be
selected.  In addition, @var{package} may contain a colon, followed by the
name of one of the outputs of the package, as in @code{gcc:doc} or
@code{binutils@@2.22:lib} (@pxref{有多个输出的软件包}).
Packages with a corresponding name (and optionally version) are searched for
among the GNU distribution modules (@pxref{软件包模块}).

@cindex propagated inputs
Sometimes packages have @dfn{propagated inputs}: these are dependencies that
automatically get installed along with the required package
(@pxref{package-propagated-inputs, @code{propagated-inputs} in
@code{package} objects}, for information about propagated inputs in package
definitions).

@anchor{package-cmd-propagated-inputs}
An example is the GNU MPC library: its C header files refer to those of the
GNU MPFR library, which in turn refer to those of the GMP library.  Thus,
when installing MPC, the MPFR and GMP libraries also get installed in the
profile; removing MPC also removes MPFR and GMP---unless they had also been
explicitly installed by the user.

Besides, packages sometimes rely on the definition of environment variables
for their search paths (see explanation of @option{--search-paths} below).
Any missing or possibly incorrect environment variable definitions are
reported here.

@item --install-from-expression=@var{exp}
@itemx -e @var{exp}
Install the package @var{exp} evaluates to.

@var{exp} must be a Scheme expression that evaluates to a @code{<package>}
object.  This option is notably useful to disambiguate between same-named
variants of a package, with expressions such as @code{(@@ (gnu packages
base) guile-final)}.

Note that this option installs the first output of the specified package,
which may be insufficient when needing a specific output of a
multiple-output package.

@item --install-from-file=@var{file}
@itemx -f @var{file}
Install the package that the code within @var{file} evaluates to.

As an example, @var{file} might contain a definition like this
(@pxref{定义软件包}):

@lisp
@include package-hello.scm
@end lisp

Developers may find it useful to include such a @file{guix.scm} file in the
root of their project source tree that can be used to test development
snapshots and create reproducible development environments (@pxref{调用guix environment}).

The @var{file} may also contain a JSON representation of one or more package
definitions.  Running @code{guix package -f} on @file{hello.json} with the
following contents would result in installing the package @code{greeter}
after building @code{myhello}:

@example
@verbatiminclude package-hello.json
@end example

@item --remove=@var{package} @dots{}
@itemx -r @var{package} @dots{}
Remove the specified @var{package}s.

As for @option{--install}, each @var{package} may specify a version number
and/or output name in addition to the package name.  For instance, @samp{-r
glibc:debug} would remove the @code{debug} output of @code{glibc}.

@item --upgrade[=@var{regexp} @dots{}]
@itemx -u [@var{regexp} @dots{}]
@cindex upgrading packages
Upgrade all the installed packages.  If one or more @var{regexp}s are
specified, upgrade only installed packages whose name matches a
@var{regexp}.  Also see the @option{--do-not-upgrade} option below.

Note that this upgrades package to the latest version of packages found in
the distribution currently installed.  To update your distribution, you
should regularly run @command{guix pull} (@pxref{调用guix pull}).

@cindex package transformations, upgrades
When upgrading, package transformations that were originally applied when
creating the profile are automatically re-applied (@pxref{软件包变换选项。}).  For example, assume you first installed Emacs
from the tip of its development branch with:

@example
guix install emacs-next --with-branch=emacs-next=master
@end example

Next time you run @command{guix upgrade}, Guix will again pull the tip of
the Emacs development branch and build @code{emacs-next} from that checkout.

Note that transformation options such as @option{--with-branch} and
@option{--with-source} depend on external state; it is up to you to ensure
that they work as expected.  You can also discard a transformations that
apply to a package by running:

@example
guix install @var{package}
@end example

@item --do-not-upgrade[=@var{regexp} @dots{}]
When used together with the @option{--upgrade} option, do @emph{not} upgrade
any packages whose name matches a @var{regexp}.  For example, to upgrade all
packages in the current profile except those containing the substring
``emacs'':

@example
$ guix package --upgrade . --do-not-upgrade emacs
@end example

@item @anchor{profile-manifest}--manifest=@var{file}
@itemx -m @var{file}
@cindex profile declaration
@cindex profile manifest
Create a new generation of the profile from the manifest object returned by
the Scheme code in @var{file}.  This option can be repeated several times,
in which case the manifests are concatenated.

This allows you to @emph{declare} the profile's contents rather than
constructing it through a sequence of @option{--install} and similar
commands.  The advantage is that @var{file} can be put under version
control, copied to different machines to reproduce the same profile, and so
on.

@c FIXME: Add reference to (guix profile) documentation when available.
@var{file} must return a @dfn{manifest} object, which is roughly a list of
packages:

@findex packages->manifest
@lisp
(use-package-modules guile emacs)

(packages->manifest
 (list emacs
       guile-2.0
       ;; Use a specific package output.
       (list guile-2.0 "debug")))
@end lisp

@findex specifications->manifest
In this example we have to know which modules define the @code{emacs} and
@code{guile-2.0} variables to provide the right @code{use-package-modules}
line, which can be cumbersome.  We can instead provide regular package
specifications and let @code{specifications->manifest} look up the
corresponding package objects, like this:

@lisp
(specifications->manifest
 '("emacs" "guile@@2.2" "guile@@2.2:debug"))
@end lisp

@xref{export-manifest, @option{--export-manifest}}, to learn how to obtain a
manifest file from an existing profile.

@item --roll-back
@cindex rolling back
@cindex undoing transactions
@cindex transactions, undoing
Roll back to the previous @dfn{generation} of the profile---i.e., undo the
last transaction.

When combined with options such as @option{--install}, roll back occurs
before any other actions.

When rolling back from the first generation that actually contains installed
packages, the profile is made to point to the @dfn{zeroth generation}, which
contains no files apart from its own metadata.

After having rolled back, installing, removing, or upgrading packages
overwrites previous future generations.  Thus, the history of the
generations in a profile is always linear.

@item --switch-generation=@var{pattern}
@itemx -S @var{pattern}
@cindex generations
Switch to a particular generation defined by @var{pattern}.

@var{pattern} may be either a generation number or a number prefixed with
``+'' or ``-''.  The latter means: move forward/backward by a specified
number of generations.  For example, if you want to return to the latest
generation after @option{--roll-back}, use @option{--switch-generation=+1}.

The difference between @option{--roll-back} and
@option{--switch-generation=-1} is that @option{--switch-generation} will
not make a zeroth generation, so if a specified generation does not exist,
the current generation will not be changed.

@item --search-paths[=@var{kind}]
@cindex search paths
Report environment variable definitions, in Bash syntax, that may be needed
in order to use the set of installed packages.  These environment variables
are used to specify @dfn{search paths} for files used by some of the
installed packages.

For example, GCC needs the @env{CPATH} and @env{LIBRARY_PATH} environment
variables to be defined so it can look for headers and libraries in the
user's profile (@pxref{Environment Variables,,, gcc, Using the GNU Compiler
Collection (GCC)}).  If GCC and, say, the C library are installed in the
profile, then @option{--search-paths} will suggest setting these variables
to @file{@var{profile}/include} and @file{@var{profile}/lib}, respectively.

The typical use case is to define these environment variables in the shell:

@example
$ eval `guix package --search-paths`
@end example

@var{kind} may be one of @code{exact}, @code{prefix}, or @code{suffix},
meaning that the returned environment variable definitions will either be
exact settings, or prefixes or suffixes of the current value of these
variables.  When omitted, @var{kind} defaults to @code{exact}.

This option can also be used to compute the @emph{combined} search paths of
several profiles.  Consider this example:

@example
$ guix package -p foo -i guile
$ guix package -p bar -i guile-json
$ guix package -p foo -p bar --search-paths
@end example

The last command above reports about the @env{GUILE_LOAD_PATH} variable,
even though, taken individually, neither @file{foo} nor @file{bar} would
lead to that recommendation.


@cindex profile, choosing
@item --profile=@var{profile}
@itemx -p @var{profile}
Use @var{profile} instead of the user's default profile.

@var{profile} must be the name of a file that will be created upon
completion.  Concretely, @var{profile} will be a mere symbolic link
(``symlink'') pointing to the actual profile where packages are installed:

@example
$ guix install hello -p ~/code/my-profile
@dots{}
$ ~/code/my-profile/bin/hello
Hello, world!
@end example

All it takes to get rid of the profile is to remove this symlink and its
siblings that point to specific generations:

@example
$ rm ~/code/my-profile ~/code/my-profile-*-link
@end example

@item --list-profiles
List all the user's profiles:

@example
$ guix package --list-profiles
/home/charlie/.guix-profile
/home/charlie/code/my-profile
/home/charlie/code/devel-profile
/home/charlie/tmp/test
@end example

When running as root, list all the profiles of all the users.

@cindex collisions, in a profile
@cindex colliding packages in profiles
@cindex profile collisions
@item --allow-collisions
Allow colliding packages in the new profile.  Use at your own risk!

By default, @command{guix package} reports as an error @dfn{collisions} in
the profile.  Collisions happen when two or more different versions or
variants of a given package end up in the profile.

@item --bootstrap
Use the bootstrap Guile to build the profile.  This option is only useful to
distribution developers.

@end table

In addition to these actions, @command{guix package} supports the following
options to query the current state of a profile, or the availability of
packages:

@table @option

@item --search=@var{regexp}
@itemx -s @var{regexp}
@anchor{guix-search}
@cindex searching for packages
List the available packages whose name, synopsis, or description matches
@var{regexp} (in a case-insensitive fashion), sorted by relevance.  Print
all the metadata of matching packages in @code{recutils} format (@pxref{Top,
GNU recutils databases,, recutils, GNU recutils manual}).

This allows specific fields to be extracted using the @command{recsel}
command, for instance:

@example
$ guix package -s malloc | recsel -p name,version,relevance
name: jemalloc
version: 4.5.0
relevance: 6

name: glibc
version: 2.25
relevance: 1

name: libgc
version: 7.6.0
relevance: 1
@end example

Similarly, to show the name of all the packages available under the terms of
the GNU@tie{}LGPL version 3:

@example
$ guix package -s "" | recsel -p name -e 'license ~ "LGPL 3"'
name: elfutils

name: gmp
@dots{}
@end example

It is also possible to refine search results using several @code{-s} flags
to @command{guix package}, or several arguments to @command{guix search}.
For example, the following command returns a list of board games (this time
using the @command{guix search} alias):

@example
$ guix search '\<board\>' game | recsel -p name
name: gnubg
@dots{}
@end example

If we were to omit @code{-s game}, we would also get software packages that
deal with printed circuit boards; removing the angle brackets around
@code{board} would further add packages that have to do with keyboards.

And now for a more elaborate example.  The following command searches for
cryptographic libraries, filters out Haskell, Perl, Python, and Ruby
libraries, and prints the name and synopsis of the matching packages:

@example
$ guix search crypto library | \
    recsel -e '! (name ~ "^(ghc|perl|python|ruby)")' -p name,synopsis
@end example

@noindent
@xref{Selection Expressions,,, recutils, GNU recutils manual}, for more
information on @dfn{selection expressions} for @code{recsel -e}.

@item --show=@var{package}
Show details about @var{package}, taken from the list of available packages,
in @code{recutils} format (@pxref{Top, GNU recutils databases,, recutils,
GNU recutils manual}).

@example
$ guix package --show=python | recsel -p name,version
name: python
version: 2.7.6

name: python
version: 3.3.5
@end example

You may also specify the full name of a package to only get details about a
specific version of it (this time using the @command{guix show} alias):
@example
$ guix show python@@3.4 | recsel -p name,version
name: python
version: 3.4.3
@end example



@item --list-installed[=@var{regexp}]
@itemx -I [@var{regexp}]
List the currently installed packages in the specified profile, with the
most recently installed packages shown last.  When @var{regexp} is
specified, list only installed packages whose name matches @var{regexp}.

For each installed package, print the following items, separated by tabs:
the package name, its version string, the part of the package that is
installed (for instance, @code{out} for the default output, @code{include}
for its headers, etc.), and the path of this package in the store.

@item --list-available[=@var{regexp}]
@itemx -A [@var{regexp}]
List packages currently available in the distribution for this system
(@pxref{GNU发行版}).  When @var{regexp} is specified, list only
available packages whose name matches @var{regexp}.

For each package, print the following items separated by tabs: its name, its
version string, the parts of the package (@pxref{有多个输出的软件包}), and the source location of its definition.

@item --list-generations[=@var{pattern}]
@itemx -l [@var{pattern}]
@cindex generations
Return a list of generations along with their creation dates; for each
generation, show the installed packages, with the most recently installed
packages shown last.  Note that the zeroth generation is never shown.

For each installed package, print the following items, separated by tabs:
the name of a package, its version string, the part of the package that is
installed (@pxref{有多个输出的软件包}), and the location of this
package in the store.

When @var{pattern} is used, the command returns only matching generations.
Valid patterns include:

@itemize
@item @emph{Integers and comma-separated integers}.  Both patterns denote
generation numbers.  For instance, @option{--list-generations=1} returns the
first one.

And @option{--list-generations=1,8,2} outputs three generations in the
specified order.  Neither spaces nor trailing commas are allowed.

@item @emph{Ranges}.  @option{--list-generations=2..9} prints the
specified generations and everything in between.  Note that the start of a
range must be smaller than its end.

It is also possible to omit the endpoint.  For example,
@option{--list-generations=2..}, returns all generations starting from the
second one.

@item @emph{Durations}.  You can also get the last @emph{N}@tie{}days, weeks,
or months by passing an integer along with the first letter of the
duration.  For example, @option{--list-generations=20d} lists generations
that are up to 20 days old.
@end itemize

@item --delete-generations[=@var{pattern}]
@itemx -d [@var{pattern}]
When @var{pattern} is omitted, delete all generations except the current
one.

This command accepts the same patterns as @option{--list-generations}.  When
@var{pattern} is specified, delete the matching generations.  When
@var{pattern} specifies a duration, generations @emph{older} than the
specified duration match.  For instance, @option{--delete-generations=1m}
deletes generations that are more than one month old.

If the current generation matches, it is @emph{not} deleted.  Also, the
zeroth generation is never deleted.

Note that deleting generations prevents rolling back to them.  Consequently,
this command must be used with care.

@cindex manifest, exporting
@anchor{export-manifest}
@item --export-manifest
Write to standard output a manifest suitable for @option{--manifest}
corresponding to the chosen profile(s).

This option is meant to help you migrate from the ``imperative'' operating
mode---running @command{guix install}, @command{guix upgrade}, etc.---to the
declarative mode that @option{--manifest} offers.

Be aware that the resulting manifest @emph{approximates} what your profile
actually contains; for instance, depending on how your profile was created,
it can refer to packages or package versions that are not exactly what you
specified.

Keep in mind that a manifest is purely symbolic: it only contains package
names and possibly versions, and their meaning varies over time.  If you
wish to ``pin'' channels to the revisions that were used to build the
profile(s), see @option{--export-channels} below.

@cindex pinning, channel revisions of a profile
@item --export-channels
Write to standard output the list of channels used by the chosen profile(s),
in a format suitable for @command{guix pull --channels} or @command{guix
time-machine --channels} (@pxref{通道}).

Together with @option{--export-manifest}, this option provides information
allowing you to replicate the current profile (@pxref{Replicating Guix}).

However, note that the output of this command @emph{approximates} what was
actually used to build this profile.  In particular, a single profile might
have been built from several different revisions of the same channel.  In
that case, @option{--export-manifest} chooses the last one and writes the
list of other revisions in a comment.  If you really need to pick packages
from different channel revisions, you can use inferiors in your manifest to
do so (@pxref{Inferiors}).

Together with @option{--export-manifest}, this is a good starting point if
you are willing to migrate from the ``imperative'' model to the fully
declarative model consisting of a manifest file along with a channels file
pinning the exact channel revision(s) you want.
@end table

Finally, since @command{guix package} may actually start build processes, it
supports all the common build options (@pxref{普通的构建选项}).  It
also supports package transformation options, such as
@option{--with-source}, and preserves them across upgrades (@pxref{软件包变换选项。}).

@node substitutes
@section substitutes

@cindex substitutes
@cindex pre-built binaries
Guix supports transparent source/binary deployment, which means that it can
either build things locally, or download pre-built items from a server, or
both.  We call these pre-built items @dfn{substitutes}---they are
substitutes for local build results.  In many cases, downloading a
substitute is much faster than building things locally.

Substitutes can be anything resulting from a derivation build
(@pxref{Derivations}).  Of course, in the common case, they are pre-built
package binaries, but source tarballs, for instance, which also result from
derivation builds, can be available as substitutes.

@menu
* 官方的substitute服务器::  substitute的一个特殊来源。
* 授权substitute服务器。::  怎么开启或关闭substitute。
* Getting Substitutes from Other Servers::  Substitute diversity.
* 验证substitute::         Guix怎样验证substitute。
* 代理设置::             怎样通过代理获取substitute。
* substitute失败::         当substitute失败时会发生什么。
* 关于信任二进制文件::  你怎么能信任二进制的 blob 呢？
@end menu

@node 官方的substitute服务器
@subsection 官方的substitute服务器

@cindex build farm
The @code{@value{SUBSTITUTE-SERVER}} server is a front-end to an official
build farm that builds packages from Guix continuously for some
architectures, and makes them available as substitutes.  This is the default
source of substitutes; it can be overridden by passing the
@option{--substitute-urls} option either to @command{guix-daemon}
(@pxref{daemon-substitute-urls,, @code{guix-daemon --substitute-urls}})  or
to client tools such as @command{guix package}
(@pxref{client-substitute-urls,, client @option{--substitute-urls} option}).

Substitute URLs can be either HTTP or HTTPS.  HTTPS is recommended because
communications are encrypted; conversely, using HTTP makes all
communications visible to an eavesdropper, who could use the information
gathered to determine, for instance, whether your system has unpatched
security vulnerabilities.

Substitutes from the official build farm are enabled by default when using
Guix System (@pxref{GNU发行版}).  However, they are disabled by
default when using Guix on a foreign distribution, unless you have
explicitly enabled them via one of the recommended installation steps
(@pxref{安装}).  The following paragraphs describe how to enable or
disable substitutes for the official build farm; the same procedure can also
be used to enable substitutes for any other substitute server.

@node 授权substitute服务器。
@subsection 授权substitute服务器。

@cindex security
@cindex substitutes，对其授权
@cindex access control list (ACL), for substitutes
@cindex ACL (access control list), for substitutes
To allow Guix to download substitutes from @code{@value{SUBSTITUTE-SERVER}}
or a mirror thereof, you must add its public key to the access control list
(ACL) of archive imports, using the @command{guix archive} command
(@pxref{调用guix archive}).  Doing so implies that you trust
@code{@value{SUBSTITUTE-SERVER}} to not be compromised and to serve genuine
substitutes.

@quotation 注
If you are using Guix System, you can skip this section: Guix System
authorizes substitutes from @code{@value{SUBSTITUTE-SERVER}} by default.
@end quotation

The public key for @code{@value{SUBSTITUTE-SERVER}} is installed along with
Guix, in @code{@var{prefix}/share/guix/@value{SUBSTITUTE-SERVER}.pub}, where
@var{prefix} is the installation prefix of Guix.  If you installed Guix from
source, make sure you checked the GPG signature of
@file{guix-@value{VERSION}.tar.gz}, which contains this public key file.
Then, you can run something like this:

@example
# guix archive --authorize < @var{prefix}/share/guix/@value{SUBSTITUTE-SERVER}.pub
@end example

Once this is in place, the output of a command like @code{guix build} should
change from something like:

@example
$ guix build emacs --dry-run
The following derivations would be built:
   /gnu/store/yr7bnx8xwcayd6j95r2clmkdl1qh688w-emacs-24.3.drv
   /gnu/store/x8qsh1hlhgjx6cwsjyvybnfv2i37z23w-dbus-1.6.4.tar.gz.drv
   /gnu/store/1ixwp12fl950d15h2cj11c73733jay0z-alsa-lib-1.0.27.1.tar.bz2.drv
   /gnu/store/nlma1pw0p603fpfiqy7kn4zm105r5dmw-util-linux-2.21.drv
@dots{}
@end example

@noindent
to something like:

@example
$ guix build emacs --dry-run
112.3 MB would be downloaded:
   /gnu/store/pk3n22lbq6ydamyymqkkz7i69wiwjiwi-emacs-24.3
   /gnu/store/2ygn4ncnhrpr61rssa6z0d9x22si0va3-libjpeg-8d
   /gnu/store/71yz6lgx4dazma9dwn2mcjxaah9w77jq-cairo-1.12.16
   /gnu/store/7zdhgp0n1518lvfn8mb96sxqfmvqrl7v-libxrender-0.9.7
@dots{}
@end example

@noindent
The text changed from ``The following derivations would be built'' to
``112.3 MB would be downloaded''.  This indicates that substitutes from
@code{@value{SUBSTITUTE-SERVER}} are usable and will be downloaded, when
possible, for future builds.

@cindex substitutes, how to disable
The substitute mechanism can be disabled globally by running
@code{guix-daemon} with @option{--no-substitutes} (@pxref{调用guix-daemon}).  It can also be disabled temporarily by passing the
@option{--no-substitutes} option to @command{guix package}, @command{guix
build}, and other command-line tools.

@node Getting Substitutes from Other Servers
@subsection Getting Substitutes from Other Servers

@cindex substitute servers, adding more
Guix can look up and fetch substitutes from several servers.  This is useful
when you are using packages from additional channels for which the official
server does not have substitutes but another server provides them.  Another
situation where this is useful is when you would prefer to download from
your organization's substitute server, resorting to the official server only
as a fallback or dismissing it altogether.

You can give Guix a list of substitute server URLs and it will check them in
the specified order.  You also need to explicitly authorize the public keys
of substitute servers to instruct Guix to accept the substitutes they sign.

On Guix System, this is achieved by modifying the configuration of the
@code{guix} service.  Since the @code{guix} service is part of the default
lists of services, @code{%base-services} and @code{%desktop-services}, you
can use @code{modify-services} to change its configuration and add the URLs
and substitute keys that you want (@pxref{服务参考,
@code{modify-services}}).

As an example, suppose you want to fetch substitutes from
@code{guix.example.org} and to authorize the signing key of that server, in
addition to the default @code{@value{SUBSTITUTE-SERVER}}.  The resulting
operating system configuration will look something like:

@lisp
(operating-system
  ;; @dots{}
  (services
    ;; Assume we're starting from '%desktop-services'.  Replace it
    ;; with the list of services you're actually using.
    (modify-services %desktop-services
      (guix-service-type config =>
                        (guix-configuration
                          (inherit config)
                          (substitute-urls
                            (append (list "https://guix.example.org")
                                    %default-substitute-urls))
                          (authorized-keys
                            (append (list (local-file "./key.pub"))
                                    %default-authorized-guix-keys)))))))
@end lisp

This assumes that the file @file{key.pub} contains the signing key of
@code{guix.example.org}.  With this change in place in your operating system
configuration file (say @file{/etc/config.scm}), you can reconfigure and
restart the @code{guix-daemon} service or reboot so the changes take effect:

@example
$ sudo guix system reconfigure /etc/config.scm
$ sudo herd restart guix-daemon
@end example

If you're running Guix on a ``foreign distro'', you would instead take the
following steps to get substitutes from additional servers:

@enumerate
@item
Edit the service configuration file for @code{guix-daemon}; when using
systemd, this is normally @file{/etc/systemd/system/guix-daemon.service}.
Add the @option{--substitute-urls} option on the @command{guix-daemon}
command line and list the URLs of interest (@pxref{daemon-substitute-urls,
@code{guix-daemon --substitute-urls}}):

@example
@dots{} --substitute-urls='https://guix.example.org https://@value{SUBSTITUTE-SERVER}'
@end example

@item
Restart the daemon.  For systemd, it goes like this:

@example
systemctl daemon-reload
systemctl restart guix-daemon.service
@end example

@item
Authorize the key of the new server (@pxref{调用guix archive}):

@example
guix archive --authorize < key.pub
@end example

Again this assumes @file{key.pub} contains the public key that
@code{guix.example.org} uses to sign substitutes.
@end enumerate

Now you're all set! Substitutes will be preferably taken from
@code{https://guix.example.org}, using @code{@value{SUBSTITUTE-SERVER}} as a
fallback.  Of course you can list as many substitute servers as you like,
with the caveat that substitute lookup can be slowed down if too many
servers need to be contacted.

Note that there are also situations where one may want to add the URL of a
substitute server @emph{without} authorizing its key.  @xref{验证substitute}, to understand this fine point.

@node 验证substitute
@subsection 验证substitute

@cindex digital signatures
Guix detects and raises an error when attempting to use a substitute that
has been tampered with.  Likewise, it ignores substitutes that are not
signed, or that are not signed by one of the keys listed in the ACL.

There is one exception though: if an unauthorized server provides
substitutes that are @emph{bit-for-bit identical} to those provided by an
authorized server, then the unauthorized server becomes eligible for
downloads.  For example, assume we have chosen two substitute servers with
this option:

@example
--substitute-urls="https://a.example.org https://b.example.org"
@end example

@noindent
@cindex 可复现的构建
If the ACL contains only the key for @samp{b.example.org}, and if
@samp{a.example.org} happens to serve the @emph{exact same} substitutes,
then Guix will download substitutes from @samp{a.example.org} because it
comes first in the list and can be considered a mirror of
@samp{b.example.org}.  In practice, independent build machines usually
produce the same binaries, thanks to bit-reproducible builds (see below).

When using HTTPS, the server's X.509 certificate is @emph{not} validated (in
other words, the server is not authenticated), contrary to what HTTPS
clients such as Web browsers usually do.  This is because Guix authenticates
substitute information itself, as explained above, which is what we care
about (whereas X.509 certificates are about authenticating bindings between
domain names and public keys).

@node 代理设置
@subsection 代理设置

@vindex http_proxy
@vindex https_proxy
Substitutes are downloaded over HTTP or HTTPS@.  The @env{http_proxy} and
@env{https_proxy} environment variables can be set in the environment of
@command{guix-daemon} and are honored for downloads of substitutes.  Note
that the value of those environment variables in the environment where
@command{guix build}, @command{guix package}, and other client commands are
run has @emph{absolutely no effect}.

@node substitute失败
@subsection substitute失败

Even when a substitute for a derivation is available, sometimes the
substitution attempt will fail.  This can happen for a variety of reasons:
the substitute server might be offline, the substitute may recently have
been deleted, the connection might have been interrupted, etc.

When substitutes are enabled and a substitute for a derivation is available,
but the substitution attempt fails, Guix will attempt to build the
derivation locally depending on whether or not @option{--fallback} was given
(@pxref{fallback-option,, common build option @option{--fallback}}).
Specifically, if @option{--fallback} was omitted, then no local build will
be performed, and the derivation is considered to have failed.  However, if
@option{--fallback} was given, then Guix will attempt to build the
derivation locally, and the success or failure of the derivation depends on
the success or failure of the local build.  Note that when substitutes are
disabled or no substitute is available for the derivation in question, a
local build will @emph{always} be performed, regardless of whether or not
@option{--fallback} was given.

To get an idea of how many substitutes are available right now, you can try
running the @command{guix weather} command (@pxref{调用guix weather}).
This command provides statistics on the substitutes provided by a server.

@node 关于信任二进制文件
@subsection 关于信任二进制文件

@cindex trust, of pre-built binaries
Today, each individual's control over their own computing is at the mercy of
institutions, corporations, and groups with enough power and determination
to subvert the computing infrastructure and exploit its weaknesses.  While
using @code{@value{SUBSTITUTE-SERVER}} substitutes can be convenient, we
encourage users to also build on their own, or even run their own build
farm, such that @code{@value{SUBSTITUTE-SERVER}} is less of an interesting
target.  One way to help is by publishing the software you build using
@command{guix publish} so that others have one more choice of server to
download substitutes from (@pxref{调用guix publish}).

Guix has the foundations to maximize build reproducibility
(@pxref{功能}).  In most cases, independent builds of a given package or
derivation should yield bit-identical results.  Thus, through a diverse set
of independent package builds, we can strengthen the integrity of our
systems.  The @command{guix challenge} command aims to help users assess
substitute servers, and to assist developers in finding out about
non-deterministic package builds (@pxref{调用guix challenge}).
Similarly, the @option{--check} option of @command{guix build} allows users
to check whether previously-installed substitutes are genuine by rebuilding
them locally (@pxref{build-check, @command{guix build --check}}).

In the future, we want Guix to have support to publish and retrieve binaries
to/from other users, in a peer-to-peer fashion.  If you would like to
discuss this project, join us on @email{guix-devel@@gnu.org}.

@node 有多个输出的软件包
@section 有多个输出的软件包

@cindex multiple-output packages
@cindex package outputs
@cindex outputs

Often, packages defined in Guix have a single @dfn{output}---i.e., the
source package leads to exactly one directory in the store.  When running
@command{guix install glibc}, one installs the default output of the GNU
libc package; the default output is called @code{out}, but its name can be
omitted as shown in this command.  In this particular case, the default
output of @code{glibc} contains all the C header files, shared libraries,
static libraries, Info documentation, and other supporting files.

Sometimes it is more appropriate to separate the various types of files
produced from a single source package into separate outputs.  For instance,
the GLib C library (used by GTK+ and related packages)  installs more than
20 MiB of reference documentation as HTML pages.  To save space for users
who do not need it, the documentation goes to a separate output, called
@code{doc}.  To install the main GLib output, which contains everything but
the documentation, one would run:

@example
guix install glib
@end example

@cindex documentation
The command to install its documentation is:

@example
guix install glib:doc
@end example

Some packages install programs with different ``dependency footprints''.
For instance, the WordNet package installs both command-line tools and
graphical user interfaces (GUIs).  The former depend solely on the C
library, whereas the latter depend on Tcl/Tk and the underlying X
libraries.  In this case, we leave the command-line tools in the default
output, whereas the GUIs are in a separate output.  This allows users who do
not need the GUIs to save space.  The @command{guix size} command can help
find out about such situations (@pxref{调用guix size}).  @command{guix
graph} can also be helpful (@pxref{调用guix graph}).

There are several such multiple-output packages in the GNU distribution.
Other conventional output names include @code{lib} for libraries and
possibly header files, @code{bin} for stand-alone programs, and @code{debug}
for debugging information (@pxref{安装调试文件}).  The outputs
of a packages are listed in the third column of the output of @command{guix
package --list-available} (@pxref{调用guix package}).


@node 调用guix gc
@section Invoking @command{guix gc}

@cindex garbage collector
@cindex disk space
Packages that are installed, but not used, may be @dfn{garbage-collected}.
The @command{guix gc} command allows users to explicitly run the garbage
collector to reclaim space from the @file{/gnu/store} directory.  It is the
@emph{only} way to remove files from @file{/gnu/store}---removing files or
directories manually may break it beyond repair!

@cindex GC根
@cindex 垃圾收集的根
The garbage collector has a set of known @dfn{roots}: any file under
@file{/gnu/store} reachable from a root is considered @dfn{live} and cannot
be deleted; any other file is considered @dfn{dead} and may be deleted.  The
set of garbage collector roots (``GC roots'' for short)  includes default
user profiles; by default, the symlinks under @file{/var/guix/gcroots}
represent these GC roots.  New GC roots can be added with @command{guix
build --root}, for example (@pxref{调用guix build}).  The @command{guix
gc --list-roots} command lists them.

Prior to running @code{guix gc --collect-garbage} to make space, it is often
useful to remove old generations from user profiles; that way, old package
builds referenced by those generations can be reclaimed.  This is achieved
by running @code{guix package --delete-generations} (@pxref{调用guix package}).

Our recommendation is to run a garbage collection periodically, or when you
are short on disk space.  For instance, to guarantee that at least 5@tie{}GB
are available on your disk, simply run:

@example
guix gc -F 5G
@end example

It is perfectly safe to run as a non-interactive periodic job
(@pxref{执行计划任务}, for how to set up such a job).  Running
@command{guix gc} with no arguments will collect as much garbage as it can,
but that is often inconvenient: you may find yourself having to rebuild or
re-download software that is ``dead'' from the GC viewpoint but that is
necessary to build other pieces of software---e.g., the compiler tool chain.

The @command{guix gc} command has three modes of operation: it can be used
to garbage-collect any dead files (the default), to delete specific files
(the @option{--delete} option), to print garbage-collector information, or
for more advanced queries.  The garbage collection options are as follows:

@table @code
@item --collect-garbage[=@var{min}]
@itemx -C [@var{min}]
Collect garbage---i.e., unreachable @file{/gnu/store} files and
sub-directories.  This is the default operation when no option is specified.

When @var{min} is given, stop once @var{min} bytes have been collected.
@var{min} may be a number of bytes, or it may include a unit as a suffix,
such as @code{MiB} for mebibytes and @code{GB} for gigabytes (@pxref{Block
size, size specifications,, coreutils, GNU Coreutils}).

When @var{min} is omitted, collect all the garbage.

@item --free-space=@var{free}
@itemx -F @var{free}
Collect garbage until @var{free} space is available under @file{/gnu/store},
if possible; @var{free} denotes storage space, such as @code{500MiB}, as
described above.

When @var{free} or more is already available in @file{/gnu/store}, do
nothing and exit immediately.

@item --delete-generations[=@var{duration}]
@itemx -d [@var{duration}]
Before starting the garbage collection process, delete all the generations
older than @var{duration}, for all the user profiles; when run as root, this
applies to all the profiles @emph{of all the users}.

For example, this command deletes all the generations of all your profiles
that are older than 2 months (except generations that are current), and then
proceeds to free space until at least 10 GiB are available:

@example
guix gc -d 2m -F 10G
@end example

@item --delete
@itemx -D
Attempt to delete all the store files and directories specified as
arguments.  This fails if some of the files are not in the store, or if they
are still live.

@item --list-failures
List store items corresponding to cached build failures.

This prints nothing unless the daemon was started with
@option{--cache-failures} (@pxref{调用guix-daemon,
@option{--cache-failures}}).

@item --list-roots
List the GC roots owned by the user; when run as root, list @emph{all} the
GC roots.

@item --list-busy
List store items in use by currently running processes.  These store items
are effectively considered GC roots: they cannot be deleted.

@item --clear-failures
Remove the specified store items from the failed-build cache.

Again, this option only makes sense when the daemon is started with
@option{--cache-failures}.  Otherwise, it does nothing.

@item --list-dead
Show the list of dead files and directories still present in the
store---i.e., files and directories no longer reachable from any root.

@item --list-live
Show the list of live store files and directories.

@end table

In addition, the references among existing store files can be queried:

@table @code

@item --references
@itemx --referrers
@cindex package dependencies
List the references (respectively, the referrers) of store files given as
arguments.

@item --requisites
@itemx -R
@cindex closure
List the requisites of the store files passed as arguments.  Requisites
include the store files themselves, their references, and the references of
these, recursively.  In other words, the returned list is the
@dfn{transitive closure} of the store files.

@xref{调用guix size}, for a tool to profile the size of the closure of
an element.  @xref{调用guix graph}, for a tool to visualize the graph
of references.

@item --derivers
@cindex derivation
Return the derivation(s) leading to the given store items
(@pxref{Derivations}).

For example, this command:

@example
guix gc --derivers $(guix package -I ^emacs$ | cut -f4)
@end example

@noindent
returns the @file{.drv} file(s) leading to the @code{emacs} package
installed in your profile.

Note that there may be zero matching @file{.drv} files, for instance because
these files have been garbage-collected.  There can also be more than one
matching @file{.drv} due to fixed-output derivations.
@end table

Lastly, the following options allow you to check the integrity of the store
and to control disk usage.

@table @option

@item --verify[=@var{options}]
@cindex integrity, of the store
@cindex integrity checking
Verify the integrity of the store.

By default, make sure that all the store items marked as valid in the
database of the daemon actually exist in @file{/gnu/store}.

When provided, @var{options} must be a comma-separated list containing one
or more of @code{contents} and @code{repair}.

When passing @option{--verify=contents}, the daemon computes the content
hash of each store item and compares it against its hash in the database.
Hash mismatches are reported as data corruptions.  Because it traverses
@emph{all the files in the store}, this command can take a long time,
especially on systems with a slow disk drive.

@cindex repairing the store
@cindex corruption, recovering from
Using @option{--verify=repair} or @option{--verify=contents,repair} causes
the daemon to try to repair corrupt store items by fetching substitutes for
them (@pxref{substitutes}).  Because repairing is not atomic, and thus
potentially dangerous, it is available only to the system administrator.  A
lightweight alternative, when you know exactly which items in the store are
corrupt, is @command{guix build --repair} (@pxref{调用guix build}).

@item --optimize
@cindex 去重
Optimize the store by hard-linking identical files---this is
@dfn{deduplication}.

The daemon performs deduplication after each successful build or archive
import, unless it was started with @option{--disable-deduplication}
(@pxref{调用guix-daemon, @option{--disable-deduplication}}).  Thus,
this option is primarily useful when the daemon was running with
@option{--disable-deduplication}.

@end table

@node 调用guix pull
@section Invoking @command{guix pull}

@cindex upgrading Guix
@cindex updating Guix
@cindex @command{guix pull}
@cindex pull
@cindex security, @command{guix pull}
@cindex authenticity, of code obtained with @command{guix pull}
Packages are installed or upgraded to the latest version available in the
distribution currently available on your local machine.  To update that
distribution, along with the Guix tools, you must run @command{guix pull}:
the command downloads the latest Guix source code and package descriptions,
and deploys it.  Source code is downloaded from a @uref{https://git-scm.com,
Git} repository, by default the official GNU@tie{}Guix repository, though
this can be customized.  @command{guix pull} ensures that the code it
downloads is @emph{authentic} by verifying that commits are signed by Guix
developers.

Specifically, @command{guix pull} downloads code from the @dfn{channels}
(@pxref{通道}) specified by one of the followings, in this order:

@enumerate
@item
the @option{--channels} option;
@item
the user's @file{~/.config/guix/channels.scm} file;
@item
the system-wide @file{/etc/guix/channels.scm} file;
@item
the built-in default channels specified in the @code{%default-channels}
variable.
@end enumerate

On completion, @command{guix package} will use packages and package versions
from this just-retrieved copy of Guix.  Not only that, but all the Guix
commands and Scheme modules will also be taken from that latest version.
New @command{guix} sub-commands added by the update also become available.

Any user can update their Guix copy using @command{guix pull}, and the
effect is limited to the user who ran @command{guix pull}.  For instance,
when user @code{root} runs @command{guix pull}, this has no effect on the
version of Guix that user @code{alice} sees, and vice versa.

The result of running @command{guix pull} is a @dfn{profile} available under
@file{~/.config/guix/current} containing the latest Guix.  Thus, make sure
to add it to the beginning of your search path so that you use the latest
version, and similarly for the Info manual (@pxref{文档}):

@example
export PATH="$HOME/.config/guix/current/bin:$PATH"
export INFOPATH="$HOME/.config/guix/current/share/info:$INFOPATH"
@end example

The @option{--list-generations} or @option{-l} option lists past generations
produced by @command{guix pull}, along with details about their provenance:

@example
$ guix pull -l
Generation 1	Jun 10 2018 00:18:18
  guix 65956ad
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: 65956ad3526ba09e1f7a40722c96c6ef7c0936fe

Generation 2	Jun 11 2018 11:02:49
  guix e0cc7f6
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: e0cc7f669bec22c37481dd03a7941c7d11a64f1d
  2 new packages: keepalived, libnfnetlink
  6 packages upgraded: emacs-nix-mode@@2.0.4,
    guile2.0-guix@@0.14.0-12.77a1aac, guix@@0.14.0-12.77a1aac,
    heimdal@@7.5.0, milkytracker@@1.02.00, nix@@2.0.4

Generation 3	Jun 13 2018 23:31:07	(current)
  guix 844cc1c
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: 844cc1c8f394f03b404c5bb3aee086922373490c
  28 new packages: emacs-helm-ls-git, emacs-helm-mu, @dots{}
  69 packages upgraded: borg@@1.1.6, cheese@@3.28.0, @dots{}
@end example

@xref{调用guix describe, @command{guix describe}}, for other ways to
describe the current status of Guix.

This @code{~/.config/guix/current} profile works exactly like the profiles
created by @command{guix package} (@pxref{调用guix package}).  That is,
you can list generations, roll back to the previous generation---i.e., the
previous Guix---and so on:

@example
$ guix pull --roll-back
switched from generation 3 to 2
$ guix pull --delete-generations=1
deleting /var/guix/profiles/per-user/charlie/current-guix-1-link
@end example

You can also use @command{guix package} (@pxref{调用guix package})  to
manage the profile by naming it explicitly:
@example
$ guix package -p ~/.config/guix/current --roll-back
switched from generation 3 to 2
$ guix package -p ~/.config/guix/current --delete-generations=1
deleting /var/guix/profiles/per-user/charlie/current-guix-1-link
@end example

The @command{guix pull} command is usually invoked with no arguments, but it
supports the following options:

@table @code
@item --url=@var{url}
@itemx --commit=@var{commit}
@itemx --branch=@var{branch}
Download code for the @code{guix} channel from the specified @var{url}, at
the given @var{commit} (a valid Git commit ID represented as a hexadecimal
string), or @var{branch}.

@cindex @file{channels.scm}, configuration file
@cindex configuration file for channels
These options are provided for convenience, but you can also specify your
configuration in the @file{~/.config/guix/channels.scm} file or using the
@option{--channels} option (see below).

@item --channels=@var{file}
@itemx -C @var{file}
Read the list of channels from @var{file} instead of
@file{~/.config/guix/channels.scm} or @file{/etc/guix/channels.scm}.
@var{file} must contain Scheme code that evaluates to a list of channel
objects.  @xref{通道}, for more information.

@cindex channel news
@item --news
@itemx -N
Display the list of packages added or upgraded since the previous
generation, as well as, occasionally, news written by channel authors for
their users (@pxref{通道, Writing Channel News}).

The package information is the same as displayed upon @command{guix pull}
completion, but without ellipses; it is also similar to the output of
@command{guix pull -l} for the last generation (see below).

@item --list-generations[=@var{pattern}]
@itemx -l [@var{pattern}]
List all the generations of @file{~/.config/guix/current} or, if
@var{pattern} is provided, the subset of generations that match
@var{pattern}.  The syntax of @var{pattern} is the same as with @code{guix
package --list-generations} (@pxref{调用guix package}).

@item --roll-back
@cindex rolling back
@cindex undoing transactions
@cindex transactions, undoing
Roll back to the previous @dfn{generation} of
@file{~/.config/guix/current}---i.e., undo the last transaction.

@item --switch-generation=@var{pattern}
@itemx -S @var{pattern}
@cindex generations
Switch to a particular generation defined by @var{pattern}.

@var{pattern} may be either a generation number or a number prefixed with
``+'' or ``-''.  The latter means: move forward/backward by a specified
number of generations.  For example, if you want to return to the latest
generation after @option{--roll-back}, use @option{--switch-generation=+1}.

@item --delete-generations[=@var{pattern}]
@itemx -d [@var{pattern}]
When @var{pattern} is omitted, delete all generations except the current
one.

This command accepts the same patterns as @option{--list-generations}.  When
@var{pattern} is specified, delete the matching generations.  When
@var{pattern} specifies a duration, generations @emph{older} than the
specified duration match.  For instance, @option{--delete-generations=1m}
deletes generations that are more than one month old.

If the current generation matches, it is @emph{not} deleted.

Note that deleting generations prevents rolling back to them.  Consequently,
this command must be used with care.

@xref{调用guix describe}, for a way to display information about the
current generation only.

@item --profile=@var{profile}
@itemx -p @var{profile}
Use @var{profile} instead of @file{~/.config/guix/current}.

@item --dry-run
@itemx -n
Show which channel commit(s) would be used and what would be built or
substituted but do not actually do it.

@item --allow-downgrades
Allow pulling older or unrelated revisions of channels than those currently
in use.

@cindex downgrade attacks, protection against
By default, @command{guix pull} protects against so-called ``downgrade
attacks'' whereby the Git repository of a channel would be reset to an
earlier or unrelated revision of itself, potentially leading you to install
older, known-vulnerable versions of software packages.

@quotation 注
Make sure you understand its security implications before using
@option{--allow-downgrades}.
@end quotation

@item --disable-authentication
Allow pulling channel code without authenticating it.

@cindex authentication, of channel code
By default, @command{guix pull} authenticates code downloaded from channels
by verifying that its commits are signed by authorized developers, and
raises an error if this is not the case.  This option instructs it to not
perform any such verification.

@quotation 注
Make sure you understand its security implications before using
@option{--disable-authentication}.
@end quotation

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of the
system type of the build host.

@item --bootstrap
Use the bootstrap Guile to build the latest Guix.  This option is only
useful to Guix developers.
@end table

The @dfn{channel} mechanism allows you to instruct @command{guix pull} which
repository and branch to pull from, as well as @emph{additional}
repositories containing package modules that should be deployed.
@xref{通道}, for more information.

In addition, @command{guix pull} supports all the common build options
(@pxref{普通的构建选项}).

@node Invoking guix time-machine
@section Invoking @command{guix time-machine}

@cindex @command{guix time-machine}
@cindex pinning, channels
@cindex replicating Guix
@cindex reproducibility, of Guix

The @command{guix time-machine} command provides access to other revisions
of Guix, for example to install older versions of packages, or to reproduce
a computation in an identical environment.  The revision of Guix to be used
is defined by a commit or by a channel description file created by
@command{guix describe} (@pxref{调用guix describe}).

The general syntax is:

@example
guix time-machine @var{options}@dots{} -- @var{command} @var {arg}@dots{}
@end example

where @var{command} and @var{arg}@dots{} are passed unmodified to the
@command{guix} command of the specified revision.  The @var{options} that
define this revision are the same as for @command{guix pull}
(@pxref{调用guix pull}):

@table @code
@item --url=@var{url}
@itemx --commit=@var{commit}
@itemx --branch=@var{branch}
Use the @code{guix} channel from the specified @var{url}, at the given
@var{commit} (a valid Git commit ID represented as a hexadecimal string), or
@var{branch}.

@item --channels=@var{file}
@itemx -C @var{file}
Read the list of channels from @var{file}.  @var{file} must contain Scheme
code that evaluates to a list of channel objects.  @xref{通道} for more
information.
@end table

As for @command{guix pull}, the absence of any options means that the latest
commit on the master branch will be used.  The command

@example
guix time-machine -- build hello
@end example

will thus build the package @code{hello} as defined in the master branch,
which is in general a newer revision of Guix than you have installed.  Time
travel works in both directions!

Note that @command{guix time-machine} can trigger builds of channels and
their dependencies, and these are controlled by the standard build options
(@pxref{普通的构建选项}).

@node Inferiors
@section Inferiors

@c TODO: Remove this once we're more confident about API stability.
@quotation 注
The functionality described here is a ``technology preview'' as of version
@value{VERSION}.  As such, the interface is subject to change.
@end quotation

@cindex inferiors
@cindex composition of Guix revisions
Sometimes you might need to mix packages from the revision of Guix you're
currently running with packages available in a different revision of Guix.
Guix @dfn{inferiors} allow you to achieve that by composing different Guix
revisions in arbitrary ways.

@cindex inferior packages
Technically, an ``inferior'' is essentially a separate Guix process
connected to your main Guix process through a REPL (@pxref{调用guix repl}).  The @code{(guix inferior)} module allows you to create inferiors
and to communicate with them.  It also provides a high-level interface to
browse and manipulate the packages that an inferior provides---@dfn{inferior
packages}.

When combined with channels (@pxref{通道}), inferiors provide a simple
way to interact with a separate revision of Guix.  For example, let's assume
you want to install in your profile the current @code{guile} package, along
with the @code{guile-json} as it existed in an older revision of
Guix---perhaps because the newer @code{guile-json} has an incompatible API
and you want to run your code against the old API@.  To do that, you could
write a manifest for use by @code{guix package --manifest} (@pxref{调用guix package}); in that manifest, you would create an inferior for that old
Guix revision you care about, and you would look up the @code{guile-json}
package in the inferior:

@lisp
(use-modules (guix inferior) (guix channels)
             (srfi srfi-1))   ;for 'first'

(define channels
  ;; This is the old revision from which we want to
  ;; extract guile-json.
  (list (channel
         (name 'guix)
         (url "https://git.savannah.gnu.org/git/guix.git")
         (commit
          "65956ad3526ba09e1f7a40722c96c6ef7c0936fe"))))

(define inferior
  ;; An inferior representing the above revision.
  (inferior-for-channels channels))

;; Now create a manifest with the current "guile" package
;; and the old "guile-json" package.
(packages->manifest
 (list (first (lookup-inferior-packages inferior "guile-json"))
       (specification->package "guile")))
@end lisp

On its first run, @command{guix package --manifest} might have to build the
channel you specified before it can create the inferior; subsequent runs
will be much faster because the Guix revision will be cached.

The @code{(guix inferior)} module provides the following procedures to open
an inferior:

@deffn {Scheme Procedure} inferior-for-channels @var{channels} @
   [#:cache-directory] [#:ttl] Return an inferior for @var{channels}, a list of
channels.  Use the cache at @var{cache-directory}, where entries can be
reclaimed after @var{ttl} seconds.  This procedure opens a new connection to
the build daemon.

As a side effect, this procedure may build or substitute binaries for
@var{channels}, which can take time.
@end deffn

@deffn {Scheme Procedure} open-inferior @var{directory} @
  [#:command "bin/guix"] Open the inferior Guix in @var{directory}, running
@code{@var{directory}/@var{command} repl} or equivalent.  Return @code{#f}
if the inferior could not be launched.
@end deffn

@cindex inferior packages
The procedures listed below allow you to obtain and manipulate inferior
packages.

@deffn {Scheme Procedure} inferior-packages @var{inferior}
Return the list of packages known to @var{inferior}.
@end deffn

@deffn {Scheme Procedure} lookup-inferior-packages @var{inferior} @var{name} @
   [@var{version}] Return the sorted list of inferior packages matching
@var{name} in @var{inferior}, with highest version numbers first.  If
@var{version} is true, return only packages with a version number prefixed
by @var{version}.
@end deffn

@deffn {Scheme Procedure} inferior-package? @var{obj}
Return true if @var{obj} is an inferior package.
@end deffn

@deffn {Scheme Procedure} inferior-package-name @var{package}
@deffnx {Scheme Procedure} inferior-package-version @var{package}
@deffnx {Scheme Procedure} inferior-package-synopsis @var{package}
@deffnx {Scheme Procedure} inferior-package-description @var{package}
@deffnx {Scheme Procedure} inferior-package-home-page @var{package}
@deffnx {Scheme Procedure} inferior-package-location @var{package}
@deffnx {Scheme Procedure} inferior-package-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-native-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-propagated-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-transitive-propagated-inputs @var{package}
@deffnx {Scheme Procedure} inferior-package-native-search-paths @var{package}
@deffnx {Scheme Procedure} inferior-package-transitive-native-search-paths @var{package}
@deffnx {Scheme Procedure} inferior-package-search-paths @var{package}
These procedures are the counterpart of package record accessors
(@pxref{软件包引用}).  Most of them work by querying the inferior
@var{package} comes from, so the inferior must still be live when you call
these procedures.
@end deffn

Inferior packages can be used transparently like any other package or
file-like object in G-expressions (@pxref{G-表达式}).  They are also
transparently handled by the @code{packages->manifest} procedure, which is
commonly used in manifests (@pxref{调用guix package, the
@option{--manifest} option of @command{guix package}}).  Thus you can insert
an inferior package pretty much anywhere you would insert a regular package:
in manifests, in the @code{packages} field of your @code{operating-system}
declaration, and so on.

@node 调用guix describe
@section Invoking @command{guix describe}

@cindex reproducibility
@cindex replicating Guix
Often you may want to answer questions like: ``Which revision of Guix am I
using?'' or ``Which channels am I using?'' This is useful information in
many situations: if you want to @emph{replicate} an environment on a
different machine or user account, if you want to report a bug or to
determine what change in the channels you are using caused it, or if you
want to record your system state for reproducibility purposes.  The
@command{guix describe} command answers these questions.

When run from a @command{guix pull}ed @command{guix}, @command{guix
describe} displays the channel(s) that it was built from, including their
repository URL and commit IDs (@pxref{通道}):

@example
$ guix describe
Generation 10	Sep 03 2018 17:32:44	(current)
  guix e0fa68c
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: e0fa68c7718fffd33d81af415279d6ddb518f727
@end example

If you're familiar with the Git version control system, this is similar in
spirit to @command{git describe}; the output is also similar to that of
@command{guix pull --list-generations}, but limited to the current
generation (@pxref{调用guix pull, the @option{--list-generations}
option}).  Because the Git commit ID shown above unambiguously refers to a
snapshot of Guix, this information is all it takes to describe the revision
of Guix you're using, and also to replicate it.

To make it easier to replicate Guix, @command{guix describe} can also be
asked to return a list of channels instead of the human-readable description
above:

@example
$ guix describe -f channels
(list (channel
        (name 'guix)
        (url "https://git.savannah.gnu.org/git/guix.git")
        (commit
          "e0fa68c7718fffd33d81af415279d6ddb518f727")
        (introduction
          (make-channel-introduction
            "9edb3f66fd807b096b48283debdcddccfea34bad"
            (openpgp-fingerprint
              "BBB0 2DDF 2CEA F6A8 0D1D  E643 A2A0 6DF2 A33A 54FA")))))
@end example

@noindent
You can save this to a file and feed it to @command{guix pull -C} on some
other machine or at a later point in time, which will instantiate @emph{this
exact Guix revision} (@pxref{调用guix pull, the @option{-C} option}).
From there on, since you're able to deploy the same revision of Guix, you
can just as well @emph{replicate a complete software environment}.  We
humbly think that this is @emph{awesome}, and we hope you'll like it too!

The details of the options supported by @command{guix describe} are as
follows:

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce output in the specified @var{format}, one of:

@table @code
@item human
produce human-readable output;
@item channels
produce a list of channel specifications that can be passed to @command{guix
pull -C} or installed as @file{~/.config/guix/channels.scm} (@pxref{调用guix pull});
@item channels-sans-intro
like @code{channels}, but omit the @code{introduction} field; use it to
produce a channel specification suitable for Guix version 1.1.0 or
earlier---the @code{introduction} field has to do with channel
authentication (@pxref{通道, Channel Authentication}) and is not
supported by these older versions;
@item json
@cindex JSON
produce a list of channel specifications in JSON format;
@item recutils
produce a list of channel specifications in Recutils format.
@end table

@item --list-formats
Display available formats for @option{--format} option.

@item --profile=@var{profile}
@itemx -p @var{profile}
Display information about @var{profile}.
@end table

@node 调用guix archive
@section Invoking @command{guix archive}

@cindex @command{guix archive}
@cindex 归档
The @command{guix archive} command allows users to @dfn{export} files from
the store into a single archive, and to later @dfn{import} them on a machine
that runs Guix.  In particular, it allows store files to be transferred from
one machine to the store on another machine.

@quotation 注
If you're looking for a way to produce archives in a format suitable for
tools other than Guix, @pxref{调用guix pack}.
@end quotation

@cindex exporting store items
To export store files as an archive to standard output, run:

@example
guix archive --export @var{options} @var{specifications}...
@end example

@var{specifications} may be either store file names or package
specifications, as for @command{guix package} (@pxref{调用guix package}).  For instance, the following command creates an archive
containing the @code{gui} output of the @code{git} package and the main
output of @code{emacs}:

@example
guix archive --export git:gui /gnu/store/...-emacs-24.3 > great.nar
@end example

If the specified packages are not built yet, @command{guix archive}
automatically builds them.  The build process may be controlled with the
common build options (@pxref{普通的构建选项}).

To transfer the @code{emacs} package to a machine connected over SSH, one
would run:

@example
guix archive --export -r emacs | ssh the-machine guix archive --import
@end example

@noindent
Similarly, a complete user profile may be transferred from one machine to
another like this:

@example
guix archive --export -r $(readlink -f ~/.guix-profile) | \
  ssh the-machine guix archive --import
@end example

@noindent
However, note that, in both examples, all of @code{emacs} and the profile as
well as all of their dependencies are transferred (due to @option{-r}),
regardless of what is already available in the store on the target machine.
The @option{--missing} option can help figure out which items are missing
from the target store.  The @command{guix copy} command simplifies and
optimizes this whole process, so this is probably what you should use in
this case (@pxref{调用guix copy}).

@cindex nar, archive format
@cindex normalized archive (nar)
@cindex nar bundle, archive format
Each store item is written in the @dfn{normalized archive} or @dfn{nar}
format (described below), and the output of @command{guix archive --export}
(and input of @command{guix archive --import}) is a @dfn{nar bundle}.

The nar format is comparable in spirit to `tar', but with differences that
make it more appropriate for our purposes.  First, rather than recording all
Unix metadata for each file, the nar format only mentions the file type
(regular, directory, or symbolic link); Unix permissions and owner/group are
dismissed.  Second, the order in which directory entries are stored always
follows the order of file names according to the C locale collation order.
This makes archive production fully deterministic.

That nar bundle format is essentially the concatenation of zero or more nars
along with metadata for each store item it contains: its file name,
references, corresponding derivation, and a digital signature.

@c FIXME: Add xref to daemon doc about signatures.
When exporting, the daemon digitally signs the contents of the archive, and
that digital signature is appended.  When importing, the daemon verifies the
signature and rejects the import in case of an invalid signature or if the
signing key is not authorized.

The main options are:

@table @code
@item --export
Export the specified store files or packages (see below).  Write the
resulting archive to the standard output.

Dependencies are @emph{not} included in the output, unless
@option{--recursive} is passed.

@item -r
@itemx --recursive
When combined with @option{--export}, this instructs @command{guix archive}
to include dependencies of the given items in the archive.  Thus, the
resulting archive is self-contained: it contains the closure of the exported
store items.

@item --import
Read an archive from the standard input, and import the files listed therein
into the store.  Abort if the archive has an invalid digital signature, or
if it is signed by a public key not among the authorized keys (see
@option{--authorize} below).

@item --missing
Read a list of store file names from the standard input, one per line, and
write on the standard output the subset of these files missing from the
store.

@item --generate-key[=@var{parameters}]
@cindex signing, archives
Generate a new key pair for the daemon.  This is a prerequisite before
archives can be exported with @option{--export}.  This operation is usually
instantaneous but it can take time if the system's entropy pool needs to be
refilled.  On Guix System, @code{guix-service-type} takes care of generating
this key pair the first boot.

The generated key pair is typically stored under @file{/etc/guix}, in
@file{signing-key.pub} (public key) and @file{signing-key.sec} (private key,
which must be kept secret).  When @var{parameters} is omitted, an ECDSA key
using the Ed25519 curve is generated, or, for Libgcrypt versions before
1.6.0, it is a 4096-bit RSA key.  Alternatively, @var{parameters} can
specify @code{genkey} parameters suitable for Libgcrypt (@pxref{General
public-key related Functions, @code{gcry_pk_genkey},, gcrypt, The Libgcrypt
Reference Manual}).

@item --authorize
@cindex authorizing, archives
Authorize imports signed by the public key passed on standard input.  The
public key must be in ``s-expression advanced format''---i.e., the same
format as the @file{signing-key.pub} file.

The list of authorized keys is kept in the human-editable file
@file{/etc/guix/acl}.  The file contains
@url{https://people.csail.mit.edu/rivest/Sexp.txt, ``advanced-format
s-expressions''} and is structured as an access-control list in the
@url{https://theworld.com/~cme/spki.txt, Simple Public-Key Infrastructure
(SPKI)}.

@item --extract=@var{directory}
@itemx -x @var{directory}
Read a single-item archive as served by substitute servers
(@pxref{substitutes}) and extract it to @var{directory}.  This is a
low-level operation needed in only very narrow use cases; see below.

For example, the following command extracts the substitute for Emacs served
by @code{@value{SUBSTITUTE-SERVER}} to @file{/tmp/emacs}:

@example
$ wget -O - \
  https://@value{SUBSTITUTE-SERVER}/nar/gzip/@dots{}-emacs-24.5 \
  | gunzip | guix archive -x /tmp/emacs
@end example

Single-item archives are different from multiple-item archives produced by
@command{guix archive --export}; they contain a single store item, and they
do @emph{not} embed a signature.  Thus this operation does @emph{no}
signature verification and its output should be considered unsafe.

The primary purpose of this operation is to facilitate inspection of archive
contents coming from possibly untrusted substitute servers (@pxref{调用guix challenge}).

@item --list
@itemx -t
Read a single-item archive as served by substitute servers
(@pxref{substitutes}) and print the list of files it contains, as in this
example:

@example
$ wget -O - \
  https://@value{SUBSTITUTE-SERVER}/nar/lzip/@dots{}-emacs-26.3 \
  | lzip -d | guix archive -t
@end example

@end table

@c *********************************************************************
@node 通道
@chapter 通道

@cindex channels
@cindex @file{channels.scm}, configuration file
@cindex configuration file for channels
@cindex @command{guix pull}, configuration file
@cindex configuration of @command{guix pull}
Guix and its package collection are updated by running @command{guix pull}
(@pxref{调用guix pull}).  By default @command{guix pull} downloads and
deploys Guix itself from the official GNU@tie{}Guix repository.  This can be
customized by defining @dfn{channels} in the
@file{~/.config/guix/channels.scm} file.  A channel specifies a URL and
branch of a Git repository to be deployed, and @command{guix pull} can be
instructed to pull from one or more channels.  In other words, channels can
be used to @emph{customize} and to @emph{extend} Guix, as we will see
below.  Guix is able to take into account security concerns and deal with
authenticated updates.

@menu
* Specifying Additional Channels::  拓展软件包集合。
* Using a Custom Guix Channel::  Using a customized Guix.
* Replicating Guix::         Running the @emph{exact same} Guix.
* Channel Authentication::   How Guix verifies what it fetches.
* Channels with Substitutes::  Using channels with available substitutes.
* 创建一个频道::       How to write your custom channel.
* Package Modules in a Sub-directory::  Specifying the channel's package 
                                          modules location.
* Declaring Channel Dependencies::  How to depend on other channels.
* Specifying Channel Authorizations::  Defining channel authors 
                                         authorizations.
* Primary URL::              Distinguishing mirror to original.
* Writing Channel News::     Communicating information to channel's users.
@end menu

@node Specifying Additional Channels
@section Specifying Additional Channels

@cindex extending the package collection (channels)
@cindex variant packages (channels)
You can specify @emph{additional channels} to pull from.  To use a channel,
write @code{~/.config/guix/channels.scm} to instruct @command{guix pull} to
pull from it @emph{in addition} to the default Guix channel(s):

@vindex %default-channels
@lisp
;; Add variant packages to those Guix provides.
(cons (channel
        (name 'variant-packages)
        (url "https://example.org/variant-packages.git"))
      %default-channels)
@end lisp

@noindent
Note that the snippet above is (as always!)@: Scheme code; we use
@code{cons} to add a channel the list of channels that the variable
@code{%default-channels} is bound to (@pxref{Pairs, @code{cons} and lists,,
guile, GNU Guile Reference Manual}).  With this file in place, @command{guix
pull} builds not only Guix but also the package modules from your own
repository.  The result in @file{~/.config/guix/current} is the union of
Guix with your own package modules:

@example
$ guix pull --list-generations
@dots{}
Generation 19	Aug 27 2018 16:20:48
  guix d894ab8
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: d894ab8e9bfabcefa6c49d9ba2e834dd5a73a300
  variant-packages dd3df5e
    repository URL: https://example.org/variant-packages.git
    branch: master
    commit: dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb
  11 new packages: variant-gimp, variant-emacs-with-cool-features, @dots{}
  4 packages upgraded: emacs-racket-mode@@0.0.2-2.1b78827, @dots{}
@end example

@noindent
The output of @command{guix pull} above shows that Generation@tie{}19
includes both Guix and packages from the @code{variant-personal-packages}
channel.  Among the new and upgraded packages that are listed, some like
@code{variant-gimp} and @code{variant-emacs-with-cool-features} might come
from @code{variant-packages}, while others come from the Guix default
channel.

@node Using a Custom Guix Channel
@section Using a Custom Guix Channel

The channel called @code{guix} specifies where Guix itself---its
command-line tools as well as its package collection---should be
downloaded.  For instance, suppose you want to update from another copy of
the Guix repository at @code{example.org}, and specifically the
@code{super-hacks} branch, you can write in
@code{~/.config/guix/channels.scm} this specification:

@lisp
;; Tell 'guix pull' to use another repo.
(list (channel
        (name 'guix)
        (url "https://example.org/another-guix.git")
        (branch "super-hacks")))
@end lisp

@noindent
From there on, @command{guix pull} will fetch code from the
@code{super-hacks} branch of the repository at @code{example.org}.  The
authentication concern is addressed below ((@pxref{验证substitute}).

@node Replicating Guix
@section Replicating Guix

@cindex pinning, channels
@cindex replicating Guix
@cindex reproducibility, of Guix
The @command{guix pull --list-generations} output above shows precisely
which commits were used to build this instance of Guix.  We can thus
replicate it, say, on another machine, by providing a channel specification
in @file{~/.config/guix/channels.scm} that is ``pinned'' to these commits:

@lisp
;; Deploy specific commits of my channels of interest.
(list (channel
       (name 'guix)
       (url "https://git.savannah.gnu.org/git/guix.git")
       (commit "6298c3ffd9654d3231a6f25390b056483e8f407c"))
      (channel
       (name 'variant-packages)
       (url "https://example.org/variant-packages.git")
       (commit "dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb")))
@end lisp

The @command{guix describe --format=channels} command can even generate this
list of channels directly (@pxref{调用guix describe}).  The resulting
file can be used with the -C options of @command{guix pull} (@pxref{调用guix pull}) or @command{guix time-machine} (@pxref{调用guix archive}).

At this point the two machines run the @emph{exact same Guix}, with access
to the @emph{exact same packages}.  The output of @command{guix build gimp}
on one machine will be exactly the same, bit for bit, as the output of the
same command on the other machine.  It also means both machines have access
to all the source code of Guix and, transitively, to all the source code of
every package it defines.

This gives you super powers, allowing you to track the provenance of binary
artifacts with very fine grain, and to reproduce software environments at
will---some sort of ``meta reproducibility'' capabilities, if you will.
@xref{Inferiors}, for another way to take advantage of these super powers.

@node Channel Authentication
@section Channel Authentication

@anchor{channel-authentication}
@cindex authentication, of channel code
The @command{guix pull} and @command{guix time-machine} commands
@dfn{authenticate} the code retrieved from channels: they make sure each
commit that is fetched is signed by an authorized developer.  The goal is to
protect from unauthorized modifications to the channel that would lead users
to run malicious code.

As a user, you must provide a @dfn{channel introduction} in your channels
file so that Guix knows how to authenticate its first commit.  A channel
specification, including its introduction, looks something along these
lines:

@lisp
(channel
  (name 'some-channel)
  (url "https://example.org/some-channel.git")
  (introduction
   (make-channel-introduction
    "6f0d8cc0d88abb59c324b2990bfee2876016bb86"
    (openpgp-fingerprint
     "CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"))))
@end lisp

The specification above shows the name and URL of the channel.  The call to
@code{make-channel-introduction} above specifies that authentication of this
channel starts at commit @code{6f0d8cc@dots{}}, which is signed by the
OpenPGP key with fingerprint @code{CABB A931@dots{}}.

For the main channel, called @code{guix}, you automatically get that
information from your Guix installation.  For other channels, include the
channel introduction provided by the channel authors in your
@file{channels.scm} file.  Make sure you retrieve the channel introduction
from a trusted source since that is the root of your trust.

If you're curious about the authentication mechanics, read on!

@node Channels with Substitutes
@section Channels with Substitutes

When running @command{guix pull}, Guix will first compile the definitions of
every available package.  This is an expensive operation for which
substitutes (@pxref{substitutes}) may be available.  The following snippet
in @file{channels.scm} will ensure that @command{guix pull} uses the latest
commit with available substitutes for the package definitions: this is done
by querying the continuous integration server at
@url{https://ci.guix.gnu.org}.

@lisp
(use-modules (guix ci))

(list (channel-with-substitutes-available
       %default-guix-channel
       "https://ci.guix.gnu.org"))
@end lisp

Note that this does not mean that all the packages that you will install
after running @command{guix pull} will have available substitutes.  It only
ensures that @command{guix pull} will not try to compile package
definitions.  This is particularly useful when using machines with limited
resources.

@node 创建一个频道
@section 创建一个频道

@cindex personal packages (channels)
@cindex channels, for personal packages
Let's say you have a bunch of custom package variants or personal packages
that you think would make little sense to contribute to the Guix project,
but would like to have these packages transparently available to you at the
command line.  You would first write modules containing those package
definitions (@pxref{软件包模块}), maintain them in a Git repository,
and then you and anyone else can use it as an additional channel to get
packages from.  Neat, no?

@c What follows stems from discussions at
@c <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22629#134> as well as
@c earlier discussions on guix-devel@gnu.org.
@quotation Warning
Before you, dear user, shout---``woow this is @emph{soooo coool}!''---and
publish your personal channel to the world, we would like to share a few
words of caution:

@itemize
@item
Before publishing a channel, please consider contributing your package
definitions to Guix proper (@pxref{贡献}).  Guix as a project is
open to free software of all sorts, and packages in Guix proper are readily
available to all Guix users and benefit from the project's quality assurance
process.

@item
When you maintain package definitions outside Guix, we, Guix developers,
consider that @emph{the compatibility burden is on you}.  Remember that
package modules and package definitions are just Scheme code that uses
various programming interfaces (APIs).  We want to remain free to change
these APIs to keep improving Guix, possibly in ways that break your
channel.  We never change APIs gratuitously, but we will @emph{not} commit
to freezing APIs either.

@item
Corollary: if you're using an external channel and that channel breaks,
please @emph{report the issue to the channel authors}, not to the Guix
project.
@end itemize

You've been warned! Having said this, we believe external channels are a
practical way to exert your freedom to augment Guix' package collection and
to share your improvements, which are basic tenets of
@uref{https://www.gnu.org/philosophy/free-sw.html, free software}.  Please
email us at @email{guix-devel@@gnu.org} if you'd like to discuss this.
@end quotation

To create a channel, create a Git repository containing your own package
modules and make it available.  The repository can contain anything, but a
useful channel will contain Guile modules that export packages.  Once you
start using a channel, Guix will behave as if the root directory of that
channel's Git repository has been added to the Guile load path (@pxref{Load
Paths,,, guile, GNU Guile Reference Manual}).  For example, if your channel
contains a file at @file{my-packages/my-tools.scm} that defines a Guile
module, then the module will be available under the name @code{(my-packages
my-tools)}, and you will be able to use it like any other module
(@pxref{模块,,, guile, GNU Guile Reference Manual}).

As a channel author, consider bundling authentication material with your
channel so that users can authenticate it.  @xref{验证substitute},
and @ref{Specifying Channel Authorizations}, for info on how to do it.


@node Package Modules in a Sub-directory
@section Package Modules in a Sub-directory

@cindex subdirectory, channels
As a channel author, you may want to keep your channel modules in a
sub-directory.  If your modules are in the sub-directory @file{guix}, you
must add a meta-data file @file{.guix-channel} that contains:

@lisp
(channel
  (version 0)
  (directory "guix"))
@end lisp

@node Declaring Channel Dependencies
@section Declaring Channel Dependencies

@cindex dependencies, channels
@cindex meta-data, channels
Channel authors may decide to augment a package collection provided by other
channels.  They can declare their channel to be dependent on other channels
in a meta-data file @file{.guix-channel}, which is to be placed in the root
of the channel repository.

The meta-data file should contain a simple S-expression like this:

@lisp
(channel
 (version 0)
 (dependencies
  (channel
   (name some-collection)
   (url "https://example.org/first-collection.git")

   ;; The 'introduction' bit below is optional: you would
   ;; provide it for dependencies that can be authenticated.
   (introduction
    (channel-introduction
      (version 0)
      (commit "a8883b58dc82e167c96506cf05095f37c2c2c6cd")
      (signer "CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"))))
  (channel
   (name some-other-collection)
   (url "https://example.org/second-collection.git")
   (branch "testing"))))
@end lisp

In the above example this channel is declared to depend on two other
channels, which will both be fetched automatically.  The modules provided by
the channel will be compiled in an environment where the modules of all
these declared channels are available.

For the sake of reliability and maintainability, you should avoid
dependencies on channels that you don't control, and you should aim to keep
the number of dependencies to a minimum.

@node Specifying Channel Authorizations
@section Specifying Channel Authorizations

@cindex channel authorizations
@anchor{channel-authorizations}
As we saw above, Guix ensures the source code it pulls from channels comes
from authorized developers.  As a channel author, you need to specify the
list of authorized developers in the @file{.guix-authorizations} file in the
channel's Git repository.  The authentication rule is simple: each commit
must be signed by a key listed in the @file{.guix-authorizations} file of
its parent commit(s)@footnote{Git commits form a @dfn{directed acyclic
graph} (DAG).  Each commit can have zero or more parents; ``regular''
commits have one parent and merge commits have two parent commits.  Read
@uref{https://eagain.net/articles/git-for-computer-scientists/, @i{Git for
Computer Scientists}} for a great overview.} The @file{.guix-authorizations}
file looks like this:

@lisp
;; Example '.guix-authorizations' file.

(authorizations
 (version 0)               ;current file format version

 (("AD17 A21E F8AE D8F1 CC02  DBD9 F8AE D8F1 765C 61E3"
   (name "alice"))
  ("2A39 3FFF 68F4 EF7A 3D29  12AF 68F4 EF7A 22FB B2D5"
   (name "bob"))
  ("CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"
   (name "charlie"))))
@end lisp

Each fingerprint is followed by optional key/value pairs, as in the example
above.  Currently these key/value pairs are ignored.

This authentication rule creates a chicken-and-egg issue: how do we
authenticate the first commit? Related to that: how do we deal with channels
whose repository history contains unsigned commits and lack
@file{.guix-authorizations}? And how do we fork existing channels?

@cindex channel introduction
Channel introductions answer these questions by describing the first commit
of a channel that should be authenticated.  The first time a channel is
fetched with @command{guix pull} or @command{guix time-machine}, the command
looks up the introductory commit and verifies that it is signed by the
specified OpenPGP key.  From then on, it authenticates commits according to
the rule above.

Additionally, your channel must provide all the OpenPGP keys that were ever
mentioned in @file{.guix-authorizations}, stored as @file{.key} files, which
can be either binary or ``ASCII-armored''.  By default, those @file{.key}
files are searched for in the branch named @code{keyring} but you can
specify a different branch name in @code{.guix-channel} like so:

@lisp
(channel
  (version 0)
  (keyring-reference "my-keyring-branch"))
@end lisp

To summarize, as the author of a channel, there are three things you have to
do to allow users to authenticate your code:

@enumerate
@item
Export the OpenPGP keys of past and present committers with @command{gpg
--export} and store them in @file{.key} files, by default in a branch named
@code{keyring} (we recommend making it an @dfn{orphan branch}).

@item
Introduce an initial @file{.guix-authorizations} in the channel's
repository.  Do that in a signed commit (@pxref{提交权利}, for
information on how to sign Git commits.)

@item
Advertise the channel introduction, for instance on your channel's web
page.  The channel introduction, as we saw above, is the commit/key
pair---i.e., the commit that introduced @file{.guix-authorizations}, and the
fingerprint of the OpenPGP used to sign it.
@end enumerate

Before pushing to your public Git repository, you can run @command{guix
git-authenticate} to verify that you did sign all the commits you are about
to push with an authorized key:

@example
guix git authenticate @var{commit} @var{signer}
@end example

@noindent
where @var{commit} and @var{signer} are your channel introduction.
@xref{调用guix edit。}, for details.

Publishing a signed channel requires discipline: any mistake, such as an
unsigned commit or a commit signed by an unauthorized key, will prevent
users from pulling from your channel---well, that's the whole point of
authentication! Pay attention to merges in particular: merge commits are
considered authentic if and only if they are signed by a key present in the
@file{.guix-authorizations} file of @emph{both} branches.

@node Primary URL
@section Primary URL

@cindex primary URL, channels
Channel authors can indicate the primary URL of their channel's Git
repository in the @file{.guix-channel} file, like so:

@lisp
(channel
  (version 0)
  (url "https://example.org/guix.git"))
@end lisp

This allows @command{guix pull} to determine whether it is pulling code from
a mirror of the channel; when that is the case, it warns the user that the
mirror might be stale and displays the primary URL@.  That way, users cannot
be tricked into fetching code from a stale mirror that does not receive
security updates.

This feature only makes sense for authenticated repositories, such as the
official @code{guix} channel, for which @command{guix pull} ensures the code
it fetches is authentic.

@node Writing Channel News
@section Writing Channel News

@cindex news, for channels
Channel authors may occasionally want to communicate to their users
information about important changes in the channel.  You'd send them all an
email, but that's not convenient.

Instead, channels can provide a @dfn{news file}; when the channel users run
@command{guix pull}, that news file is automatically read and @command{guix
pull --news} can display the announcements that correspond to the new
commits that have been pulled, if any.

To do that, channel authors must first declare the name of the news file in
their @file{.guix-channel} file:

@lisp
(channel
  (version 0)
  (news-file "etc/news.txt"))
@end lisp

The news file itself, @file{etc/news.txt} in this example, must look
something like this:

@lisp
(channel-news
  (version 0)
  (entry (tag "the-bug-fix")
         (title (en "Fixed terrible bug")
                (fr "Oh la la"))
         (body (en "@@emph@{Good news@}!  It's fixed!")
               (eo "Certe ĝi pli bone funkcias nun!")))
  (entry (commit "bdcabe815cd28144a2d2b4bc3c5057b051fa9906")
         (title (en "Added a great package")
                (ca "Què vol dir guix?"))
         (body (en "Don't miss the @@code@{hello@} package!"))))
@end lisp

While the news file is using the Scheme syntax, avoid naming it with a
@file{.scm} extension or else it will get picked up when building the
channel and yield an error since it is not a valid module.  Alternatively,
you can move the channel module to a subdirectory and store the news file in
another directory.

The file consists of a list of @dfn{news entries}.  Each entry is associated
with a commit or tag: it describes changes made in this commit, possibly in
preceding commits as well.  Users see entries only the first time they
obtain the commit the entry refers to.

The @code{title} field should be a one-line summary while @code{body} can be
arbitrarily long, and both can contain Texinfo markup (@pxref{Overview,,,
texinfo, GNU Texinfo}).  Both the title and body are a list of language
tag/message tuples, which allows @command{guix pull} to display news in the
language that corresponds to the user's locale.

If you want to translate news using a gettext-based workflow, you can
extract translatable strings with @command{xgettext} (@pxref{xgettext
Invocation,,, gettext, GNU Gettext Utilities}).  For example, assuming you
write news entries in English first, the command below creates a PO file
containing the strings to translate:

@example
xgettext -o news.po -l scheme -ken etc/news.txt
@end example

To sum up, yes, you could use your channel as a blog.  But beware, this is
@emph{not quite} what your users might expect.

@c *********************************************************************
@node 开发
@chapter 开发

@cindex software development
If you are a software developer, Guix provides tools that you should find
helpful---independently of the language you're developing in.  This is what
this chapter is about.

The @command{guix environment} command provides a convenient way to set up
@dfn{development environments} containing all the dependencies and tools
necessary to work on the software package of your choice.  The @command{guix
pack} command allows you to create @dfn{application bundles} that can be
easily distributed to users who do not run Guix.

@menu
* 调用guix environment::   设置开发环境。
* 调用guix pack::          创建软件bundle。
* The GCC toolchain::        Working with languages supported by GCC.
* Invoking guix git authenticate::  Authenticating Git repositories.
@end menu

@node 调用guix environment
@section Invoking @command{guix environment}

@cindex reproducible build environments
@cindex development environments
@cindex @command{guix environment}
@cindex environment, package build environment
The purpose of @command{guix environment} is to assist hackers in creating
reproducible development environments without polluting their package
profile.  The @command{guix environment} tool takes one or more packages,
builds all of their inputs, and creates a shell environment to use them.

The general syntax is:

@example
guix environment @var{options} @var{package}@dots{}
@end example

The following example spawns a new shell set up for the development of
GNU@tie{}Guile:

@example
guix environment guile
@end example

If the needed dependencies are not built yet, @command{guix environment}
automatically builds them.  The environment of the new shell is an augmented
version of the environment that @command{guix environment} was run in.  It
contains the necessary search paths for building the given package added to
the existing environment variables.  To create a ``pure'' environment, in
which the original environment variables have been unset, use the
@option{--pure} option@footnote{Users sometimes wrongfully augment
environment variables such as @env{PATH} in their @file{~/.bashrc} file.  As
a consequence, when @command{guix environment} launches it, Bash may read
@file{~/.bashrc}, thereby introducing ``impurities'' in these environment
variables.  It is an error to define such environment variables in
@file{.bashrc}; instead, they should be defined in @file{.bash_profile},
which is sourced only by log-in shells.  @xref{Bash Startup Files,,, bash,
The GNU Bash Reference Manual}, for details on Bash start-up files.}.

Exiting from a Guix environment is the same as exiting from the shell, and
will place the user back in the old environment before @command{guix
environment} was invoked.  The next garbage collection (@pxref{调用guix gc}) will clean up packages that were installed from within the environment
and are no longer used outside of it.

@vindex GUIX_ENVIRONMENT
@command{guix environment} defines the @env{GUIX_ENVIRONMENT} variable in
the shell it spawns; its value is the file name of the profile of this
environment.  This allows users to, say, define a specific prompt for
development environments in their @file{.bashrc} (@pxref{Bash Startup
Files,,, bash, The GNU Bash Reference Manual}):

@example
if [ -n "$GUIX_ENVIRONMENT" ]
then
    export PS1="\u@@\h \w [dev]\$ "
fi
@end example

@noindent
...@: or to browse the profile:

@example
$ ls "$GUIX_ENVIRONMENT/bin"
@end example

Additionally, more than one package may be specified, in which case the
union of the inputs for the given packages are used.  For example, the
command below spawns a shell where all of the dependencies of both Guile and
Emacs are available:

@example
guix environment guile emacs
@end example

Sometimes an interactive shell session is not desired.  An arbitrary command
may be invoked by placing the @code{--} token to separate the command from
the rest of the arguments:

@example
guix environment guile -- make -j4
@end example

In other situations, it is more convenient to specify the list of packages
needed in the environment.  For example, the following command runs
@command{python} from an environment containing Python@tie{}2.7 and NumPy:

@example
guix environment --ad-hoc python2-numpy python-2.7 -- python
@end example

Furthermore, one might want the dependencies of a package and also some
additional packages that are not build-time or runtime dependencies, but are
useful when developing nonetheless.  Because of this, the @option{--ad-hoc}
flag is positional.  Packages appearing before @option{--ad-hoc} are
interpreted as packages whose dependencies will be added to the
environment.  Packages appearing after are interpreted as packages that will
be added to the environment directly.  For example, the following command
creates a Guix development environment that additionally includes Git and
strace:

@example
guix environment --pure guix --ad-hoc git strace
@end example

@cindex container
Sometimes it is desirable to isolate the environment as much as possible,
for maximal purity and reproducibility.  In particular, when using Guix on a
host distro that is not Guix System, it is desirable to prevent access to
@file{/usr/bin} and other system-wide resources from the development
environment.  For example, the following command spawns a Guile REPL in a
``container'' where only the store and the current working directory are
mounted:

@example
guix environment --ad-hoc --container guile -- guile
@end example

@quotation 注
The @option{--container} option requires Linux-libre 3.19 or newer.
@end quotation

@cindex certificates
Another typical use case for containers is to run security-sensitive
applications such as a web browser.  To run Eolie, we must expose and share
some files and directories; we include @code{nss-certs} and expose
@file{/etc/ssl/certs/} for HTTPS authentication; finally we preserve the
@env{DISPLAY} environment variable since containerized graphical
applications won't display without it.

@example
guix environment --preserve='^DISPLAY$' --container --network \
  --expose=/etc/machine-id \
  --expose=/etc/ssl/certs/ \
  --share=$HOME/.local/share/eolie/=$HOME/.local/share/eolie/ \
  --ad-hoc eolie nss-certs dbus --  eolie
@end example

The available options are summarized below.

@table @code
@item --root=@var{file}
@itemx -r @var{file}
@cindex persistent environment
@cindex garbage collector root, for environments
Make @var{file} a symlink to the profile for this environment, and register
it as a garbage collector root.

This is useful if you want to protect your environment from garbage
collection, to make it ``persistent''.

When this option is omitted, the environment is protected from garbage
collection only for the duration of the @command{guix environment} session.
This means that next time you recreate the same environment, you could have
to rebuild or re-download packages.  @xref{调用guix gc}, for more on GC
roots.

@item --expression=@var{expr}
@itemx -e @var{expr}
Create an environment for the package or list of packages that @var{expr}
evaluates to.

For example, running:

@example
guix environment -e '(@@ (gnu packages maths) petsc-openmpi)'
@end example

starts a shell with the environment for this specific variant of the PETSc
package.

Running:

@example
guix environment --ad-hoc -e '(@@ (gnu) %base-packages)'
@end example

starts a shell with all the base system packages available.

The above commands only use the default output of the given packages.  To
select other outputs, two element tuples can be specified:

@example
guix environment --ad-hoc -e '(list (@@ (gnu packages bash) bash) "include")'
@end example

@item --load=@var{file}
@itemx -l @var{file}
Create an environment for the package or list of packages that the code
within @var{file} evaluates to.

As an example, @var{file} might contain a definition like this
(@pxref{定义软件包}):

@lisp
@verbatiminclude environment-gdb.scm
@end lisp

@item --manifest=@var{file}
@itemx -m @var{file}
Create an environment for the packages contained in the manifest object
returned by the Scheme code in @var{file}.  This option can be repeated
several times, in which case the manifests are concatenated.

This is similar to the same-named option in @command{guix package}
(@pxref{profile-manifest, @option{--manifest}}) and uses the same manifest
files.

@item --ad-hoc
Include all specified packages in the resulting environment, as if an @i{ad
hoc} package were defined with them as inputs.  This option is useful for
quickly creating an environment without having to write a package expression
to contain the desired inputs.

For instance, the command:

@example
guix environment --ad-hoc guile guile-sdl -- guile
@end example

runs @command{guile} in an environment where Guile and Guile-SDL are
available.

Note that this example implicitly asks for the default output of
@code{guile} and @code{guile-sdl}, but it is possible to ask for a specific
output---e.g., @code{glib:bin} asks for the @code{bin} output of @code{glib}
(@pxref{有多个输出的软件包}).

This option may be composed with the default behavior of @command{guix
environment}.  Packages appearing before @option{--ad-hoc} are interpreted
as packages whose dependencies will be added to the environment, the default
behavior.  Packages appearing after are interpreted as packages that will be
added to the environment directly.

@item --pure
Unset existing environment variables when building the new environment,
except those specified with @option{--preserve} (see below).  This has the
effect of creating an environment in which search paths only contain package
inputs.

@item --preserve=@var{regexp}
@itemx -E @var{regexp}
When used alongside @option{--pure}, preserve the environment variables
matching @var{regexp}---in other words, put them on a ``white list'' of
environment variables that must be preserved.  This option can be repeated
several times.

@example
guix environment --pure --preserve=^SLURM --ad-hoc openmpi @dots{} \
  -- mpirun @dots{}
@end example

This example runs @command{mpirun} in a context where the only environment
variables defined are @env{PATH}, environment variables whose name starts
with @samp{SLURM}, as well as the usual ``precious'' variables (@env{HOME},
@env{USER}, etc.).

@item --search-paths
Display the environment variable definitions that make up the environment.

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}.

@item --container
@itemx -C
@cindex container
Run @var{command} within an isolated container.  The current working
directory outside the container is mapped inside the container.
Additionally, unless overridden with @option{--user}, a dummy home directory
is created that matches the current user's home directory, and
@file{/etc/passwd} is configured accordingly.

The spawned process runs as the current user outside the container.  Inside
the container, it has the same UID and GID as the current user, unless
@option{--user} is passed (see below).

@item --network
@itemx -N
For containers, share the network namespace with the host system.
Containers created without this flag only have access to the loopback
device.

@item --link-profile
@itemx -P
For containers, link the environment profile to @file{~/.guix-profile}
within the container and set @code{GUIX_ENVIRONMENT} to that.  This is
equivalent to making @file{~/.guix-profile} a symlink to the actual profile
within the container.  Linking will fail and abort the environment if the
directory already exists, which will certainly be the case if @command{guix
environment} was invoked in the user's home directory.

Certain packages are configured to look in @file{~/.guix-profile} for
configuration files and data;@footnote{For example, the @code{fontconfig}
package inspects @file{~/.guix-profile/share/fonts} for additional fonts.}
@option{--link-profile} allows these programs to behave as expected within
the environment.

@item --user=@var{user}
@itemx -u @var{user}
For containers, use the username @var{user} in place of the current user.
The generated @file{/etc/passwd} entry within the container will contain the
name @var{user}, the home directory will be @file{/home/@var{user}}, and no
user GECOS data will be copied.  Furthermore, the UID and GID inside the
container are 1000.  @var{user} need not exist on the system.

Additionally, any shared or exposed path (see @option{--share} and
@option{--expose} respectively) whose target is within the current user's
home directory will be remapped relative to @file{/home/USER}; this includes
the automatic mapping of the current working directory.

@example
# will expose paths as /home/foo/wd, /home/foo/test, and /home/foo/target
cd $HOME/wd
guix environment --container --user=foo \
     --expose=$HOME/test \
     --expose=/tmp/target=$HOME/target
@end example

While this will limit the leaking of user identity through home paths and
each of the user fields, this is only one useful component of a broader
privacy/anonymity solution---not one in and of itself.

@item --no-cwd
For containers, the default behavior is to share the current working
directory with the isolated container and immediately change to that
directory within the container.  If this is undesirable, @option{--no-cwd}
will cause the current working directory to @emph{not} be automatically
shared and will change to the user's home directory within the container
instead.  See also @option{--user}.

@item --expose=@var{source}[=@var{target}]
@itemx --share=@var{source}[=@var{target}]
For containers, @option{--expose} (resp. @option{--share}) exposes the file
system @var{source} from the host system as the read-only (resp. writable)
file system @var{target} within the container.  If @var{target} is not
specified, @var{source} is used as the target mount point in the container.

The example below spawns a Guile REPL in a container in which the user's
home directory is accessible read-only via the @file{/exchange} directory:

@example
guix environment --container --expose=$HOME=/exchange --ad-hoc guile -- guile
@end example

@end table

@command{guix environment} also supports all of the common build options
that @command{guix build} supports (@pxref{普通的构建选项}) as well as
package transformation options (@pxref{软件包变换选项。}).

@node 调用guix pack
@section Invoking @command{guix pack}

Occasionally you want to pass software to people who are not (yet!)  lucky
enough to be using Guix.  You'd tell them to run @command{guix package -i
@var{something}}, but that's not possible in this case.  This is where
@command{guix pack} comes in.

@quotation 注
If you are looking for ways to exchange binaries among machines that already
run Guix, @pxref{调用guix copy}, @ref{调用guix publish}, and
@ref{调用guix archive}.
@end quotation

@cindex pack
@cindex bundle
@cindex application bundle
@cindex software bundle
The @command{guix pack} command creates a shrink-wrapped @dfn{pack} or
@dfn{software bundle}: it creates a tarball or some other archive containing
the binaries of the software you're interested in, and all its
dependencies.  The resulting archive can be used on any machine that does
not have Guix, and people can run the exact same binaries as those you have
with Guix.  The pack itself is created in a bit-reproducible fashion, so
anyone can verify that it really contains the build results that you pretend
to be shipping.

For example, to create a bundle containing Guile, Emacs, Geiser, and all
their dependencies, you can run:

@example
$ guix pack guile emacs geiser
@dots{}
/gnu/store/@dots{}-pack.tar.gz
@end example

The result here is a tarball containing a @file{/gnu/store} directory with
all the relevant packages.  The resulting tarball contains a @dfn{profile}
with the three packages of interest; the profile is the same as would be
created by @command{guix package -i}.  It is this mechanism that is used to
create Guix's own standalone binary tarball (@pxref{二进制文件安装}).

Users of this pack would have to run
@file{/gnu/store/@dots{}-profile/bin/guile} to run Guile, which you may find
inconvenient.  To work around it, you can create, say, a @file{/opt/gnu/bin}
symlink to the profile:

@example
guix pack -S /opt/gnu/bin=bin guile emacs geiser
@end example

@noindent
That way, users can happily type @file{/opt/gnu/bin/guile} and enjoy.

@cindex relocatable binaries, with @command{guix pack}
What if the recipient of your pack does not have root privileges on their
machine, and thus cannot unpack it in the root file system? In that case,
you will want to use the @option{--relocatable} option (see below).  This
option produces @dfn{relocatable binaries}, meaning they they can be placed
anywhere in the file system hierarchy: in the example above, users can
unpack your tarball in their home directory and directly run
@file{./opt/gnu/bin/guile}.

@cindex Docker, build an image with guix pack
Alternatively, you can produce a pack in the Docker image format using the
following command:

@example
guix pack -f docker -S /bin=bin guile guile-readline
@end example

@noindent
The result is a tarball that can be passed to the @command{docker load}
command, followed by @code{docker run}:

@example
docker load < @var{file}
docker run -ti guile-guile-readline /bin/guile
@end example

@noindent
where @var{file} is the image returned by @var{guix pack}, and
@code{guile-guile-readline} is its ``image tag''.  See the
@uref{https://docs.docker.com/engine/reference/commandline/load/, Docker
documentation} for more information.

@cindex Singularity, build an image with guix pack
@cindex SquashFS, build an image with guix pack
Yet another option is to produce a SquashFS image with the following
command:

@example
guix pack -f squashfs bash guile emacs geiser
@end example

@noindent
The result is a SquashFS file system image that can either be mounted or
directly be used as a file system container image with the
@uref{https://www.sylabs.io/docs/, Singularity container execution
environment}, using commands like @command{singularity shell} or
@command{singularity exec}.

Several command-line options allow you to customize your pack:

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce a pack in the given @var{format}.

The available formats are:

@table @code
@item tarball
This is the default format.  It produces a tarball containing all the
specified binaries and symlinks.

@item docker
This produces a tarball that follows the
@uref{https://github.com/docker/docker/blob/master/image/spec/v1.2.md,
Docker Image Specification}.  The ``repository name'' as it appears in the
output of the @command{docker images} command is computed from package names
passed on the command line or in the manifest file.

@item squashfs
This produces a SquashFS image containing all the specified binaries and
symlinks, as well as empty mount points for virtual file systems like
procfs.

@quotation 注
Singularity @emph{requires} you to provide @file{/bin/sh} in the image.  For
that reason, @command{guix pack -f squashfs} always implies @code{-S
/bin=bin}.  Thus, your @command{guix pack} invocation must always start with
something like:

@example
guix pack -f squashfs bash @dots{}
@end example

If you forget the @code{bash} (or similar) package, @command{singularity
run} and @command{singularity exec} will fail with an unhelpful ``no such
file or directory'' message.
@end quotation
@end table

@cindex relocatable binaries
@item --relocatable
@itemx -R
Produce @dfn{relocatable binaries}---i.e., binaries that can be placed
anywhere in the file system hierarchy and run from there.

When this option is passed once, the resulting binaries require support for
@dfn{user namespaces} in the kernel Linux; when passed
@emph{twice}@footnote{Here's a trick to memorize it: @code{-RR}, which adds
PRoot support, can be thought of as the abbreviation of ``Really
Relocatable''.  Neat, isn't it?}, relocatable binaries fall to back to other
techniques if user namespaces are unavailable, and essentially work
anywhere---see below for the implications.

For example, if you create a pack containing Bash with:

@example
guix pack -RR -S /mybin=bin bash
@end example

@noindent
...@: you can copy that pack to a machine that lacks Guix, and from your
home directory as a normal user, run:

@example
tar xf pack.tar.gz
./mybin/sh
@end example

@noindent
In that shell, if you type @code{ls /gnu/store}, you'll notice that
@file{/gnu/store} shows up and contains all the dependencies of @code{bash},
even though the machine actually lacks @file{/gnu/store} altogether! That is
probably the simplest way to deploy Guix-built software on a non-Guix
machine.

@quotation 注
By default, relocatable binaries rely on the @dfn{user namespace} feature of
the kernel Linux, which allows unprivileged users to mount or change root.
Old versions of Linux did not support it, and some GNU/Linux distributions
turn it off.

To produce relocatable binaries that work even in the absence of user
namespaces, pass @option{--relocatable} or @option{-R} @emph{twice}.  In
that case, binaries will try user namespace support and fall back to another
@dfn{execution engine} if user namespaces are not supported.  The following
execution engines are supported:

@table @code
@item default
Try user namespaces and fall back to PRoot if user namespaces are not
supported (see below).

@item performance
Try user namespaces and fall back to Fakechroot if user namespaces are not
supported (see below).

@item userns
Run the program through user namespaces and abort if they are not supported.

@item proot
Run through PRoot.  The @uref{https://proot-me.github.io/, PRoot} program
provides the necessary support for file system virtualization.  It achieves
that by using the @code{ptrace} system call on the running program.  This
approach has the advantage to work without requiring special kernel support,
but it incurs run-time overhead every time a system call is made.

@item fakechroot
Run through Fakechroot.  @uref{https://github.com/dex4er/fakechroot/,
Fakechroot} virtualizes file system accesses by intercepting calls to C
library functions such as @code{open}, @code{stat}, @code{exec}, and so on.
Unlike PRoot, it incurs very little overhead.  However, it does not always
work: for example, some file system accesses made from within the C library
are not intercepted, and file system accesses made @i{via} direct syscalls
are not intercepted either, leading to erratic behavior.
@end table

@vindex GUIX_EXECUTION_ENGINE
When running a wrapped program, you can explicitly request one of the
execution engines listed above by setting the @env{GUIX_EXECUTION_ENGINE}
environment variable accordingly.
@end quotation

@cindex entry point, for Docker images
@item --entry-point=@var{command}
Use @var{command} as the @dfn{entry point} of the resulting pack, if the
pack format supports it---currently @code{docker} and @code{squashfs}
(Singularity)  support it.  @var{command} must be relative to the profile
contained in the pack.

The entry point specifies the command that tools like @code{docker run} or
@code{singularity run} automatically start by default.  For example, you can
do:

@example
guix pack -f docker --entry-point=bin/guile guile
@end example

The resulting pack can easily be loaded and @code{docker run} with no extra
arguments will spawn @code{bin/guile}:

@example
docker load -i pack.tar.gz
docker run @var{image-id}
@end example

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This has the same purpose as the same-named option in @command{guix build}
(@pxref{额外的构建选项, @option{--expression} in @command{guix
build}}).

@item --manifest=@var{file}
@itemx -m @var{file}
Use the packages contained in the manifest object returned by the Scheme
code in @var{file}.  This option can be repeated several times, in which
case the manifests are concatenated.

This has a similar purpose as the same-named option in @command{guix
package} (@pxref{profile-manifest, @option{--manifest}}) and uses the same
manifest files.  It allows you to define a collection of packages once and
use it both for creating profiles and for creating archives for use on
machines that do not have Guix installed.  Note that you can specify
@emph{either} a manifest file @emph{or} a list of packages, but not both.

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of the
system type of the build host.

@item --target=@var{triplet}
@cindex cross-compilation
Cross-build for @var{triplet}, which must be a valid GNU triplet, such as
@code{"aarch64-linux-gnu"} (@pxref{Specifying target triplets, GNU
configuration triplets,, autoconf, Autoconf}).

@item --compression=@var{tool}
@itemx -C @var{tool}
Compress the resulting tarball using @var{tool}---one of @code{gzip},
@code{zstd}, @code{bzip2}, @code{xz}, @code{lzip}, or @code{none} for no
compression.

@item --symlink=@var{spec}
@itemx -S @var{spec}
Add the symlinks specified by @var{spec} to the pack.  This option can
appear several times.

@var{spec} has the form @code{@var{source}=@var{target}}, where @var{source}
is the symlink that will be created and @var{target} is the symlink target.

For instance, @code{-S /opt/gnu/bin=bin} creates a @file{/opt/gnu/bin}
symlink pointing to the @file{bin} sub-directory of the profile.

@item --save-provenance
Save provenance information for the packages passed on the command line.
Provenance information includes the URL and commit of the channels in use
(@pxref{通道}).

Provenance information is saved in the
@file{/gnu/store/@dots{}-profile/manifest} file in the pack, along with the
usual package metadata---the name and version of each package, their
propagated inputs, and so on.  It is useful information to the recipient of
the pack, who then knows how the pack was (supposedly) obtained.

This option is not enabled by default because, like timestamps, provenance
information contributes nothing to the build process.  In other words, there
is an infinity of channel URLs and commit IDs that can lead to the same
pack.  Recording such ``silent'' metadata in the output thus potentially
breaks the source-to-binary bitwise reproducibility property.

@item --root=@var{file}
@itemx -r @var{file}
@cindex garbage collector root, for packs
Make @var{file} a symlink to the resulting pack, and register it as a
garbage collector root.

@item --localstatedir
@itemx --profile-name=@var{name}
Include the ``local state directory'', @file{/var/guix}, in the resulting
pack, and notably the @file{/var/guix/profiles/per-user/root/@var{name}}
profile---by default @var{name} is @code{guix-profile}, which corresponds to
@file{~root/.guix-profile}.

@file{/var/guix} contains the store database (@pxref{仓库}) as well as
garbage-collector roots (@pxref{调用guix gc}).  Providing it in the
pack means that the store is ``complete'' and manageable by Guix; not
providing it pack means that the store is ``dead'': items cannot be added to
it or removed from it after extraction of the pack.

One use case for this is the Guix self-contained binary tarball
(@pxref{二进制文件安装}).

@item --derivation
@itemx -d
Print the name of the derivation that builds the pack.

@item --bootstrap
Use the bootstrap binaries to build the pack.  This option is only useful to
Guix developers.
@end table

In addition, @command{guix pack} supports all the common build options
(@pxref{普通的构建选项}) and all the package transformation options
(@pxref{软件包变换选项。}).


@node The GCC toolchain
@section The GCC toolchain

@cindex GCC
@cindex ld-wrapper
@cindex linker wrapper
@cindex toolchain, for C development
@cindex toolchain, for Fortran development

If you need a complete toolchain for compiling and linking C or C++ source
code, use the @code{gcc-toolchain} package.  This package provides a
complete GCC toolchain for C/C++ development, including GCC itself, the GNU
C Library (headers and binaries, plus debugging symbols in the @code{debug}
output), Binutils, and a linker wrapper.

The wrapper's purpose is to inspect the @code{-L} and @code{-l} switches
passed to the linker, add corresponding @code{-rpath} arguments, and invoke
the actual linker with this new set of arguments.  You can instruct the
wrapper to refuse to link against libraries not in the store by setting the
@env{GUIX_LD_WRAPPER_ALLOW_IMPURITIES} environment variable to @code{no}.

The package @code{gfortran-toolchain} provides a complete GCC toolchain for
Fortran development.  For other languages, please use @samp{guix search gcc
toolchain} (@pxref{guix-search,, Invoking guix package}).


@node Invoking guix git authenticate
@section Invoking @command{guix git authenticate}

The @command{guix git authenticate} command authenticates a Git checkout
following the same rule as for channels (@pxref{channel-authentication,
channel authentication}).  That is, starting from a given commit, it ensures
that all subsequent commits are signed by an OpenPGP key whose fingerprint
appears in the @file{.guix-authorizations} file of its parent commit(s).

You will find this command useful if you maintain a channel.  But in fact,
this authentication mechanism is useful in a broader context, so you might
want to use it for Git repositories that have nothing to do with Guix.

The general syntax is:

@example
guix git authenticate @var{commit} @var{signer} [@var{options}@dots{}]
@end example

By default, this command authenticates the Git checkout in the current
directory; it outputs nothing and exits with exit code zero on success and
non-zero on failure.  @var{commit} above denotes the first commit where
authentication takes place, and @var{signer} is the OpenPGP fingerprint of
public key used to sign @var{commit}.  Together, they form a ``channel
introduction'' (@pxref{channel-authentication, channel introduction}).  The
options below allow you to fine-tune the process.

@table @code
@item --repository=@var{directory}
@itemx -r @var{directory}
Open the Git repository in @var{directory} instead of the current directory.

@item --keyring=@var{reference}
@itemx -k @var{reference}
Load OpenPGP keyring from @var{reference}, the reference of a branch such as
@code{origin/keyring} or @code{my-keyring}.  The branch must contain OpenPGP
public keys in @file{.key} files, either in binary form or
``ASCII-armored''.  By default the keyring is loaded from the branch named
@code{keyring}.

@item --stats
Display commit signing statistics upon completion.

@item --cache-key=@var{key}
Previously-authenticated commits are cached in a file under
@file{~/.cache/guix/authentication}.  This option forces the cache to be
stored in file @var{key} in that directory.

@item --historical-authorizations=@var{file}
By default, any commit whose parent commit(s) lack the
@file{.guix-authorizations} file is considered inauthentic.  In contrast,
this option considers the authorizations in @var{file} for any commit that
lacks @file{.guix-authorizations}.  The format of @var{file} is the same as
that of @file{.guix-authorizations} (@pxref{channel-authorizations,
@file{.guix-authorizations} format}).
@end table


@c *********************************************************************
@node 编程接口
@chapter 编程接口

GNU Guix provides several Scheme programming interfaces (APIs) to define,
build, and query packages.  The first interface allows users to write
high-level package definitions.  These definitions refer to familiar
packaging concepts, such as the name and version of a package, its build
system, and its dependencies.  These definitions can then be turned into
concrete build actions.

Build actions are performed by the Guix daemon, on behalf of users.  In a
standard setup, the daemon has write access to the store---the
@file{/gnu/store} directory---whereas users do not.  The recommended setup
also has the daemon perform builds in chroots, under specific build users,
to minimize interference with the rest of the system.

@cindex derivation
Lower-level APIs are available to interact with the daemon and the store.
To instruct the daemon to perform a build action, users actually provide it
with a @dfn{derivation}.  A derivation is a low-level representation of the
build actions to be taken, and the environment in which they should
occur---derivations are to package definitions what assembly is to C
programs.  The term ``derivation'' comes from the fact that build results
@emph{derive} from them.

This chapter describes all these APIs in turn, starting from high-level
package definitions.

@menu
* 软件包模块::          从程序员的角度看软件包。
* 定义软件包::          定义新软件包。
* Defining Package Variants::  Customizing packages.
* 构建系统::             指定如何构建软件包。
* Build Phases::             Phases of the build process of a package.
* Build Utilities::          Helpers for your package definitions and more.
* 仓库::                   操纵软件包仓库。
* Derivations::              软件包derivation的底层接口。
* 仓库monad::              仓库的纯函数式接口。
* G-表达式::              操纵构建表达式。
* 调用guix repl::          Programming Guix in Guile
@end menu

@node 软件包模块
@section 软件包模块

From a programming viewpoint, the package definitions of the GNU
distribution are provided by Guile modules in the @code{(gnu packages
@dots{})} name space@footnote{Note that packages under the @code{(gnu
packages @dots{})} module name space are not necessarily ``GNU packages''.
This module naming scheme follows the usual Guile module naming convention:
@code{gnu} means that these modules are distributed as part of the GNU
system, and @code{packages} identifies modules that define packages.}
(@pxref{模块, Guile modules,, guile, GNU Guile Reference Manual}).  For
instance, the @code{(gnu packages emacs)} module exports a variable named
@code{emacs}, which is bound to a @code{<package>} object (@pxref{定义软件包}).

The @code{(gnu packages @dots{})} module name space is automatically scanned
for packages by the command-line tools.  For instance, when running
@code{guix install emacs}, all the @code{(gnu packages @dots{})} modules are
scanned until one that exports a package object whose name is @code{emacs}
is found.  This package search facility is implemented in the @code{(gnu
packages)} module.

@cindex 定制软件包
@cindex package module search path
Users can store package definitions in modules with different names---e.g.,
@code{(my-packages emacs)}@footnote{Note that the file name and module name
must match.  For instance, the @code{(my-packages emacs)} module must be
stored in a @file{my-packages/emacs.scm} file relative to the load path
specified with @option{--load-path} or @env{GUIX_PACKAGE_PATH}.
@xref{Modules and the File System,,, guile, GNU Guile Reference Manual}, for
details.}.  There are two ways to make these package definitions visible to
the user interfaces:

@enumerate
@item
By adding the directory containing your package modules to the search path
with the @code{-L} flag of @command{guix package} and other commands
(@pxref{普通的构建选项}), or by setting the @env{GUIX_PACKAGE_PATH}
environment variable described below.

@item
By defining a @dfn{channel} and configuring @command{guix pull} so that it
pulls from it.  A channel is essentially a Git repository containing package
modules.  @xref{通道}, for more information on how to define and use
channels.
@end enumerate

@env{GUIX_PACKAGE_PATH} works similarly to other search path variables:

@defvr {Environment Variable} GUIX_PACKAGE_PATH
This is a colon-separated list of directories to search for additional
package modules.  Directories listed in this variable take precedence over
the own modules of the distribution.
@end defvr

The distribution is fully @dfn{bootstrapped} and @dfn{self-contained}: each
package is built based solely on other packages in the distribution.  The
root of this dependency graph is a small set of @dfn{bootstrap binaries},
provided by the @code{(gnu packages bootstrap)} module.  For more
information on bootstrapping, @pxref{引导}.

@node 定义软件包
@section 定义软件包

The high-level interface to package definitions is implemented in the
@code{(guix packages)} and @code{(guix build-system)} modules.  As an
example, the package definition, or @dfn{recipe}, for the GNU Hello package
looks like this:

@lisp
(define-module (gnu packages hello)
  #:use-module (guix packages)
  #:use-module (guix download)
  #:use-module (guix build-system gnu)
  #:use-module (guix licenses)
  #:use-module (gnu packages gawk))

(define-public hello
  (package
    (name "hello")
    (version "2.10")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
    (build-system gnu-build-system)
    (arguments '(#:configure-flags '("--enable-silent-rules")))
    (inputs `(("gawk" ,gawk)))
    (synopsis "Hello, GNU world: An example GNU package")
    (description "Guess what GNU Hello prints!")
    (home-page "https://www.gnu.org/software/hello/")
    (license gpl3+)))
@end lisp

@noindent
Without being a Scheme expert, the reader may have guessed the meaning of
the various fields here.  This expression binds the variable @code{hello} to
a @code{<package>} object, which is essentially a record (@pxref{SRFI-9,
Scheme records,, guile, GNU Guile Reference Manual}).  This package object
can be inspected using procedures found in the @code{(guix packages)}
module; for instance, @code{(package-name hello)}
returns---surprise!---@code{"hello"}.

With luck, you may be able to import part or all of the definition of the
package you are interested in from another repository, using the @code{guix
import} command (@pxref{调用guix import}).

In the example above, @code{hello} is defined in a module of its own,
@code{(gnu packages hello)}.  Technically, this is not strictly necessary,
but it is convenient to do so: all the packages defined in modules under
@code{(gnu packages @dots{})} are automatically known to the command-line
tools (@pxref{软件包模块}).

There are a few points worth noting in the above package definition:

@itemize
@item
The @code{source} field of the package is an @code{<origin>} object
(@pxref{origin参考手册}, for the complete reference).  Here, the
@code{url-fetch} method from @code{(guix download)} is used, meaning that
the source is a file to be downloaded over FTP or HTTP.

The @code{mirror://gnu} prefix instructs @code{url-fetch} to use one of the
GNU mirrors defined in @code{(guix download)}.

The @code{sha256} field specifies the expected SHA256 hash of the file being
downloaded.  It is mandatory, and allows Guix to check the integrity of the
file.  The @code{(base32 @dots{})} form introduces the base32 representation
of the hash.  You can obtain this information with @code{guix download}
(@pxref{调用guix download}) and @code{guix hash} (@pxref{调用guix hash}).

@cindex patches
When needed, the @code{origin} form can also have a @code{patches} field
listing patches to be applied, and a @code{snippet} field giving a Scheme
expression to modify the source code.

@item
@cindex GNU Build System
The @code{build-system} field specifies the procedure to build the package
(@pxref{构建系统}).  Here, @code{gnu-build-system} represents the
familiar GNU Build System, where packages may be configured, built, and
installed with the usual @code{./configure && make && make check && make
install} command sequence.

When you start packaging non-trivial software, you may need tools to
manipulate those build phases, manipulate files, and so on.  @xref{工具}, for more on this.

@item
The @code{arguments} field specifies options for the build system
(@pxref{构建系统}).  Here it is interpreted by @code{gnu-build-system}
as a request run @file{configure} with the @option{--enable-silent-rules}
flag.

@cindex quote
@cindex quoting
@findex '
@findex quote
What about these quote (@code{'}) characters? They are Scheme syntax to
introduce a literal list; @code{'} is synonymous with @code{quote}.
@xref{Expression Syntax, quoting,, guile, GNU Guile Reference Manual}, for
details.  Here the value of the @code{arguments} field is a list of
arguments passed to the build system down the road, as with @code{apply}
(@pxref{Fly Evaluation, @code{apply},, guile, GNU Guile Reference Manual}).

The hash-colon (@code{#:}) sequence defines a Scheme @dfn{keyword}
(@pxref{Keywords,,, guile, GNU Guile Reference Manual}), and
@code{#:configure-flags} is a keyword used to pass a keyword argument to the
build system (@pxref{Coding With Keywords,,, guile, GNU Guile Reference
Manual}).

@item
The @code{inputs} field specifies inputs to the build process---i.e.,
build-time or run-time dependencies of the package.  Here, we define an
input called @code{"gawk"} whose value is that of the @code{gawk} variable;
@code{gawk} is itself bound to a @code{<package>} object.

@cindex backquote (quasiquote)
@findex `
@findex quasiquote
@cindex comma (unquote)
@findex ,
@findex unquote
@findex ,@@
@findex unquote-splicing
Again, @code{`} (a backquote, synonymous with @code{quasiquote}) allows us
to introduce a literal list in the @code{inputs} field, while @code{,} (a
comma, synonymous with @code{unquote}) allows us to insert a value in that
list (@pxref{Expression Syntax, unquote,, guile, GNU Guile Reference
Manual}).

Note that GCC, Coreutils, Bash, and other essential tools do not need to be
specified as inputs here.  Instead, @code{gnu-build-system} takes care of
ensuring that they are present (@pxref{构建系统}).

However, any other dependencies need to be specified in the @code{inputs}
field.  Any dependency not specified here will simply be unavailable to the
build process, possibly leading to a build failure.
@end itemize

@xref{软件包引用}, for a full description of possible fields.

Once a package definition is in place, the package may actually be built
using the @code{guix build} command-line tool (@pxref{调用guix build}),
troubleshooting any build failures you encounter (@pxref{调试构建错误}).  You can easily jump back to the package definition using the
@command{guix edit} command (@pxref{调用guix edit。}).  @xref{打包指导}, for more information on how to test package definitions, and
@ref{调用guix lint}, for information on how to check a definition for
style conformance.
@vindex GUIX_PACKAGE_PATH
Lastly, @pxref{通道}, for information on how to extend the distribution
by adding your own package definitions in a ``channel''.

Finally, updating the package definition to a new upstream version can be
partly automated by the @command{guix refresh} command (@pxref{调用guix refresh}).

Behind the scenes, a derivation corresponding to the @code{<package>} object
is first computed by the @code{package-derivation} procedure.  That
derivation is stored in a @file{.drv} file under @file{/gnu/store}.  The
build actions it prescribes may then be realized by using the
@code{build-derivations} procedure (@pxref{仓库}).

@deffn {Scheme Procedure} package-derivation @var{store} @var{package} [@var{system}]
Return the @code{<derivation>} object of @var{package} for @var{system}
(@pxref{Derivations}).

@var{package} must be a valid @code{<package>} object, and @var{system} must
be a string denoting the target system type---e.g., @code{"x86_64-linux"}
for an x86_64 Linux-based GNU system.  @var{store} must be a connection to
the daemon, which operates on the store (@pxref{仓库}).
@end deffn

@noindent
@cindex cross-compilation
Similarly, it is possible to compute a derivation that cross-builds a
package for some other system:

@deffn {Scheme Procedure} package-cross-derivation @var{store} @
            @var{package} @var{target} [@var{system}] Return the @code{<derivation>}
object of @var{package} cross-built from @var{system} to @var{target}.

@var{target} must be a valid GNU triplet denoting the target hardware and
operating system, such as @code{"aarch64-linux-gnu"} (@pxref{Specifying
Target Triplets,,, autoconf, Autoconf}).
@end deffn

Once you have package definitions, you can easily define @emph{variants} of
those packages.  @xref{定义软件包}, for more on that.

@menu
* 软件包引用::          软件包数据类型。
* origin参考手册::       origin数据类型。
@end menu


@node 软件包引用
@subsection @code{package} Reference

This section summarizes all the options available in @code{package}
declarations (@pxref{定义软件包}).

@deftp {Data Type} package
This is the data type representing a package recipe.

@table @asis
@item @code{名字}
The name of the package, as a string.

@item @code{version}
The version of the package, as a string.

@item @code{source}
An object telling how the source code for the package should be acquired.
Most of the time, this is an @code{origin} object, which denotes a file
fetched from the Internet (@pxref{origin参考手册}).  It can also be any
other ``file-like'' object such as a @code{local-file}, which denotes a file
from the local file system (@pxref{G-表达式, @code{local-file}}).

@item @code{build-system}
The build system that should be used to build the package (@pxref{构建系统}).

@item @code{arguments} (default: @code{'()})
The arguments that should be passed to the build system.  This is a list,
typically containing sequential keyword-value pairs.

@item @code{inputs} (default: @code{'()})
@itemx @code{native-inputs} (default: @code{'()})
@itemx @code{propagated-inputs} (default: @code{'()})
@cindex inputs, of packages
These fields list dependencies of the package.  Each one is a list of
tuples, where each tuple has a label for the input (a string) as its first
element, a package, origin, or derivation as its second element, and
optionally the name of the output thereof that should be used, which
defaults to @code{"out"} (@pxref{有多个输出的软件包}, for more
on package outputs).  For example, the list below specifies three inputs:

@lisp
`(("libffi" ,libffi)
  ("libunistring" ,libunistring)
  ("glib:bin" ,glib "bin"))  ;the "bin" output of Glib
@end lisp

@cindex cross compilation, package dependencies
The distinction between @code{native-inputs} and @code{inputs} is necessary
when considering cross-compilation.  When cross-compiling, dependencies
listed in @code{inputs} are built for the @emph{target} architecture;
conversely, dependencies listed in @code{native-inputs} are built for the
architecture of the @emph{build} machine.

@code{native-inputs} is typically used to list tools needed at build time,
but not at run time, such as Autoconf, Automake, pkg-config, Gettext, or
Bison.  @command{guix lint} can report likely mistakes in this area
(@pxref{调用guix lint}).

@anchor{package-propagated-inputs}
Lastly, @code{propagated-inputs} is similar to @code{inputs}, but the
specified packages will be automatically installed to profiles
(@pxref{功能, the role of profiles in Guix}) alongside the package they
belong to (@pxref{package-cmd-propagated-inputs, @command{guix package}},
for information on how @command{guix package} deals with propagated inputs).

For example this is necessary when packaging a C/C++ library that needs
headers of another library to compile, or when a pkg-config file refers to
another one @i{via} its @code{Requires} field.

Another example where @code{propagated-inputs} is useful is for languages
that lack a facility to record the run-time search path akin to the
@code{RUNPATH} of ELF files; this includes Guile, Python, Perl, and more.
When packaging libraries written in those languages, ensure they can find
library code they depend on at run time by listing run-time dependencies in
@code{propagated-inputs} rather than @code{inputs}.

@item @code{outputs} (default: @code{'("out")})
The list of output names of the package.  @xref{有多个输出的软件包}, for typical uses of additional outputs.

@item @code{native-search-paths} (default: @code{'()})
@itemx @code{search-paths} (default: @code{'()})
A list of @code{search-path-specification} objects describing search-path
environment variables honored by the package.

@item @code{replacement} (default: @code{#f})
This must be either @code{#f} or a package object that will be used as a
@dfn{replacement} for this package.  @xref{安全更新, grafts}, for
details.

@item @code{synopsis}
A one-line description of the package.

@item @code{description}
A more elaborate description of the package.

@item @code{license}
@cindex license, of packages
The license of the package; a value from @code{(guix licenses)}, or a list
of such values.

@item @code{home-page}
The URL to the home-page of the package, as a string.

@item @code{supported-systems} (default: @code{%supported-systems})
The list of systems supported by the package, as strings of the form
@code{architecture-kernel}, for example @code{"x86_64-linux"}.

@item @code{location} (default: source location of the @code{package} form)
The source location of the package.  It is useful to override this when
inheriting from another package, in which case this field is not
automatically corrected.
@end table
@end deftp

@deffn {Scheme Syntax} this-package
When used in the @emph{lexical scope} of a package field definition, this
identifier resolves to the package being defined.

The example below shows how to add a package as a native input of itself
when cross-compiling:

@lisp
(package
  (name "guile")
  ;; ...

  ;; When cross-compiled, Guile, for example, depends on
  ;; a native version of itself.  Add it here.
  (native-inputs (if (%current-target-system)
                     `(("self" ,this-package))
                     '())))
@end lisp

It is an error to refer to @code{this-package} outside a package definition.
@end deffn

Because packages are regular Scheme objects that capture a complete
dependency graph and associated build procedures, it is often useful to
write procedures that take a package and return a modified version thereof
according to some parameters.  Below are a few examples.

@cindex tool chain, choosing a package's tool chain
@deffn {Scheme Procedure} package-with-c-toolchain @var{package} @var{toolchain}
Return a variant of @var{package} that uses @var{toolchain} instead of the
default GNU C/C++ toolchain.  @var{toolchain} must be a list of inputs
(label/package tuples) providing equivalent functionality, such as the
@code{gcc-toolchain} package.

The example below returns a variant of the @code{hello} package built with
GCC@tie{}10.x and the rest of the GNU tool chain (Binutils and the GNU C
Library) instead of the default tool chain:

@lisp
(let ((toolchain (specification->package "gcc-toolchain@@10")))
  (package-with-c-toolchain hello `(("toolchain" ,toolchain))))
@end lisp

The build tool chain is part of the @dfn{implicit inputs} of packages---it's
usually not listed as part of the various ``inputs'' fields and is instead
pulled in by the build system.  Consequently, this procedure works by
changing the build system of @var{package} so that it pulls in
@var{toolchain} instead of the defaults.  @ref{构建系统}, for more on
build systems.
@end deffn

@node origin参考手册
@subsection @code{origin} Reference

This section documents @dfn{origins}.  An @code{origin} declaration
specifies data that must be ``produced''---downloaded, usually---and whose
content hash is known in advance.  Origins are primarily used to represent
the source code of packages (@pxref{定义软件包}).  For that reason,
the @code{origin} form allows you to declare patches to apply to the
original source code as well as code snippets to modify it.

@deftp {Data Type} origin
This is the data type representing a source code origin.

@table @asis
@item @code{uri}
An object containing the URI of the source.  The object type depends on the
@code{method} (see below).  For example, when using the @var{url-fetch}
method of @code{(guix download)}, the valid @code{uri} values are: a URL
represented as a string, or a list thereof.

@cindex fixed-output derivations, for download
@item @code{method}
A monadic procedure that handles the given URI@.  The procedure must accept
at least three arguments: the value of the @code{uri} field and the hash
algorithm and hash value specified by the @code{hash} field.  It must return
a store item or a derivation in the store monad (@pxref{仓库monad});
most methods return a fixed-output derivation (@pxref{Derivations}).

Commonly used methods include @code{url-fetch}, which fetches data from a
URL, and @code{git-fetch}, which fetches data from a Git repository (see
below).

@item @code{sha256}
A bytevector containing the SHA-256 hash of the source.  This is equivalent
to providing a @code{content-hash} SHA256 object in the @code{hash} field
described below.

@item @code{hash}
The @code{content-hash} object of the source---see below for how to use
@code{content-hash}.

You can obtain this information using @code{guix download} (@pxref{调用guix download}) or @code{guix hash} (@pxref{调用guix hash}).

@item @code{file-name} (default: @code{#f})
The file name under which the source code should be saved.  When this is
@code{#f}, a sensible default value will be used in most cases.  In case the
source is fetched from a URL, the file name from the URL will be used.  For
version control checkouts, it is recommended to provide the file name
explicitly because the default is not very descriptive.

@item @code{patches} (default: @code{'()})
A list of file names, origins, or file-like objects (@pxref{G-表达式,
file-like objects}) pointing to patches to be applied to the source.

This list of patches must be unconditional.  In particular, it cannot depend
on the value of @code{%current-system} or @code{%current-target-system}.

@item @code{snippet} (default: @code{#f})
A G-expression (@pxref{G-表达式}) or S-expression that will be run in
the source directory.  This is a convenient way to modify the source,
sometimes more convenient than a patch.

@item @code{patch-flags} (default: @code{'("-p1")})
A list of command-line flags that should be passed to the @code{patch}
command.

@item @code{patch-inputs} (default: @code{#f})
Input packages or derivations to the patching process.  When this is
@code{#f}, the usual set of inputs necessary for patching are provided, such
as GNU@tie{}Patch.

@item @code{modules} (default: @code{'()})
A list of Guile modules that should be loaded during the patching process
and while running the code in the @code{snippet} field.

@item @code{patch-guile} (default: @code{#f})
The Guile package that should be used in the patching process.  When this is
@code{#f}, a sensible default is used.
@end table
@end deftp

@deftp {Data Type} content-hash @var{value} [@var{algorithm}]
Construct a content hash object for the given @var{algorithm}, and with
@var{value} as its hash value.  When @var{algorithm} is omitted, assume it
is @code{sha256}.

@var{value} can be a literal string, in which case it is base32-decoded, or
it can be a bytevector.

The following forms are all equivalent:

@lisp
(content-hash "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj")
(content-hash "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj"
              sha256)
(content-hash (base32
               "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj"))
(content-hash (base64 "kkb+RPaP7uyMZmu4eXPVkM4BN8yhRd8BTHLslb6f/Rc=")
              sha256)
@end lisp

Technically, @code{content-hash} is currently implemented as a macro.  It
performs sanity checks at macro-expansion time, when possible, such as
ensuring that @var{value} has the right size for @var{algorithm}.
@end deftp

As we have seen above, how exactly the data an origin refers to is retrieved
is determined by its @code{method} field.  The @code{(guix download)} module
provides the most common method, @code{url-fetch}, described below.

@deffn {Scheme Procedure} url-fetch @var{url} @var{hash-algo} @var{hash} @
           [name] [#:executable? #f] Return a fixed-output derivation that fetches data
from @var{url} (a string, or a list of strings denoting alternate URLs),
which is expected to have hash @var{hash} of type @var{hash-algo} (a
symbol).  By default, the file name is the base name of URL; optionally,
@var{name} can specify a different file name.  When @var{executable?} is
true, make the downloaded file executable.

When one of the URL starts with @code{mirror://}, then its host part is
interpreted as the name of a mirror scheme, taken from @file{%mirror-file}.

Alternatively, when URL starts with @code{file://}, return the corresponding
file name in the store.
@end deffn

Likewise, the @code{(guix git-download)} module defines the @code{git-fetch}
origin method, which fetches data from a Git version control repository, and
the @code{git-reference} data type to describe the repository and revision
to fetch.

@deffn {Scheme Procedure} git-fetch @var{ref} @var{hash-algo} @var{hash}
Return a fixed-output derivation that fetches @var{ref}, a
@code{<git-reference>} object.  The output is expected to have recursive
hash @var{hash} of type @var{hash-algo} (a symbol).  Use @var{name} as the
file name, or a generic name if @code{#f}.
@end deffn

@deftp {Data Type} git-reference
This data type represents a Git reference for @code{git-fetch} to retrieve.

@table @asis
@item @code{url}
The URL of the Git repository to clone.

@item @code{commit}
This string denotes either the commit to fetch (a hexadecimal string, either
the full SHA1 commit or a ``short'' commit string; the latter is not
recommended) or the tag to fetch.

@item @code{recursive?} (default: @code{#f})
This Boolean indicates whether to recursively fetch Git sub-modules.
@end table

The example below denotes the @code{v2.10} tag of the GNU@tie{}Hello
repository:

@lisp
(git-reference
  (url "https://git.savannah.gnu.org/git/hello.git")
  (commit "v2.10"))
@end lisp

This is equivalent to the reference below, which explicitly names the
commit:

@lisp
(git-reference
  (url "https://git.savannah.gnu.org/git/hello.git")
  (commit "dc7dc56a00e48fe6f231a58f6537139fe2908fb9"))
@end lisp
@end deftp

For Mercurial repositories, the module @code{(guix hg-download)} defines the
@code{hg-fetch} origin method and @code{hg-reference} data type for support
of the Mercurial version control system.

@deffn {Scheme Procedure} hg-fetch @var{ref} @var{hash-algo} @var{hash} @
           [name] Return a fixed-output derivation that fetches @var{ref}, a
@code{<hg-reference>} object.  The output is expected to have recursive hash
@var{hash} of type @var{hash-algo} (a symbol).  Use @var{name} as the file
name, or a generic name if @code{#false}.
@end deffn

@node Defining Package Variants
@section Defining Package Variants

@cindex customizing packages
@cindex variants, of packages
One of the nice things with Guix is that, given a package definition, you
can easily @emph{derive} variants of that package---for a different upstream
version, with different dependencies, different compilation options, and so
on.  Some of these custom packages can be defined straight from the command
line (@pxref{软件包变换选项。}).  This section describes how
to define package variants in code.  This can be useful in ``manifests''
(@pxref{profile-manifest, @option{--manifest}}) and in your own package
collection (@pxref{创建一个频道}), among others!

@cindex inherit, for package definitions
As discussed earlier, packages are first-class objects in the Scheme
language.  The @code{(guix packages)} module provides the @code{package}
construct to define new package objects (@pxref{软件包引用}).  The
easiest way to define a package variant is using the @code{inherit} keyword
together with @code{package}.  This allows you to inherit from a package
definition while overriding the fields you want.

For example, given the @code{hello} variable, which contains a definition
for the current version of GNU@tie{}Hello, here's how you would define a
variant for version 2.2 (released in 2006, it's vintage!):

@lisp
(use-modules (gnu packages base))    ;for 'hello'

(define hello-2.2
  (package
    (inherit hello)
    (version "2.2")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "0lappv4slgb5spyqbh6yl5r013zv72yqg2pcl30mginf3wdqd8k9"))))))
@end lisp

The example above corresponds to what the @option{--with-source} package
transformation option does.  Essentially @code{hello-2.2} preserves all the
fields of @code{hello}, except @code{version} and @code{source}, which it
overrides.  Note that the original @code{hello} variable is still there, in
the @code{(gnu packages base)} module, unchanged.  When you define a custom
package like this, you are really @emph{adding} a new package definition;
the original one remains available.

You can just as well define variants with a different set of dependencies
than the original package.  For example, the default @code{gdb} package
depends on @code{guile}, but since that is an optional dependency, you can
define a variant that removes that dependency like so:

@lisp
(use-modules (gnu packages gdb)    ;for 'gdb'
             (srfi srfi-1))        ;for 'alist-delete'

(define gdb-sans-guile
  (package
    (inherit gdb)
    (inputs (alist-delete "guile"
                          (package-inputs gdb)))))
@end lisp

The @code{alist-delete} call above removes the tuple from the @code{inputs}
field that has @code{"guile"} as its first element (@pxref{SRFI-1
Association Lists,,, guile, GNU Guile Reference Manual}).

In some cases, you may find it useful to write functions (``procedures'', in
Scheme parlance) that return a package based on some parameters.  For
example, consider the @code{luasocket} library for the Lua programming
language.  We want to create @code{luasocket} packages for major versions of
Lua.  One way to do that is to define a procedure that takes a Lua package
and returns a @code{luasocket} package that depends on it:

@lisp
(define (make-lua-socket name lua)
  ;; Return a luasocket package built with LUA.
  (package
    (name name)
    (version "3.0")
    ;; several fields omitted
    (inputs
     `(("lua" ,lua)))
    (synopsis "Socket library for Lua")))

(define-public lua5.1-socket
  (make-lua-socket "lua5.1-socket" lua-5.1))

(define-public lua5.2-socket
  (make-lua-socket "lua5.2-socket" lua-5.2))
@end lisp

Here we have defined packages @code{lua5.1-socket} and @code{lua5.2-socket}
by calling @code{make-lua-socket} with different arguments.
@xref{Procedures,,, guile, GNU Guile Reference Manual}, for more info on
procedures.  Having top-level public definitions for these two packages
means that they can be referred to from the command line (@pxref{软件包模块}).

@cindex package transformations
These are pretty simple package variants.  As a convenience, the @code{(guix
transformations)} module provides a high-level interface that directly maps
to the more sophisticated package transformation options (@pxref{软件包变换选项。}):

@deffn {Scheme Procedure} options->transformation @var{opts}
Return a procedure that, when passed an object to build (package,
derivation, etc.), applies the transformations specified by @var{opts} and
returns the resulting objects.  @var{opts} must be a list of symbol/string
pairs such as:

@lisp
((with-branch . "guile-gcrypt=master")
 (without-tests . "libgcrypt"))
@end lisp

Each symbol names a transformation and the corresponding string is an
argument to that transformation.
@end deffn

For instance, a manifest equivalent to this command:

@example
guix build guix \
  --with-branch=guile-gcrypt=master \
  --with-debug-info=zlib
@end example

@noindent
... would look like this:

@lisp
(use-modules (guix transformations))

(define transform
  ;; The package transformation procedure.
  (options->transformation
   '((with-branch . "guile-gcrypt=master")
     (with-debug-info . "zlib"))))

(packages->manifest
 (list (transform (specification->package "guix"))))
@end lisp

@cindex input rewriting
@cindex dependency graph rewriting
The @code{options->transformation} procedure is convenient, but it's perhaps
also not as flexible as you may like.  How is it implemented? The astute
reader probably noticed that most package transformation options go beyond
the superficial changes shown in the first examples of this section: they
involve @dfn{input rewriting}, whereby the dependency graph of a package is
rewritten by replacing specific inputs by others.

Dependency graph rewriting, for the purposes of swapping packages in the
graph, is what the @code{package-input-rewriting} procedure in @code{(guix
packages)} implements.

@deffn {Scheme Procedure} package-input-rewriting @var{replacements} @
           [@var{rewrite-name}] [#:deep? #t] Return a procedure that, when passed a
package, replaces its direct and indirect dependencies, including implicit
inputs when @var{deep?} is true, according to @var{replacements}.
@var{replacements} is a list of package pairs; the first element of each
pair is the package to replace, and the second one is the replacement.

Optionally, @var{rewrite-name} is a one-argument procedure that takes the
name of a package and returns its new name after rewrite.
@end deffn

@noindent
Consider this example:

@lisp
(define libressl-instead-of-openssl
  ;; This is a procedure to replace OPENSSL by LIBRESSL,
  ;; recursively.
  (package-input-rewriting `((,openssl . ,libressl))))

(define git-with-libressl
  (libressl-instead-of-openssl git))
@end lisp

@noindent
Here we first define a rewriting procedure that replaces @var{openssl} with
@var{libressl}.  Then we use it to define a @dfn{variant} of the @var{git}
package that uses @var{libressl} instead of @var{openssl}.  This is exactly
what the @option{--with-input} command-line option does (@pxref{软件包变换选项。, @option{--with-input}}).

The following variant of @code{package-input-rewriting} can match packages
to be replaced by name rather than by identity.

@deffn {Scheme Procedure} package-input-rewriting/spec @var{replacements} [#:deep? #t]
Return a procedure that, given a package, applies the given
@var{replacements} to all the package graph, including implicit inputs
unless @var{deep?} is false.  @var{replacements} is a list of
spec/procedures pair; each spec is a package specification such as
@code{"gcc"} or @code{"guile@@2"}, and each procedure takes a matching
package and returns a replacement for that package.
@end deffn

The example above could be rewritten this way:

@lisp
(define libressl-instead-of-openssl
  ;; Replace all the packages called "openssl" with LibreSSL.
  (package-input-rewriting/spec `(("openssl" . ,(const libressl)))))
@end lisp

The key difference here is that, this time, packages are matched by spec and
not by identity.  In other words, any package in the graph that is called
@code{openssl} will be replaced.

A more generic procedure to rewrite a package dependency graph is
@code{package-mapping}: it supports arbitrary changes to nodes in the graph.

@deffn {Scheme Procedure} package-mapping @var{proc} [@var{cut?}] [#:deep? #f]
Return a procedure that, given a package, applies @var{proc} to all the
packages depended on and returns the resulting package.  The procedure stops
recursion when @var{cut?} returns true for a given package.  When
@var{deep?} is true, @var{proc} is applied to implicit inputs as well.
@end deffn


@node 构建系统
@section 构建系统

@cindex build system
Each package definition specifies a @dfn{build system} and arguments for
that build system (@pxref{定义软件包}).  This @code{build-system}
field represents the build procedure of the package, as well as implicit
dependencies of that build procedure.

Build systems are @code{<build-system>} objects.  The interface to create
and manipulate them is provided by the @code{(guix build-system)} module,
and actual build systems are exported by specific modules.

@cindex bag (low-level package representation)
Under the hood, build systems first compile package objects to @dfn{bags}.
A @dfn{bag} is like a package, but with less ornamentation---in other words,
a bag is a lower-level representation of a package, which includes all the
inputs of that package, including some that were implicitly added by the
build system.  This intermediate representation is then compiled to a
derivation (@pxref{Derivations}).  The @code{package-with-c-toolchain} is an
example of a way to change the implicit inputs that a package's build system
pulls in (@pxref{软件包引用, @code{package-with-c-toolchain}}).

Build systems accept an optional list of @dfn{arguments}.  In package
definitions, these are passed @i{via} the @code{arguments} field
(@pxref{定义软件包}).  They are typically keyword arguments
(@pxref{Optional Arguments, keyword arguments in Guile,, guile, GNU Guile
Reference Manual}).  The value of these arguments is usually evaluated in
the @dfn{build stratum}---i.e., by a Guile process launched by the daemon
(@pxref{Derivations}).

The main build system is @code{gnu-build-system}, which implements the
standard build procedure for GNU and many other packages.  It is provided by
the @code{(guix build-system gnu)} module.

@defvr {Scheme Variable} gnu-build-system
@code{gnu-build-system} represents the GNU Build System, and variants
thereof (@pxref{Configuration, configuration and makefile conventions,,
standards, GNU Coding Standards}).

@cindex build phases
In a nutshell, packages using it are configured, built, and installed with
the usual @code{./configure && make && make check && make install} command
sequence.  In practice, a few additional steps are often needed.  All these
steps are split up in separate @dfn{phases}.  @xref{构建系统}, for more
info on build phases and ways to customize them.

In addition, this build system ensures that the ``standard'' environment for
GNU packages is available.  This includes tools such as GCC, libc,
Coreutils, Bash, Make, Diffutils, grep, and sed (see the @code{(guix
build-system gnu)} module for a complete list).  We call these the
@dfn{implicit inputs} of a package, because package definitions do not have
to mention them.

This build system supports a number of keyword arguments, which can be
passed @i{via} the @code{arguments} field of a package.  Here are some of
the main parameters:

@table @code
@item #:phases
This argument specifies build-side code that evaluates to an alist of build
phases.  @xref{构建系统}, for more information.

@item #:configure-flags
This is a list of flags (strings) passed to the @command{configure} script.
@xref{定义软件包}, for an example.

@item #:make-flags
This list of strings contains flags passed as arguments to @command{make}
invocations in the @code{build}, @code{check}, and @code{install} phases.

@item #:out-of-source?
This Boolean, @code{#f} by default, indicates whether to run builds in a
build directory separate from the source tree.

When it is true, the @code{configure} phase creates a separate build
directory, changes to that directory, and runs the @code{configure} script
from there.  This is useful for packages that require it, such as
@code{glibc}.

@item #:tests?
This Boolean, @code{#t} by default, indicates whether the @code{check} phase
should run the package's test suite.

@item #:test-target
This string, @code{"check"} by default, gives the name of the makefile
target used by the @code{check} phase.

@item #:parallel-build?
@itemx #:parallel-tests?
These Boolean values specify whether to build, respectively run the test
suite, in parallel, with the @code{-j} flag of @command{make}.  When they
are true, @code{make} is passed @code{-j@var{n}}, where @var{n} is the
number specified as the @option{--cores} option of @command{guix-daemon} or
that of the @command{guix} client command (@pxref{普通的构建选项,
@option{--cores}}).

@cindex RUNPATH, validation
@item #:validate-runpath?
This Boolean, @code{#t} by default, determines whether to ``validate'' the
@code{RUNPATH} of ELF binaries (@code{.so} shared libraries as well as
executables) previously installed by the @code{install} phase.

This validation step consists in making sure that all the shared libraries
needed by an ELF binaries, which are listed as @code{DT_NEEDED} entries in
its @code{PT_DYNAMIC} segment, appear in the @code{DT_RUNPATH} entry of that
binary.  In other words, it ensures that running or using those binaries
will not result in a ``file not found'' error at run time.  @xref{Options,
@option{-rpath},, ld, The GNU Linker}, for more information on
@code{RUNPATH}.

@item #:substitutable?
This Boolean, @code{#t} by default, tells whether the package outputs should
be substitutable---i.e., whether users should be able to obtain substitutes
for them instead of building locally (@pxref{substitutes}).

@item #:allowed-references
@itemx #:disallowed-references
When true, these arguments must be a list of dependencies that must not
appear among the references of the build results.  If, upon build
completion, some of these references are retained, the build process fails.

This is useful to ensure that a package does not erroneously keep a
reference to some of it build-time inputs, in cases where doing so would,
for example, unnecessarily increase its size (@pxref{调用guix size}).
@end table

Most other build systems support these keyword arguments.
@end defvr

Other @code{<build-system>} objects are defined to support other conventions
and tools used by free software packages.  They inherit most of
@code{gnu-build-system}, and differ mainly in the set of inputs implicitly
added to the build process, and in the list of phases executed.  Some of
these build systems are listed below.

@defvr {Scheme Variable} ant-build-system
This variable is exported by @code{(guix build-system ant)}.  It implements
the build procedure for Java packages that can be built with
@url{https://ant.apache.org/, Ant build tool}.

It adds both @code{ant} and the @dfn{Java Development Kit} (JDK) as provided
by the @code{icedtea} package to the set of inputs.  Different packages can
be specified with the @code{#:ant} and @code{#:jdk} parameters,
respectively.

When the original package does not provide a suitable Ant build file, the
parameter @code{#:jar-name} can be used to generate a minimal Ant build file
@file{build.xml} with tasks to build the specified jar archive.  In this
case the parameter @code{#:source-dir} can be used to specify the source
sub-directory, defaulting to ``src''.

The @code{#:main-class} parameter can be used with the minimal ant buildfile
to specify the main class of the resulting jar.  This makes the jar file
executable.  The @code{#:test-include} parameter can be used to specify the
list of junit tests to run.  It defaults to @code{(list "**/*Test.java")}.
The @code{#:test-exclude} can be used to disable some tests.  It defaults to
@code{(list "**/Abstract*.java")}, because abstract classes cannot be run as
tests.

The parameter @code{#:build-target} can be used to specify the Ant task that
should be run during the @code{build} phase.  By default the ``jar'' task
will be run.

@end defvr

@defvr {Scheme Variable} android-ndk-build-system
@cindex Android distribution
@cindex Android NDK build system
This variable is exported by @code{(guix build-system android-ndk)}.  It
implements a build procedure for Android NDK (native development kit)
packages using a Guix-specific build process.

The build system assumes that packages install their public interface
(header) files to the subdirectory @file{include} of the @code{out} output
and their libraries to the subdirectory @file{lib} the @code{out} output.

It's also assumed that the union of all the dependencies of a package has no
conflicting files.

For the time being, cross-compilation is not supported - so right now the
libraries and header files are assumed to be host tools.

@end defvr

@defvr {Scheme Variable} asdf-build-system/source
@defvrx {Scheme Variable} asdf-build-system/sbcl
@defvrx {Scheme Variable} asdf-build-system/ecl

These variables, exported by @code{(guix build-system asdf)}, implement
build procedures for Common Lisp packages using
@url{https://common-lisp.net/project/asdf/, ``ASDF''}.  ASDF is a system
definition facility for Common Lisp programs and libraries.

The @code{asdf-build-system/source} system installs the packages in source
form, and can be loaded using any common lisp implementation, via ASDF@.
The others, such as @code{asdf-build-system/sbcl}, install binary systems in
the format which a particular implementation understands.  These build
systems can also be used to produce executable programs, or lisp images
which contain a set of packages pre-loaded.

The build system uses naming conventions.  For binary packages, the package
name should be prefixed with the lisp implementation, such as @code{sbcl-}
for @code{asdf-build-system/sbcl}.

Additionally, the corresponding source package should be labeled using the
same convention as python packages (see @ref{Python模块}), using the
@code{cl-} prefix.

In order to create executable programs and images, the build-side procedures
@code{build-program} and @code{build-image} can be used.  They should be
called in a build phase after the @code{create-asdf-configuration} phase, so
that the system which was just built can be used within the resulting
image.  @code{build-program} requires a list of Common Lisp expressions to
be passed as the @code{#:entry-program} argument.

By default, all the @file{.asd} files present in the sources are read to
find system definitions.  The @code{#:asd-files} parameter can be used to
specify the list of @file{.asd} files to read.  Furthermore, if the package
defines a system for its tests in a separate file, it will be loaded before
the tests are run if it is specified by the @code{#:test-asd-file}
parameter.  If it is not set, the files @code{<system>-tests.asd},
@code{<system>-test.asd}, @code{tests.asd}, and @code{test.asd} will be
tried if they exist.

If for some reason the package must be named in a different way than the
naming conventions suggest, or if several systems must be compiled, the
@code{#:asd-systems} parameter can be used to specify the list of system
names.

@end defvr

@defvr {Scheme Variable} cargo-build-system
@cindex Rust programming language
@cindex Cargo (Rust build system)
This variable is exported by @code{(guix build-system cargo)}.  It supports
builds of packages using Cargo, the build tool of the
@uref{https://www.rust-lang.org, Rust programming language}.

It adds @code{rustc} and @code{cargo} to the set of inputs.  A different
Rust package can be specified with the @code{#:rust} parameter.

Regular cargo dependencies should be added to the package definition
similarly to other packages; those needed only at build time to
native-inputs, others to inputs.  If you need to add source-only crates then
you should add them to via the @code{#:cargo-inputs} parameter as a list of
name and spec pairs, where the spec can be a package or a source
definition.  Note that the spec must evaluate to a path to a gzipped tarball
which includes a @code{Cargo.toml} file at its root, or it will be ignored.
Similarly, cargo dev-dependencies should be added to the package definition
via the @code{#:cargo-development-inputs} parameter.

In its @code{configure} phase, this build system will make any source inputs
specified in the @code{#:cargo-inputs} and @code{#:cargo-development-inputs}
parameters available to cargo.  It will also remove an included
@code{Cargo.lock} file to be recreated by @code{cargo} during the
@code{build} phase.  The @code{package} phase will run @code{cargo package}
to create a source crate for future use.  The @code{install} phase installs
the binaries defined by the crate.  Unless @code{install-source? #f} is
defined it will also install a source crate repository of itself and
unpacked sources, to ease in future hacking on rust packages.
@end defvr

@defvr {Scheme Variable} chicken-build-system
This variable is exported by @code{(guix build-system chicken)}.  It builds
@uref{https://call-cc.org/, CHICKEN Scheme} modules, also called ``eggs'' or
``extensions''.  CHICKEN generates C source code, which then gets compiled
by a C compiler, in this case GCC.

This build system adds @code{chicken} to the package inputs, as well as the
packages of @code{gnu-build-system}.

The build system can't (yet) deduce the egg's name automatically, so just
like with @code{go-build-system} and its @code{#:import-path}, you should
define @code{#:egg-name} in the package's @code{arguments} field.

For example, if you are packaging the @code{srfi-1} egg:

@lisp
(arguments '(#:egg-name "srfi-1"))
@end lisp

Egg dependencies must be defined in @code{propagated-inputs}, not
@code{inputs} because CHICKEN doesn't embed absolute references in compiled
eggs.  Test dependencies should go to @code{native-inputs}, as usual.
@end defvr

@defvr {Scheme Variable} copy-build-system
This variable is exported by @code{(guix build-system copy)}.  It supports
builds of simple packages that don't require much compiling, mostly just
moving files around.

It adds much of the @code{gnu-build-system} packages to the set of inputs.
Because of this, the @code{copy-build-system} does not require all the
boilerplate code often needed for the @code{trivial-build-system}.

To further simplify the file installation process, an @code{#:install-plan}
argument is exposed to let the packager specify which files go where.  The
install plan is a list of @code{(@var{source} @var{target}
[@var{filters}])}.  @var{filters} are optional.

@itemize
@item When @var{source} matches a file or directory without trailing slash, install it to @var{target}.
@itemize
@item If @var{target} has a trailing slash, install @var{source} basename beneath @var{target}.
@item Otherwise install @var{source} as @var{target}.
@end itemize

@item When @var{source} is a directory with a trailing slash, or when @var{filters} are used,
the trailing slash of @var{target} is implied with the same meaning as
above.
@itemize
@item Without @var{filters}, install the full @var{source} @emph{content} to @var{target}.
@item With @var{filters} among @code{#:include}, @code{#:include-regexp}, @code{#:exclude},
@code{#:exclude-regexp}, only select files are installed depending on the
filters.  Each filters is specified by a list of strings.
@itemize
@item With @code{#:include}, install all the files which the path suffix matches
at least one of the elements in the given list.
@item With @code{#:include-regexp}, install all the files which the
subpaths match at least one of the regular expressions in the given list.
@item The @code{#:exclude} and @code{#:exclude-regexp} filters
are the complement of their inclusion counterpart.  Without @code{#:include}
flags, install all files but those matching the exclusion filters.  If both
inclusions and exclusions are specified, the exclusions are done on top of
the inclusions.
@end itemize
@end itemize
In all cases, the paths relative to @var{source} are preserved within
@var{target}.
@end itemize

Examples:

@itemize
@item @code{("foo/bar" "share/my-app/")}: Install @file{bar} to @file{share/my-app/bar}.
@item @code{("foo/bar" "share/my-app/baz")}: Install @file{bar} to @file{share/my-app/baz}.
@item @code{("foo/" "share/my-app")}: Install the content of @file{foo} inside @file{share/my-app},
e.g., install @file{foo/sub/file} to @file{share/my-app/sub/file}.
@item @code{("foo/" "share/my-app" #:include ("sub/file"))}: Install only @file{foo/sub/file} to
@file{share/my-app/sub/file}.
@item @code{("foo/sub" "share/my-app" #:include ("file"))}: Install @file{foo/sub/file} to
@file{share/my-app/file}.
@end itemize
@end defvr


@cindex Clojure (programming language)
@cindex simple Clojure build system
@defvr {Scheme Variable} clojure-build-system
This variable is exported by @code{(guix build-system clojure)}.  It
implements a simple build procedure for @uref{https://clojure.org/, Clojure}
packages using plain old @code{compile} in Clojure.  Cross-compilation is
not supported yet.

It adds @code{clojure}, @code{icedtea} and @code{zip} to the set of inputs.
Different packages can be specified with the @code{#:clojure}, @code{#:jdk}
and @code{#:zip} parameters, respectively.

A list of source directories, test directories and jar names can be
specified with the @code{#:source-dirs}, @code{#:test-dirs} and
@code{#:jar-names} parameters, respectively.  Compile directory and main
class can be specified with the @code{#:compile-dir} and @code{#:main-class}
parameters, respectively.  Other parameters are documented below.

This build system is an extension of @code{ant-build-system}, but with the
following phases changed:

@table @code

@item build
This phase calls @code{compile} in Clojure to compile source files and runs
@command{jar} to create jars from both source files and compiled files
according to the include list and exclude list specified in
@code{#:aot-include} and @code{#:aot-exclude}, respectively.  The exclude
list has priority over the include list.  These lists consist of symbols
representing Clojure libraries or the special keyword @code{#:all}
representing all Clojure libraries found under the source directories.  The
parameter @code{#:omit-source?} decides if source should be included into
the jars.

@item check
This phase runs tests according to the include list and exclude list
specified in @code{#:test-include} and @code{#:test-exclude}, respectively.
Their meanings are analogous to that of @code{#:aot-include} and
@code{#:aot-exclude}, except that the special keyword @code{#:all} now
stands for all Clojure libraries found under the test directories.  The
parameter @code{#:tests?} decides if tests should be run.

@item install
This phase installs all jars built previously.
@end table

Apart from the above, this build system also contains an additional phase:

@table @code

@item install-doc
This phase installs all top-level files with base name matching
@code{%doc-regex}.  A different regex can be specified with the
@code{#:doc-regex} parameter.  All files (recursively) inside the
documentation directories specified in @code{#:doc-dirs} are installed as
well.
@end table
@end defvr

@defvr {Scheme Variable} cmake-build-system
This variable is exported by @code{(guix build-system cmake)}.  It
implements the build procedure for packages using the
@url{https://www.cmake.org, CMake build tool}.

It automatically adds the @code{cmake} package to the set of inputs.  Which
package is used can be specified with the @code{#:cmake} parameter.

The @code{#:configure-flags} parameter is taken as a list of flags passed to
the @command{cmake} command.  The @code{#:build-type} parameter specifies in
abstract terms the flags passed to the compiler; it defaults to
@code{"RelWithDebInfo"} (short for ``release mode with debugging
information''), which roughly means that code is compiled with @code{-O2
-g}, as is the case for Autoconf-based packages by default.
@end defvr

@defvr {Scheme Variable} dune-build-system
This variable is exported by @code{(guix build-system dune)}.  It supports
builds of packages using @uref{https://dune.build/, Dune}, a build tool for
the OCaml programming language.  It is implemented as an extension of the
@code{ocaml-build-system} which is described below.  As such, the
@code{#:ocaml} and @code{#:findlib} parameters can be passed to this build
system.

It automatically adds the @code{dune} package to the set of inputs.  Which
package is used can be specified with the @code{#:dune} parameter.

There is no @code{configure} phase because dune packages typically don't
need to be configured.  The @code{#:build-flags} parameter is taken as a
list of flags passed to the @code{dune} command during the build.

The @code{#:jbuild?} parameter can be passed to use the @code{jbuild}
command instead of the more recent @code{dune} command while building a
package.  Its default value is @code{#f}.

The @code{#:package} parameter can be passed to specify a package name,
which is useful when a package contains multiple packages and you want to
build only one of them.  This is equivalent to passing the @code{-p}
argument to @code{dune}.
@end defvr

@defvr {Scheme Variable} go-build-system
This variable is exported by @code{(guix build-system go)}.  It implements a
build procedure for Go packages using the standard
@url{https://golang.org/cmd/go/#hdr-Compile_packages_and_dependencies, Go
build mechanisms}.

The user is expected to provide a value for the key @code{#:import-path}
and, in some cases, @code{#:unpack-path}.  The
@url{https://golang.org/doc/code.html#ImportPaths, import path} corresponds
to the file system path expected by the package's build scripts and any
referring packages, and provides a unique way to refer to a Go package.  It
is typically based on a combination of the package source code's remote URI
and file system hierarchy structure.  In some cases, you will need to unpack
the package's source code to a different directory structure than the one
indicated by the import path, and @code{#:unpack-path} should be used in
such cases.

Packages that provide Go libraries should install their source code into the
built output.  The key @code{#:install-source?}, which defaults to
@code{#t}, controls whether or not the source code is installed.  It can be
set to @code{#f} for packages that only provide executable files.
@end defvr

@defvr {Scheme Variable} glib-or-gtk-build-system
This variable is exported by @code{(guix build-system glib-or-gtk)}.  It is
intended for use with packages making use of GLib or GTK+.

This build system adds the following two phases to the ones defined by
@code{gnu-build-system}:

@table @code
@item glib-or-gtk-wrap
The phase @code{glib-or-gtk-wrap} ensures that programs in @file{bin/} are
able to find GLib ``schemas'' and
@uref{https://developer.gnome.org/gtk3/stable/gtk-running.html, GTK+
modules}.  This is achieved by wrapping the programs in launch scripts that
appropriately set the @env{XDG_DATA_DIRS} and @env{GTK_PATH} environment
variables.

It is possible to exclude specific package outputs from that wrapping
process by listing their names in the
@code{#:glib-or-gtk-wrap-excluded-outputs} parameter.  This is useful when
an output is known not to contain any GLib or GTK+ binaries, and where
wrapping would gratuitously add a dependency of that output on GLib and
GTK+.

@item glib-or-gtk-compile-schemas
The phase @code{glib-or-gtk-compile-schemas} makes sure that all
@uref{https://developer.gnome.org/gio/stable/glib-compile-schemas.html,
GSettings schemas} of GLib are compiled.  Compilation is performed by the
@command{glib-compile-schemas} program.  It is provided by the package
@code{glib:bin} which is automatically imported by the build system.  The
@code{glib} package providing @command{glib-compile-schemas} can be
specified with the @code{#:glib} parameter.
@end table

Both phases are executed after the @code{install} phase.
@end defvr

@defvr {Scheme Variable} guile-build-system
This build system is for Guile packages that consist exclusively of Scheme
code and that are so lean that they don't even have a makefile, let alone a
@file{configure} script.  It compiles Scheme code using @command{guild
compile} (@pxref{Compilation,,, guile, GNU Guile Reference Manual}) and
installs the @file{.scm} and @file{.go} files in the right place.  It also
installs documentation.

This build system supports cross-compilation by using the @option{--target}
option of @samp{guild compile}.

Packages built with @code{guile-build-system} must provide a Guile package
in their @code{native-inputs} field.
@end defvr

@defvr {Scheme Variable} julia-build-system
This variable is exported by @code{(guix build-system julia)}.  It
implements the build procedure used by @uref{https://julialang.org/, julia}
packages, which essentially is similar to running @samp{julia -e 'using Pkg;
Pkg.add(package)'} in an environment where @env{JULIA_LOAD_PATH} contains
the paths to all Julia package inputs.  Tests are run by calling
@code{/test/runtests.jl}.

The Julia package name is read from the file @file{Project.toml}.  This
value can be overridden by passing the argument @code{#:julia-package-name}
(which must be correctly capitalized).

Julia packages usually manage their binary dependencies via
@code{JLLWrappers.jl}, a Julia package that creates a module (named after
the wrapped library followed by @code{_jll.jl}.

To add the binary path @code{_jll.jl} packages, you need to patch the files
under @file{src/wrappers/}, replacing the call to the macro
@code{JLLWrappers.@@generate_wrapper_header}, adding as a second argument
containing the store path the binary.

As an example, in the MbedTLS Julia package, we add a build phase
(@pxref{构建系统}) to insert the absolute file name of the wrapped
MbedTLS package:

@lisp
(add-after 'unpack 'override-binary-path
  (lambda* (#:key inputs #:allow-other-keys)
    (for-each (lambda (wrapper)
                (substitute* wrapper
                  (("generate_wrapper_header.*")
                   (string-append
                    "generate_wrapper_header(\"MbedTLS\", \""
                    (assoc-ref inputs "mbedtls-apache") "\")\n"))))
              ;; There's a Julia file for each platform, override them all.
              (find-files "src/wrappers/" "\\.jl$"))))
@end lisp

Some older packages that aren't using @file{Package.toml} yet, will require
this file to be created, too.  The function @code{julia-create-package-toml}
helps creating the file.  You need to pass the outputs and the source of the
package, it's name (the same as the @code{file-name} parameter), the package
uuid, the package version, and a list of dependencies specified by their
name and their uuid.
@end defvr

@defvr {Scheme Variable} maven-build-system
This variable is exported by @code{(guix build-system maven)}.  It
implements a build procedure for @uref{https://maven.apache.org, Maven}
packages.  Maven is a dependency and lifecycle management tool for Java.  A
user of Maven specifies dependencies and plugins in a @file{pom.xml} file
that Maven reads.  When Maven does not have one of the dependencies or
plugins in its repository, it will download them and use them to build the
package.

The maven build system ensures that maven will not try to download any
dependency by running in offline mode.  Maven will fail if a dependency is
missing.  Before running Maven, the @file{pom.xml} (and subprojects) are
modified to specify the version of dependencies and plugins that match the
versions available in the guix build environment.  Dependencies and plugins
must be installed in the fake maven repository at @file{lib/m2}, and are
symlinked into a proper repository before maven is run.  Maven is instructed
to use that repository for the build and installs built artifacts there.
Changed files are copied to the @file{lib/m2} directory of the package
output.

You can specify a @file{pom.xml} file with the @code{#:pom-file} argument,
or let the build system use the default @file{pom.xml} file in the sources.

In case you need to specify a dependency's version manually, you can use the
@code{#:local-packages} argument.  It takes an association list where the
key is the groupId of the package and its value is an association list where
the key is the artifactId of the package and its value is the version you
want to override in the @file{pom.xml}.

Some packages use dependencies or plugins that are not useful at runtime nor
at build time in Guix.  You can alter the @file{pom.xml} file to remove them
using the @code{#:exclude} argument.  Its value is an association list where
the key is the groupId of the plugin or dependency you want to remove, and
the value is a list of artifactId you want to remove.

You can override the default @code{jdk} and @code{maven} packages with the
corresponding argument, @code{#:jdk} and @code{#:maven}.

The @code{#:maven-plugins} argument is a list of maven plugins used during
the build, with the same format as the @code{inputs} fields of the package
declaration.  Its default value is @code{(default-maven-plugins)} which is
also exported.
@end defvr

@defvr {Scheme Variable} minify-build-system
This variable is exported by @code{(guix build-system minify)}.  It
implements a minification procedure for simple JavaScript packages.

It adds @code{uglify-js} to the set of inputs and uses it to compress all
JavaScript files in the @file{src} directory.  A different minifier package
can be specified with the @code{#:uglify-js} parameter, but it is expected
that the package writes the minified code to the standard output.

When the input JavaScript files are not all located in the @file{src}
directory, the parameter @code{#:javascript-files} can be used to specify a
list of file names to feed to the minifier.
@end defvr

@defvr {Scheme Variable} ocaml-build-system
This variable is exported by @code{(guix build-system ocaml)}.  It
implements a build procedure for @uref{https://ocaml.org, OCaml} packages,
which consists of choosing the correct set of commands to run for each
package.  OCaml packages can expect many different commands to be run.  This
build system will try some of them.

When the package has a @file{setup.ml} file present at the top-level, it
will run @code{ocaml setup.ml -configure}, @code{ocaml setup.ml -build} and
@code{ocaml setup.ml -install}.  The build system will assume that this file
was generated by @uref{http://oasis.forge.ocamlcore.org/, OASIS} and will
take care of setting the prefix and enabling tests if they are not
disabled.  You can pass configure and build flags with the
@code{#:configure-flags} and @code{#:build-flags}.  The @code{#:test-flags}
key can be passed to change the set of flags used to enable tests.  The
@code{#:use-make?} key can be used to bypass this system in the build and
install phases.

When the package has a @file{configure} file, it is assumed that it is a
hand-made configure script that requires a different argument format than in
the @code{gnu-build-system}.  You can add more flags with the
@code{#:configure-flags} key.

When the package has a @file{Makefile} file (or @code{#:use-make?} is
@code{#t}), it will be used and more flags can be passed to the build and
install phases with the @code{#:make-flags} key.

Finally, some packages do not have these files and use a somewhat standard
location for its build system.  In that case, the build system will run
@code{ocaml pkg/pkg.ml} or @code{ocaml pkg/build.ml} and take care of
providing the path to the required findlib module.  Additional flags can be
passed via the @code{#:build-flags} key.  Install is taken care of by
@command{opam-installer}.  In this case, the @code{opam} package must be
added to the @code{native-inputs} field of the package definition.

Note that most OCaml packages assume they will be installed in the same
directory as OCaml, which is not what we want in guix.  In particular, they
will install @file{.so} files in their module's directory, which is usually
fine because it is in the OCaml compiler directory.  In guix though, these
libraries cannot be found and we use @env{CAML_LD_LIBRARY_PATH}.  This
variable points to @file{lib/ocaml/site-lib/stubslibs} and this is where
@file{.so} libraries should be installed.
@end defvr

@defvr {Scheme Variable} python-build-system
This variable is exported by @code{(guix build-system python)}.  It
implements the more or less standard build procedure used by Python
packages, which consists in running @code{python setup.py build} and then
@code{python setup.py install --prefix=/gnu/store/@dots{}}.

For packages that install stand-alone Python programs under @code{bin/}, it
takes care of wrapping these programs so that their @env{PYTHONPATH}
environment variable points to all the Python libraries they depend on.

Which Python package is used to perform the build can be specified with the
@code{#:python} parameter.  This is a useful way to force a package to be
built for a specific version of the Python interpreter, which might be
necessary if the package is only compatible with a single interpreter
version.

By default guix calls @code{setup.py} under control of @code{setuptools},
much like @command{pip} does.  Some packages are not compatible with
setuptools (and pip), thus you can disable this by setting the
@code{#:use-setuptools?} parameter to @code{#f}.
@end defvr

@defvr {Scheme Variable} perl-build-system
This variable is exported by @code{(guix build-system perl)}.  It implements
the standard build procedure for Perl packages, which either consists in
running @code{perl Build.PL --prefix=/gnu/store/@dots{}}, followed by
@code{Build} and @code{Build install}; or in running @code{perl Makefile.PL
PREFIX=/gnu/store/@dots{}}, followed by @code{make} and @code{make install},
depending on which of @code{Build.PL} or @code{Makefile.PL} is present in
the package distribution.  Preference is given to the former if both
@code{Build.PL} and @code{Makefile.PL} exist in the package distribution.
This preference can be reversed by specifying @code{#t} for the
@code{#:make-maker?} parameter.

The initial @code{perl Makefile.PL} or @code{perl Build.PL} invocation
passes flags specified by the @code{#:make-maker-flags} or
@code{#:module-build-flags} parameter, respectively.

Which Perl package is used can be specified with @code{#:perl}.
@end defvr

@defvr {Scheme Variable} renpy-build-system
This variable is exported by @code{(guix build-system renpy)}.  It
implements the more or less standard build procedure used by Ren'py games,
which consists of loading @code{#:game} once, thereby creating bytecode for
it.

It further creates a wrapper script in @code{bin/} and a desktop entry in
@code{share/applications}, both of which can be used to launch the game.

Which Ren'py package is used can be specified with @code{#:renpy}.  Games
can also be installed in outputs other than ``out'' by using
@code{#:output}.
@end defvr

@defvr {Scheme Variable} qt-build-system
This variable is exported by @code{(guix build-system qt)}.  It is intended
for use with applications using Qt or KDE.

This build system adds the following two phases to the ones defined by
@code{cmake-build-system}:

@table @code
@item check-setup
The phase @code{check-setup} prepares the environment for running the checks
as commonly used by Qt test programs.  For now this only sets some
environment variables: @code{QT_QPA_PLATFORM=offscreen},
@code{DBUS_FATAL_WARNINGS=0} and @code{CTEST_OUTPUT_ON_FAILURE=1}.

This phase is added before the @code{check} phase.  It's a separate phase to
ease adjusting if necessary.

@item qt-wrap
The phase @code{qt-wrap} searches for Qt5 plugin paths, QML paths and some
XDG in the inputs and output.  In case some path is found, all programs in
the output's @file{bin/}, @file{sbin/}, @file{libexec/} and
@file{lib/libexec/} directories are wrapped in scripts defining the
necessary environment variables.

It is possible to exclude specific package outputs from that wrapping
process by listing their names in the @code{#:qt-wrap-excluded-outputs}
parameter.  This is useful when an output is known not to contain any Qt
binaries, and where wrapping would gratuitously add a dependency of that
output on Qt, KDE, or such.

This phase is added after the @code{install} phase.
@end table
@end defvr

@defvr {Scheme Variable} r-build-system
This variable is exported by @code{(guix build-system r)}.  It implements
the build procedure used by @uref{https://r-project.org, R} packages, which
essentially is little more than running @samp{R CMD INSTALL
--library=/gnu/store/@dots{}} in an environment where @env{R_LIBS_SITE}
contains the paths to all R package inputs.  Tests are run after
installation using the R function @code{tools::testInstalledPackage}.
@end defvr

@defvr {Scheme Variable} rakudo-build-system
This variable is exported by @code{(guix build-system rakudo)}.  It
implements the build procedure used by @uref{https://rakudo.org/, Rakudo}
for @uref{https://perl6.org/, Perl6} packages.  It installs the package to
@code{/gnu/store/@dots{}/NAME-VERSION/share/perl6} and installs the
binaries, library files and the resources, as well as wrap the files under
the @code{bin/} directory.  Tests can be skipped by passing @code{#f} to the
@code{tests?} parameter.

Which rakudo package is used can be specified with @code{rakudo}.  Which
perl6-tap-harness package used for the tests can be specified with
@code{#:prove6} or removed by passing @code{#f} to the @code{with-prove6?}
parameter.  Which perl6-zef package used for tests and installing can be
specified with @code{#:zef} or removed by passing @code{#f} to the
@code{with-zef?} parameter.
@end defvr

@defvr {Scheme Variable} texlive-build-system
This variable is exported by @code{(guix build-system texlive)}.  It is used
to build TeX packages in batch mode with a specified engine.  The build
system sets the @env{TEXINPUTS} variable to find all TeX source files in the
inputs.

By default it runs @code{luatex} on all files ending on @code{ins}.  A
different engine and format can be specified with the @code{#:tex-format}
argument.  Different build targets can be specified with the
@code{#:build-targets} argument, which expects a list of file names.  The
build system adds only @code{texlive-bin} and @code{texlive-latex-base}
(both from @code{(gnu packages tex}) to the inputs.  Both can be overridden
with the arguments @code{#:texlive-bin} and @code{#:texlive-latex-base},
respectively.

The @code{#:tex-directory} parameter tells the build system where to install
the built files under the texmf tree.
@end defvr

@defvr {Scheme Variable} ruby-build-system
This variable is exported by @code{(guix build-system ruby)}.  It implements
the RubyGems build procedure used by Ruby packages, which involves running
@code{gem build} followed by @code{gem install}.

The @code{source} field of a package that uses this build system typically
references a gem archive, since this is the format that Ruby developers use
when releasing their software.  The build system unpacks the gem archive,
potentially patches the source, runs the test suite, repackages the gem, and
installs it.  Additionally, directories and tarballs may be referenced to
allow building unreleased gems from Git or a traditional source release
tarball.

Which Ruby package is used can be specified with the @code{#:ruby}
parameter.  A list of additional flags to be passed to the @command{gem}
command can be specified with the @code{#:gem-flags} parameter.
@end defvr

@defvr {Scheme Variable} waf-build-system
This variable is exported by @code{(guix build-system waf)}.  It implements
a build procedure around the @code{waf} script.  The common
phases---@code{configure}, @code{build}, and @code{install}---are
implemented by passing their names as arguments to the @code{waf} script.

The @code{waf} script is executed by the Python interpreter.  Which Python
package is used to run the script can be specified with the @code{#:python}
parameter.
@end defvr

@defvr {Scheme Variable} scons-build-system
This variable is exported by @code{(guix build-system scons)}.  It
implements the build procedure used by the SCons software construction
tool.  This build system runs @code{scons} to build the package, @code{scons
test} to run tests, and then @code{scons install} to install the package.

Additional flags to be passed to @code{scons} can be specified with the
@code{#:scons-flags} parameter.  The default build and install targets can
be overridden with @code{#:build-targets} and @code{#:install-targets}
respectively.  The version of Python used to run SCons can be specified by
selecting the appropriate SCons package with the @code{#:scons} parameter.
@end defvr

@defvr {Scheme Variable} haskell-build-system
This variable is exported by @code{(guix build-system haskell)}.  It
implements the Cabal build procedure used by Haskell packages, which
involves running @code{runhaskell Setup.hs configure
--prefix=/gnu/store/@dots{}} and @code{runhaskell Setup.hs build}.  Instead
of installing the package by running @code{runhaskell Setup.hs install}, to
avoid trying to register libraries in the read-only compiler store
directory, the build system uses @code{runhaskell Setup.hs copy}, followed
by @code{runhaskell Setup.hs register}.  In addition, the build system
generates the package documentation by running @code{runhaskell Setup.hs
haddock}, unless @code{#:haddock? #f} is passed.  Optional Haddock
parameters can be passed with the help of the @code{#:haddock-flags}
parameter.  If the file @code{Setup.hs} is not found, the build system looks
for @code{Setup.lhs} instead.

Which Haskell compiler is used can be specified with the @code{#:haskell}
parameter which defaults to @code{ghc}.
@end defvr

@defvr {Scheme Variable} dub-build-system
This variable is exported by @code{(guix build-system dub)}.  It implements
the Dub build procedure used by D packages, which involves running @code{dub
build} and @code{dub run}.  Installation is done by copying the files
manually.

Which D compiler is used can be specified with the @code{#:ldc} parameter
which defaults to @code{ldc}.
@end defvr

@anchor{emacs-build-system}
@defvr {Scheme Variable} emacs-build-system
This variable is exported by @code{(guix build-system emacs)}.  It
implements an installation procedure similar to the packaging system of
Emacs itself (@pxref{Packages,,, emacs, The GNU Emacs Manual}).

It first creates the @code{@code{package}-autoloads.el} file, then it byte
compiles all Emacs Lisp files.  Differently from the Emacs packaging system,
the Info documentation files are moved to the standard documentation
directory and the @file{dir} file is deleted.  The Elisp package files are
installed directly under @file{share/emacs/site-lisp}.
@end defvr

@defvr {Scheme Variable} font-build-system
This variable is exported by @code{(guix build-system font)}.  It implements
an installation procedure for font packages where upstream provides
pre-compiled TrueType, OpenType, etc.@: font files that merely need to be
copied into place.  It copies font files to standard locations in the output
directory.
@end defvr

@defvr {Scheme Variable} meson-build-system
This variable is exported by @code{(guix build-system meson)}.  It
implements the build procedure for packages that use
@url{https://mesonbuild.com, Meson} as their build system.

It adds both Meson and @uref{https://ninja-build.org/, Ninja} to the set of
inputs, and they can be changed with the parameters @code{#:meson} and
@code{#:ninja} if needed.  The default Meson is @code{meson-for-build},
which is special because it doesn't clear the @code{RUNPATH} of binaries and
libraries when they are installed.

This build system is an extension of @code{gnu-build-system}, but with the
following phases changed to some specific for Meson:

@table @code

@item configure
The phase runs @code{meson} with the flags specified in
@code{#:configure-flags}.  The flag @option{--buildtype} is always set to
@code{debugoptimized} unless something else is specified in
@code{#:build-type}.

@item build
The phase runs @code{ninja} to build the package in parallel by default, but
this can be changed with @code{#:parallel-build?}.

@item check
The phase runs @code{ninja} with the target specified in
@code{#:test-target}, which is @code{"test"} by default.

@item install
The phase runs @code{ninja install} and can not be changed.
@end table

Apart from that, the build system also adds the following phases:

@table @code

@item fix-runpath
This phase ensures that all binaries can find the libraries they need.  It
searches for required libraries in subdirectories of the package being
built, and adds those to @code{RUNPATH} where needed.  It also removes
references to libraries left over from the build phase by
@code{meson-for-build}, such as test dependencies, that aren't actually
required for the program to run.

@item glib-or-gtk-wrap
This phase is the phase provided by @code{glib-or-gtk-build-system}, and it
is not enabled by default.  It can be enabled with @code{#:glib-or-gtk?}.

@item glib-or-gtk-compile-schemas
This phase is the phase provided by @code{glib-or-gtk-build-system}, and it
is not enabled by default.  It can be enabled with @code{#:glib-or-gtk?}.
@end table
@end defvr

@defvr {Scheme Variable} linux-module-build-system
@code{linux-module-build-system} allows building Linux kernel modules.

@cindex build phases
This build system is an extension of @code{gnu-build-system}, but with the
following phases changed:

@table @code

@item configure
This phase configures the environment so that the Linux kernel's Makefile
can be used to build the external kernel module.

@item build
This phase uses the Linux kernel's Makefile in order to build the external
kernel module.

@item install
This phase uses the Linux kernel's Makefile in order to install the external
kernel module.
@end table

It is possible and useful to specify the Linux kernel to use for building
the module (in the @code{arguments} form of a package using the
@code{linux-module-build-system}, use the key @code{#:linux} to specify it).
@end defvr

@defvr {Scheme Variable} node-build-system
This variable is exported by @code{(guix build-system node)}.  It implements
the build procedure used by @uref{https://nodejs.org, Node.js}, which
implements an approximation of the @code{npm install} command, followed by
an @code{npm test} command.

Which Node.js package is used to interpret the @code{npm} commands can be
specified with the @code{#:node} parameter which defaults to @code{node}.
@end defvr

Lastly, for packages that do not need anything as sophisticated, a
``trivial'' build system is provided.  It is trivial in the sense that it
provides basically no support: it does not pull any implicit inputs, and
does not have a notion of build phases.

@defvr {Scheme Variable} trivial-build-system
This variable is exported by @code{(guix build-system trivial)}.

This build system requires a @code{#:builder} argument.  This argument must
be a Scheme expression that builds the package output(s)---as with
@code{build-expression->derivation} (@pxref{Derivations,
@code{build-expression->derivation}}).
@end defvr

@node Build Phases
@section Build Phases

@cindex build phases, for packages
Almost all package build systems implement a notion @dfn{build phases}: a
sequence of actions that the build system executes, when you build the
package, leading to the installed byproducts in the store.  A notable
exception is the ``bare-bones'' @code{trivial-build-system} (@pxref{构建系统}).

As discussed in the previous section, those build systems provide a standard
list of phases.  For @code{gnu-build-system}, the main build phases are the
following:

@table @code
@item unpack
Unpack the source tarball, and change the current directory to the extracted
source tree.  If the source is actually a directory, copy it to the build
tree, and enter that directory.

@item patch-source-shebangs
Patch shebangs encountered in source files so they refer to the right store
file names.  For instance, this changes @code{#!/bin/sh} to
@code{#!/gnu/store/@dots{}-bash-4.3/bin/sh}.

@item configure
Run the @file{configure} script with a number of default options, such as
@option{--prefix=/gnu/store/@dots{}}, as well as the options specified by
the @code{#:configure-flags} argument.

@item build
Run @code{make} with the list of flags specified with @code{#:make-flags}.
If the @code{#:parallel-build?} argument is true (the default), build with
@code{make -j}.

@item check
Run @code{make check}, or some other target specified with
@code{#:test-target}, unless @code{#:tests? #f} is passed.  If the
@code{#:parallel-tests?} argument is true (the default), run @code{make
check -j}.

@item install
Run @code{make install} with the flags listed in @code{#:make-flags}.

@item patch-shebangs
Patch shebangs on the installed executable files.

@item strip
Strip debugging symbols from ELF files (unless @code{#:strip-binaries?} is
false), copying them to the @code{debug} output when available
(@pxref{安装调试文件}).
@end table

Other build systems have similar phases, with some variations.  For example,
@code{cmake-build-system} has same-named phases but its @code{configure}
phases runs @code{cmake} instead of @code{./configure}.  Others, such as
@code{python-build-system}, have a wholly different list of standard
phases.  All this code runs on the @dfn{build side}: it is evaluated when
you actually build the package, in a dedicated build process spawned by the
build daemon (@pxref{调用guix-daemon}).

Build phases are represented as association lists or ``alists''
(@pxref{Association Lists,,, guile, GNU Guile Reference Manual}) where each
key is a symbol for the name of the phase and the associated value is a
procedure that accepts an arbitrary number of arguments.  By convention,
those procedures receive information about the build in the form of
@dfn{keyword parameters}, which they can use or ignore.

@vindex %standard-phases
For example, here is how @code{(guix build gnu-build-system)} defines
@code{%standard-phases}, the variable holding its alist of build
phases@footnote{We present a simplified view of those build phases, but do
take a look at @code{(guix build gnu-build-system)} to see all the
details!}:

@lisp
;; The build phases of 'gnu-build-system'.

(define* (unpack #:key source #:allow-other-keys)
  ;; Extract the source tarball.
  (invoke "tar" "xvf" source))

(define* (configure #:key outputs #:allow-other-keys)
  ;; Run the 'configure' script.  Install to output "out".
  (let ((out (assoc-ref outputs "out")))
    (invoke "./configure"
            (string-append "--prefix=" out))))

(define* (build #:allow-other-keys)
  ;; Compile.
  (invoke "make"))

(define* (check #:key (test-target "check") (tests? #true)
                #:allow-other-keys)
  ;; Run the test suite.
  (if tests?
      (invoke "make" test-target)
      (display "test suite not run\n")))

(define* (install #:allow-other-keys)
  ;; Install files to the prefix 'configure' specified.
  (invoke "make" "install"))

(define %standard-phases
  ;; The list of standard phases (quite a few are omitted
  ;; for brevity).  Each element is a symbol/procedure pair.
  (list (cons 'unpack unpack)
        (cons 'configure configure)
        (cons 'build build)
        (cons 'check check)
        (cons 'install install)))
@end lisp

This shows how @code{%standard-phases} is defined as a list of
symbol/procedure pairs (@pxref{Pairs,,, guile, GNU Guile Reference
Manual}).  The first pair associates the @code{unpack} procedure with the
@code{unpack} symbol---a name; the second pair defines the @code{configure}
phase similarly, and so on.  When building a package that uses
@code{gnu-build-system} with its default list of phases, those phases are
executed sequentially.  You can see the name of each phase started and
completed in the build log of packages that you build.

Let's now look at the procedures themselves.  Each one is defined with
@code{define*}: @code{#:key} lists keyword parameters the procedure accepts,
possibly with a default value, and @code{#:allow-other-keys} specifies that
other keyword parameters are ignored (@pxref{Optional Arguments,,, guile,
GNU Guile Reference Manual}).

The @code{unpack} procedure honors the @code{source} parameter, which the
build system uses to pass the file name of the source tarball (or version
control checkout), and it ignores other parameters.  The @code{configure}
phase only cares about the @code{outputs} parameter, an alist mapping
package output names to their store file name (@pxref{有多个输出的软件包}).  It extracts the file name of for @code{out}, the default output,
and passes it to @command{./configure} as the installation prefix, meaning
that @command{make install} will eventually copy all the files in that
directory (@pxref{Configuration, configuration and makefile conventions,,
standards, GNU Coding Standards}).  @code{build} and @code{install} ignore
all their arguments.  @code{check} honors the @code{test-target} argument,
which specifies the name of the Makefile target to run tests; it prints a
message and skips tests when @code{tests?} is false.

@cindex build phases, customizing
The list of phases used for a particular package can be changed with the
@code{#:phases} parameter of the build system.  Changing the set of build
phases boils down to building a new alist of phases based on the
@code{%standard-phases} alist described above.  This can be done with
standard alist procedures such as @code{alist-delete} (@pxref{SRFI-1
Association Lists,,, guile, GNU Guile Reference Manual}); however, it is
more convenient to do so with @code{modify-phases} (@pxref{工具,
@code{modify-phases}}).

Here is an example of a package definition that removes the @code{configure}
phase of @code{%standard-phases} and inserts a new phase before the
@code{build} phase, called @code{set-prefix-in-makefile}:

@lisp
(define-public example
  (package
    (name "example")
    ;; other fields omitted
    (build-system gnu-build-system)
    (arguments
     '(#:phases (modify-phases %standard-phases
                  (delete 'configure)
                  (add-before 'build 'set-prefix-in-makefile
                    (lambda* (#:key outputs #:allow-other-keys)
                      ;; Modify the makefile so that its
                      ;; 'PREFIX' variable points to "out".
                      (let ((out (assoc-ref outputs "out")))
                        (substitute* "Makefile"
                          (("PREFIX =.*")
                           (string-append "PREFIX = "
                                          out "\n")))
                        #true))))))))
@end lisp

The new phase that is inserted is written as an anonymous procedure,
introduced with @code{lambda*}; it honors the @code{outputs} parameter we
have seen before.  @xref{工具}, for more about the helpers used
by this phase, and for more examples of @code{modify-phases}.

@cindex code staging
@cindex staging, of code
Keep in mind that build phases are code evaluated at the time the package is
actually built.  This explains why the whole @code{modify-phases} expression
above is quoted (it comes after the @code{'} or apostrophe): it is
@dfn{staged} for later execution.  @xref{G-表达式}, for an explanation
of code staging and the @dfn{code strata} involved.

@node Build Utilities
@section Build Utilities

As soon as you start writing non-trivial package definitions
(@pxref{定义软件包}) or other build actions (@pxref{G-表达式}),
you will likely start looking for helpers for ``shell-like''
actions---creating directories, copying and deleting files recursively,
manipulating build phases, and so on.  The @code{(guix build utils)} module
provides such utility procedures.

Most build systems load @code{(guix build utils)} (@pxref{构建系统}).
Thus, when writing custom build phases for your package definitions, you can
usually assume those procedures are in scope.

When writing G-expressions, you can import @code{(guix build utils)} on the
``build side'' using @code{with-imported-modules} and then put it in scope
with the @code{use-modules} form (@pxref{Using Guile Modules,,, guile, GNU
Guile Reference Manual}):

@lisp
(with-imported-modules '((guix build utils))  ;import it
  (computed-file "empty-tree"
                 #~(begin
                     ;; Put it in scope.
                     (use-modules (guix build utils))

                     ;; Happily use its 'mkdir-p' procedure.
                     (mkdir-p (string-append #$output "/a/b/c")))))
@end lisp

The remainder of this section is the reference for most of the utility
procedures provided by @code{(guix build utils)}.

@c TODO Document what's missing.

@subsection Dealing with Store File Names

This section documents procedures that deal with store file names.

@deffn {Scheme Procedure} %store-directory
Return the directory name of the store.
@end deffn

@deffn {Scheme Procedure} store-file-name? @var{file}
Return true if @var{file} is in the store.
@end deffn

@deffn {Scheme Procedure} strip-store-file-name @var{file}
Strip the @file{/gnu/store} and hash from @var{file}, a store file name.
The result is typically a @code{"@var{package}-@var{version}"} string.
@end deffn

@deffn {Scheme Procedure} package-name->name+version @var{name}
Given @var{name}, a package name like @code{"foo-0.9.1b"}, return two
values: @code{"foo"} and @code{"0.9.1b"}.  When the version part is
unavailable, @var{name} and @code{#f} are returned.  The first hyphen
followed by a digit is considered to introduce the version part.
@end deffn

@subsection File Types

The procedures below deal with files and file types.

@deffn {Scheme Procedure} directory-exists? @var{dir}
Return @code{#t} if @var{dir} exists and is a directory.
@end deffn

@deffn {Scheme Procedure} executable-file? @var{file}
Return @code{#t} if @var{file} exists and is executable.
@end deffn

@deffn {Scheme Procedure} symbolic-link? @var{file}
Return @code{#t} if @var{file} is a symbolic link (aka. a ``symlink'').
@end deffn

@deffn {Scheme Procedure} elf-file? @var{file}
@deffnx {Scheme Procedure} ar-file? @var{file}
@deffnx {Scheme Procedure} gzip-file? @var{file}
Return @code{#t} if @var{file} is, respectively, an ELF file, an @code{ar}
archive (such as a @file{.a} static library), or a gzip file.
@end deffn

@deffn {Scheme Procedure} reset-gzip-timestamp @var{file} [#:keep-mtime? #t]
If @var{file} is a gzip file, reset its embedded timestamp (as with
@command{gzip --no-name}) and return true.  Otherwise return @code{#f}.
When @var{keep-mtime?} is true, preserve @var{file}'s modification time.
@end deffn

@subsection File Manipulation

The following procedures and macros help create, modify, and delete files.
They provide functionality comparable to common shell utilities such as
@command{mkdir -p}, @command{cp -r}, @command{rm -r}, and @command{sed}.
They complement Guile's extensive, but low-level, file system interface
(@pxref{POSIX,,, guile, GNU Guile Reference Manual}).

@deffn {Scheme Syntax} with-directory-excursion @var{directory} @var{body}@dots{}
Run @var{body} with @var{directory} as the process's current directory.

Essentially, this macro changes the current directory to @var{directory}
before evaluating @var{body}, using @code{chdir} (@pxref{Processes,,, guile,
GNU Guile Reference Manual}).  It changes back to the initial directory when
the dynamic extent of @var{body} is left, be it @i{via} normal procedure
return or @i{via} a non-local exit such as an exception.
@end deffn

@deffn {Scheme Procedure} mkdir-p @var{dir}
Create directory @var{dir} and all its ancestors.
@end deffn

@deffn {Scheme Procedure} install-file @var{file} @var{directory}
Create @var{directory} if it does not exist and copy @var{file} in there
under the same name.
@end deffn

@deffn {Scheme Procedure} make-file-writable @var{file}
Make @var{file} writable for its owner.
@end deffn

@deffn {Scheme Procedure} copy-recursively @var{source} @var{destination} @
  [#:log (current-output-port)] [#:follow-symlinks? #f] [#:keep-mtime? #f]
Copy @var{source} directory to @var{destination}.  Follow symlinks if
@var{follow-symlinks?} is true; otherwise, just preserve them.  When
@var{keep-mtime?} is true, keep the modification time of the files in
@var{source} on those of @var{destination}.  Write verbose output to the
@var{log} port.
@end deffn

@deffn {Scheme Procedure} delete-file-recursively @var{dir} @
  [#:follow-mounts? #f] Delete @var{dir} recursively, like @command{rm -rf},
without following symlinks.  Don't follow mount points either, unless
@var{follow-mounts?} is true.  Report but ignore errors.
@end deffn

@deffn {Scheme Syntax} substitute* @var{file} @
  ((@var{regexp} @var{match-var}@dots{}) @var{body}@dots{}) @dots{} Substitute
@var{regexp} in @var{file} by the string returned by @var{body}.  @var{body}
is evaluated with each @var{match-var} bound to the corresponding positional
regexp sub-expression.  For example:

@lisp
(substitute* file
  (("hello")
   "good morning\n")
  (("foo([a-z]+)bar(.*)$" all letters end)
   (string-append "baz" letter end)))
@end lisp

Here, anytime a line of @var{file} contains @code{hello}, it is replaced by
@code{good morning}.  Anytime a line of @var{file} matches the second
regexp, @code{all} is bound to the complete match, @code{letters} is bound
to the first sub-expression, and @code{end} is bound to the last one.

When one of the @var{match-var} is @code{_}, no variable is bound to the
corresponding match substring.

Alternatively, @var{file} may be a list of file names, in which case they
are all subject to the substitutions.

Be careful about using @code{$} to match the end of a line; by itself it
won't match the terminating newline of a line.
@end deffn

@subsection File Search

@cindex file, searching
This section documents procedures to search and filter files.

@deffn {Scheme Procedure} file-name-predicate @var{regexp}
Return a predicate that returns true when passed a file name whose base name
matches @var{regexp}.
@end deffn

@deffn {Scheme Procedure} find-files @var{dir} [@var{pred}] @
  [#:stat lstat] [#:directories? #f] [#:fail-on-error? #f] Return the
lexicographically sorted list of files under @var{dir} for which @var{pred}
returns true.  @var{pred} is passed two arguments: the absolute file name,
and its stat buffer; the default predicate always returns true.  @var{pred}
can also be a regular expression, in which case it is equivalent to
@code{(file-name-predicate @var{pred})}.  @var{stat} is used to obtain file
information; using @code{lstat} means that symlinks are not followed.  If
@var{directories?} is true, then directories will also be included.  If
@var{fail-on-error?} is true, raise an exception upon error.
@end deffn

Here are a few examples where we assume that the current directory is the
root of the Guix source tree:

@lisp
;; List all the regular files in the current directory.
(find-files ".")
@result{} ("./.dir-locals.el" "./.gitignore" @dots{})

;; List all the .scm files under gnu/services.
(find-files "gnu/services" "\\.scm$")
@result{} ("gnu/services/admin.scm" "gnu/services/audio.scm" @dots{})

;; List ar files in the current directory.
(find-files "." (lambda (file stat) (ar-file? file)))
@result{} ("./libformat.a" "./libstore.a" @dots{})
@end lisp

@deffn {Scheme Procedure} which @var{program}
Return the complete file name for @var{program} as found in @code{$PATH}, or
@code{#f} if @var{program} could not be found.
@end deffn

@subsection Build Phases

@cindex build phases
The @code{(guix build utils)} also contains tools to manipulate build phases
as used by build systems (@pxref{构建系统}).  Build phases are
represented as association lists or ``alists'' (@pxref{Association Lists,,,
guile, GNU Guile Reference Manual}) where each key is a symbol naming the
phase and the associated value is a procedure (@pxref{构建系统}).

Guile core and the @code{(srfi srfi-1)} module both provide tools to
manipulate alists.  The @code{(guix build utils)} module complements those
with tools written with build phases in mind.

@cindex build phases, modifying
@deffn {Scheme Syntax} modify-phases @var{phases} @var{clause}@dots{}
Modify @var{phases} sequentially as per each @var{clause}, which may have
one of the following forms:

@lisp
(delete @var{old-phase-name})
(replace @var{old-phase-name} @var{new-phase})
(add-before @var{old-phase-name} @var{new-phase-name} @var{new-phase})
(add-after @var{old-phase-name} @var{new-phase-name} @var{new-phase})
@end lisp

Where every @var{phase-name} above is an expression evaluating to a symbol,
and @var{new-phase} an expression evaluating to a procedure.
@end deffn

The example below is taken from the definition of the @code{grep} package.
It adds a phase to run after the @code{install} phase, called
@code{fix-egrep-and-fgrep}.  That phase is a procedure (@code{lambda*} is
for anonymous procedures) that takes a @code{#:outputs} keyword argument and
ignores extra keyword arguments (@pxref{Optional Arguments,,, guile, GNU
Guile Reference Manual}, for more on @code{lambda*} and optional and keyword
arguments.)  The phase uses @code{substitute*} to modify the installed
@file{egrep} and @file{fgrep} scripts so that they refer to @code{grep} by
its absolute file name:

@lisp
(modify-phases %standard-phases
  (add-after 'install 'fix-egrep-and-fgrep
    ;; Patch 'egrep' and 'fgrep' to execute 'grep' via its
    ;; absolute file name instead of searching for it in $PATH.
    (lambda* (#:key outputs #:allow-other-keys)
      (let* ((out (assoc-ref outputs "out"))
             (bin (string-append out "/bin")))
        (substitute* (list (string-append bin "/egrep")
                           (string-append bin "/fgrep"))
          (("^exec grep")
           (string-append "exec " bin "/grep")))
        #t))))
@end lisp

In the example below, phases are modified in two ways: the standard
@code{configure} phase is deleted, presumably because the package does not
have a @file{configure} script or anything similar, and the default
@code{install} phase is replaced by one that manually copies the executable
files to be installed:

@lisp
(modify-phases %standard-phases
  (delete 'configure)      ;no 'configure' script
  (replace 'install
    (lambda* (#:key outputs #:allow-other-keys)
      ;; The package's Makefile doesn't provide an "install"
      ;; rule so do it by ourselves.
      (let ((bin (string-append (assoc-ref outputs "out")
                                "/bin")))
        (install-file "footswitch" bin)
        (install-file "scythe" bin)
        #t))))
@end lisp

@c TODO: Add more examples.

@node 仓库
@section 仓库

@cindex 仓库
@cindex store items
@cindex store paths

Conceptually, the @dfn{store} is the place where derivations that have been
built successfully are stored---by default, @file{/gnu/store}.
Sub-directories in the store are referred to as @dfn{store items} or
sometimes @dfn{store paths}.  The store has an associated database that
contains information such as the store paths referred to by each store path,
and the list of @emph{valid} store items---results of successful builds.
This database resides in @file{@var{localstatedir}/guix/db}, where
@var{localstatedir} is the state directory specified @i{via}
@option{--localstatedir} at configure time, usually @file{/var}.

The store is @emph{always} accessed by the daemon on behalf of its clients
(@pxref{调用guix-daemon}).  To manipulate the store, clients connect to
the daemon over a Unix-domain socket, send requests to it, and read the
result---these are remote procedure calls, or RPCs.

@quotation 注
Users must @emph{never} modify files under @file{/gnu/store} directly.  This
would lead to inconsistencies and break the immutability assumptions of
Guix's functional model (@pxref{介绍}).

@xref{调用guix gc, @command{guix gc --verify}}, for information on how
to check the integrity of the store and attempt recovery from accidental
modifications.
@end quotation

The @code{(guix store)} module provides procedures to connect to the daemon,
and to perform RPCs.  These are described below.  By default,
@code{open-connection}, and thus all the @command{guix} commands, connect to
the local daemon or to the URI specified by the @env{GUIX_DAEMON_SOCKET}
environment variable.

@defvr {Environment Variable} GUIX_DAEMON_SOCKET
When set, the value of this variable should be a file name or a URI
designating the daemon endpoint.  When it is a file name, it denotes a
Unix-domain socket to connect to.  In addition to file names, the supported
URI schemes are:

@table @code
@item file
@itemx unix
These are for Unix-domain sockets.
@code{file:///var/guix/daemon-socket/socket} is equivalent to
@file{/var/guix/daemon-socket/socket}.

@item guix
@cindex daemon, remote access
@cindex remote access to the daemon
@cindex daemon, cluster setup
@cindex clusters, daemon setup
These URIs denote connections over TCP/IP, without encryption nor
authentication of the remote host.  The URI must specify the host name and
optionally a port number (by default port 44146 is used):

@example
guix://master.guix.example.org:1234
@end example

This setup is suitable on local networks, such as clusters, where only
trusted nodes may connect to the build daemon at
@code{master.guix.example.org}.

The @option{--listen} option of @command{guix-daemon} can be used to
instruct it to listen for TCP connections (@pxref{调用guix-daemon,
@option{--listen}}).

@item ssh
@cindex SSH access to build daemons
These URIs allow you to connect to a remote daemon over SSH@.  This feature
requires Guile-SSH (@pxref{需求}) and a working @command{guile}
binary in @env{PATH} on the destination machine.  It supports public key and
GSSAPI authentication.  A typical URL might look like this:

@example
ssh://charlie@@guix.example.org:22
@end example

As for @command{guix copy}, the usual OpenSSH client configuration files are
honored (@pxref{调用guix copy}).
@end table

Additional URI schemes may be supported in the future.

@c XXX: Remove this note when the protocol incurs fewer round trips
@c and when (guix derivations) no longer relies on file system access.
@quotation 注
The ability to connect to remote build daemons is considered experimental as
of @value{VERSION}.  Please get in touch with us to share any problems or
suggestions you may have (@pxref{贡献}).
@end quotation
@end defvr

@deffn {Scheme Procedure} open-connection [@var{uri}] [#:reserve-space? #t]
Connect to the daemon over the Unix-domain socket at @var{uri} (a string).
When @var{reserve-space?} is true, instruct it to reserve a little bit of
extra space on the file system so that the garbage collector can still
operate should the disk become full.  Return a server object.

@var{file} defaults to @code{%default-socket-path}, which is the normal
location given the options that were passed to @command{configure}.
@end deffn

@deffn {Scheme Procedure} close-connection @var{server}
Close the connection to @var{server}.
@end deffn

@defvr {Scheme Variable} current-build-output-port
This variable is bound to a SRFI-39 parameter, which refers to the port
where build and error logs sent by the daemon should be written.
@end defvr

Procedures that make RPCs all take a server object as their first argument.

@deffn {Scheme Procedure} valid-path? @var{server} @var{path}
@cindex invalid store items
Return @code{#t} when @var{path} designates a valid store item and @code{#f}
otherwise (an invalid item may exist on disk but still be invalid, for
instance because it is the result of an aborted or failed build).

A @code{&store-protocol-error} condition is raised if @var{path} is not
prefixed by the store directory (@file{/gnu/store}).
@end deffn

@deffn {Scheme Procedure} add-text-to-store @var{server} @var{name} @var{text} [@var{references}]
Add @var{text} under file @var{name} in the store, and return its store
path.  @var{references} is the list of store paths referred to by the
resulting store path.
@end deffn

@deffn {Scheme Procedure} build-derivations @var{store} @var{derivations} @
  [@var{mode}] Build @var{derivations}, a list of @code{<derivation>} objects,
@file{.drv} file names, or derivation/output pairs, using the specified
@var{mode}---@code{(build-mode normal)} by default.
@end deffn

Note that the @code{(guix monads)} module provides a monad as well as
monadic versions of the above procedures, with the goal of making it more
convenient to work with code that accesses the store (@pxref{仓库monad}).

@c FIXME
@i{This section is currently incomplete.}

@node Derivations
@section Derivations

@cindex derivations
Low-level build actions and the environment in which they are performed are
represented by @dfn{derivations}.  A derivation contains the following
pieces of information:

@itemize
@item
The outputs of the derivation---derivations produce at least one file or
directory in the store, but may produce more.

@item
@cindex build-time dependencies
@cindex dependencies, build-time
The inputs of the derivations---i.e., its build-time dependencies---which
may be other derivations or plain files in the store (patches, build
scripts, etc.).

@item
The system type targeted by the derivation---e.g., @code{x86_64-linux}.

@item
The file name of a build script in the store, along with the arguments to be
passed.

@item
A list of environment variables to be defined.

@end itemize

@cindex derivation path
Derivations allow clients of the daemon to communicate build actions to the
store.  They exist in two forms: as an in-memory representation, both on the
client- and daemon-side, and as files in the store whose name end in
@file{.drv}---these files are referred to as @dfn{derivation paths}.
Derivations paths can be passed to the @code{build-derivations} procedure to
perform the build actions they prescribe (@pxref{仓库}).

@cindex fixed-output derivations
Operations such as file downloads and version-control checkouts for which
the expected content hash is known in advance are modeled as
@dfn{fixed-output derivations}.  Unlike regular derivations, the outputs of
a fixed-output derivation are independent of its inputs---e.g., a source
code download produces the same result regardless of the download method and
tools being used.

@cindex references
@cindex run-time dependencies
@cindex dependencies, run-time
The outputs of derivations---i.e., the build results---have a set of
@dfn{references}, as reported by the @code{references} RPC or the
@command{guix gc --references} command (@pxref{调用guix gc}).
References are the set of run-time dependencies of the build results.
References are a subset of the inputs of the derivation; this subset is
automatically computed by the build daemon by scanning all the files in the
outputs.

The @code{(guix derivations)} module provides a representation of
derivations as Scheme objects, along with procedures to create and otherwise
manipulate derivations.  The lowest-level primitive to create a derivation
is the @code{derivation} procedure:

@deffn {Scheme Procedure} derivation @var{store} @var{name} @var{builder} @
  @var{args} [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @ [#:recursive?
#f] [#:inputs '()] [#:env-vars '()] @ [#:system (%current-system)]
[#:references-graphs #f] @ [#:allowed-references #f]
[#:disallowed-references #f] @ [#:leaked-env-vars #f] [#:local-build? #f] @
[#:substitutable? #t] [#:properties '()] Build a derivation with the given
arguments, and return the resulting @code{<derivation>} object.

When @var{hash} and @var{hash-algo} are given, a @dfn{fixed-output
derivation} is created---i.e., one whose result is known in advance, such as
a file download.  If, in addition, @var{recursive?} is true, then that fixed
output may be an executable file or a directory and @var{hash} must be the
hash of an archive containing this output.

When @var{references-graphs} is true, it must be a list of file name/store
path pairs.  In that case, the reference graph of each store path is
exported in the build environment in the corresponding file, in a simple
text format.

When @var{allowed-references} is true, it must be a list of store items or
outputs that the derivation's output may refer to.  Likewise,
@var{disallowed-references}, if true, must be a list of things the outputs
may @emph{not} refer to.

When @var{leaked-env-vars} is true, it must be a list of strings denoting
environment variables that are allowed to ``leak'' from the daemon's
environment to the build environment.  This is only applicable to
fixed-output derivations---i.e., when @var{hash} is true.  The main use is
to allow variables such as @code{http_proxy} to be passed to derivations
that download files.

When @var{local-build?} is true, declare that the derivation is not a good
candidate for offloading and should rather be built locally (@pxref{下发工作给后台进程的设置}).  This is the case for small derivations where the costs of
data transfers would outweigh the benefits.

When @var{substitutable?} is false, declare that substitutes of the
derivation's output should not be used (@pxref{substitutes}).  This is
useful, for instance, when building packages that capture details of the
host CPU instruction set.

@var{properties} must be an association list describing ``properties'' of
the derivation.  It is kept as-is, uninterpreted, in the derivation.
@end deffn

@noindent
Here's an example with a shell script as its builder, assuming @var{store}
is an open connection to the daemon, and @var{bash} points to a Bash
executable in the store:

@lisp
(use-modules (guix utils)
             (guix store)
             (guix derivations))

(let ((builder   ; add the Bash script to the store
        (add-text-to-store store "my-builder.sh"
                           "echo hello world > $out\n" '())))
  (derivation store "foo"
              bash `("-e" ,builder)
              #:inputs `((,bash) (,builder))
              #:env-vars '(("HOME" . "/homeless"))))
@result{} #<derivation /gnu/store/@dots{}-foo.drv => /gnu/store/@dots{}-foo>
@end lisp

As can be guessed, this primitive is cumbersome to use directly.  A better
approach is to write build scripts in Scheme, of course! The best course of
action for that is to write the build code as a ``G-expression'', and to
pass it to @code{gexp->derivation}.  For more information,
@pxref{G-表达式}.

Once upon a time, @code{gexp->derivation} did not exist and constructing
derivations with build code written in Scheme was achieved with
@code{build-expression->derivation}, documented below.  This procedure is
now deprecated in favor of the much nicer @code{gexp->derivation}.

@deffn {Scheme Procedure} build-expression->derivation @var{store} @
       @var{name} @var{exp} @ [#:system (%current-system)] [#:inputs '()] @
[#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @ [#:recursive? #f]
[#:env-vars '()] [#:modules '()] @ [#:references-graphs #f]
[#:allowed-references #f] @ [#:disallowed-references #f] @ [#:local-build?
#f] [#:substitutable? #t] [#:guile-for-build #f] Return a derivation that
executes Scheme expression @var{exp} as a builder for derivation
@var{name}.  @var{inputs} must be a list of @code{(name drv-path sub-drv)}
tuples; when @var{sub-drv} is omitted, @code{"out"} is assumed.
@var{modules} is a list of names of Guile modules from the current search
path to be copied in the store, compiled, and made available in the load
path during the execution of @var{exp}---e.g., @code{((guix build utils)
(guix build gnu-build-system))}.

@var{exp} is evaluated in an environment where @code{%outputs} is bound to a
list of output/path pairs, and where @code{%build-inputs} is bound to a list
of string/output-path pairs made from @var{inputs}.  Optionally,
@var{env-vars} is a list of string pairs specifying the name and value of
environment variables visible to the builder.  The builder terminates by
passing the result of @var{exp} to @code{exit}; thus, when @var{exp} returns
@code{#f}, the build is considered to have failed.

@var{exp} is built using @var{guile-for-build} (a derivation).  When
@var{guile-for-build} is omitted or is @code{#f}, the value of the
@code{%guile-for-build} fluid is used instead.

See the @code{derivation} procedure for the meaning of
@var{references-graphs}, @var{allowed-references},
@var{disallowed-references}, @var{local-build?}, and @var{substitutable?}.
@end deffn

@noindent
Here's an example of a single-output derivation that creates a directory
containing one file:

@lisp
(let ((builder '(let ((out (assoc-ref %outputs "out")))
                  (mkdir out)    ; create /gnu/store/@dots{}-goo
                  (call-with-output-file (string-append out "/test")
                    (lambda (p)
                      (display '(hello guix) p))))))
  (build-expression->derivation store "goo" builder))

@result{} #<derivation /gnu/store/@dots{}-goo.drv => @dots{}>
@end lisp


@node 仓库monad
@section 仓库monad

@cindex monad

The procedures that operate on the store described in the previous sections
all take an open connection to the build daemon as their first argument.
Although the underlying model is functional, they either have side effects
or depend on the current state of the store.

The former is inconvenient: the connection to the build daemon has to be
carried around in all those functions, making it impossible to compose
functions that do not take that parameter with functions that do.  The
latter can be problematic: since store operations have side effects and/or
depend on external state, they have to be properly sequenced.

@cindex monadic values
@cindex monadic functions
This is where the @code{(guix monads)} module comes in.  This module
provides a framework for working with @dfn{monads}, and a particularly
useful monad for our uses, the @dfn{store monad}.  Monads are a construct
that allows two things: associating ``context'' with values (in our case,
the context is the store), and building sequences of computations (here
computations include accesses to the store).  Values in a monad---values
that carry this additional context---are called @dfn{monadic values};
procedures that return such values are called @dfn{monadic procedures}.

Consider this ``normal'' procedure:

@lisp
(define (sh-symlink store)
  ;; Return a derivation that symlinks the 'bash' executable.
  (let* ((drv (package-derivation store bash))
         (out (derivation->output-path drv))
         (sh  (string-append out "/bin/bash")))
    (build-expression->derivation store "sh"
                                  `(symlink ,sh %output))))
@end lisp

Using @code{(guix monads)} and @code{(guix gexp)}, it may be rewritten as a
monadic function:

@lisp
(define (sh-symlink)
  ;; Same, but return a monadic value.
  (mlet %store-monad ((drv (package->derivation bash)))
    (gexp->derivation "sh"
                      #~(symlink (string-append #$drv "/bin/bash")
                                 #$output))))
@end lisp

There are several things to note in the second version: the @code{store}
parameter is now implicit and is ``threaded'' in the calls to the
@code{package->derivation} and @code{gexp->derivation} monadic procedures,
and the monadic value returned by @code{package->derivation} is @dfn{bound}
using @code{mlet} instead of plain @code{let}.

As it turns out, the call to @code{package->derivation} can even be omitted
since it will take place implicitly, as we will see later
(@pxref{G-表达式}):

@lisp
(define (sh-symlink)
  (gexp->derivation "sh"
                    #~(symlink (string-append #$bash "/bin/bash")
                               #$output)))
@end lisp

@c See
@c <https://syntaxexclamation.wordpress.com/2014/06/26/escaping-continuations/>
@c for the funny quote.
Calling the monadic @code{sh-symlink} has no effect.  As someone once said,
``you exit a monad like you exit a building on fire: by running''.  So, to
exit the monad and get the desired effect, one must use
@code{run-with-store}:

@lisp
(run-with-store (open-connection) (sh-symlink))
@result{} /gnu/store/...-sh-symlink
@end lisp

Note that the @code{(guix monad-repl)} module extends the Guile REPL with
new ``meta-commands'' to make it easier to deal with monadic procedures:
@code{run-in-store}, and @code{enter-store-monad}.  The former is used to
``run'' a single monadic value through the store:

@example
scheme@@(guile-user)> ,run-in-store (package->derivation hello)
$1 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>
@end example

The latter enters a recursive REPL, where all the return values are
automatically run through the store:

@example
scheme@@(guile-user)> ,enter-store-monad
store-monad@@(guile-user) [1]> (package->derivation hello)
$2 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>
store-monad@@(guile-user) [1]> (text-file "foo" "Hello!")
$3 = "/gnu/store/@dots{}-foo"
store-monad@@(guile-user) [1]> ,q
scheme@@(guile-user)>
@end example

@noindent
Note that non-monadic values cannot be returned in the @code{store-monad}
REPL.

The main syntactic forms to deal with monads in general are provided by the
@code{(guix monads)} module and are described below.

@deffn {Scheme Syntax} with-monad @var{monad} @var{body} ...
Evaluate any @code{>>=} or @code{return} forms in @var{body} as being in
@var{monad}.
@end deffn

@deffn {Scheme Syntax} return @var{val}
Return a monadic value that encapsulates @var{val}.
@end deffn

@deffn {Scheme Syntax} >>= @var{mval} @var{mproc} ...
@dfn{Bind} monadic value @var{mval}, passing its ``contents'' to monadic
procedures @var{mproc}@dots{}@footnote{This operation is commonly referred
to as ``bind'', but that name denotes an unrelated procedure in Guile.  Thus
we use this somewhat cryptic symbol inherited from the Haskell language.}.
There can be one @var{mproc} or several of them, as in this example:

@lisp
(run-with-state
    (with-monad %state-monad
      (>>= (return 1)
           (lambda (x) (return (+ 1 x)))
           (lambda (x) (return (* 2 x)))))
  'some-state)

@result{} 4
@result{} some-state
@end lisp
@end deffn

@deffn {Scheme Syntax} mlet @var{monad} ((@var{var} @var{mval}) ...) @
       @var{body} ...
@deffnx {Scheme Syntax} mlet* @var{monad} ((@var{var} @var{mval}) ...) @
       @var{body} ...  Bind the variables @var{var} to the monadic values
@var{mval} in @var{body}, which is a sequence of expressions.  As with the
bind operator, this can be thought of as ``unpacking'' the raw, non-monadic
value ``contained'' in @var{mval} and making @var{var} refer to that raw,
non-monadic value within the scope of the @var{body}.  The form (@var{var}
-> @var{val}) binds @var{var} to the ``normal'' value @var{val}, as per
@code{let}.  The binding operations occur in sequence from left to right.
The last expression of @var{body} must be a monadic expression, and its
result will become the result of the @code{mlet} or @code{mlet*} when run in
the @var{monad}.

@code{mlet*} is to @code{mlet} what @code{let*} is to @code{let}
(@pxref{Local Bindings,,, guile, GNU Guile Reference Manual}).
@end deffn

@deffn {Scheme System} mbegin @var{monad} @var{mexp} ...
Bind @var{mexp} and the following monadic expressions in sequence, returning
the result of the last expression.  Every expression in the sequence must be
a monadic expression.

This is akin to @code{mlet}, except that the return values of the monadic
expressions are ignored.  In that sense, it is analogous to @code{begin},
but applied to monadic expressions.
@end deffn

@deffn {Scheme System} mwhen @var{condition} @var{mexp0} @var{mexp*} ...
When @var{condition} is true, evaluate the sequence of monadic expressions
@var{mexp0}..@var{mexp*} as in an @code{mbegin}.  When @var{condition} is
false, return @code{*unspecified*} in the current monad.  Every expression
in the sequence must be a monadic expression.
@end deffn

@deffn {Scheme System} munless @var{condition} @var{mexp0} @var{mexp*} ...
When @var{condition} is false, evaluate the sequence of monadic expressions
@var{mexp0}..@var{mexp*} as in an @code{mbegin}.  When @var{condition} is
true, return @code{*unspecified*} in the current monad.  Every expression in
the sequence must be a monadic expression.
@end deffn

@cindex state monad
The @code{(guix monads)} module provides the @dfn{state monad}, which allows
an additional value---the state---to be @emph{threaded} through monadic
procedure calls.

@defvr {Scheme Variable} %state-monad
The state monad.  Procedures in the state monad can access and change the
state that is threaded.

Consider the example below.  The @code{square} procedure returns a value in
the state monad.  It returns the square of its argument, but also increments
the current state value:

@lisp
(define (square x)
  (mlet %state-monad ((count (current-state)))
    (mbegin %state-monad
      (set-current-state (+ 1 count))
      (return (* x x)))))

(run-with-state (sequence %state-monad (map square (iota 3))) 0)
@result{} (0 1 4)
@result{} 3
@end lisp

When ``run'' through @code{%state-monad}, we obtain that additional state
value, which is the number of @code{square} calls.
@end defvr

@deffn {Monadic Procedure} current-state
Return the current state as a monadic value.
@end deffn

@deffn {Monadic Procedure} set-current-state @var{value}
Set the current state to @var{value} and return the previous state as a
monadic value.
@end deffn

@deffn {Monadic Procedure} state-push @var{value}
Push @var{value} to the current state, which is assumed to be a list, and
return the previous state as a monadic value.
@end deffn

@deffn {Monadic Procedure} state-pop
Pop a value from the current state and return it as a monadic value.  The
state is assumed to be a list.
@end deffn

@deffn {Scheme Procedure} run-with-state @var{mval} [@var{state}]
Run monadic value @var{mval} starting with @var{state} as the initial
state.  Return two values: the resulting value, and the resulting state.
@end deffn

The main interface to the store monad, provided by the @code{(guix store)}
module, is as follows.

@defvr {Scheme Variable} %store-monad
The store monad---an alias for @code{%state-monad}.

Values in the store monad encapsulate accesses to the store.  When its
effect is needed, a value of the store monad must be ``evaluated'' by
passing it to the @code{run-with-store} procedure (see below).
@end defvr

@deffn {Scheme Procedure} run-with-store @var{store} @var{mval} [#:guile-for-build] [#:system (%current-system)]
Run @var{mval}, a monadic value in the store monad, in @var{store}, an open
store connection.
@end deffn

@deffn {Monadic Procedure} text-file @var{name} @var{text} [@var{references}]
Return as a monadic value the absolute file name in the store of the file
containing @var{text}, a string.  @var{references} is a list of store items
that the resulting text file refers to; it defaults to the empty list.
@end deffn

@deffn {Monadic Procedure} binary-file @var{name} @var{data} [@var{references}]
Return as a monadic value the absolute file name in the store of the file
containing @var{data}, a bytevector.  @var{references} is a list of store
items that the resulting binary file refers to; it defaults to the empty
list.
@end deffn

@deffn {Monadic Procedure} interned-file @var{file} [@var{name}] @
         [#:recursive? #t] [#:select? (const #t)] Return the name of @var{file} once
interned in the store.  Use @var{name} as its store name, or the basename of
@var{file} if @var{name} is omitted.

When @var{recursive?} is true, the contents of @var{file} are added
recursively; if @var{file} designates a flat file and @var{recursive?} is
true, its contents are added, and its permission bits are kept.

When @var{recursive?} is true, call @code{(@var{select?} @var{file}
@var{stat})} for each directory entry, where @var{file} is the entry's
absolute file name and @var{stat} is the result of @code{lstat}; exclude
entries for which @var{select?} does not return true.

The example below adds a file to the store, under two different names:

@lisp
(run-with-store (open-connection)
  (mlet %store-monad ((a (interned-file "README"))
                      (b (interned-file "README" "LEGU-MIN")))
    (return (list a b))))

@result{} ("/gnu/store/rwm@dots{}-README" "/gnu/store/44i@dots{}-LEGU-MIN")
@end lisp

@end deffn

The @code{(guix packages)} module exports the following package-related
monadic procedures:

@deffn {Monadic Procedure} package-file @var{package} [@var{file}] @
       [#:system (%current-system)] [#:target #f] @ [#:output "out"] Return as a
monadic value in the absolute file name of @var{file} within the
@var{output} directory of @var{package}.  When @var{file} is omitted, return
the name of the @var{output} directory of @var{package}.  When @var{target}
is true, use it as a cross-compilation target triplet.

Note that this procedure does @emph{not} build @var{package}.  Thus, the
result might or might not designate an existing file.  We recommend not
using this procedure unless you know what you are doing.
@end deffn

@deffn {Monadic Procedure} package->derivation @var{package} [@var{system}]
@deffnx {Monadic Procedure} package->cross-derivation @var{package} @
          @var{target} [@var{system}] Monadic version of @code{package-derivation} and
@code{package-cross-derivation} (@pxref{定义软件包}).
@end deffn


@node G-表达式
@section G-表达式

@cindex G-expression
@cindex build code quoting
So we have ``derivations'', which represent a sequence of build actions to
be performed to produce an item in the store (@pxref{Derivations}).  These
build actions are performed when asking the daemon to actually build the
derivations; they are run by the daemon in a container (@pxref{调用guix-daemon}).

@cindex code staging
@cindex staging, of code
@cindex strata of code
It should come as no surprise that we like to write these build actions in
Scheme.  When we do that, we end up with two @dfn{strata} of Scheme
code@footnote{The term @dfn{stratum} in this context was coined by Manuel
Serrano et al.@: in the context of their work on Hop.  Oleg Kiselyov, who
has written insightful
@url{http://okmij.org/ftp/meta-programming/#meta-scheme, essays and code on
this topic}, refers to this kind of code generation as @dfn{staging}.}: the
``host code''---code that defines packages, talks to the daemon, etc.---and
the ``build code''---code that actually performs build actions, such as
making directories, invoking @command{make}, and so on (@pxref{构建系统}).

To describe a derivation and its build actions, one typically needs to embed
build code inside host code.  It boils down to manipulating build code as
data, and the homoiconicity of Scheme---code has a direct representation as
data---comes in handy for that.  But we need more than the normal
@code{quasiquote} mechanism in Scheme to construct build expressions.

The @code{(guix gexp)} module implements @dfn{G-expressions}, a form of
S-expressions adapted to build expressions.  G-expressions, or @dfn{gexps},
consist essentially of three syntactic forms: @code{gexp}, @code{ungexp},
and @code{ungexp-splicing} (or simply: @code{#~}, @code{#$}, and
@code{#$@@}), which are comparable to @code{quasiquote}, @code{unquote}, and
@code{unquote-splicing}, respectively (@pxref{Expression Syntax,
@code{quasiquote},, guile, GNU Guile Reference Manual}).  However, there are
major differences:

@itemize
@item
Gexps are meant to be written to a file and run or manipulated by other
processes.

@item
When a high-level object such as a package or derivation is unquoted inside
a gexp, the result is as if its output file name had been introduced.

@item
Gexps carry information about the packages or derivations they refer to, and
these dependencies are automatically added as inputs to the build processes
that use them.
@end itemize

@cindex lowering, of high-level objects in gexps
This mechanism is not limited to package and derivation objects:
@dfn{compilers} able to ``lower'' other high-level objects to derivations or
files in the store can be defined, such that these objects can also be
inserted into gexps.  For example, a useful type of high-level objects that
can be inserted in a gexp is ``file-like objects'', which make it easy to
add files to the store and to refer to them in derivations and such (see
@code{local-file} and @code{plain-file} below).

To illustrate the idea, here is an example of a gexp:

@lisp
(define build-exp
  #~(begin
      (mkdir #$output)
      (chdir #$output)
      (symlink (string-append #$coreutils "/bin/ls")
               "list-files")))
@end lisp

This gexp can be passed to @code{gexp->derivation}; we obtain a derivation
that builds a directory containing exactly one symlink to
@file{/gnu/store/@dots{}-coreutils-8.22/bin/ls}:

@lisp
(gexp->derivation "the-thing" build-exp)
@end lisp

As one would expect, the @code{"/gnu/store/@dots{}-coreutils-8.22"} string
is substituted to the reference to the @var{coreutils} package in the actual
build code, and @var{coreutils} is automatically made an input to the
derivation.  Likewise, @code{#$output} (equivalent to @code{(ungexp
output)}) is replaced by a string containing the directory name of the
output of the derivation.

@cindex cross compilation
In a cross-compilation context, it is useful to distinguish between
references to the @emph{native} build of a package---that can run on the
host---versus references to cross builds of a package.  To that end, the
@code{#+} plays the same role as @code{#$}, but is a reference to a native
package build:

@lisp
(gexp->derivation "vi"
   #~(begin
       (mkdir #$output)
       (mkdir (string-append #$output "/bin"))
       (system* (string-append #+coreutils "/bin/ln")
                "-s"
                (string-append #$emacs "/bin/emacs")
                (string-append #$output "/bin/vi")))
   #:target "aarch64-linux-gnu")
@end lisp

@noindent
In the example above, the native build of @var{coreutils} is used, so that
@command{ln} can actually run on the host; but then the cross-compiled build
of @var{emacs} is referenced.

@cindex imported modules, for gexps
@findex with-imported-modules
Another gexp feature is @dfn{imported modules}: sometimes you want to be
able to use certain Guile modules from the ``host environment'' in the gexp,
so those modules should be imported in the ``build environment''.  The
@code{with-imported-modules} form allows you to express that:

@lisp
(let ((build (with-imported-modules '((guix build utils))
               #~(begin
                   (use-modules (guix build utils))
                   (mkdir-p (string-append #$output "/bin"))))))
  (gexp->derivation "empty-dir"
                    #~(begin
                        #$build
                        (display "success!\n")
                        #t)))
@end lisp

@noindent
In this example, the @code{(guix build utils)} module is automatically
pulled into the isolated build environment of our gexp, such that
@code{(use-modules (guix build utils))} works as expected.

@cindex module closure
@findex source-module-closure
Usually you want the @emph{closure} of the module to be imported---i.e., the
module itself and all the modules it depends on---rather than just the
module; failing to do that, attempts to use the module will fail because of
missing dependent modules.  The @code{source-module-closure} procedure
computes the closure of a module by looking at its source file headers,
which comes in handy in this case:

@lisp
(use-modules (guix modules))   ;for 'source-module-closure'

(with-imported-modules (source-module-closure
                         '((guix build utils)
                           (gnu build vm)))
  (gexp->derivation "something-with-vms"
                    #~(begin
                        (use-modules (guix build utils)
                                     (gnu build vm))
                        @dots{})))
@end lisp

@cindex extensions, for gexps
@findex with-extensions
In the same vein, sometimes you want to import not just pure-Scheme modules,
but also ``extensions'' such as Guile bindings to C libraries or other
``full-blown'' packages.  Say you need the @code{guile-json} package
available on the build side, here's how you would do it:

@lisp
(use-modules (gnu packages guile))  ;for 'guile-json'

(with-extensions (list guile-json)
  (gexp->derivation "something-with-json"
                    #~(begin
                        (use-modules (json))
                        @dots{})))
@end lisp

The syntactic form to construct gexps is summarized below.

@deffn {Scheme Syntax} #~@var{exp}
@deffnx {Scheme Syntax} (gexp @var{exp})
Return a G-expression containing @var{exp}.  @var{exp} may contain one or
more of the following forms:

@table @code
@item #$@var{obj}
@itemx (ungexp @var{obj})
Introduce a reference to @var{obj}.  @var{obj} may have one of the supported
types, for example a package or a derivation, in which case the
@code{ungexp} form is replaced by its output file name---e.g.,
@code{"/gnu/store/@dots{}-coreutils-8.22}.

If @var{obj} is a list, it is traversed and references to supported objects
are substituted similarly.

If @var{obj} is another gexp, its contents are inserted and its dependencies
are added to those of the containing gexp.

If @var{obj} is another kind of object, it is inserted as is.

@item #$@var{obj}:@var{output}
@itemx (ungexp @var{obj} @var{output})
This is like the form above, but referring explicitly to the @var{output} of
@var{obj}---this is useful when @var{obj} produces multiple outputs
(@pxref{有多个输出的软件包}).

@item #+@var{obj}
@itemx #+@var{obj}:output
@itemx (ungexp-native @var{obj})
@itemx (ungexp-native @var{obj} @var{output})
Same as @code{ungexp}, but produces a reference to the @emph{native} build
of @var{obj} when used in a cross compilation context.

@item #$output[:@var{output}]
@itemx (ungexp output [@var{output}])
Insert a reference to derivation output @var{output}, or to the main output
when @var{output} is omitted.

This only makes sense for gexps passed to @code{gexp->derivation}.

@item #$@@@var{lst}
@itemx (ungexp-splicing @var{lst})
Like the above, but splices the contents of @var{lst} inside the containing
list.

@item #+@@@var{lst}
@itemx (ungexp-native-splicing @var{lst})
Like the above, but refers to native builds of the objects listed in
@var{lst}.

@end table

G-expressions created by @code{gexp} or @code{#~} are run-time objects of
the @code{gexp?} type (see below).
@end deffn

@deffn {Scheme Syntax} with-imported-modules @var{modules} @var{body}@dots{}
Mark the gexps defined in @var{body}@dots{} as requiring @var{modules} in
their execution environment.

Each item in @var{modules} can be the name of a module, such as @code{(guix
build utils)}, or it can be a module name, followed by an arrow, followed by
a file-like object:

@lisp
`((guix build utils)
  (guix gcrypt)
  ((guix config) => ,(scheme-file "config.scm"
                                  #~(define-module @dots{}))))
@end lisp

@noindent
In the example above, the first two modules are taken from the search path,
and the last one is created from the given file-like object.

This form has @emph{lexical} scope: it has an effect on the gexps directly
defined in @var{body}@dots{}, but not on those defined, say, in procedures
called from @var{body}@dots{}.
@end deffn

@deffn {Scheme Syntax} with-extensions @var{extensions} @var{body}@dots{}
Mark the gexps defined in @var{body}@dots{} as requiring @var{extensions} in
their build and execution environment.  @var{extensions} is typically a list
of package objects such as those defined in the @code{(gnu packages guile)}
module.

Concretely, the packages listed in @var{extensions} are added to the load
path while compiling imported modules in @var{body}@dots{}; they are also
added to the load path of the gexp returned by @var{body}@dots{}.
@end deffn

@deffn {Scheme Procedure} gexp? @var{obj}
Return @code{#t} if @var{obj} is a G-expression.
@end deffn

G-expressions are meant to be written to disk, either as code building some
derivation, or as plain files in the store.  The monadic procedures below
allow you to do that (@pxref{仓库monad}, for more information about
monads).

@deffn {Monadic Procedure} gexp->derivation @var{name} @var{exp} @
       [#:system (%current-system)] [#:target #f] [#:graft? #t] @ [#:hash #f]
[#:hash-algo #f] @ [#:recursive? #f] [#:env-vars '()] [#:modules '()] @
[#:module-path @code{%load-path}] @ [#:effective-version "2.2"] @
[#:references-graphs #f] [#:allowed-references #f] @
[#:disallowed-references #f] @ [#:leaked-env-vars #f] @ [#:script-name
(string-append @var{name} "-builder")] @ [#:deprecation-warnings #f] @
[#:local-build? #f] [#:substitutable? #t] @ [#:properties '()]
[#:guile-for-build #f] Return a derivation @var{name} that runs @var{exp} (a
gexp) with @var{guile-for-build} (a derivation) on @var{system}; @var{exp}
is stored in a file called @var{script-name}.  When @var{target} is true, it
is used as the cross-compilation target triplet for packages referred to by
@var{exp}.

@var{modules} is deprecated in favor of @code{with-imported-modules}.  Its
meaning is to make @var{modules} available in the evaluation context of
@var{exp}; @var{modules} is a list of names of Guile modules searched in
@var{module-path} to be copied in the store, compiled, and made available in
the load path during the execution of @var{exp}---e.g., @code{((guix build
utils) (guix build gnu-build-system))}.

@var{effective-version} determines the string to use when adding extensions
of @var{exp} (see @code{with-extensions}) to the search path---e.g.,
@code{"2.2"}.

@var{graft?} determines whether packages referred to by @var{exp} should be
grafted when applicable.

When @var{references-graphs} is true, it must be a list of tuples of one of
the following forms:

@example
(@var{file-name} @var{package})
(@var{file-name} @var{package} @var{output})
(@var{file-name} @var{derivation})
(@var{file-name} @var{derivation} @var{output})
(@var{file-name} @var{store-item})
@end example

The right-hand-side of each element of @var{references-graphs} is
automatically made an input of the build process of @var{exp}.  In the build
environment, each @var{file-name} contains the reference graph of the
corresponding item, in a simple text format.

@var{allowed-references} must be either @code{#f} or a list of output names
and packages.  In the latter case, the list denotes store items that the
result is allowed to refer to.  Any reference to another store item will
lead to a build error.  Similarly for @var{disallowed-references}, which can
list items that must not be referenced by the outputs.

@var{deprecation-warnings} determines whether to show deprecation warnings
while compiling modules.  It can be @code{#f}, @code{#t}, or
@code{'detailed}.

The other arguments are as for @code{derivation} (@pxref{Derivations}).
@end deffn

@cindex file-like objects
The @code{local-file}, @code{plain-file}, @code{computed-file},
@code{program-file}, and @code{scheme-file} procedures below return
@dfn{file-like objects}.  That is, when unquoted in a G-expression, these
objects lead to a file in the store.  Consider this G-expression:

@lisp
#~(system* #$(file-append glibc "/sbin/nscd") "-f"
           #$(local-file "/tmp/my-nscd.conf"))
@end lisp

The effect here is to ``intern'' @file{/tmp/my-nscd.conf} by copying it to
the store.  Once expanded, for instance @i{via} @code{gexp->derivation}, the
G-expression refers to that copy under @file{/gnu/store}; thus, modifying or
removing the file in @file{/tmp} does not have any effect on what the
G-expression does.  @code{plain-file} can be used similarly; it differs in
that the file content is directly passed as a string.

@deffn {Scheme Procedure} local-file @var{file} [@var{name}] @
   [#:recursive? #f] [#:select? (const #t)] Return an object representing local
file @var{file} to add to the store; this object can be used in a gexp.  If
@var{file} is a literal string denoting a relative file name, it is looked
up relative to the source file where it appears; if @var{file} is not a
literal string, it is looked up relative to the current working directory at
run time.  @var{file} will be added to the store under @var{name}--by
default the base name of @var{file}.

When @var{recursive?} is true, the contents of @var{file} are added
recursively; if @var{file} designates a flat file and @var{recursive?} is
true, its contents are added, and its permission bits are kept.

When @var{recursive?} is true, call @code{(@var{select?} @var{file}
@var{stat})} for each directory entry, where @var{file} is the entry's
absolute file name and @var{stat} is the result of @code{lstat}; exclude
entries for which @var{select?} does not return true.

This is the declarative counterpart of the @code{interned-file} monadic
procedure (@pxref{仓库monad, @code{interned-file}}).
@end deffn

@deffn {Scheme Procedure} plain-file @var{name} @var{content}
Return an object representing a text file called @var{name} with the given
@var{content} (a string or a bytevector) to be added to the store.

This is the declarative counterpart of @code{text-file}.
@end deffn

@deffn {Scheme Procedure} computed-file @var{name} @var{gexp} @
          [#:local-build? #t] [#:options '()] Return an object representing the store
item @var{name}, a file or directory computed by @var{gexp}.  When
@var{local-build?} is true (the default), the derivation is built locally.
@var{options} is a list of additional arguments to pass to
@code{gexp->derivation}.

This is the declarative counterpart of @code{gexp->derivation}.
@end deffn

@deffn {Monadic Procedure} gexp->script @var{name} @var{exp} @
  [#:guile (default-guile)] [#:module-path %load-path] @ [#:system
(%current-system)] [#:target #f] Return an executable script @var{name} that
runs @var{exp} using @var{guile}, with @var{exp}'s imported modules in its
search path.  Look up @var{exp}'s modules in @var{module-path}.

The example below builds a script that simply invokes the @command{ls}
command:

@lisp
(use-modules (guix gexp) (gnu packages base))

(gexp->script "list-files"
              #~(execl #$(file-append coreutils "/bin/ls")
                       "ls"))
@end lisp

When ``running'' it through the store (@pxref{仓库monad,
@code{run-with-store}}), we obtain a derivation that produces an executable
file @file{/gnu/store/@dots{}-list-files} along these lines:

@example
#!/gnu/store/@dots{}-guile-2.0.11/bin/guile -ds
!#
(execl "/gnu/store/@dots{}-coreutils-8.22"/bin/ls" "ls")
@end example
@end deffn

@deffn {Scheme Procedure} program-file @var{name} @var{exp} @
          [#:guile #f] [#:module-path %load-path] Return an object representing the
executable store item @var{name} that runs @var{gexp}.  @var{guile} is the
Guile package used to execute that script.  Imported modules of @var{gexp}
are looked up in @var{module-path}.

This is the declarative counterpart of @code{gexp->script}.
@end deffn

@deffn {Monadic Procedure} gexp->file @var{name} @var{exp} @
            [#:set-load-path? #t] [#:module-path %load-path] @ [#:splice? #f] @ [#:guile
(default-guile)] Return a derivation that builds a file @var{name}
containing @var{exp}.  When @var{splice?} is true, @var{exp} is considered
to be a list of expressions that will be spliced in the resulting file.

When @var{set-load-path?} is true, emit code in the resulting file to set
@code{%load-path} and @code{%load-compiled-path} to honor @var{exp}'s
imported modules.  Look up @var{exp}'s modules in @var{module-path}.

The resulting file holds references to all the dependencies of @var{exp} or
a subset thereof.
@end deffn

@deffn {Scheme Procedure} scheme-file @var{name} @var{exp} @
          [#:splice? #f] [#:set-load-path? #t] Return an object representing the
Scheme file @var{name} that contains @var{exp}.

This is the declarative counterpart of @code{gexp->file}.
@end deffn

@deffn {Monadic Procedure} text-file* @var{name} @var{text} @dots{}
Return as a monadic value a derivation that builds a text file containing
all of @var{text}.  @var{text} may list, in addition to strings, objects of
any type that can be used in a gexp: packages, derivations, local file
objects, etc.  The resulting store file holds references to all these.

This variant should be preferred over @code{text-file} anytime the file to
create will reference items from the store.  This is typically the case when
building a configuration file that embeds store file names, like this:

@lisp
(define (profile.sh)
  ;; Return the name of a shell script in the store that
  ;; initializes the 'PATH' environment variable.
  (text-file* "profile.sh"
              "export PATH=" coreutils "/bin:"
              grep "/bin:" sed "/bin\n"))
@end lisp

In this example, the resulting @file{/gnu/store/@dots{}-profile.sh} file
will reference @var{coreutils}, @var{grep}, and @var{sed}, thereby
preventing them from being garbage-collected during its lifetime.
@end deffn

@deffn {Scheme Procedure} mixed-text-file @var{name} @var{text} @dots{}
Return an object representing store file @var{name} containing @var{text}.
@var{text} is a sequence of strings and file-like objects, as in:

@lisp
(mixed-text-file "profile"
                 "export PATH=" coreutils "/bin:" grep "/bin")
@end lisp

This is the declarative counterpart of @code{text-file*}.
@end deffn

@deffn {Scheme Procedure} file-union @var{name} @var{files}
Return a @code{<computed-file>} that builds a directory containing all of
@var{files}.  Each item in @var{files} must be a two-element list where the
first element is the file name to use in the new directory, and the second
element is a gexp denoting the target file.  Here's an example:

@lisp
(file-union "etc"
            `(("hosts" ,(plain-file "hosts"
                                    "127.0.0.1 localhost"))
              ("bashrc" ,(plain-file "bashrc"
                                     "alias ls='ls --color=auto'"))))
@end lisp

This yields an @code{etc} directory containing these two files.
@end deffn

@deffn {Scheme Procedure} directory-union @var{name} @var{things}
Return a directory that is the union of @var{things}, where @var{things} is
a list of file-like objects denoting directories.  For example:

@lisp
(directory-union "guile+emacs" (list guile emacs))
@end lisp

yields a directory that is the union of the @code{guile} and @code{emacs}
packages.
@end deffn

@deffn {Scheme Procedure} file-append @var{obj} @var{suffix} @dots{}
Return a file-like object that expands to the concatenation of @var{obj} and
@var{suffix}, where @var{obj} is a lowerable object and each @var{suffix} is
a string.

As an example, consider this gexp:

@lisp
(gexp->script "run-uname"
              #~(system* #$(file-append coreutils
                                        "/bin/uname")))
@end lisp

The same effect could be achieved with:

@lisp
(gexp->script "run-uname"
              #~(system* (string-append #$coreutils
                                        "/bin/uname")))
@end lisp

There is one difference though: in the @code{file-append} case, the
resulting script contains the absolute file name as a string, whereas in the
second case, the resulting script contains a @code{(string-append @dots{})}
expression to construct the file name @emph{at run time}.
@end deffn

@deffn {Scheme Syntax} let-system @var{system} @var{body}@dots{}
@deffnx {Scheme Syntax} let-system (@var{system} @var{target}) @var{body}@dots{}
Bind @var{system} to the currently targeted system---e.g.,
@code{"x86_64-linux"}---within @var{body}.

In the second case, additionally bind @var{target} to the current
cross-compilation target---a GNU triplet such as
@code{"arm-linux-gnueabihf"}---or @code{#f} if we are not cross-compiling.

@code{let-system} is useful in the occasional case where the object spliced
into the gexp depends on the target system, as in this example:

@lisp
#~(system*
   #+(let-system system
       (cond ((string-prefix? "armhf-" system)
              (file-append qemu "/bin/qemu-system-arm"))
             ((string-prefix? "x86_64-" system)
              (file-append qemu "/bin/qemu-system-x86_64"))
             (else
              (error "dunno!"))))
   "-net" "user" #$image)
@end lisp
@end deffn

@deffn {Scheme Syntax} with-parameters ((@var{parameter} @var{value}) @dots{}) @var{exp}
This macro is similar to the @code{parameterize} form for dynamically-bound
@dfn{parameters} (@pxref{Parameters,,, guile, GNU Guile Reference Manual}).
The key difference is that it takes effect when the file-like object
returned by @var{exp} is lowered to a derivation or store item.

A typical use of @code{with-parameters} is to force the system in effect for
a given object:

@lisp
(with-parameters ((%current-system "i686-linux"))
  coreutils)
@end lisp

The example above returns an object that corresponds to the i686 build of
Coreutils, regardless of the current value of @code{%current-system}.
@end deffn


Of course, in addition to gexps embedded in ``host'' code, there are also
modules containing build tools.  To make it clear that they are meant to be
used in the build stratum, these modules are kept in the @code{(guix build
@dots{})} name space.

@cindex lowering, of high-level objects in gexps
Internally, high-level objects are @dfn{lowered}, using their compiler, to
either derivations or store items.  For instance, lowering a package yields
a derivation, and lowering a @code{plain-file} yields a store item.  This is
achieved using the @code{lower-object} monadic procedure.

@deffn {Monadic Procedure} lower-object @var{obj} [@var{system}] @
           [#:target #f] Return as a value in @code{%store-monad} the derivation or
store item corresponding to @var{obj} for @var{system}, cross-compiling for
@var{target} if @var{target} is true.  @var{obj} must be an object that has
an associated gexp compiler, such as a @code{<package>}.
@end deffn

@node 调用guix repl
@section Invoking @command{guix repl}

@cindex REPL, read-eval-print loop, script
The @command{guix repl} command makes it easier to program Guix in Guile by
launching a Guile @dfn{read-eval-print loop} (REPL) for interactive
programming (@pxref{Using Guile Interactively,,, guile, GNU Guile Reference
Manual}), or by running Guile scripts (@pxref{Running Guile Scripts,,,
guile, GNU Guile Reference Manual}).  Compared to just launching the
@command{guile} command, @command{guix repl} guarantees that all the Guix
modules and all its dependencies are available in the search path.

The general syntax is:

@example
guix repl @var{options} [@var{file} @var{args}]
@end example

When a @var{file} argument is provided, @var{file} is executed as a Guile
scripts:

@example
guix repl my-script.scm
@end example

To pass arguments to the script, use @code{--} to prevent them from being
interpreted as arguments to @command{guix repl} itself:

@example
guix repl -- my-script.scm --input=foo.txt
@end example

To make a script executable directly from the shell, using the guix
executable that is on the user's search path, add the following two lines at
the top of the script:

@example
@code{#!/usr/bin/env -S guix repl --}
@code{!#}
@end example

Without a file name argument, a Guile REPL is started:

@example
$ guix repl
scheme@@(guile-user)> ,use (gnu packages base)
scheme@@(guile-user)> coreutils
$1 = #<package coreutils@@8.29 gnu/packages/base.scm:327 3e28300>
@end example

@cindex inferiors
In addition, @command{guix repl} implements a simple machine-readable REPL
protocol for use by @code{(guix inferior)}, a facility to interact with
@dfn{inferiors}, separate processes running a potentially different revision
of Guix.

The available options are as follows:

@table @code
@item --type=@var{type}
@itemx -t @var{type}
Start a REPL of the given @var{TYPE}, which can be one of the following:

@table @code
@item guile
This is default, and it spawns a standard full-featured Guile REPL.
@item machine
Spawn a REPL that uses the machine-readable protocol.  This is the protocol
that the @code{(guix inferior)} module speaks.
@end table

@item --listen=@var{endpoint}
By default, @command{guix repl} reads from standard input and writes to
standard output.  When this option is passed, it will instead listen for
connections on @var{endpoint}.  Here are examples of valid options:

@table @code
@item --listen=tcp:37146
Accept connections on localhost on port 37146.

@item --listen=unix:/tmp/socket
Accept connections on the Unix-domain socket @file{/tmp/socket}.
@end table

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{软件包模块}).

This allows users to define their own packages and make them visible to the
script or REPL.

@item -q
Inhibit loading of the @file{~/.guile} file.  By default, that configuration
file is loaded when spawning a @code{guile} REPL.
@end table

@c *********************************************************************
@node 工具
@chapter 工具

This section describes Guix command-line utilities.  Some of them are
primarily targeted at developers and users who write new package
definitions, while others are more generally useful.  They complement the
Scheme programming interface of Guix in a convenient way.

@menu
* 调用guix build::         用命令行构建软件包。
* 调用guix edit。::       编辑软件包定义。
* 调用guix download::      下载一个文件并打印它的hash。
* 调用guix hash::          计算一个文件的密码学hash。
* 调用guix import::        导入软件包定义。
* 调用guix refresh::       更新软件包定义。
* 调用guix lint::          从软件包定义里寻找错误。
* 调用guix size::          分析硬盘使用情况。
* 调用guix graph::         展示软件包的关系图。
* 调用guix publish::       分享substitute。
* 调用guix challenge::     挑战subtitute服务器。
* 调用guix copy::          复制到远程的仓库，或从远程的仓库复制。
* 调用guix container::     进程隔离。
* 调用guix weather::       评估substitute的可用性。
* 调用guix processes::     列出客户端进程。
@end menu

@node 调用guix build
@section 调用@command{guix build}

@cindex package building
@cindex @command{guix build}
The @command{guix build} command builds packages or derivations and their
dependencies, and prints the resulting store paths.  Note that it does not
modify the user's profile---this is the job of the @command{guix package}
command (@pxref{调用guix package}).  Thus, it is mainly useful for
distribution developers.

The general syntax is:

@example
guix build @var{options} @var{package-or-derivation}@dots{}
@end example

As an example, the following command builds the latest versions of Emacs and
of Guile, displays their build logs, and finally displays the resulting
directories:

@example
guix build emacs guile
@end example

Similarly, the following command builds all the available packages:

@example
guix build --quiet --keep-going \
  $(guix package -A | cut -f1,2 --output-delimiter=@@)
@end example

@var{package-or-derivation} may be either the name of a package found in the
software distribution such as @code{coreutils} or @code{coreutils@@8.20}, or
a derivation such as @file{/gnu/store/@dots{}-coreutils-8.19.drv}.  In the
former case, a package with the corresponding name (and optionally version)
is searched for among the GNU distribution modules (@pxref{软件包模块}).

Alternatively, the @option{--expression} option may be used to specify a
Scheme expression that evaluates to a package; this is useful when
disambiguating among several same-named packages or package variants is
needed.

There may be zero or more @var{options}.  The available options are
described in the subsections below.

@menu
* 普通的构建选项::    大部分命令的构建选项。
* 软件包变换选项。::  创建软件包的变体。
* 额外的构建选项::    只属于'guix build'的选项。
* 调试构建错误::       真实的打包经验。
@end menu

@node 普通的构建选项
@subsection 普通的构建选项

A number of options that control the build process are common to
@command{guix build} and other commands that can spawn builds, such as
@command{guix package} or @command{guix archive}.  These are the following:

@table @code

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{软件包模块}).

This allows users to define their own packages and make them visible to the
command-line tools.

@item --keep-failed
@itemx -K
Keep the build tree of failed builds.  Thus, if a build fails, its build
tree is kept under @file{/tmp}, in a directory whose name is shown at the
end of the build log.  This is useful when debugging build issues.
@xref{调试构建错误}, for tips and tricks on how to debug build
issues.

This option implies @option{--no-offload}, and it has no effect when
connecting to a remote daemon with a @code{guix://} URI (@pxref{仓库,
the @env{GUIX_DAEMON_SOCKET} variable}).

@item --keep-going
@itemx -k
Keep going when some of the derivations fail to build; return only once all
the builds have either completed or failed.

The default behavior is to stop as soon as one of the specified derivations
has failed.

@item --dry-run
@itemx -n
Do not build the derivations.

@anchor{fallback-option}
@item --fallback
When substituting a pre-built binary fails, fall back to building packages
locally (@pxref{substitute失败}).

@item --substitute-urls=@var{urls}
@anchor{client-substitute-urls}
Consider @var{urls} the whitespace-separated list of substitute source URLs,
overriding the default list of URLs of @command{guix-daemon}
(@pxref{daemon-substitute-urls,, @command{guix-daemon} URLs}).

This means that substitutes may be downloaded from @var{urls}, provided they
are signed by a key authorized by the system administrator
(@pxref{substitutes}).

When @var{urls} is the empty string, substitutes are effectively disabled.

@item --no-substitutes
不要为构建商品使用substitute。即，总是在本地构建，而不是下载预构建的二进制文件（@pxref{substitutes}）。

@item --no-grafts
Do not ``graft'' packages.  In practice, this means that package updates
available as grafts are not applied.  @xref{安全更新}, for more
information on grafts.

@item --rounds=@var{n}
Build each derivation @var{n} times in a row, and raise an error if
consecutive build results are not bit-for-bit identical.

This is a useful way to detect non-deterministic builds processes.
Non-deterministic build processes are a problem because they make it
practically impossible for users to @emph{verify} whether third-party
binaries are genuine.  @xref{调用guix challenge}, for more.

当和@option{--keep-failed}一起使用时，不同的输出保存在@file{/gnu/store/@dots{}-check}。这让检查两个结果的区别更容易。

@item --no-offload
Do not use offload builds to other machines (@pxref{下发工作给后台进程的设置}).
That is, always build things locally instead of offloading builds to remote
machines.

@item --max-silent-time=@var{seconds}
当构建或substitution进程超过@var{seconds}秒仍然保持静默，就把它结束掉并报告构建失败。

By default, the daemon's setting is honored (@pxref{调用guix-daemon,
@option{--max-silent-time}}).

@item --timeout=@var{seconds}
类似地，当构建或substitution进程执行超过@var{seconds}秒，就把它结束掉并报告构建失败。

By default, the daemon's setting is honored (@pxref{调用guix-daemon,
@option{--timeout}}).

@c Note: This option is actually not part of %standard-build-options but
@c most programs honor it.
@cindex verbosity, of the command-line tools
@cindex build logs, verbosity
@item -v @var{level}
@itemx --verbosity=@var{level}
Use the given verbosity @var{level}, an integer.  Choosing 0 means that no
output is produced, 1 is for quiet output; 2 is similar to 1 but it
additionally displays download URLs; 3 shows all the build log output on
standard error.

@item --cores=@var{n}
@itemx -c @var{n}
Allow the use of up to @var{n} CPU cores for the build.  The special value
@code{0} means to use as many CPU cores as available.

@item --max-jobs=@var{n}
@itemx -M @var{n}
Allow at most @var{n} build jobs in parallel.  @xref{调用guix-daemon,
@option{--max-jobs}}, for details about this option and the equivalent
@command{guix-daemon} option.

@item --debug=@var{level}
Produce debugging output coming from the build daemon.  @var{level} must be
an integer between 0 and 5; higher means more verbose output.  Setting a
level of 4 or more may be helpful when debugging setup issues with the build
daemon.

@end table

Behind the scenes, @command{guix build} is essentially an interface to the
@code{package-derivation} procedure of the @code{(guix packages)} module,
and to the @code{build-derivations} procedure of the @code{(guix
derivations)} module.

In addition to options explicitly passed on the command line, @command{guix
build} and other @command{guix} commands that support building honor the
@env{GUIX_BUILD_OPTIONS} environment variable.

@defvr {Environment Variable} GUIX_BUILD_OPTIONS
Users can define this variable to a list of command line options that will
automatically be used by @command{guix build} and other @command{guix}
commands that can perform builds, as in the example below:

@example
$ export GUIX_BUILD_OPTIONS="--no-substitutes -c 2 -L /foo/bar"
@end example

These options are parsed independently, and the result is appended to the
parsed command-line options.
@end defvr


@node 软件包变换选项。
@subsection 软件包变换选项。

@cindex package variants
Another set of command-line options supported by @command{guix build} and
also @command{guix package} are @dfn{package transformation options}.  These
are options that make it possible to define @dfn{package variants}---for
instance, packages built from different source code.  This is a convenient
way to create customized packages on the fly without having to type in the
definitions of package variants (@pxref{定义软件包}).

Package transformation options are preserved across upgrades: @command{guix
upgrade} attempts to apply transformation options initially used when
creating the profile to the upgraded packages.

The available options are listed below.  Most commands support them and also
support a @option{--help-transform} option that lists all the available
options and a synopsis (these options are not shown in the @option{--help}
output for brevity).

@table @code

@item --with-source=@var{source}
@itemx --with-source=@var{package}=@var{source}
@itemx --with-source=@var{package}@@@var{version}=@var{source}
Use @var{source} as the source of @var{package}, and @var{version} as its
version number.  @var{source} must be a file name or a URL, as for
@command{guix download} (@pxref{调用guix download}).

When @var{package} is omitted, it is taken to be the package name specified
on the command line that matches the base of @var{source}---e.g., if
@var{source} is @code{/src/guile-2.0.10.tar.gz}, the corresponding package
is @code{guile}.

Likewise, when @var{version} is omitted, the version string is inferred from
@var{source}; in the previous example, it is @code{2.0.10}.

This option allows users to try out versions of packages other than the one
provided by the distribution.  The example below downloads
@file{ed-1.7.tar.gz} from a GNU mirror and uses that as the source for the
@code{ed} package:

@example
guix build ed --with-source=mirror://gnu/ed/ed-1.7.tar.gz
@end example

As a developer, @option{--with-source} makes it easy to test release
candidates:

@example
guix build guile --with-source=../guile-2.0.9.219-e1bb7.tar.xz
@end example

@dots{} or to build from a checkout in a pristine environment:

@example
$ git clone git://git.sv.gnu.org/guix.git
$ guix build guix --with-source=guix@@1.0=./guix
@end example

@item --with-input=@var{package}=@var{replacement}
Replace dependency on @var{package} by a dependency on @var{replacement}.
@var{package} must be a package name, and @var{replacement} must be a
package specification such as @code{guile} or @code{guile@@1.8}.

For instance, the following command builds Guix, but replaces its dependency
on the current stable version of Guile with a dependency on the legacy
version of Guile, @code{guile@@2.0}:

@example
guix build --with-input=guile=guile@@2.0 guix
@end example

This is a recursive, deep replacement.  So in this example, both @code{guix}
and its dependency @code{guile-json} (which also depends on @code{guile})
get rebuilt against @code{guile@@2.0}.

This is implemented using the @code{package-input-rewriting} Scheme
procedure (@pxref{定义软件包, @code{package-input-rewriting}}).

@item --with-graft=@var{package}=@var{replacement}
This is similar to @option{--with-input} but with an important difference:
instead of rebuilding the whole dependency chain, @var{replacement} is built
and then @dfn{grafted} onto the binaries that were initially referring to
@var{package}.  @xref{安全更新}, for more information on grafts.

For example, the command below grafts version 3.5.4 of GnuTLS onto Wget and
all its dependencies, replacing references to the version of GnuTLS they
currently refer to:

@example
guix build --with-graft=gnutls=gnutls@@3.5.4 wget
@end example

This has the advantage of being much faster than rebuilding everything.  But
there is a caveat: it works if and only if @var{package} and
@var{replacement} are strictly compatible---for example, if they provide a
library, the application binary interface (ABI) of those libraries must be
compatible.  If @var{replacement} is somehow incompatible with
@var{package}, then the resulting package may be unusable.  Use with care!

@cindex debugging info, rebuilding
@item --with-debug-info=@var{package}
Build @var{package} in a way that preserves its debugging info and graft it
onto packages that depend on it.  This is useful if @var{package} does not
already provide debugging info as a @code{debug} output (@pxref{安装调试文件}).

For example, suppose you're experiencing a crash in Inkscape and would like
to see what's up in GLib, a library deep down in Inkscape's dependency
graph.  GLib lacks a @code{debug} output, so debugging is tough.
Fortunately, you rebuild GLib with debugging info and tack it on Inkscape:

@example
guix install inkscape --with-debug-info=glib
@end example

Only GLib needs to be recompiled so this takes a reasonable amount of time.
@xref{安装调试文件}, for more info.

@quotation 注
Under the hood, this option works by passing the @samp{#:strip-binaries? #f}
to the build system of the package of interest (@pxref{构建系统}).
Most build systems support that option but some do not.  In that case, an
error is raised.

Likewise, if a C/C++ package is built without @code{-g} (which is rarely the
case), debugging info will remain unavailable even when
@code{#:strip-binaries?} is false.
@end quotation

@cindex tool chain, changing the build tool chain of a package
@item --with-c-toolchain=@var{package}=@var{toolchain}
This option changes the compilation of @var{package} and everything that
depends on it so that they get built with @var{toolchain} instead of the
default GNU tool chain for C/C++.

Consider this example:

@example
guix build octave-cli \
  --with-c-toolchain=fftw=gcc-toolchain@@10 \
  --with-c-toolchain=fftwf=gcc-toolchain@@10
@end example

The command above builds a variant of the @code{fftw} and @code{fftwf}
packages using version 10 of @code{gcc-toolchain} instead of the default
tool chain, and then builds a variant of the GNU@tie{}Octave command-line
interface using them.  GNU@tie{}Octave itself is also built with
@code{gcc-toolchain@@10}.

This other example builds the Hardware Locality (@code{hwloc}) library and
its dependents up to @code{intel-mpi-benchmarks} with the Clang C compiler:

@example
guix build --with-c-toolchain=hwloc=clang-toolchain \
           intel-mpi-benchmarks
@end example

@quotation 注
There can be application binary interface (ABI) incompatibilities among tool
chains.  This is particularly true of the C++ standard library and run-time
support libraries such as that of OpenMP@.  By rebuilding all dependents
with the same tool chain, @option{--with-c-toolchain} minimizes the risks of
incompatibility but cannot entirely eliminate them.  Choose @var{package}
wisely.
@end quotation

@item --with-git-url=@var{package}=@var{url}
@cindex Git, using the latest commit
@cindex latest commit, building
Build @var{package} from the latest commit of the @code{master} branch of
the Git repository at @var{url}.  Git sub-modules of the repository are
fetched, recursively.

For example, the following command builds the NumPy Python library against
the latest commit of the master branch of Python itself:

@example
guix build python-numpy \
  --with-git-url=python=https://github.com/python/cpython
@end example

This option can also be combined with @option{--with-branch} or
@option{--with-commit} (see below).

@cindex continuous integration
Obviously, since it uses the latest commit of the given branch, the result
of such a command varies over time.  Nevertheless it is a convenient way to
rebuild entire software stacks against the latest commit of one or more
packages.  This is particularly useful in the context of continuous
integration (CI).

Checkouts are kept in a cache under @file{~/.cache/guix/checkouts} to speed
up consecutive accesses to the same repository.  You may want to clean it up
once in a while to save disk space.

@item --with-branch=@var{package}=@var{branch}
Build @var{package} from the latest commit of @var{branch}.  If the
@code{source} field of @var{package} is an origin with the @code{git-fetch}
method (@pxref{origin参考手册}) or a @code{git-checkout} object, the
repository URL is taken from that @code{source}.  Otherwise you have to use
@option{--with-git-url} to specify the URL of the Git repository.

For instance, the following command builds @code{guile-sqlite3} from the
latest commit of its @code{master} branch, and then builds @code{guix}
(which depends on it) and @code{cuirass} (which depends on @code{guix})
against this specific @code{guile-sqlite3} build:

@example
guix build --with-branch=guile-sqlite3=master cuirass
@end example

@item --with-commit=@var{package}=@var{commit}
This is similar to @option{--with-branch}, except that it builds from
@var{commit} rather than the tip of a branch.  @var{commit} must be a valid
Git commit SHA1 identifier or a tag.

@item --with-patch=@var{package}=@var{file}
Add @var{file} to the list of patches applied to @var{package}, where
@var{package} is a spec such as @code{python@@3.8} or @code{glibc}.
@var{file} must contain a patch; it is applied with the flags specified in
the @code{origin} of @var{package} (@pxref{origin参考手册}), which by
default includes @code{-p1} (@pxref{patch Directories,,, diffutils,
Comparing and Merging Files}).

As an example, the command below rebuilds Coreutils with the GNU C Library
(glibc) patched with the given patch:

@example
guix build coreutils --with-patch=glibc=./glibc-frob.patch
@end example

In this example, glibc itself as well as everything that leads to Coreutils
in the dependency graph is rebuilt.

@cindex upstream, latest version
@item --with-latest=@var{package}
So you like living on the bleeding edge? This option is for you! It replaces
occurrences of @var{package} in the dependency graph with its latest
upstream version, as reported by @command{guix refresh} (@pxref{调用guix refresh}).

It does so by determining the latest upstream release of @var{package} (if
possible), downloading it, and authenticating it @emph{if} it comes with an
OpenPGP signature.

As an example, the command below builds Guix against the latest version of
Guile-JSON:

@example
guix build guix --with-latest=guile-json
@end example

There are limitations.  First, in cases where the tool cannot or does not
know how to authenticate source code, you are at risk of running malicious
code; a warning is emitted in this case.  Second, this option simply changes
the source used in the existing package definitions, which is not always
sufficient: there might be additional dependencies that need to be added,
patches to apply, and more generally the quality assurance work that Guix
developers normally do will be missing.

You've been warned! In all the other cases, it's a snappy way to stay on
top.  We encourage you to submit patches updating the actual package
definitions once you have successfully tested an upgrade
(@pxref{贡献}).

@cindex test suite, skipping
@item --without-tests=@var{package}
Build @var{package} without running its tests.  This can be useful in
situations where you want to skip the lengthy test suite of a intermediate
package, or if a package's test suite fails in a non-deterministic fashion.
It should be used with care because running the test suite is a good way to
ensure a package is working as intended.

Turning off tests leads to a different store item.  Consequently, when using
this option, anything that depends on @var{package} must be rebuilt, as in
this example:

@example
guix install --without-tests=python python-notebook
@end example

The command above installs @code{python-notebook} on top of @code{python}
built without running its test suite.  To do so, it also rebuilds everything
that depends on @code{python}, including @code{python-notebook} itself.

Internally, @option{--without-tests} relies on changing the @code{#:tests?}
option of a package's @code{check} phase (@pxref{构建系统}).  Note that
some packages use a customized @code{check} phase that does not respect a
@code{#:tests? #f} setting.  Therefore, @option{--without-tests} has no
effect on these packages.

@end table

Wondering how to achieve the same effect using Scheme code, for example in
your manifest, or how to write your own package transformation?
@xref{定义软件包}, for an overview of the programming
interfaces available.

@node 额外的构建选项
@subsection 额外的构建选项

The command-line options presented below are specific to @command{guix
build}.

@table @code

@item --quiet
@itemx -q
Build quietly, without displaying the build log; this is equivalent to
@option{--verbosity=0}.  Upon completion, the build log is kept in
@file{/var} (or similar) and can always be retrieved using the
@option{--log-file} option.

@item --file=@var{file}
@itemx -f @var{file}
Build the package, derivation, or other file-like object that the code
within @var{file} evaluates to (@pxref{G-表达式, file-like objects}).

As an example, @var{file} might contain a package definition like this
(@pxref{定义软件包}):

@lisp
@include package-hello.scm
@end lisp

The @var{file} may also contain a JSON representation of one or more package
definitions.  Running @code{guix build -f} on @file{hello.json} with the
following contents would result in building the packages @code{myhello} and
@code{greeter}:

@example
@verbatiminclude package-hello.json
@end example

@item --manifest=@var{manifest}
@itemx -m @var{manifest}
Build all packages listed in the given @var{manifest}
(@pxref{profile-manifest, @option{--manifest}}).

@item --expression=@var{expr}
@itemx -e @var{expr}
Build the package or derivation @var{expr} evaluates to.

For example, @var{expr} may be @code{(@@ (gnu packages guile)  guile-1.8)},
which unambiguously designates this specific variant of version 1.8 of
Guile.

Alternatively, @var{expr} may be a G-expression, in which case it is used as
a build program passed to @code{gexp->derivation} (@pxref{G-表达式}).

Lastly, @var{expr} may refer to a zero-argument monadic procedure
(@pxref{仓库monad}).  The procedure must return a derivation as a
monadic value, which is then passed through @code{run-with-store}.

@item --source
@itemx -S
Build the source derivations of the packages, rather than the packages
themselves.

For instance, @code{guix build -S gcc} returns something like
@file{/gnu/store/@dots{}-gcc-4.7.2.tar.bz2}, which is the GCC source
tarball.

The returned source tarball is the result of applying any patches and code
snippets specified in the package @code{origin} (@pxref{定义软件包}).

@cindex source, verification
As with other derivations, the result of building a source derivation can be
verified using the @option{--check} option (@pxref{build-check}).  This is
useful to validate that a (potentially already built or substituted, thus
cached) package source matches against its declared hash.

Note that @command{guix build -S} compiles the sources only of the specified
packages.  They do not include the sources of statically linked dependencies
and by themselves are insufficient for reproducing the packages.

@item --sources
Fetch and return the source of @var{package-or-derivation} and all their
dependencies, recursively.  This is a handy way to obtain a local copy of
all the source code needed to build @var{packages}, allowing you to
eventually build them even without network access.  It is an extension of
the @option{--source} option and can accept one of the following optional
argument values:

@table @code
@item package
This value causes the @option{--sources} option to behave in the same way as
the @option{--source} option.

@item all
Build the source derivations of all packages, including any source that
might be listed as @code{inputs}.  This is the default value.

@example
$ guix build --sources tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzdata2015b.tar.gz.drv
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
@end example

@item transitive
Build the source derivations of all packages, as well of all transitive
inputs to the packages.  This can be used e.g.@: to prefetch package source
for later offline building.

@example
$ guix build --sources=transitive tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
   /gnu/store/@dots{}-findutils-4.4.2.tar.xz.drv
   /gnu/store/@dots{}-grep-2.21.tar.xz.drv
   /gnu/store/@dots{}-coreutils-8.23.tar.xz.drv
   /gnu/store/@dots{}-make-4.1.tar.xz.drv
   /gnu/store/@dots{}-bash-4.3.tar.xz.drv
@dots{}
@end example

@end table

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of the
system type of the build host.  The @command{guix build} command allows you
to repeat this option several times, in which case it builds for all the
specified systems; other commands ignore extraneous @option{-s} options.

@quotation 注
The @option{--system} flag is for @emph{native} compilation and must not be
confused with cross-compilation.  See @option{--target} below for
information on cross-compilation.
@end quotation

An example use of this is on Linux-based systems, which can emulate
different personalities.  For instance, passing @option{--system=i686-linux}
on an @code{x86_64-linux} system or @option{--system=armhf-linux} on an
@code{aarch64-linux} system allows you to build packages in a complete
32-bit environment.

@quotation 注
Building for an @code{armhf-linux} system is unconditionally enabled on
@code{aarch64-linux} machines, although certain aarch64 chipsets do not
allow for this functionality, notably the ThunderX.
@end quotation

Similarly, when transparent emulation with QEMU and @code{binfmt_misc} is
enabled (@pxref{虚拟化服务, @code{qemu-binfmt-service-type}}),
you can build for any system for which a QEMU @code{binfmt_misc} handler is
installed.

Builds for a system other than that of the machine you are using can also be
offloaded to a remote machine of the right architecture.  @xref{下发工作给后台进程的设置}, for more information on offloading.

@item --target=@var{triplet}
@cindex cross-compilation
Cross-build for @var{triplet}, which must be a valid GNU triplet, such as
@code{"aarch64-linux-gnu"} (@pxref{Specifying Target Triplets, GNU
configuration triplets,, autoconf, Autoconf}).

@anchor{build-check}
@item --check
@cindex determinism, checking
@cindex reproducibility, checking
Rebuild @var{package-or-derivation}, which are already available in the
store, and raise an error if the build results are not bit-for-bit
identical.

This mechanism allows you to check whether previously installed substitutes
are genuine (@pxref{substitutes}), or whether the build result of a package
is deterministic.  @xref{调用guix challenge}, for more background
information and tools.

当和@option{--keep-failed}一起使用时，不同的输出保存在@file{/gnu/store/@dots{}-check}。这让检查两个结果的区别更容易。

@item --repair
@cindex repairing store items
@cindex corruption, recovering from
Attempt to repair the specified store items, if they are corrupt, by
re-downloading or rebuilding them.

This operation is not atomic and thus restricted to @code{root}.

@item --derivations
@itemx -d
Return the derivation paths, not the output paths, of the given packages.

@item --root=@var{file}
@itemx -r @var{file}
@cindex GC roots, adding
@cindex garbage collector roots, adding
Make @var{file} a symlink to the result, and register it as a garbage
collector root.

Consequently, the results of this @command{guix build} invocation are
protected from garbage collection until @var{file} is removed.  When that
option is omitted, build results are eligible for garbage collection as soon
as the build completes.  @xref{调用guix gc}, for more on GC roots.

@item --log-file
@cindex build logs, access
Return the build log file names or URLs for the given
@var{package-or-derivation}, or raise an error if build logs are missing.

This works regardless of how packages or derivations are specified.  For
instance, the following invocations are equivalent:

@example
guix build --log-file $(guix build -d guile)
guix build --log-file $(guix build guile)
guix build --log-file guile
guix build --log-file -e '(@@ (gnu packages guile) guile-2.0)'
@end example

If a log is unavailable locally, and unless @option{--no-substitutes} is
passed, the command looks for a corresponding log on one of the substitute
servers (as specified with @option{--substitute-urls}).

So for instance, imagine you want to see the build log of GDB on MIPS, but
you are actually on an @code{x86_64} machine:

@example
$ guix build --log-file gdb -s aarch64-linux
https://@value{SUBSTITUTE-SERVER}/log/@dots{}-gdb-7.10
@end example

You can freely access a huge library of build logs!
@end table

@node 调试构建错误
@subsection 调试构建错误

@cindex build failures, debugging
When defining a new package (@pxref{定义软件包}), you will probably
find yourself spending some time debugging and tweaking the build until it
succeeds.  To do that, you need to operate the build commands yourself in an
environment as close as possible to the one the build daemon uses.

To that end, the first thing to do is to use the @option{--keep-failed} or
@option{-K} option of @command{guix build}, which will keep the failed build
tree in @file{/tmp} or whatever directory you specified as @env{TMPDIR}
(@pxref{普通的构建选项, @option{--keep-failed}}).

From there on, you can @command{cd} to the failed build tree and source the
@file{environment-variables} file, which contains all the environment
variable definitions that were in place when the build failed.  So let's say
you're debugging a build failure in package @code{foo}; a typical session
would look like this:

@example
$ guix build foo -K
@dots{} @i{build fails}
$ cd /tmp/guix-build-foo.drv-0
$ source ./environment-variables
$ cd foo-1.2
@end example

Now, you can invoke commands as if you were the daemon (almost) and
troubleshoot your build process.

Sometimes it happens that, for example, a package's tests pass when you run
them manually but they fail when the daemon runs them.  This can happen
because the daemon runs builds in containers where, unlike in our
environment above, network access is missing, @file{/bin/sh} does not exist,
etc. (@pxref{设置构建环境}).

In such cases, you may need to run inspect the build process from within a
container similar to the one the build daemon creates:

@example
$ guix build -K foo
@dots{}
$ cd /tmp/guix-build-foo.drv-0
$ guix environment --no-grafts -C foo --ad-hoc strace gdb
[env]# source ./environment-variables
[env]# cd foo-1.2
@end example

Here, @command{guix environment -C} creates a container and spawns a new
shell in it (@pxref{调用guix environment}).  The @command{--ad-hoc
strace gdb} part adds the @command{strace} and @command{gdb} commands to the
container, which you may find handy while debugging.  The
@option{--no-grafts} option makes sure we get the exact same environment,
with ungrafted packages (@pxref{安全更新}, for more info on grafts).

To get closer to a container like that used by the build daemon, we can
remove @file{/bin/sh}:

@example
[env]# rm /bin/sh
@end example

(Don't worry, this is harmless: this is all happening in the throw-away
container created by @command{guix environment}.)

The @command{strace} command is probably not in the search path, but we can
run:

@example
[env]# $GUIX_ENVIRONMENT/bin/strace -f -o log make check
@end example

In this way, not only you will have reproduced the environment variables the
daemon uses, you will also be running the build process in a container
similar to the one the daemon uses.


@node 调用guix edit。
@section Invoking @command{guix edit}

@cindex @command{guix edit}
@cindex package definition, editing
So many packages, so many source files! The @command{guix edit} command
facilitates the life of users and packagers by pointing their editor at the
source file containing the definition of the specified packages.  For
instance:

@example
guix edit gcc@@4.9 vim
@end example

@noindent
launches the program specified in the @env{VISUAL} or in the @env{EDITOR}
environment variable to view the recipe of GCC@tie{}4.9.3 and that of Vim.

If you are using a Guix Git checkout (@pxref{从Git构建}), or have
created your own packages on @env{GUIX_PACKAGE_PATH} (@pxref{软件包模块}), you will be able to edit the package recipes.  In other cases,
you will be able to examine the read-only recipes for packages currently in
the store.

Instead of @env{GUIX_PACKAGE_PATH}, the command-line option
@option{--load-path=@var{directory}} (or in short @option{-L
@var{directory}}) allows you to add @var{directory} to the front of the
package module search path and so make your own packages visible.

@node 调用guix download
@section Invoking @command{guix download}

@cindex @command{guix download}
@cindex downloading package sources
When writing a package definition, developers typically need to download a
source tarball, compute its SHA256 hash, and write that hash in the package
definition (@pxref{定义软件包}).  The @command{guix download} tool
helps with this task: it downloads a file from the given URI, adds it to the
store, and prints both its file name in the store and its SHA256 hash.

The fact that the downloaded file is added to the store saves bandwidth:
when the developer eventually tries to build the newly defined package with
@command{guix build}, the source tarball will not have to be downloaded
again because it is already in the store.  It is also a convenient way to
temporarily stash files, which may be deleted eventually (@pxref{调用guix gc}).

The @command{guix download} command supports the same URIs as used in
package definitions.  In particular, it supports @code{mirror://} URIs.
@code{https} URIs (HTTP over TLS) are supported @emph{provided} the Guile
bindings for GnuTLS are available in the user's environment; when they are
not available, an error is raised.  @xref{Guile Preparations, how to install
the GnuTLS bindings for Guile,, gnutls-guile, GnuTLS-Guile}, for more
information.

@command{guix download} verifies HTTPS server certificates by loading the
certificates of X.509 authorities from the directory pointed to by the
@env{SSL_CERT_DIR} environment variable (@pxref{X.509证书}), unless
@option{--no-check-certificate} is used.

The following options are available:

@table @code
@item --hash=@var{algorithm}
@itemx -H @var{algorithm}
Compute a hash using the specified @var{algorithm}.  @xref{调用guix hash}, for more information.

@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.  For more information
on the valid values for @var{fmt}, @pxref{调用guix hash}.

@item --no-check-certificate
Do not validate the X.509 certificates of HTTPS servers.

When using this option, you have @emph{absolutely no guarantee} that you are
communicating with the authentic server responsible for the given URL, which
makes you vulnerable to ``man-in-the-middle'' attacks.

@item --output=@var{file}
@itemx -o @var{file}
Save the downloaded file to @var{file} instead of adding it to the store.
@end table

@node 调用guix hash
@section Invoking @command{guix hash}

@cindex @command{guix hash}
The @command{guix hash} command computes the hash of a file.  It is
primarily a convenience tool for anyone contributing to the distribution: it
computes the cryptographic hash of a file, which can be used in the
definition of a package (@pxref{定义软件包}).

The general syntax is:

@example
guix hash @var{option} @var{file}
@end example

When @var{file} is @code{-} (a hyphen), @command{guix hash} computes the
hash of data read from standard input.  @command{guix hash} has the
following options:

@table @code

@item --hash=@var{algorithm}
@itemx -H @var{algorithm}
Compute a hash using the specified @var{algorithm}, @code{sha256} by
default.

@var{algorithm} must the name of a cryptographic hash algorithm supported by
Libgcrypt @i{via} Guile-Gcrypt---e.g., @code{sha512} or @code{sha3-256}
(@pxref{Hash Functions,,, guile-gcrypt, Guile-Gcrypt Reference Manual}).

@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.

Supported formats: @code{base64}, @code{nix-base32}, @code{base32},
@code{base16} (@code{hex} and @code{hexadecimal} can be used as well).

If the @option{--format} option is not specified, @command{guix hash} will
output the hash in @code{nix-base32}.  This representation is used in the
definitions of packages.

@item --recursive
@itemx -r
Compute the hash on @var{file} recursively.

@c FIXME: Replace xref above with xref to an ``Archive'' section when
@c it exists.
In this case, the hash is computed on an archive containing @var{file},
including its children if it is a directory.  Some of the metadata of
@var{file} is part of the archive; for instance, when @var{file} is a
regular file, the hash is different depending on whether @var{file} is
executable or not.  Metadata such as time stamps has no impact on the hash
(@pxref{调用guix archive}).

@item --exclude-vcs
@itemx -x
When combined with @option{--recursive}, exclude version control system
directories (@file{.bzr}, @file{.git}, @file{.hg}, etc.).

@vindex git-fetch
As an example, here is how you would compute the hash of a Git checkout,
which is useful when using the @code{git-fetch} method (@pxref{origin参考手册}):

@example
$ git clone http://example.org/foo.git
$ cd foo
$ guix hash -rx .
@end example
@end table

@node 调用guix import
@section Invoking @command{guix import}

@cindex importing packages
@cindex package import
@cindex package conversion
@cindex Invoking @command{guix import}
The @command{guix import} command is useful for people who would like to add
a package to the distribution with as little work as possible---a legitimate
demand.  The command knows of a few repositories from which it can
``import'' package metadata.  The result is a package definition, or a
template thereof, in the format we know (@pxref{定义软件包}).

The general syntax is:

@example
guix import @var{importer} @var{options}@dots{}
@end example

@var{importer} specifies the source from which to import package metadata,
and @var{options} specifies a package identifier and other options specific
to @var{importer}.

Some of the importers rely on the ability to run the @command{gpgv}
command.  For these, GnuPG must be installed and in @code{$PATH}; run
@code{guix install gnupg} if needed.

Currently, the available ``importers'' are:

@table @code
@item gnu
Import metadata for the given GNU package.  This provides a template for the
latest version of that GNU package, including the hash of its source
tarball, and its canonical synopsis and description.

Additional information such as the package dependencies and its license
needs to be figured out manually.

For example, the following command returns a package definition for
GNU@tie{}Hello:

@example
guix import gnu hello
@end example

Specific command-line options are:

@table @code
@item --key-download=@var{policy}
As for @command{guix refresh}, specify the policy to handle missing OpenPGP
keys when verifying the package signature.  @xref{调用guix refresh,
@option{--key-download}}.
@end table

@item pypi
@cindex pypi
Import metadata from the @uref{https://pypi.python.org/, Python Package
Index}.  Information is taken from the JSON-formatted description available
at @code{pypi.python.org} and usually includes all the relevant information,
including package dependencies.  For maximum efficiency, it is recommended
to install the @command{unzip} utility, so that the importer can unzip
Python wheels and gather data from them.

The command below imports metadata for the @code{itsdangerous} Python
package:

@example
guix import pypi itsdangerous
@end example

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

@item gem
@cindex gem
Import metadata from @uref{https://rubygems.org/, RubyGems}.  Information is
taken from the JSON-formatted description available at @code{rubygems.org}
and includes most relevant information, including runtime dependencies.
There are some caveats, however.  The metadata doesn't distinguish between
synopses and descriptions, so the same string is used for both fields.
Additionally, the details of non-Ruby dependencies required to build native
extensions is unavailable and left as an exercise to the packager.

The command below imports metadata for the @code{rails} Ruby package:

@example
guix import gem rails
@end example

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

@item cpan
@cindex CPAN
Import metadata from @uref{https://www.metacpan.org/, MetaCPAN}.
Information is taken from the JSON-formatted metadata provided through
@uref{https://fastapi.metacpan.org/, MetaCPAN's API} and includes most
relevant information, such as module dependencies.  License information
should be checked closely.  If Perl is available in the store, then the
@code{corelist} utility will be used to filter core modules out of the list
of dependencies.

The command command below imports metadata for the Acme::Boolean Perl
module:

@example
guix import cpan Acme::Boolean
@end example

@item cran
@cindex CRAN
@cindex Bioconductor
Import metadata from @uref{https://cran.r-project.org/, CRAN}, the central
repository for the @uref{https://r-project.org, GNU@tie{}R statistical and
graphical environment}.

Information is extracted from the @file{DESCRIPTION} file of the package.

The command command below imports metadata for the Cairo R package:

@example
guix import cran Cairo
@end example

When @option{--recursive} is added, the importer will traverse the
dependency graph of the given upstream package recursively and generate
package expressions for all those packages that are not yet in Guix.

When @option{--style=specification} is added, the importer will generate
package definitions whose inputs are package specifications instead of
references to package variables.  This is useful when generated package
definitions are to be appended to existing user modules, as the list of used
package modules need not be changed.  The default is
@option{--style=variable}.

When @option{--archive=bioconductor} is added, metadata is imported from
@uref{https://www.bioconductor.org/, Bioconductor}, a repository of R
packages for the analysis and comprehension of high-throughput genomic data
in bioinformatics.

Information is extracted from the @file{DESCRIPTION} file contained in the
package archive.

The command below imports metadata for the GenomicRanges R package:

@example
guix import cran --archive=bioconductor GenomicRanges
@end example

Finally, you can also import R packages that have not yet been published on
CRAN or Bioconductor as long as they are in a git repository.  Use
@option{--archive=git} followed by the URL of the git repository:

@example
guix import cran --archive=git https://github.com/immunogenomics/harmony
@end example

@item texlive
@cindex TeX Live
@cindex CTAN
Import metadata from @uref{https://www.ctan.org/, CTAN}, the comprehensive
TeX archive network for TeX packages that are part of the
@uref{https://www.tug.org/texlive/, TeX Live distribution}.

Information about the package is obtained through the XML API provided by
CTAN, while the source code is downloaded from the SVN repository of the Tex
Live project.  This is done because the CTAN does not keep versioned
archives.

The command command below imports metadata for the @code{fontspec} TeX
package:

@example
guix import texlive fontspec
@end example

When @option{--archive=@var{directory}} is added, the source code is
downloaded not from the @file{latex} sub-directory of the
@file{texmf-dist/source} tree in the TeX Live SVN repository, but from the
specified sibling @var{directory} under the same root.

The command below imports metadata for the @code{ifxetex} package from CTAN
while fetching the sources from the directory @file{texmf/source/generic}:

@example
guix import texlive --archive=generic ifxetex
@end example

@item json
@cindex JSON, import
Import package metadata from a local JSON file.  Consider the following
example package definition in JSON format:

@example
@{
  "name": "hello",
  "version": "2.10",
  "source": "mirror://gnu/hello/hello-2.10.tar.gz",
  "build-system": "gnu",
  "home-page": "https://www.gnu.org/software/hello/",
  "synopsis": "Hello, GNU world: An example GNU package",
  "description": "GNU Hello prints a greeting.",
  "license": "GPL-3.0+",
  "native-inputs": ["gettext"]
@}
@end example

The field names are the same as for the @code{<package>} record
(@xref{定义软件包}).  References to other packages are provided as
JSON lists of quoted package specification strings such as @code{guile} or
@code{guile@@2.0}.

The importer also supports a more explicit source definition using the
common fields for @code{<origin>} records:

@example
@{
  @dots{}
  "source": @{
    "method": "url-fetch",
    "uri": "mirror://gnu/hello/hello-2.10.tar.gz",
    "sha256": @{
      "base32": "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"
    @}
  @}
  @dots{}
@}
@end example

The command below reads metadata from the JSON file @code{hello.json} and
outputs a package expression:

@example
guix import json hello.json
@end example

@item hackage
@cindex hackage
Import metadata from the Haskell community's central package archive
@uref{https://hackage.haskell.org/, Hackage}.  Information is taken from
Cabal files and includes all the relevant information, including package
dependencies.

Specific command-line options are:

@table @code
@item --stdin
@itemx -s
Read a Cabal file from standard input.
@item --no-test-dependencies
@itemx -t
Do not include dependencies required only by the test suites.
@item --cabal-environment=@var{alist}
@itemx -e @var{alist}
@var{alist} is a Scheme alist defining the environment in which the Cabal
conditionals are evaluated.  The accepted keys are: @code{os}, @code{arch},
@code{impl} and a string representing the name of a flag.  The value
associated with a flag has to be either the symbol @code{true} or
@code{false}.  The value associated with other keys has to conform to the
Cabal file format definition.  The default value associated with the keys
@code{os}, @code{arch} and @code{impl} is @samp{linux}, @samp{x86_64} and
@samp{ghc}, respectively.
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

The command below imports metadata for the latest version of the HTTP
Haskell package without including test dependencies and specifying the value
of the flag @samp{network-uri} as @code{false}:

@example
guix import hackage -t -e "'((\"network-uri\" . false))" HTTP
@end example

A specific package version may optionally be specified by following the
package name by an at-sign and a version number as in the following example:

@example
guix import hackage mtl@@2.1.3.1
@end example

@item stackage
@cindex stackage
The @code{stackage} importer is a wrapper around the @code{hackage} one.  It
takes a package name, looks up the package version included in a long-term
support (LTS) @uref{https://www.stackage.org, Stackage} release and uses the
@code{hackage} importer to retrieve its metadata.  Note that it is up to you
to select an LTS release compatible with the GHC compiler used by Guix.

Specific command-line options are:

@table @code
@item --no-test-dependencies
@itemx -t
Do not include dependencies required only by the test suites.
@item --lts-version=@var{version}
@itemx -l @var{version}
@var{version} is the desired LTS release version.  If omitted the latest
release is used.
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

The command below imports metadata for the HTTP Haskell package included in
the LTS Stackage release version 7.18:

@example
guix import stackage --lts-version=7.18 HTTP
@end example

@item elpa
@cindex elpa
Import metadata from an Emacs Lisp Package Archive (ELPA) package repository
(@pxref{Packages,,, emacs, The GNU Emacs Manual}).

Specific command-line options are:

@table @code
@item --archive=@var{repo}
@itemx -a @var{repo}
@var{repo} identifies the archive repository from which to retrieve the
information.  Currently the supported repositories and their identifiers
are:
@itemize -
@item
@uref{https://elpa.gnu.org/packages, GNU}, selected by the @code{gnu}
identifier.  This is the default.

Packages from @code{elpa.gnu.org} are signed with one of the keys contained
in the GnuPG keyring at @file{share/emacs/25.1/etc/package-keyring.gpg} (or
similar) in the @code{emacs} package (@pxref{Package Installation, ELPA
package signatures,, emacs, The GNU Emacs Manual}).

@item
@uref{https://stable.melpa.org/packages, MELPA-Stable}, selected by the
@code{melpa-stable} identifier.

@item
@uref{https://melpa.org/packages, MELPA}, selected by the @code{melpa}
identifier.
@end itemize

@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

@item crate
@cindex crate
Import metadata from the crates.io Rust package repository
@uref{https://crates.io, crates.io}, as in this example:

@example
guix import crate blake2-rfc
@end example

The crate importer also allows you to specify a version string:

@example
guix import crate constant-time-eq@@0.1.0
@end example

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@end table

@item opam
@cindex OPAM
@cindex OCaml
Import metadata from the @uref{https://opam.ocaml.org/, OPAM} package
repository used by the OCaml community.

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@item --repo
Select the given repository (a repository name).  Possible values include:
@itemize
@item @code{opam}, the default opam repository,
@item @code{coq} or @code{coq-released}, the stable repository for coq packages,
@item @code{coq-core-dev}, the repository that contains development versions of coq,
@item @code{coq-extra-dev}, the repository that contains development versions
      of coq packages.
@end itemize
@end table

@item go
@cindex go
Import metadata for a Go module using @uref{https://proxy.golang.org,
proxy.golang.org}.

@example
guix import go gopkg.in/yaml.v2
@end example

It is possible to use a package specification with a @code{@@VERSION} suffix
to import a specific version.

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively and
generate package expressions for all those packages that are not yet in
Guix.
@item --pin-versions
When using this option, the importer preserves the exact versions of the Go
modules dependencies instead of using their latest available versions.  This
can be useful when attempting to import packages that recursively depend on
former versions of themselves to build.  When using this mode, the symbol of
the package is made by appending the version to its name, so that multiple
versions of the same package can coexist.
@end table
@end table

The structure of the @command{guix import} code is modular.  It would be
useful to have more importers for other package formats, and your help is
welcome here (@pxref{贡献}).

@node 调用guix refresh
@section Invoking @command{guix refresh}

@cindex @command{guix refresh}
The primary audience of the @command{guix refresh} command is packagers.  As
a user, you may be interested in the @option{--with-latest} option, which
can bring you package update superpowers built upon @command{guix refresh}
(@pxref{软件包变换选项。, @option{--with-latest}}).  By
default, @command{guix refresh} reports any packages provided by the
distribution that are outdated compared to the latest upstream version, like
this:

@example
$ guix refresh
gnu/packages/gettext.scm:29:13: gettext would be upgraded from 0.18.1.1 to 0.18.2.1
gnu/packages/glib.scm:77:12: glib would be upgraded from 2.34.3 to 2.37.0
@end example

Alternatively, one can specify packages to consider, in which case a warning
is emitted for packages that lack an updater:

@example
$ guix refresh coreutils guile guile-ssh
gnu/packages/ssh.scm:205:2: warning: no updater for guile-ssh
gnu/packages/guile.scm:136:12: guile would be upgraded from 2.0.12 to 2.0.13
@end example

@command{guix refresh} browses the upstream repository of each package and
determines the highest version number of the releases therein.  The command
knows how to update specific types of packages: GNU packages, ELPA packages,
etc.---see the documentation for @option{--type} below.  There are many
packages, though, for which it lacks a method to determine whether a new
upstream release is available.  However, the mechanism is extensible, so
feel free to get in touch with us to add a new method!

@table @code

@item --recursive
Consider the packages specified, and all the packages upon which they
depend.

@example
$ guix refresh --recursive coreutils
gnu/packages/acl.scm:40:13: acl would be upgraded from 2.2.53 to 2.3.1
gnu/packages/m4.scm:30:12: 1.4.18 is already the latest version of m4
gnu/packages/xml.scm:68:2: warning: no updater for expat
gnu/packages/multiprecision.scm:40:12: 6.1.2 is already the latest version of gmp
@dots{}
@end example

@end table

Sometimes the upstream name differs from the package name used in Guix, and
@command{guix refresh} needs a little help.  Most updaters honor the
@code{upstream-name} property in package definitions, which can be used to
that effect:

@lisp
(define-public network-manager
  (package
    (name "network-manager")
    ;; @dots{}
    (properties '((upstream-name . "NetworkManager")))))
@end lisp

When passed @option{--update}, it modifies distribution source files to
update the version numbers and source tarball hashes of those package
recipes (@pxref{定义软件包}).  This is achieved by downloading each
package's latest source tarball and its associated OpenPGP signature,
authenticating the downloaded tarball against its signature using
@command{gpgv}, and finally computing its hash---note that GnuPG must be
installed and in @code{$PATH}; run @code{guix install gnupg} if needed.

When the public key used to sign the tarball is missing from the user's
keyring, an attempt is made to automatically retrieve it from a public key
server; when this is successful, the key is added to the user's keyring;
otherwise, @command{guix refresh} reports an error.

The following options are supported:

@table @code

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to precisely refer to a package, as in this example:

@example
guix refresh -l -e '(@@@@ (gnu packages commencement) glibc-final)'
@end example

This command lists the dependents of the ``final'' libc (essentially all the
packages).

@item --update
@itemx -u
Update distribution source files (package recipes) in place.  This is
usually run from a checkout of the Guix source tree (@pxref{在安装之前运行Guix}):

@example
$ ./pre-inst-env guix refresh -s non-core -u
@end example

@xref{定义软件包}, for more information on package definitions.

@item --select=[@var{subset}]
@itemx -s @var{subset}
Select all the packages in @var{subset}, one of @code{core} or
@code{non-core}.

The @code{core} subset refers to all the packages at the core of the
distribution---i.e., packages that are used to build ``everything else''.
This includes GCC, libc, Binutils, Bash, etc.  Usually, changing one of
these packages in the distribution entails a rebuild of all the others.
Thus, such updates are an inconvenience to users in terms of build time or
bandwidth used to achieve the upgrade.

The @code{non-core} subset refers to the remaining packages.  It is
typically useful in cases where an update of the core packages would be
inconvenient.

@item --manifest=@var{file}
@itemx -m @var{file}
Select all the packages from the manifest in @var{file}.  This is useful to
check if any packages of the user manifest can be updated.

@item --type=@var{updater}
@itemx -t @var{updater}
Select only packages handled by @var{updater} (may be a comma-separated list
of updaters).  Currently, @var{updater} may be one of:

@table @code
@item gnu
the updater for GNU packages;
@item savannah
the updater for packages hosted at @uref{https://savannah.gnu.org,
Savannah};
@item sourceforge
the updater for packages hosted at @uref{https://sourceforge.net,
SourceForge};
@item gnome
the updater for GNOME packages;
@item kde
the updater for KDE packages;
@item xorg
the updater for X.org packages;
@item kernel.org
the updater for packages hosted on kernel.org;
@item elpa
the updater for @uref{https://elpa.gnu.org/, ELPA} packages;
@item cran
the updater for @uref{https://cran.r-project.org/, CRAN} packages;
@item bioconductor
the updater for @uref{https://www.bioconductor.org/, Bioconductor} R
packages;
@item cpan
the updater for @uref{https://www.cpan.org/, CPAN} packages;
@item pypi
the updater for @uref{https://pypi.python.org, PyPI} packages.
@item gem
the updater for @uref{https://rubygems.org, RubyGems} packages.
@item github
the updater for @uref{https://github.com, GitHub} packages.
@item hackage
the updater for @uref{https://hackage.haskell.org, Hackage} packages.
@item stackage
the updater for @uref{https://www.stackage.org, Stackage} packages.
@item crate
the updater for @uref{https://crates.io, Crates} packages.
@item launchpad
the updater for @uref{https://launchpad.net, Launchpad} packages.
@item generic-html
a generic updater that crawls the HTML page where the source tarball of the
package is hosted, when applicable.
@end table

For instance, the following command only checks for updates of Emacs
packages hosted at @code{elpa.gnu.org} and for updates of CRAN packages:

@example
$ guix refresh --type=elpa,cran
gnu/packages/statistics.scm:819:13: r-testthat would be upgraded from 0.10.0 to 0.11.0
gnu/packages/emacs.scm:856:13: emacs-auctex would be upgraded from 11.88.6 to 11.88.9
@end example

@item --list-updaters
@itemx -L
List available updaters and exit (see @option{--type} above).

For each updater, display the fraction of packages it covers; at the end,
display the fraction of packages covered by all these updaters.
@end table

In addition, @command{guix refresh} can be passed one or more package names,
as in this example:

@example
$ ./pre-inst-env guix refresh -u emacs idutils gcc@@4.8
@end example

@noindent
The command above specifically updates the @code{emacs} and @code{idutils}
packages.  The @option{--select} option would have no effect in this case.
You might also want to update definitions that correspond to the packages
installed in your profile:

@example
$ ./pre-inst-env guix refresh -u \
       $(guix package --list-installed | cut -f1)
@end example

When considering whether to upgrade a package, it is sometimes convenient to
know which packages would be affected by the upgrade and should be checked
for compatibility.  For this the following option may be used when passing
@command{guix refresh} one or more package names:

@table @code

@item --list-dependent
@itemx -l
List top-level dependent packages that would need to be rebuilt as a result
of upgrading one or more packages.

@xref{调用guix graph, the @code{reverse-package} type of @command{guix
graph}}, for information on how to visualize the list of dependents of a
package.

@end table

Be aware that the @option{--list-dependent} option only @emph{approximates}
the rebuilds that would be required as a result of an upgrade.  More
rebuilds might be required under some circumstances.

@example
$ guix refresh --list-dependent flex
Building the following 120 packages would ensure 213 dependent packages are rebuilt:
hop@@2.4.0 geiser@@0.4 notmuch@@0.18 mu@@0.9.9.5 cflow@@1.4 idutils@@4.6 @dots{}
@end example

The command above lists a set of packages that could be built to check for
compatibility with an upgraded @code{flex} package.

@table @code

@item --list-transitive
List all the packages which one or more packages depend upon.

@example
$ guix refresh --list-transitive flex
flex@@2.6.4 depends on the following 25 packages: perl@@5.28.0 help2man@@1.47.6
bison@@3.0.5 indent@@2.2.10 tar@@1.30 gzip@@1.9 bzip2@@1.0.6 xz@@5.2.4 file@@5.33 @dots{}
@end example

@end table

The command above lists a set of packages which, when changed, would cause
@code{flex} to be rebuilt.

The following options can be used to customize GnuPG operation:

@table @code

@item --gpg=@var{command}
Use @var{command} as the GnuPG 2.x command.  @var{command} is searched for
in @code{$PATH}.

@item --keyring=@var{file}
Use @var{file} as the keyring for upstream keys.  @var{file} must be in the
@dfn{keybox format}.  Keybox files usually have a name ending in @file{.kbx}
and the GNU@tie{}Privacy Guard (GPG) can manipulate these files
(@pxref{kbxutil, @command{kbxutil},, gnupg, Using the GNU Privacy Guard},
for information on a tool to manipulate keybox files).

When this option is omitted, @command{guix refresh} uses
@file{~/.config/guix/upstream/trustedkeys.kbx} as the keyring for upstream
signing keys.  OpenPGP signatures are checked against keys from this
keyring; missing keys are downloaded to this keyring as well (see
@option{--key-download} below).

You can export keys from your default GPG keyring into a keybox file using
commands like this one:

@example
gpg --export rms@@gnu.org | kbxutil --import-openpgp >> mykeyring.kbx
@end example

Likewise, you can fetch keys to a specific keybox file like this:

@example
gpg --no-default-keyring --keyring mykeyring.kbx \
  --recv-keys @value{OPENPGP-SIGNING-KEY-ID}
@end example

@xref{GPG Configuration Options, @option{--keyring},, gnupg, Using the GNU
Privacy Guard}, for more information on GPG's @option{--keyring} option.

@item --key-download=@var{policy}
Handle missing OpenPGP keys according to @var{policy}, which may be one of:

@table @code
@item always
Always download missing OpenPGP keys from the key server, and add them to
the user's GnuPG keyring.

@item never
Never try to download missing OpenPGP keys.  Instead just bail out.

@item interactive
When a package signed with an unknown OpenPGP key is encountered, ask the
user whether to download it or not.  This is the default behavior.
@end table

@item --key-server=@var{host}
Use @var{host} as the OpenPGP key server when importing a public key.

@item --load-path=@var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{软件包模块}).

This allows users to define their own packages and make them visible to the
command-line tools.

@end table

The @code{github} updater uses the @uref{https://developer.github.com/v3/,
GitHub API} to query for new releases.  When used repeatedly e.g.@: when
refreshing all packages, GitHub will eventually refuse to answer any further
API requests.  By default 60 API requests per hour are allowed, and a full
refresh on all GitHub packages in Guix requires more than this.
Authentication with GitHub through the use of an API token alleviates these
limits.  To use an API token, set the environment variable
@env{GUIX_GITHUB_TOKEN} to a token procured from
@uref{https://github.com/settings/tokens} or otherwise.


@node 调用guix lint
@section Invoking @command{guix lint}

@cindex @command{guix lint}
@cindex package, checking for errors
The @command{guix lint} command is meant to help package developers avoid
common errors and use a consistent style.  It runs a number of checks on a
given set of packages in order to find common mistakes in their
definitions.  Available @dfn{checkers} include (see @option{--list-checkers}
for a complete list):

@table @code
@item synopsis
@itemx description
Validate certain typographical and stylistic rules about package
descriptions and synopses.

@item inputs-should-be-native
Identify inputs that should most likely be native inputs.

@item source
@itemx home-page
@itemx mirror-url
@itemx github-url
@itemx source-file-name
Probe @code{home-page} and @code{source} URLs and report those that are
invalid.  Suggest a @code{mirror://} URL when applicable.  If the
@code{source} URL redirects to a GitHub URL, recommend usage of the GitHub
URL@.  Check that the source file name is meaningful, e.g.@: is not just a
version number or ``git-checkout'', without a declared @code{file-name}
(@pxref{origin参考手册}).

@item source-unstable-tarball
Parse the @code{source} URL to determine if a tarball from GitHub is
autogenerated or if it is a release tarball.  Unfortunately GitHub's
autogenerated tarballs are sometimes regenerated.

@item derivation
Check that the derivation of the given packages can be successfully computed
for all the supported systems (@pxref{Derivations}).

@item profile-collisions
Check whether installing the given packages in a profile would lead to
collisions.  Collisions occur when several packages with the same name but a
different version or a different store file name are propagated.
@xref{软件包引用, @code{propagated-inputs}}, for more information on
propagated inputs.

@item archival
@cindex Software Heritage, source code archive
@cindex archival of source code, Software Heritage
Checks whether the package's source code is archived at
@uref{https://www.softwareheritage.org, Software Heritage}.

When the source code that is not archived comes from a version-control
system (VCS)---e.g., it's obtained with @code{git-fetch}, send Software
Heritage a ``save'' request so that it eventually archives it.  This ensures
that the source will remain available in the long term, and that Guix can
fall back to Software Heritage should the source code disappear from its
original host.  The status of recent ``save'' requests can be
@uref{https://archive.softwareheritage.org/save/#requests, viewed on-line}.

When source code is a tarball obtained with @code{url-fetch}, simply print a
message when it is not archived.  As of this writing, Software Heritage does
not allow requests to save arbitrary tarballs; we are working on ways to
ensure that non-VCS source code is also archived.

Software Heritage
@uref{https://archive.softwareheritage.org/api/#rate-limiting, limits the
request rate per IP address}.  When the limit is reached, @command{guix
lint} prints a message and the @code{archival} checker stops doing anything
until that limit has been reset.

@item cve
@cindex security vulnerabilities
@cindex CVE, Common Vulnerabilities and Exposures
Report known vulnerabilities found in the Common Vulnerabilities and
Exposures (CVE) databases of the current and past year
@uref{https://nvd.nist.gov/vuln/data-feeds, published by the US NIST}.

To view information about a particular vulnerability, visit pages such as:

@itemize
@item
@indicateurl{https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-YYYY-ABCD}
@item
@indicateurl{https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-YYYY-ABCD}
@end itemize

@noindent
where @code{CVE-YYYY-ABCD} is the CVE identifier---e.g.,
@code{CVE-2015-7554}.

Package developers can specify in package recipes the
@uref{https://nvd.nist.gov/products/cpe,Common Platform Enumeration (CPE)}
name and version of the package when they differ from the name or version
that Guix uses, as in this example:

@lisp
(package
  (name "grub")
  ;; @dots{}
  ;; CPE calls this package "grub2".
  (properties '((cpe-name . "grub2")
                (cpe-version . "2.3"))))
@end lisp

@c See <https://www.openwall.com/lists/oss-security/2017/03/15/3>.
Some entries in the CVE database do not specify which version of a package
they apply to, and would thus ``stick around'' forever.  Package developers
who found CVE alerts and verified they can be ignored can declare them as in
this example:

@lisp
(package
  (name "t1lib")
  ;; @dots{}
  ;; These CVEs no longer apply and can be safely ignored.
  (properties `((lint-hidden-cve . ("CVE-2011-0433"
                                    "CVE-2011-1553"
                                    "CVE-2011-1554"
                                    "CVE-2011-5244")))))
@end lisp

@item formatting
Warn about obvious source code formatting issues: trailing white space, use
of tabulations, etc.
@end table

The general syntax is:

@example
guix lint @var{options} @var{package}@dots{}
@end example

If no package is given on the command line, then all packages are checked.
The @var{options} may be zero or more of the following:

@table @code
@item --list-checkers
@itemx -l
List and describe all the available checkers that will be run on packages
and exit.

@item --checkers
@itemx -c
Only enable the checkers specified in a comma-separated list using the names
returned by @option{--list-checkers}.

@item --exclude
@itemx -x
Only disable the checkers specified in a comma-separated list using the
names returned by @option{--list-checkers}.

@item --no-network
@itemx -n
Only enable the checkers that do not depend on Internet access.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{软件包模块}).

This allows users to define their own packages and make them visible to the
command-line tools.

@end table

@node 调用guix size
@section Invoking @command{guix size}

@cindex size
@cindex package size
@cindex closure
@cindex @command{guix size}
The @command{guix size} command helps package developers profile the disk
usage of packages.  It is easy to overlook the impact of an additional
dependency added to a package, or the impact of using a single output for a
package that could easily be split (@pxref{有多个输出的软件包}).  Such are the typical issues that @command{guix size} can
highlight.

The command can be passed one or more package specifications such as
@code{gcc@@4.8} or @code{guile:debug}, or a file name in the store.
Consider this example:

@example
$ guix size coreutils
store item                               total    self
/gnu/store/@dots{}-gcc-5.5.0-lib           60.4    30.1  38.1%
/gnu/store/@dots{}-glibc-2.27              30.3    28.8  36.6%
/gnu/store/@dots{}-coreutils-8.28          78.9    15.0  19.0%
/gnu/store/@dots{}-gmp-6.1.2               63.1     2.7   3.4%
/gnu/store/@dots{}-bash-static-4.4.12       1.5     1.5   1.9%
/gnu/store/@dots{}-acl-2.2.52              61.1     0.4   0.5%
/gnu/store/@dots{}-attr-2.4.47             60.6     0.2   0.3%
/gnu/store/@dots{}-libcap-2.25             60.5     0.2   0.2%
total: 78.9 MiB
@end example

@cindex closure
The store items listed here constitute the @dfn{transitive closure} of
Coreutils---i.e., Coreutils and all its dependencies, recursively---as would
be returned by:

@example
$ guix gc -R /gnu/store/@dots{}-coreutils-8.23
@end example

Here the output shows three columns next to store items.  The first column,
labeled ``total'', shows the size in mebibytes (MiB) of the closure of the
store item---that is, its own size plus the size of all its dependencies.
The next column, labeled ``self'', shows the size of the item itself.  The
last column shows the ratio of the size of the item itself to the space
occupied by all the items listed here.

In this example, we see that the closure of Coreutils weighs in at
79@tie{}MiB, most of which is taken by libc and GCC's run-time support
libraries.  (That libc and GCC's libraries represent a large fraction of the
closure is not a problem @i{per se} because they are always available on the
system anyway.)

Since the command also accepts store file names, assessing the size of a
build result is straightforward:

@example
guix size $(guix system build config.scm)
@end example

When the package(s) passed to @command{guix size} are available in the
store@footnote{More precisely, @command{guix size} looks for the
@emph{ungrafted} variant of the given package(s), as returned by @code{guix
build @var{package} --no-grafts}.  @xref{安全更新}, for information
on grafts.}, @command{guix size} queries the daemon to determine its
dependencies, and measures its size in the store, similar to @command{du -ms
--apparent-size} (@pxref{du invocation,,, coreutils, GNU Coreutils}).

When the given packages are @emph{not} in the store, @command{guix size}
reports information based on the available substitutes
(@pxref{substitutes}).  This makes it possible it to profile disk usage of
store items that are not even on disk, only available remotely.

You can also specify several package names:

@example
$ guix size coreutils grep sed bash
store item                               total    self
/gnu/store/@dots{}-coreutils-8.24          77.8    13.8  13.4%
/gnu/store/@dots{}-grep-2.22               73.1     0.8   0.8%
/gnu/store/@dots{}-bash-4.3.42             72.3     4.7   4.6%
/gnu/store/@dots{}-readline-6.3            67.6     1.2   1.2%
@dots{}
total: 102.3 MiB
@end example

@noindent
In this example we see that the combination of the four packages takes
102.3@tie{}MiB in total, which is much less than the sum of each closure
since they have a lot of dependencies in common.

When looking at the profile returned by @command{guix size}, you may find
yourself wondering why a given package shows up in the profile at all.  To
understand it, you can use @command{guix graph --path -t references} to
display the shortest path between the two packages (@pxref{调用guix graph}).

The available options are:

@table @option

@item --substitute-urls=@var{urls}
Use substitute information from @var{urls}.  @xref{client-substitute-urls,
the same option for @code{guix build}}.

@item --sort=@var{key}
Sort lines according to @var{key}, one of the following options:

@table @code
@item self
the size of each item (the default);
@item closure
the total size of the item's closure.
@end table

@item --map-file=@var{file}
Write a graphical map of disk usage in PNG format to @var{file}.

For the example above, the map looks like this:

@image{images/coreutils-size-map,5in,, map of Coreutils disk usage produced
by @command{guix size}}

This option requires that
@uref{https://wingolog.org/software/guile-charting/, Guile-Charting} be
installed and visible in Guile's module search path.  When that is not the
case, @command{guix size} fails as it tries to load it.

@item --system=@var{system}
@itemx -s @var{system}
Consider packages for @var{system}---e.g., @code{x86_64-linux}.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{软件包模块}).

This allows users to define their own packages and make them visible to the
command-line tools.
@end table

@node 调用guix graph
@section Invoking @command{guix graph}

@cindex DAG
@cindex @command{guix graph}
@cindex package dependencies
Packages and their dependencies form a @dfn{graph}, specifically a directed
acyclic graph (DAG).  It can quickly become difficult to have a mental model
of the package DAG, so the @command{guix graph} command provides a visual
representation of the DAG@.  By default, @command{guix graph} emits a DAG
representation in the input format of @uref{https://www.graphviz.org/,
Graphviz}, so its output can be passed directly to the @command{dot} command
of Graphviz.  It can also emit an HTML page with embedded JavaScript code to
display a ``chord diagram'' in a Web browser, using the
@uref{https://d3js.org/, d3.js} library, or emit Cypher queries to construct
a graph in a graph database supporting the
@uref{https://www.opencypher.org/, openCypher} query language.  With
@option{--path}, it simply displays the shortest path between two packages.
The general syntax is:

@example
guix graph @var{options} @var{package}@dots{}
@end example

For example, the following command generates a PDF file representing the
package DAG for the GNU@tie{}Core Utilities, showing its build-time
dependencies:

@example
guix graph coreutils | dot -Tpdf > dag.pdf
@end example

The output looks like this:

@image{images/coreutils-graph,2in,,Dependency graph of the GNU Coreutils}

Nice little graph, no?

You may find it more pleasant to navigate the graph interactively with
@command{xdot} (from the @code{xdot} package):

@example
guix graph coreutils | xdot -
@end example

But there is more than one graph! The one above is concise: it is the graph
of package objects, omitting implicit inputs such as GCC, libc, grep, etc.
It is often useful to have such a concise graph, but sometimes one may want
to see more details.  @command{guix graph} supports several types of graphs,
allowing you to choose the level of detail:

@table @code
@item package
This is the default type used in the example above.  It shows the DAG of
package objects, excluding implicit dependencies.  It is concise, but
filters out many details.

@item reverse-package
This shows the @emph{reverse} DAG of packages.  For example:

@example
guix graph --type=reverse-package ocaml
@end example

...@: yields the graph of packages that @emph{explicitly} depend on OCaml
(if you are also interested in cases where OCaml is an implicit dependency,
see @code{reverse-bag} below).

Note that for core packages this can yield huge graphs.  If all you want is
to know the number of packages that depend on a given package, use
@command{guix refresh --list-dependent} (@pxref{调用guix refresh,
@option{--list-dependent}}).

@item bag-emerged
This is the package DAG, @emph{including} implicit inputs.

For instance, the following command:

@example
guix graph --type=bag-emerged coreutils
@end example

...@: yields this bigger graph:

@image{images/coreutils-bag-graph,,5in,Detailed dependency graph of the GNU
Coreutils}

At the bottom of the graph, we see all the implicit inputs of
@var{gnu-build-system} (@pxref{构建系统, @code{gnu-build-system}}).

Now, note that the dependencies of these implicit inputs---that is, the
@dfn{bootstrap dependencies} (@pxref{引导})---are not shown here,
for conciseness.

@item bag
Similar to @code{bag-emerged}, but this time including all the bootstrap
dependencies.

@item bag-with-origins
Similar to @code{bag}, but also showing origins and their dependencies.

@item reverse-bag
This shows the @emph{reverse} DAG of packages.  Unlike
@code{reverse-package}, it also takes implicit dependencies into account.
For example:

@example
guix graph -t reverse-bag dune
@end example

@noindent
...@: yields the graph of all packages that depend on Dune, directly or
indirectly.  Since Dune is an @emph{implicit} dependency of many packages
@i{via} @code{dune-build-system}, this shows a large number of packages,
whereas @code{reverse-package} would show very few if any.

@item derivation
This is the most detailed representation: It shows the DAG of derivations
(@pxref{Derivations}) and plain store items.  Compared to the above
representation, many additional nodes are visible, including build scripts,
patches, Guile modules, etc.

For this type of graph, it is also possible to pass a @file{.drv} file name
instead of a package name, as in:

@example
guix graph -t derivation $(guix system build -d my-config.scm)
@end example

@item 模块
This is the graph of @dfn{package modules} (@pxref{软件包模块}).  For
example, the following command shows the graph for the package module that
defines the @code{guile} package:

@example
guix graph -t module guile | xdot -
@end example
@end table

All the types above correspond to @emph{build-time dependencies}.  The
following graph type represents the @emph{run-time dependencies}:

@table @code
@item references
This is the graph of @dfn{references} of a package output, as returned by
@command{guix gc --references} (@pxref{调用guix gc}).

If the given package output is not available in the store, @command{guix
graph} attempts to obtain dependency information from substitutes.

Here you can also pass a store file name instead of a package name.  For
example, the command below produces the reference graph of your profile
(which can be big!):

@example
guix graph -t references $(readlink -f ~/.guix-profile)
@end example

@item referrers
This is the graph of the @dfn{referrers} of a store item, as returned by
@command{guix gc --referrers} (@pxref{调用guix gc}).

This relies exclusively on local information from your store.  For instance,
let us suppose that the current Inkscape is available in 10 profiles on your
machine; @command{guix graph -t referrers inkscape} will show a graph rooted
at Inkscape and with those 10 profiles linked to it.

It can help determine what is preventing a store item from being garbage
collected.

@end table

@cindex shortest path, between packages
Often, the graph of the package you are interested in does not fit on your
screen, and anyway all you want to know is @emph{why} that package actually
depends on some seemingly unrelated package.  The @option{--path} option
instructs @command{guix graph} to display the shortest path between two
packages (or derivations, or store items, etc.):

@example
$ guix graph --path emacs libunistring
emacs@@26.3
mailutils@@3.9
libunistring@@0.9.10
$ guix graph --path -t derivation emacs libunistring
/gnu/store/@dots{}-emacs-26.3.drv
/gnu/store/@dots{}-mailutils-3.9.drv
/gnu/store/@dots{}-libunistring-0.9.10.drv
$ guix graph --path -t references emacs libunistring
/gnu/store/@dots{}-emacs-26.3
/gnu/store/@dots{}-libidn2-2.2.0
/gnu/store/@dots{}-libunistring-0.9.10
@end example

The available options are the following:

@table @option
@item --type=@var{type}
@itemx -t @var{type}
Produce a graph output of @var{type}, where @var{type} must be one of the
values listed above.

@item --list-types
List the supported graph types.

@item --backend=@var{backend}
@itemx -b @var{backend}
Produce a graph using the selected @var{backend}.

@item --list-backends
List the supported graph backends.

Currently, the available backends are Graphviz and d3.js.

@item --path
Display the shortest path between two nodes of the type specified by
@option{--type}.  The example below shows the shortest path between
@code{libreoffice} and @code{llvm} according to the references of
@code{libreoffice}:

@example
$ guix graph --path -t references libreoffice llvm
/gnu/store/@dots{}-libreoffice-6.4.2.2
/gnu/store/@dots{}-libepoxy-1.5.4
/gnu/store/@dots{}-mesa-19.3.4
/gnu/store/@dots{}-llvm-9.0.1
@end example

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to precisely refer to a package, as in this example:

@example
guix graph -e '(@@@@ (gnu packages commencement) gnu-make-final)'
@end example

@item --system=@var{system}
@itemx -s @var{system}
Display the graph for @var{system}---e.g., @code{i686-linux}.

The package dependency graph is largely architecture-independent, but there
are some architecture-dependent bits that this option allows you to
visualize.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{软件包模块}).

This allows users to define their own packages and make them visible to the
command-line tools.
@end table

On top of that, @command{guix graph} supports all the usual package
transformation options (@pxref{软件包变换选项。}).  This makes
it easy to view the effect of a graph-rewriting transformation such as
@option{--with-input}.  For example, the command below outputs the graph of
@code{git} once @code{openssl} has been replaced by @code{libressl}
everywhere in the graph:

@example
guix graph git --with-input=openssl=libressl
@end example

So many possibilities, so much fun!

@node 调用guix publish
@section Invoking @command{guix publish}

@cindex @command{guix publish}
The purpose of @command{guix publish} is to enable users to easily share
their store with others, who can then use it as a substitute server
(@pxref{substitutes}).

When @command{guix publish} runs, it spawns an HTTP server which allows
anyone with network access to obtain substitutes from it.  This means that
any machine running Guix can also act as if it were a build farm, since the
HTTP interface is compatible with Cuirass, the software behind the
@code{@value{SUBSTITUTE-SERVER}} build farm.

For security, each substitute is signed, allowing recipients to check their
authenticity and integrity (@pxref{substitutes}).  Because @command{guix
publish} uses the signing key of the system, which is only readable by the
system administrator, it must be started as root; the @option{--user} option
makes it drop root privileges early on.

The signing key pair must be generated before @command{guix publish} is
launched, using @command{guix archive --generate-key} (@pxref{调用guix archive}).

When the @option{--advertise} option is passed, the server advertises its
availability on the local network using multicast DNS (mDNS) and DNS service
discovery (DNS-SD), currently @i{via} Guile-Avahi (@pxref{Top,,,
guile-avahi, Using Avahi in Guile Scheme Programs}).

The general syntax is:

@example
guix publish @var{options}@dots{}
@end example

Running @command{guix publish} without any additional arguments will spawn
an HTTP server on port 8080:

@example
guix publish
@end example

Once a publishing server has been authorized, the daemon may download
substitutes from it.  @xref{Getting Substitutes from Other Servers}.

By default, @command{guix publish} compresses archives on the fly as it
serves them.  This ``on-the-fly'' mode is convenient in that it requires no
setup and is immediately available.  However, when serving lots of clients,
we recommend using the @option{--cache} option, which enables caching of the
archives before they are sent to clients---see below for details.  The
@command{guix weather} command provides a handy way to check what a server
provides (@pxref{调用guix weather}).

As a bonus, @command{guix publish} also serves as a content-addressed mirror
for source files referenced in @code{origin} records (@pxref{origin参考手册}).  For instance, assuming @command{guix publish} is running on
@code{example.org}, the following URL returns the raw
@file{hello-2.10.tar.gz} file with the given SHA256 hash (represented in
@code{nix-base32} format, @pxref{调用guix hash}):

@example
http://example.org/file/hello-2.10.tar.gz/sha256/0ssi1@dots{}ndq1i
@end example

Obviously, these URLs only work for files that are in the store; in other
cases, they return 404 (``Not Found'').

@cindex build logs, publication
Build logs are available from @code{/log} URLs like:

@example
http://example.org/log/gwspk@dots{}-guile-2.2.3
@end example

@noindent
When @command{guix-daemon} is configured to save compressed build logs, as
is the case by default (@pxref{调用guix-daemon}), @code{/log} URLs
return the compressed log as-is, with an appropriate @code{Content-Type}
and/or @code{Content-Encoding} header.  We recommend running
@command{guix-daemon} with @option{--log-compression=gzip} since Web
browsers can automatically decompress it, which is not the case with Bzip2
compression.

The following options are available:

@table @code
@item --port=@var{port}
@itemx -p @var{port}
Listen for HTTP requests on @var{port}.

@item --listen=@var{host}
Listen on the network interface for @var{host}.  The default is to accept
connections from any interface.

@item --user=@var{user}
@itemx -u @var{user}
Change privileges to @var{user} as soon as possible---i.e., once the server
socket is open and the signing key has been read.

@item --compression[=@var{method}[:@var{level}]]
@itemx -C [@var{method}[:@var{level}]]
Compress data using the given @var{method} and @var{level}.  @var{method} is
one of @code{lzip}, @code{zstd}, and @code{gzip}; when @var{method} is
omitted, @code{gzip} is used.

When @var{level} is zero, disable compression.  The range 1 to 9 corresponds
to different compression levels: 1 is the fastest, and 9 is the best
(CPU-intensive).  The default is 3.

Usually, @code{lzip} compresses noticeably better than @code{gzip} for a
small increase in CPU usage; see
@uref{https://nongnu.org/lzip/lzip_benchmark.html,benchmarks on the lzip Web
page}.  However, @code{lzip} achieves low decompression throughput (on the
order of 50@tie{}MiB/s on modern hardware), which can be a bottleneck for
someone who downloads over a fast network connection.

The compression ratio of @code{zstd} is between that of @code{lzip} and that
of @code{gzip}; its main advantage is a
@uref{https://facebook.github.io/zstd/,high decompression speed}.

Unless @option{--cache} is used, compression occurs on the fly and the
compressed streams are not cached.  Thus, to reduce load on the machine that
runs @command{guix publish}, it may be a good idea to choose a low
compression level, to run @command{guix publish} behind a caching proxy, or
to use @option{--cache}.  Using @option{--cache} has the advantage that it
allows @command{guix publish} to add @code{Content-Length} HTTP header to
its responses.

This option can be repeated, in which case every substitute gets compressed
using all the selected methods, and all of them are advertised.  This is
useful when users may not support all the compression methods: they can
select the one they support.

@item --cache=@var{directory}
@itemx -c @var{directory}
Cache archives and meta-data (@code{.narinfo} URLs) to @var{directory} and
only serve archives that are in cache.

When this option is omitted, archives and meta-data are created on-the-fly.
This can reduce the available bandwidth, especially when compression is
enabled, since this may become CPU-bound.  Another drawback of the default
mode is that the length of archives is not known in advance, so
@command{guix publish} does not add a @code{Content-Length} HTTP header to
its responses, which in turn prevents clients from knowing the amount of
data being downloaded.

Conversely, when @option{--cache} is used, the first request for a store
item (@i{via} a @code{.narinfo} URL) triggers a background process to
@dfn{bake} the archive---computing its @code{.narinfo} and compressing the
archive, if needed.  Once the archive is cached in @var{directory},
subsequent requests succeed and are served directly from the cache, which
guarantees that clients get the best possible bandwidth.

That first @code{.narinfo} request nonetheless returns 200, provided the
requested store item is ``small enough'', below the cache bypass
threshold---see @option{--cache-bypass-threshold} below.  That way, clients
do not have to wait until the archive is baked.  For larger store items, the
first @code{.narinfo} request returns 404, meaning that clients have to wait
until the archive is baked.

The ``baking'' process is performed by worker threads.  By default, one
thread per CPU core is created, but this can be customized.  See
@option{--workers} below.

When @option{--ttl} is used, cached entries are automatically deleted when
they have expired.

@item --workers=@var{N}
When @option{--cache} is used, request the allocation of @var{N} worker
threads to ``bake'' archives.

@item --ttl=@var{ttl}
Produce @code{Cache-Control} HTTP headers that advertise a time-to-live
(TTL) of @var{ttl}.  @var{ttl} must denote a duration: @code{5d} means 5
days, @code{1m} means 1 month, and so on.

This allows the user's Guix to keep substitute information in cache for
@var{ttl}.  However, note that @code{guix publish} does not itself guarantee
that the store items it provides will indeed remain available for as long as
@var{ttl}.

Additionally, when @option{--cache} is used, cached entries that have not
been accessed for @var{ttl} and that no longer have a corresponding item in
the store, may be deleted.

@item --cache-bypass-threshold=@var{size}
When used in conjunction with @option{--cache}, store items smaller than
@var{size} are immediately available, even when they are not yet in cache.
@var{size} is a size in bytes, or it can be suffixed by @code{M} for
megabytes and so on.  The default is @code{10M}.

``Cache bypass'' allows you to reduce the publication delay for clients at
the expense of possibly additional I/O and CPU use on the server side:
depending on the client access patterns, those store items can end up being
baked several times until a copy is available in cache.

Increasing the threshold may be useful for sites that have few users, or to
guarantee that users get substitutes even for store items that are not
popular.

@item --nar-path=@var{path}
Use @var{path} as the prefix for the URLs of ``nar'' files (@pxref{调用guix archive, normalized archives}).

By default, nars are served at a URL such as
@code{/nar/gzip/@dots{}-coreutils-8.25}.  This option allows you to change
the @code{/nar} part to @var{path}.

@item --public-key=@var{file}
@itemx --private-key=@var{file}
Use the specific @var{file}s as the public/private key pair used to sign the
store items being published.

The files must correspond to the same key pair (the private key is used for
signing and the public key is merely advertised in the signature metadata).
They must contain keys in the canonical s-expression format as produced by
@command{guix archive --generate-key} (@pxref{调用guix archive}).  By
default, @file{/etc/guix/signing-key.pub} and
@file{/etc/guix/signing-key.sec} are used.

@item --repl[=@var{port}]
@itemx -r [@var{port}]
Spawn a Guile REPL server (@pxref{REPL Servers,,, guile, GNU Guile Reference
Manual}) on @var{port} (37146 by default).  This is used primarily for
debugging a running @command{guix publish} server.
@end table

Enabling @command{guix publish} on Guix System is a one-liner: just
instantiate a @code{guix-publish-service-type} service in the
@code{services} field of the @code{operating-system} declaration
(@pxref{guix-publish-service-type, @code{guix-publish-service-type}}).

If you are instead running Guix on a ``foreign distro'', follow these
instructions:

@itemize
@item
If your host distro uses the systemd init system:

@example
# ln -s ~root/.guix-profile/lib/systemd/system/guix-publish.service \
        /etc/systemd/system/
# systemctl start guix-publish && systemctl enable guix-publish
@end example

@item
如果你的主机的发行版使用Upstart init系统：

@example
# ln -s ~root/.guix-profile/lib/upstart/system/guix-publish.conf /etc/init/
# start guix-publish
@end example

@item
Otherwise, proceed similarly with your distro's init system.
@end itemize

@node 调用guix challenge
@section Invoking @command{guix challenge}

@cindex 可复现的构建
@cindex verifiable builds
@cindex @command{guix challenge}
@cindex challenge
Do the binaries provided by this server really correspond to the source code
it claims to build? Is a package build process deterministic? These are the
questions the @command{guix challenge} command attempts to answer.

The former is obviously an important question: Before using a substitute
server (@pxref{substitutes}), one had better @emph{verify} that it provides
the right binaries, and thus @emph{challenge} it.  The latter is what
enables the former: If package builds are deterministic, then independent
builds of the package should yield the exact same result, bit for bit; if a
server provides a binary different from the one obtained locally, it may be
either corrupt or malicious.

We know that the hash that shows up in @file{/gnu/store} file names is the
hash of all the inputs of the process that built the file or
directory---compilers, libraries, build scripts,
etc. (@pxref{介绍}).  Assuming deterministic build processes, one
store file name should map to exactly one build output.  @command{guix
challenge} checks whether there is, indeed, a single mapping by comparing
the build outputs of several independent builds of any given store item.

The command output looks like this:

@smallexample
$ guix challenge --substitute-urls="https://@value{SUBSTITUTE-SERVER} https://guix.example.org"
updating list of substitutes from 'https://@value{SUBSTITUTE-SERVER}'... 100.0%
updating list of substitutes from 'https://guix.example.org'... 100.0%
/gnu/store/@dots{}-openssl-1.0.2d contents differ:
  local hash: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
  https://@value{SUBSTITUTE-SERVER}/nar/@dots{}-openssl-1.0.2d: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
  https://guix.example.org/nar/@dots{}-openssl-1.0.2d: 1zy4fmaaqcnjrzzajkdn3f5gmjk754b43qkq47llbyak9z0qjyim
  differing files:
    /lib/libcrypto.so.1.1
    /lib/libssl.so.1.1

/gnu/store/@dots{}-git-2.5.0 contents differ:
  local hash: 00p3bmryhjxrhpn2gxs2fy0a15lnip05l97205pgbk5ra395hyha
  https://@value{SUBSTITUTE-SERVER}/nar/@dots{}-git-2.5.0: 069nb85bv4d4a6slrwjdy8v1cn4cwspm3kdbmyb81d6zckj3nq9f
  https://guix.example.org/nar/@dots{}-git-2.5.0: 0mdqa9w1p6cmli6976v4wi0sw9r4p5prkj7lzfd1877wk11c9c73
  differing file:
    /libexec/git-core/git-fsck

/gnu/store/@dots{}-pius-2.1.1 contents differ:
  local hash: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
  https://@value{SUBSTITUTE-SERVER}/nar/@dots{}-pius-2.1.1: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
  https://guix.example.org/nar/@dots{}-pius-2.1.1: 1cy25x1a4fzq5rk0pmvc8xhwyffnqz95h2bpvqsz2mpvlbccy0gs
  differing file:
    /share/man/man1/pius.1.gz

@dots{}

6,406 store items were analyzed:
  - 4,749 (74.1%) were identical
  - 525 (8.2%) differed
  - 1,132 (17.7%) were inconclusive
@end smallexample

@noindent
In this example, @command{guix challenge} first scans the store to determine
the set of locally-built derivations---as opposed to store items that were
downloaded from a substitute server---and then queries all the substitute
servers.  It then reports those store items for which the servers obtained a
result different from the local build.

@cindex non-determinism, in package builds
As an example, @code{guix.example.org} always gets a different answer.
Conversely, @code{@value{SUBSTITUTE-SERVER}} agrees with local builds,
except in the case of Git.  This might indicate that the build process of
Git is non-deterministic, meaning that its output varies as a function of
various things that Guix does not fully control, in spite of building
packages in isolated environments (@pxref{功能}).  Most common sources
of non-determinism include the addition of timestamps in build results, the
inclusion of random numbers, and directory listings sorted by inode number.
See @uref{https://reproducible-builds.org/docs/}, for more information.

To find out what is wrong with this Git binary, the easiest approach is to
run:

@example
guix challenge git \
  --diff=diffoscope \
  --substitute-urls="https://@value{SUBSTITUTE-SERVER} https://guix.example.org"
@end example

This automatically invokes @command{diffoscope}, which displays detailed
information about files that differ.

Alternatively, we can do something along these lines (@pxref{调用guix archive}):

@example
$ wget -q -O - https://@value{SUBSTITUTE-SERVER}/nar/lzip/@dots{}-git-2.5.0 \
   | lzip -d | guix archive -x /tmp/git
$ diff -ur --no-dereference /gnu/store/@dots{}-git.2.5.0 /tmp/git
@end example

This command shows the difference between the files resulting from the local
build, and the files resulting from the build on
@code{@value{SUBSTITUTE-SERVER}} (@pxref{Overview, Comparing and Merging
Files,, diffutils, Comparing and Merging Files}).  The @command{diff}
command works great for text files.  When binary files differ, a better
option is @uref{https://diffoscope.org/, Diffoscope}, a tool that helps
visualize differences for all kinds of files.

Once you have done that work, you can tell whether the differences are due
to a non-deterministic build process or to a malicious server.  We try hard
to remove sources of non-determinism in packages to make it easier to verify
substitutes, but of course, this is a process that involves not just Guix,
but a large part of the free software community.  In the meantime,
@command{guix challenge} is one tool to help address the problem.

If you are writing packages for Guix, you are encouraged to check whether
@code{@value{SUBSTITUTE-SERVER}} and other substitute servers obtain the
same build result as you did with:

@example
$ guix challenge @var{package}
@end example

@noindent
where @var{package} is a package specification such as @code{guile@@2.0} or
@code{glibc:debug}.

The general syntax is:

@example
guix challenge @var{options} [@var{packages}@dots{}]
@end example

When a difference is found between the hash of a locally-built item and that
of a server-provided substitute, or among substitutes provided by different
servers, the command displays it as in the example above and its exit code
is 2 (other non-zero exit codes denote other kinds of errors).

The one option that matters is:

@table @code

@item --substitute-urls=@var{urls}
Consider @var{urls} the whitespace-separated list of substitute source URLs
to compare to.

@item --diff=@var{mode}
Upon mismatches, show differences according to @var{mode}, one of:

@table @asis
@item @code{simple} (the default)
Show the list of files that differ.

@item @code{diffoscope}
@itemx @var{command}
Invoke @uref{https://diffoscope.org/, Diffoscope}, passing it two
directories whose contents do not match.

When @var{command} is an absolute file name, run @var{command} instead of
Diffoscope.

@item @code{none}
Do not show further details about the differences.
@end table

Thus, unless @option{--diff=none} is passed, @command{guix challenge}
downloads the store items from the given substitute servers so that it can
compare them.

@item --verbose
@itemx -v
Show details about matches (identical contents) in addition to information
about mismatches.

@end table

@node 调用guix copy
@section Invoking @command{guix copy}

@cindex copy, of store items, over SSH
@cindex SSH, copy of store items
@cindex sharing store items across machines
@cindex transferring store items across machines
The @command{guix copy} command copies items from the store of one machine
to that of another machine over a secure shell (SSH)
connection@footnote{This command is available only when Guile-SSH was
found.  @xref{需求}, for details.}.  For example, the following
command copies the @code{coreutils} package, the user's profile, and all
their dependencies over to @var{host}, logged in as @var{user}:

@example
guix copy --to=@var{user}@@@var{host} \
          coreutils $(readlink -f ~/.guix-profile)
@end example

If some of the items to be copied are already present on @var{host}, they
are not actually sent.

The command below retrieves @code{libreoffice} and @code{gimp} from
@var{host}, assuming they are available there:

@example
guix copy --from=@var{host} libreoffice gimp
@end example

The SSH connection is established using the Guile-SSH client, which is
compatible with OpenSSH: it honors @file{~/.ssh/known_hosts} and
@file{~/.ssh/config}, and uses the SSH agent for authentication.

The key used to sign items that are sent must be accepted by the remote
machine.  Likewise, the key used by the remote machine to sign items you are
retrieving must be in @file{/etc/guix/acl} so it is accepted by your own
daemon.  @xref{调用guix archive}, for more information about store item
authentication.

The general syntax is:

@example
guix copy [--to=@var{spec}|--from=@var{spec}] @var{items}@dots{}
@end example

You must always specify one of the following options:

@table @code
@item --to=@var{spec}
@itemx --from=@var{spec}
Specify the host to send to or receive from.  @var{spec} must be an SSH spec
such as @code{example.org}, @code{charlie@@example.org}, or
@code{charlie@@example.org:2222}.
@end table

The @var{items} can be either package names, such as @code{gimp}, or store
items, such as @file{/gnu/store/@dots{}-idutils-4.6}.

When specifying the name of a package to send, it is first built if needed,
unless @option{--dry-run} was specified.  Common build options are supported
(@pxref{普通的构建选项}).


@node 调用guix container
@section Invoking @command{guix container}
@cindex container
@cindex @command{guix container}
@quotation 注
As of version @value{VERSION}, this tool is experimental.  The interface is
subject to radical change in the future.
@end quotation

The purpose of @command{guix container} is to manipulate processes running
within an isolated environment, commonly known as a ``container'', typically
created by the @command{guix environment} (@pxref{调用guix environment}) and @command{guix system container} (@pxref{调用guix system}) commands.

The general syntax is:

@example
guix container @var{action} @var{options}@dots{}
@end example

@var{action} specifies the operation to perform with a container, and
@var{options} specifies the context-specific arguments for the action.

The following actions are available:

@table @code
@item exec
Execute a command within the context of a running container.

The syntax is:

@example
guix container exec @var{pid} @var{program} @var{arguments}@dots{}
@end example

@var{pid} specifies the process ID of the running container.  @var{program}
specifies an executable file name within the root file system of the
container.  @var{arguments} are the additional options that will be passed
to @var{program}.

The following command launches an interactive login shell inside a Guix
system container, started by @command{guix system container}, and whose
process ID is 9001:

@example
guix container exec 9001 /run/current-system/profile/bin/bash --login
@end example

Note that the @var{pid} cannot be the parent process of a container.  It
must be PID 1 of the container or one of its child processes.

@end table

@node 调用guix weather
@section Invoking @command{guix weather}

Occasionally you're grumpy because substitutes are lacking and you end up
building packages by yourself (@pxref{substitutes}).  The @command{guix
weather} command reports on substitute availability on the specified servers
so you can have an idea of whether you'll be grumpy today.  It can sometimes
be useful info as a user, but it is primarily useful to people running
@command{guix publish} (@pxref{调用guix publish}).

@cindex statistics, for substitutes
@cindex availability of substitutes
@cindex substitute availability
@cindex weather, substitute availability
Here's a sample run:

@example
$ guix weather --substitute-urls=https://guix.example.org
computing 5,872 package derivations for x86_64-linux...
looking for 6,128 store items on https://guix.example.org..
updating list of substitutes from 'https://guix.example.org'... 100.0%
https://guix.example.org
  43.4% substitutes available (2,658 out of 6,128)
  7,032.5 MiB of nars (compressed)
  19,824.2 MiB on disk (uncompressed)
  0.030 seconds per request (182.9 seconds in total)
  33.5 requests per second

  9.8% (342 out of 3,470) of the missing items are queued
  867 queued builds
      x86_64-linux: 518 (59.7%)
      i686-linux: 221 (25.5%)
      aarch64-linux: 128 (14.8%)
  build rate: 23.41 builds per hour
      x86_64-linux: 11.16 builds per hour
      i686-linux: 6.03 builds per hour
      aarch64-linux: 6.41 builds per hour
@end example

@cindex continuous integration, statistics
As you can see, it reports the fraction of all the packages for which
substitutes are available on the server---regardless of whether substitutes
are enabled, and regardless of whether this server's signing key is
authorized.  It also reports the size of the compressed archives (``nars'')
provided by the server, the size the corresponding store items occupy in the
store (assuming deduplication is turned off), and the server's throughput.
The second part gives continuous integration (CI) statistics, if the server
supports it.  In addition, using the @option{--coverage} option,
@command{guix weather} can list ``important'' package substitutes missing on
the server (see below).

To achieve that, @command{guix weather} queries over HTTP(S) meta-data
(@dfn{narinfos}) for all the relevant store items.  Like @command{guix
challenge}, it ignores signatures on those substitutes, which is innocuous
since the command only gathers statistics and cannot install those
substitutes.

The general syntax is:

@example
guix weather @var{options}@dots{} [@var{packages}@dots{}]
@end example

When @var{packages} is omitted, @command{guix weather} checks the
availability of substitutes for @emph{all} the packages, or for those
specified with @option{--manifest}; otherwise it only considers the
specified packages.  It is also possible to query specific system types with
@option{--system}.  @command{guix weather} exits with a non-zero code when
the fraction of available substitutes is below 100%.

The available options are listed below.

@table @code
@item --substitute-urls=@var{urls}
@var{urls} is the space-separated list of substitute server URLs to query.
When this option is omitted, the default set of substitute servers is
queried.

@item --system=@var{system}
@itemx -s @var{system}
Query substitutes for @var{system}---e.g., @code{aarch64-linux}.  This
option can be repeated, in which case @command{guix weather} will query
substitutes for several system types.

@item --manifest=@var{file}
Instead of querying substitutes for all the packages, only ask for those
specified in @var{file}.  @var{file} must contain a @dfn{manifest}, as with
the @code{-m} option of @command{guix package} (@pxref{调用guix package}).

This option can be repeated several times, in which case the manifests are
concatenated.

@item --coverage[=@var{count}]
@itemx -c [@var{count}]
Report on substitute coverage for packages: list packages with at least
@var{count} dependents (zero by default) for which substitutes are
unavailable.  Dependent packages themselves are not listed: if @var{b}
depends on @var{a} and @var{a} has no substitutes, only @var{a} is listed,
even though @var{b} usually lacks substitutes as well.  The result looks
like this:

@example
$ guix weather --substitute-urls=@value{SUBSTITUTE-URL} -c 10
computing 8,983 package derivations for x86_64-linux...
looking for 9,343 store items on @value{SUBSTITUTE-URL}...
updating substitutes from '@value{SUBSTITUTE-URL}'... 100.0%
@value{SUBSTITUTE-URL}
  64.7% substitutes available (6,047 out of 9,343)
@dots{}
2502 packages are missing from '@value{SUBSTITUTE-URL}' for 'x86_64-linux', among which:
    58  kcoreaddons@@5.49.0      /gnu/store/@dots{}-kcoreaddons-5.49.0
    46  qgpgme@@1.11.1           /gnu/store/@dots{}-qgpgme-1.11.1
    37  perl-http-cookiejar@@0.008  /gnu/store/@dots{}-perl-http-cookiejar-0.008
    @dots{}
@end example

What this example shows is that @code{kcoreaddons} and presumably the 58
packages that depend on it have no substitutes at
@code{@value{SUBSTITUTE-SERVER}}; likewise for @code{qgpgme} and the 46
packages that depend on it.

If you are a Guix developer, or if you are taking care of this build farm,
you'll probably want to have a closer look at these packages: they may
simply fail to build.

@item --display-missing
Display the list of store items for which substitutes are missing.
@end table

@node 调用guix processes
@section Invoking @command{guix processes}

The @command{guix processes} command can be useful to developers and system
administrators, especially on multi-user machines and on build farms: it
lists the current sessions (connections to the daemon), as well as
information about the processes involved@footnote{Remote sessions, when
@command{guix-daemon} is started with @option{--listen} specifying a TCP
endpoint, are @emph{not} listed.}.  Here's an example of the information it
returns:

@example
$ sudo guix processes
SessionPID: 19002
ClientPID: 19090
ClientCommand: guix environment --ad-hoc python

SessionPID: 19402
ClientPID: 19367
ClientCommand: guix publish -u guix-publish -p 3000 -C 9 @dots{}

SessionPID: 19444
ClientPID: 19419
ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
LockHeld: /gnu/store/@dots{}-perl-ipc-cmd-0.96.lock
LockHeld: /gnu/store/@dots{}-python-six-bootstrap-1.11.0.lock
LockHeld: /gnu/store/@dots{}-libjpeg-turbo-2.0.0.lock
ChildPID: 20495
ChildCommand: guix offload x86_64-linux 7200 1 28800
ChildPID: 27733
ChildCommand: guix offload x86_64-linux 7200 1 28800
ChildPID: 27793
ChildCommand: guix offload x86_64-linux 7200 1 28800
@end example

In this example we see that @command{guix-daemon} has three clients:
@command{guix environment}, @command{guix publish}, and the Cuirass
continuous integration tool; their process identifier (PID) is given by the
@code{ClientPID} field.  The @code{SessionPID} field gives the PID of the
@command{guix-daemon} sub-process of this particular session.

The @code{LockHeld} fields show which store items are currently locked by
this session, which corresponds to store items being built or substituted
(the @code{LockHeld} field is not displayed when @command{guix processes} is
not running as root).  Last, by looking at the @code{ChildPID} and
@code{ChildCommand} fields, we understand that these three builds are being
offloaded (@pxref{下发工作给后台进程的设置}).

The output is in Recutils format so we can use the handy @command{recsel}
command to select sessions of interest (@pxref{Selection Expressions,,,
recutils, GNU recutils manual}).  As an example, the command shows the
command line and PID of the client that triggered the build of a Perl
package:

@example
$ sudo guix processes | \
    recsel -p ClientPID,ClientCommand -e 'LockHeld ~ "perl"'
ClientPID: 19419
ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
@end example

Additional options are listed below.

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce output in the specified @var{format}, one of:

@table @code
@item recutils
The default option.  It outputs a set of Session recutils records that
include each @code{ChildProcess} as a field.

@item normalized
Normalize the output records into record sets (@pxref{Record Sets,,,
recutils, GNU recutils manual}).  Normalizing into record sets allows joins
across record types.  The example below lists the PID of each
@code{ChildProcess} and the associated PID for @code{Session} that spawned
the @code{ChildProcess} where the @code{Session} was started using
@command{guix build}.

@example
$ guix processes --format=normalized | \
    recsel \
    -j Session \
    -t ChildProcess \
    -p Session.PID,PID \
    -e 'Session.ClientCommand ~ "guix build"'
PID: 4435
Session_PID: 4278

PID: 4554
Session_PID: 4278

PID: 4646
Session_PID: 4278
@end example
@end table
@end table

@node 系统配置
@chapter 系统配置

@cindex system configuration
Guix System supports a consistent whole-system configuration mechanism.  By
that we mean that all aspects of the global system configuration---such as
the available system services, timezone and locale settings, user
accounts---are declared in a single place.  Such a @dfn{system
configuration} can be @dfn{instantiated}---i.e., effected.

@c Yes, we're talking of Puppet, Chef, & co. here.  ↑
One of the advantages of putting all the system configuration under the
control of Guix is that it supports transactional system upgrades, and makes
it possible to roll back to a previous system instantiation, should
something go wrong with the new one (@pxref{功能}).  Another advantage
is that it makes it easy to replicate the exact same configuration across
different machines, or at different points in time, without having to resort
to additional administration tools layered on top of the own tools of the
system.

This section describes this mechanism.  First we focus on the system
administrator's viewpoint---explaining how the system is configured and
instantiated.  Then we show how this mechanism can be extended, for instance
to support new system services.

@menu
* 使用配置系统::       定制你的GNU系统。
* 操作系统参考::       操作系统声明详情。
* 文件系统::             设置文件系统挂载。
* 映射的设备::          块设备额外的处理。
* 用户帐号::             指定用户帐号。
* 键盘布局::             系统怎样理解按键。
* 区域::                   语言和文化惯例设置。
* 服务::                   指定系统服务。
* setuid程序::             以root权限运行的程序。
* X.509证书::              认证HTTPS服务器。
* Name Service Switch::      设置libc的name service switch。
* 初始的内存虚拟硬盘::  Linux-Libre引导。
* 引导设置::             设置引导程序。
* 调用guix system::        实例化一个系统配置。
* 调用 guix deploy::       Deploying a system configuration to a remote 
                               host.
* 在虚拟机里运行Guix::  怎样在虚拟机里运行Guix。
* 定义服务::             添加新的服务定义。
@end menu

@node 使用配置系统
@section 使用配置系统

The operating system is configured by providing an @code{operating-system}
declaration in a file that can then be passed to the @command{guix system}
command (@pxref{调用guix system}).  A simple setup, with the default
system services, the default Linux-Libre kernel, initial RAM disk, and boot
loader looks like this:

@findex operating-system
@lisp
@include os-config-bare-bones.texi
@end lisp

This example should be self-describing.  Some of the fields defined above,
such as @code{host-name} and @code{bootloader}, are mandatory.  Others, such
as @code{packages} and @code{services}, can be omitted, in which case they
get a default value.

Below we discuss the effect of some of the most important fields
(@pxref{操作系统参考}, for details about all the available
fields), and how to @dfn{instantiate} the operating system using
@command{guix system}.

@unnumberedsubsec Bootloader

@cindex legacy boot, on Intel machines
@cindex BIOS boot, on Intel machines
@cindex UEFI boot
@cindex EFI boot
The @code{bootloader} field describes the method that will be used to boot
your system.  Machines based on Intel processors can boot in ``legacy'' BIOS
mode, as in the example above.  However, more recent machines rely instead
on the @dfn{Unified Extensible Firmware Interface} (UEFI) to boot.  In that
case, the @code{bootloader} field should contain something along these
lines:

@lisp
(bootloader-configuration
  (bootloader grub-efi-bootloader)
  (target "/boot/efi"))
@end lisp

@xref{引导设置}, for more information on the available
configuration options.

@unnumberedsubsec Globally-Visible Packages

@vindex %base-packages
The @code{packages} field lists packages that will be globally visible on
the system, for all user accounts---i.e., in every user's @env{PATH}
environment variable---in addition to the per-user profiles (@pxref{调用guix package}).  The @code{%base-packages} variable provides all the tools
one would expect for basic user and administrator tasks---including the GNU
Core Utilities, the GNU Networking Utilities, the GNU Zile lightweight text
editor, @command{find}, @command{grep}, etc.  The example above adds
GNU@tie{}Screen to those, taken from the @code{(gnu packages screen)} module
(@pxref{软件包模块}).  The @code{(list package output)} syntax can be
used to add a specific output of a package:

@lisp
(use-modules (gnu packages))
(use-modules (gnu packages dns))

(operating-system
  ;; ...
  (packages (cons (list bind "utils")
                  %base-packages)))
@end lisp

@findex specification->package
Referring to packages by variable name, like @code{bind} above, has the
advantage of being unambiguous; it also allows typos and such to be
diagnosed right away as ``unbound variables''.  The downside is that one
needs to know which module defines which package, and to augment the
@code{use-package-modules} line accordingly.  To avoid that, one can use the
@code{specification->package} procedure of the @code{(gnu packages)} module,
which returns the best package for a given name or name and version:

@lisp
(use-modules (gnu packages))

(operating-system
  ;; ...
  (packages (append (map specification->package
                         '("tcpdump" "htop" "gnupg@@2.0"))
                    %base-packages)))
@end lisp

@unnumberedsubsec System Services

@cindex services
@vindex %base-services
The @code{services} field lists @dfn{system services} to be made available
when the system starts (@pxref{服务}).  The @code{operating-system}
declaration above specifies that, in addition to the basic services, we want
the OpenSSH secure shell daemon listening on port 2222 (@pxref{网络服务, @code{openssh-service-type}}).  Under the hood,
@code{openssh-service-type} arranges so that @command{sshd} is started with
the right command-line options, possibly with supporting configuration files
generated as needed (@pxref{定义服务}).

@cindex customization, of services
@findex modify-services
Occasionally, instead of using the base services as is, you will want to
customize them.  To do this, use @code{modify-services} (@pxref{服务参考, @code{modify-services}}) to modify the list.

For example, suppose you want to modify @code{guix-daemon} and Mingetty (the
console log-in) in the @code{%base-services} list (@pxref{基础服务,
@code{%base-services}}).  To do that, you can write the following in your
operating system declaration:

@lisp
(define %my-services
  ;; My very own list of services.
  (modify-services %base-services
    (guix-service-type config =>
                       (guix-configuration
                        (inherit config)
                        ;; Fetch substitutes from example.org.
                        (substitute-urls
                          (list "https://example.org/guix"
                                "https://ci.guix.gnu.org"))))
    (mingetty-service-type config =>
                           (mingetty-configuration
                            (inherit config)
                            ;; Automatially log in as "guest".
                            (auto-login "guest")))))

(operating-system
  ;; @dots{}
  (services %my-services))
@end lisp

This changes the configuration---i.e., the service parameters---of the
@code{guix-service-type} instance, and that of all the
@code{mingetty-service-type} instances in the @code{%base-services} list.
Observe how this is accomplished: first, we arrange for the original
configuration to be bound to the identifier @code{config} in the @var{body},
and then we write the @var{body} so that it evaluates to the desired
configuration.  In particular, notice how we use @code{inherit} to create a
new configuration which has the same values as the old configuration, but
with a few modifications.

@cindex encrypted disk
The configuration for a typical ``desktop'' usage, with an encrypted root
partition, the X11 display server, GNOME and Xfce (users can choose which of
these desktop environments to use at the log-in screen by pressing
@kbd{F1}), network management, power management, and more, would look like
this:

@lisp
@include os-config-desktop.texi
@end lisp

A graphical system with a choice of lightweight window managers instead of
full-blown desktop environments would look like this:

@lisp
@include os-config-lightweight-desktop.texi
@end lisp

This example refers to the @file{/boot/efi} file system by its UUID,
@code{1234-ABCD}.  Replace this UUID with the right UUID on your system, as
returned by the @command{blkid} command.

@xref{桌面服务}, for the exact list of services provided by
@code{%desktop-services}.  @xref{X.509证书}, for background
information about the @code{nss-certs} package that is used here.

Again, @code{%desktop-services} is just a list of service objects.  If you
want to remove services from there, you can do so using the procedures for
list filtering (@pxref{SRFI-1 Filtering and Partitioning,,, guile, GNU Guile
Reference Manual}).  For instance, the following expression returns a list
that contains all the services in @code{%desktop-services} minus the Avahi
service:

@lisp
(remove (lambda (service)
          (eq? (service-kind service) avahi-service-type))
        %desktop-services)
@end lisp

Alternatively, the @code{modify-services} macro can be used:

@lisp
(modify-services %desktop-services
  (delete avahi-service-type))
@end lisp


@unnumberedsubsec Instantiating the System

Assuming the @code{operating-system} declaration is stored in the
@file{my-system-config.scm} file, the @command{guix system reconfigure
my-system-config.scm} command instantiates that configuration, and makes it
the default GRUB boot entry (@pxref{调用guix system}).

The normal way to change the system configuration is by updating this file
and re-running @command{guix system reconfigure}.  One should never have to
touch files in @file{/etc} or to run commands that modify the system state
such as @command{useradd} or @command{grub-install}.  In fact, you must
avoid that since that would not only void your warranty but also prevent you
from rolling back to previous versions of your system, should you ever need
to.

@cindex roll-back, of the operating system
Speaking of roll-back, each time you run @command{guix system reconfigure},
a new @dfn{generation} of the system is created---without modifying or
deleting previous generations.  Old system generations get an entry in the
bootloader boot menu, allowing you to boot them in case something went wrong
with the latest generation.  Reassuring, no? The @command{guix system
list-generations} command lists the system generations available on disk.
It is also possible to roll back the system via the commands @command{guix
system roll-back} and @command{guix system switch-generation}.

Although the @command{guix system reconfigure} command will not modify
previous generations, you must take care when the current generation is not
the latest (e.g., after invoking @command{guix system roll-back}), since the
operation might overwrite a later generation (@pxref{调用guix system}).

@unnumberedsubsec The Programming Interface

At the Scheme level, the bulk of an @code{operating-system} declaration is
instantiated with the following monadic procedure (@pxref{仓库monad}):

@deffn {Monadic Procedure} operating-system-derivation os
Return a derivation that builds @var{os}, an @code{operating-system} object
(@pxref{Derivations}).

The output of the derivation is a single directory that refers to all the
packages, configuration files, and other supporting files needed to
instantiate @var{os}.
@end deffn

This procedure is provided by the @code{(gnu system)} module.  Along with
@code{(gnu services)} (@pxref{服务}), this module contains the guts of
Guix System.  Make sure to visit it!


@node 操作系统参考
@section @code{operating-system} Reference

This section summarizes all the options available in @code{operating-system}
declarations (@pxref{使用配置系统}).

@deftp {Data Type} operating-system
This is the data type representing an operating system configuration.  By
that, we mean all the global system configuration, not per-user
configuration (@pxref{使用配置系统}).

@table @asis
@item @code{kernel} (default: @code{linux-libre})
The package object of the operating system kernel to use@footnote{Currently
only the Linux-libre kernel is fully supported.  Using GNU@tie{}mach with
the GNU@tie{}Hurd is experimental and only available when building a virtual
machine disk image.}.

@cindex hurd
@item @code{hurd} (default: @code{#f})
The package object of the Hurd to be started by the kernel.  When this field
is set, produce a GNU/Hurd operating system.  In that case, @code{kernel}
must also be set to the @code{gnumach} package---the microkernel the Hurd
runs on.

@quotation Warning
This feature is experimental and only supported for disk images.
@end quotation

@item @code{kernel-loadable-modules} (default: '())
A list of objects (usually packages) to collect loadable kernel modules
from--e.g. @code{(list ddcci-driver-linux)}.

@item @code{kernel-arguments} (default: @code{%default-kernel-arguments})
List of strings or gexps representing additional arguments to pass on the
command-line of the kernel---e.g., @code{("console=ttyS0")}.

@item @code{bootloader}
The system bootloader configuration object.  @xref{引导设置}.

@item @code{label}
This is the label (a string) as it appears in the bootloader's menu entry.
The default label includes the kernel name and version.

@item @code{keyboard-layout} (default: @code{#f})
This field specifies the keyboard layout to use in the console.  It can be
either @code{#f}, in which case the default keyboard layout is used (usually
US English), or a @code{<keyboard-layout>} record. @xref{键盘布局},
for more information.

This keyboard layout is in effect as soon as the kernel has booted.  For
instance, it is the keyboard layout in effect when you type a passphrase if
your root file system is on a @code{luks-device-mapping} mapped device
(@pxref{映射的设备}).

@quotation 注
This does @emph{not} specify the keyboard layout used by the bootloader, nor
that used by the graphical display server.  @xref{引导设置},
for information on how to specify the bootloader's keyboard layout.  @xref{X窗口}, for information on how to specify the keyboard layout used by the X
Window System.
@end quotation

@item @code{initrd-modules} (default: @code{%base-initrd-modules})
@cindex initrd
@cindex initial RAM disk
The list of Linux kernel modules that need to be available in the initial
RAM disk.  @xref{初始的内存虚拟硬盘}.

@item @code{initrd} (default: @code{base-initrd})
A procedure that returns an initial RAM disk for the Linux kernel.  This
field is provided to support low-level customization and should rarely be
needed for casual use.  @xref{初始的内存虚拟硬盘}.

@item @code{firmware} (default: @code{%base-firmware})
@cindex firmware
List of firmware packages loadable by the operating system kernel.

The default includes firmware needed for Atheros- and Broadcom-based WiFi
devices (Linux-libre modules @code{ath9k} and @code{b43-open},
respectively).  @xref{硬件的考虑}, for more info on supported
hardware.

@item @code{host-name}
The host name.

@item @code{hosts-file}
@cindex hosts file
A file-like object (@pxref{G-表达式, file-like objects}) for use as
@file{/etc/hosts} (@pxref{Host Names,,, libc, The GNU C Library Reference
Manual}).  The default is a file with entries for @code{localhost} and
@var{host-name}.

@item @code{mapped-devices} (default: @code{'()})
A list of mapped devices.  @xref{映射的设备}.

@item @code{file-systems}
A list of file systems.  @xref{文件系统}.

@cindex swap devices
@cindex swap space
@item @code{swap-devices} (default: @code{'()})
A list of UUIDs, file system labels, or strings identifying devices or files
to be used for ``swap space'' (@pxref{Memory Concepts,,, libc, The GNU C
Library Reference Manual}).  Here are some examples:

@table @code
@item (list (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb"))
Use the swap partition with the given UUID@.  You can learn the UUID of a
Linux swap partition by running @command{swaplabel @var{device}}, where
@var{device} is the @file{/dev} file name of that partition.

@item (list (file-system-label "swap"))
Use the partition with label @code{swap}.  Again, the @command{swaplabel}
command allows you to view and change the label of a Linux swap partition.

@item (list "/swapfile")
Use the file @file{/swapfile} as swap space.

@item (list "/dev/sda3" "/dev/sdb2")
Use the @file{/dev/sda3} and @file{/dev/sdb2} partitions as swap space.  We
recommend referring to swap devices by UUIDs or labels as shown above
instead.
@end table

It is possible to specify a swap file in a file system on a mapped device
(under @file{/dev/mapper}), provided that the necessary device mapping and
file system are also specified.  @xref{映射的设备} and @ref{文件系统}.

@item @code{users} (default: @code{%base-user-accounts})
@itemx @code{groups} (default: @code{%base-groups})
List of user accounts and groups.  @xref{用户帐号}.

If the @code{users} list lacks a user account with UID@tie{}0, a ``root''
account with UID@tie{}0 is automatically added.

@item @code{skeletons} (default: @code{(default-skeletons)})
A list of target file name/file-like object tuples (@pxref{G-表达式,
file-like objects}).  These are the skeleton files that will be added to the
home directory of newly-created user accounts.

For instance, a valid value may look like this:

@lisp
`((".bashrc" ,(plain-file "bashrc" "echo Hello\n"))
  (".guile" ,(plain-file "guile"
                         "(use-modules (ice-9 readline))
                          (activate-readline)")))
@end lisp

@item @code{issue} (default: @code{%default-issue})
A string denoting the contents of the @file{/etc/issue} file, which is
displayed when users log in on a text console.

@item @code{packages} (default: @code{%base-packages})
A list of packages to be installed in the global profile, which is
accessible at @file{/run/current-system/profile}.  Each element is either a
package variable or a package/output tuple.  Here's a simple example of
both:

@lisp
(cons* git                     ; the default "out" output
       (list git "send-email") ; another output of git
       %base-packages)         ; the default set
@end lisp

The default set includes core utilities and it is good practice to install
non-core utilities in user profiles (@pxref{调用guix package}).

@item @code{timezone}
A timezone identifying string---e.g., @code{"Europe/Paris"}.

You can run the @command{tzselect} command to find out which timezone string
corresponds to your region.  Choosing an invalid timezone name causes
@command{guix system} to fail.

@item @code{locale} (default: @code{"en_US.utf8"})
The name of the default locale (@pxref{Locale Names,,, libc, The GNU C
Library Reference Manual}).  @xref{区域}, for more information.

@item @code{locale-definitions} (default: @code{%default-locale-definitions})
The list of locale definitions to be compiled and that may be used at run
time.  @xref{区域}.

@item @code{locale-libcs} (default: @code{(list @var{glibc})})
The list of GNU@tie{}libc packages whose locale data and tools are used to
build the locale definitions.  @xref{区域}, for compatibility
considerations that justify this option.

@item @code{name-service-switch} (default: @code{%default-nss})
Configuration of the libc name service switch (NSS)---a
@code{<name-service-switch>} object.  @xref{Name Service Switch}, for
details.

@item @code{services} (default: @code{%base-services})
A list of service objects denoting system services.  @xref{服务}.

@cindex essential services
@item @code{essential-services} (default: ...)
The list of ``essential services''---i.e., things like instances of
@code{system-service-type} and @code{host-name-service-type} (@pxref{服务参考}), which are derived from the operating system definition itself.
As a user you should @emph{never} need to touch this field.

@item @code{pam-services} (default: @code{(base-pam-services)})
@cindex PAM
@cindex pluggable authentication modules
@c FIXME: Add xref to PAM services section.
Linux @dfn{pluggable authentication module} (PAM) services.

@item @code{setuid-programs} (default: @code{%setuid-programs})
List of string-valued G-expressions denoting setuid programs.  @xref{setuid程序}.

@item @code{sudoers-file} (default: @code{%sudoers-specification})
@cindex sudoers file
The contents of the @file{/etc/sudoers} file as a file-like object
(@pxref{G-表达式, @code{local-file} and @code{plain-file}}).

This file specifies which users can use the @command{sudo} command, what
they are allowed to do, and what privileges they may gain.  The default is
that only @code{root} and members of the @code{wheel} group may use
@code{sudo}.

@end table

@deffn {Scheme Syntax} this-operating-system
When used in the @emph{lexical scope} of an operating system field
definition, this identifier resolves to the operating system being defined.

The example below shows how to refer to the operating system being defined
in the definition of the @code{label} field:

@lisp
(use-modules (gnu) (guix))

(operating-system
  ;; ...
  (label (package-full-name
          (operating-system-kernel this-operating-system))))
@end lisp

It is an error to refer to @code{this-operating-system} outside an operating
system definition.
@end deffn

@end deftp

@node 文件系统
@section 文件系统

The list of file systems to be mounted is specified in the
@code{file-systems} field of the operating system declaration (@pxref{使用配置系统}).  Each file system is declared using the
@code{file-system} form, like this:

@lisp
(file-system
  (mount-point "/home")
  (device "/dev/sda3")
  (type "ext4"))
@end lisp

As usual, some of the fields are mandatory---those shown in the example
above---while others can be omitted.  These are described below.

@deftp {Data Type} file-system
Objects of this type represent file systems to be mounted.  They contain the
following members:

@table @asis
@item @code{type}
This is a string specifying the type of the file system---e.g.,
@code{"ext4"}.

@item @code{mount-point}
This designates the place where the file system is to be mounted.

@item @code{device}
This names the ``source'' of the file system.  It can be one of three
things: a file system label, a file system UUID, or the name of a
@file{/dev} node.  Labels and UUIDs offer a way to refer to file systems
without having to hard-code their actual device name@footnote{Note that,
while it is tempting to use @file{/dev/disk/by-uuid} and similar device
names to achieve the same result, this is not recommended: These special
device nodes are created by the udev daemon and may be unavailable at the
time the device is mounted.}.

@findex file-system-label
File system labels are created using the @code{file-system-label} procedure,
UUIDs are created using @code{uuid}, and @file{/dev} node are plain
strings.  Here's an example of a file system referred to by its label, as
shown by the @command{e2label} command:

@lisp
(file-system
  (mount-point "/home")
  (type "ext4")
  (device (file-system-label "my-home")))
@end lisp

@findex uuid
UUIDs are converted from their string representation (as shown by the
@command{tune2fs -l} command) using the @code{uuid} form@footnote{The
@code{uuid} form expects 16-byte UUIDs as defined in
@uref{https://tools.ietf.org/html/rfc4122, RFC@tie{}4122}.  This is the form
of UUID used by the ext2 family of file systems and others, but it is
different from ``UUIDs'' found in FAT file systems, for instance.}, like
this:

@lisp
(file-system
  (mount-point "/home")
  (type "ext4")
  (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))
@end lisp

When the source of a file system is a mapped device (@pxref{映射的设备}), its @code{device} field @emph{must} refer to the mapped device
name---e.g., @file{"/dev/mapper/root-partition"}.  This is required so that
the system knows that mounting the file system depends on having the
corresponding device mapping established.

@item @code{flags} (default: @code{'()})
This is a list of symbols denoting mount flags.  Recognized flags include
@code{read-only}, @code{bind-mount}, @code{no-dev} (disallow access to
special files), @code{no-suid} (ignore setuid and setgid bits),
@code{no-atime} (do not update file access times), @code{strict-atime}
(update file access time), @code{lazy-time} (only update time on the
in-memory version of the file inode), and @code{no-exec} (disallow program
execution).  @xref{Mount-Unmount-Remount,,, libc, The GNU C Library
Reference Manual}, for more information on these flags.

@item @code{options} (default: @code{#f})
This is either @code{#f}, or a string denoting mount options passed to the
file system driver.  @xref{Mount-Unmount-Remount,,, libc, The GNU C Library
Reference Manual}, for details and run @command{man 8 mount} for options for
various file systems.  Note that the @code{file-system-options->alist} and
@code{alist->file-system-options} procedures from @code{(gnu system
file-systems)} can be used to convert file system options given as an
association list to the string representation, and vice-versa.

@item @code{mount?} (default: @code{#t})
This value indicates whether to automatically mount the file system when the
system is brought up.  When set to @code{#f}, the file system gets an entry
in @file{/etc/fstab} (read by the @command{mount} command) but is not
automatically mounted.

@item @code{needed-for-boot?} (default: @code{#f})
This Boolean value indicates whether the file system is needed when
booting.  If that is true, then the file system is mounted when the initial
RAM disk (initrd) is loaded.  This is always the case, for instance, for the
root file system.

@item @code{check?} (default: @code{#t})
This Boolean indicates whether the file system needs to be checked for
errors before being mounted.

@item @code{create-mount-point?} (default: @code{#f})
When true, the mount point is created if it does not exist yet.

@item @code{mount-may-fail?} (default: @code{#f})
When true, this indicates that mounting this file system can fail but that
should not be considered an error.  This is useful in unusual cases; an
example of this is @code{efivarfs}, a file system that can only be mounted
on EFI/UEFI systems.

@item @code{dependencies} (default: @code{'()})
This is a list of @code{<file-system>} or @code{<mapped-device>} objects
representing file systems that must be mounted or mapped devices that must
be opened before (and unmounted or closed after) this one.

As an example, consider a hierarchy of mounts: @file{/sys/fs/cgroup} is a
dependency of @file{/sys/fs/cgroup/cpu} and @file{/sys/fs/cgroup/memory}.

Another example is a file system that depends on a mapped device, for
example for an encrypted partition (@pxref{映射的设备}).
@end table
@end deftp

@deffn {Scheme Procedure} file-system-label @var{str}
This procedure returns an opaque file system label from @var{str}, a string:

@lisp
(file-system-label "home")
@result{} #<file-system-label "home">
@end lisp

File system labels are used to refer to file systems by label rather than by
device name.  See above for examples.
@end deffn

The @code{(gnu system file-systems)} exports the following useful variables.

@defvr {Scheme Variable} %base-file-systems
These are essential file systems that are required on normal systems, such
as @code{%pseudo-terminal-file-system} and @code{%immutable-store} (see
below).  Operating system declarations should always contain at least these.
@end defvr

@defvr {Scheme Variable} %pseudo-terminal-file-system
This is the file system to be mounted as @file{/dev/pts}.  It supports
@dfn{pseudo-terminals} created @i{via} @code{openpty} and similar functions
(@pxref{Pseudo-Terminals,,, libc, The GNU C Library Reference Manual}).
Pseudo-terminals are used by terminal emulators such as @command{xterm}.
@end defvr

@defvr {Scheme Variable} %shared-memory-file-system
This file system is mounted as @file{/dev/shm} and is used to support memory
sharing across processes (@pxref{Memory-mapped I/O, @code{shm_open},, libc,
The GNU C Library Reference Manual}).
@end defvr

@defvr {Scheme Variable} %immutable-store
This file system performs a read-only ``bind mount'' of @file{/gnu/store},
making it read-only for all the users including @code{root}.  This prevents
against accidental modification by software running as @code{root} or by
system administrators.

The daemon itself is still able to write to the store: it remounts it
read-write in its own ``name space.''
@end defvr

@defvr {Scheme Variable} %binary-format-file-system
The @code{binfmt_misc} file system, which allows handling of arbitrary
executable file types to be delegated to user space.  This requires the
@code{binfmt.ko} kernel module to be loaded.
@end defvr

@defvr {Scheme Variable} %fuse-control-file-system
The @code{fusectl} file system, which allows unprivileged users to mount and
unmount user-space FUSE file systems.  This requires the @code{fuse.ko}
kernel module to be loaded.
@end defvr

The @code{(gnu system uuid)} module provides tools to deal with file system
``unique identifiers'' (UUIDs).

@deffn {Scheme Procedure} uuid @var{str} [@var{type}]
Return an opaque UUID (unique identifier) object of the given @var{type} (a
symbol) by parsing @var{str} (a string):

@lisp
(uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")
@result{} #<<uuid> type: dce bv: @dots{}>

(uuid "1234-ABCD" 'fat)
@result{} #<<uuid> type: fat bv: @dots{}>
@end lisp

@var{type} may be one of @code{dce}, @code{iso9660}, @code{fat},
@code{ntfs}, or one of the commonly found synonyms for these.

UUIDs are another way to unambiguously refer to file systems in operating
system configuration.  See the examples above.
@end deffn


@node Btrfs file system
@subsection Btrfs file system

The Btrfs has special features, such as subvolumes, that merit being
explained in more details.  The following section attempts to cover basic as
well as complex uses of a Btrfs file system with the Guix System.

In its simplest usage, a Btrfs file system can be described, for example,
by:

@lisp
(file-system
  (mount-point "/home")
  (type "btrfs")
  (device (file-system-label "my-home")))
@end lisp

The example below is more complex, as it makes use of a Btrfs subvolume,
named @code{rootfs}.  The parent Btrfs file system is labeled
@code{my-btrfs-pool}, and is located on an encrypted device (hence the
dependency on @code{mapped-devices}):

@lisp
(file-system
  (device (file-system-label "my-btrfs-pool"))
  (mount-point "/")
  (type "btrfs")
  (options "subvol=rootfs")
  (dependencies mapped-devices))
@end lisp

Some bootloaders, for example GRUB, only mount a Btrfs partition at its top
level during the early boot, and rely on their configuration to refer to the
correct subvolume path within that top level.  The bootloaders operating in
this way typically produce their configuration on a running system where the
Btrfs partitions are already mounted and where the subvolume information is
readily available.  As an example, @command{grub-mkconfig}, the
configuration generator command shipped with GRUB, reads
@file{/proc/self/mountinfo} to determine the top-level path of a subvolume.

The Guix System produces a bootloader configuration using the operating
system configuration as its sole input; it is therefore necessary to extract
the subvolume name on which @file{/gnu/store} lives (if any)  from that
operating system configuration.  To better illustrate, consider a subvolume
named 'rootfs' which contains the root file system data.  In such situation,
the GRUB bootloader would only see the top level of the root Btrfs
partition, e.g.:

@example
/                   (top level)
├── rootfs          (subvolume directory)
    ├── gnu         (normal directory)
        ├── store   (normal directory)
[...]
@end example

Thus, the subvolume name must be prepended to the @file{/gnu/store} path of
the kernel, initrd binaries and any other files referred to in the GRUB
configuration that must be found during the early boot.

The next example shows a nested hierarchy of subvolumes and directories:

@example
/                   (top level)
├── rootfs          (subvolume)
    ├── gnu         (normal directory)
        ├── store   (subvolume)
[...]
@end example

This scenario would work without mounting the 'store' subvolume.  Mounting
'rootfs' is sufficient, since the subvolume name matches its intended mount
point in the file system hierarchy.  Alternatively, the 'store' subvolume
could be referred to by setting the @code{subvol} option to either
@code{/rootfs/gnu/store} or @code{rootfs/gnu/store}.

Finally, a more contrived example of nested subvolumes:

@example
/                           (top level)
├── root-snapshots          (subvolume)
    ├── root-current        (subvolume)
        ├── guix-store      (subvolume)
[...]
@end example

Here, the 'guix-store' subvolume doesn't match its intended mount point, so
it is necessary to mount it.  The subvolume must be fully specified, by
passing its file name to the @code{subvol} option.  To illustrate, the
'guix-store' subvolume could be mounted on @file{/gnu/store} by using a file
system declaration such as:

@lisp
(file-system
  (device (file-system-label "btrfs-pool-1"))
  (mount-point "/gnu/store")
  (type "btrfs")
  (options "subvol=root-snapshots/root-current/guix-store,\
compress-force=zstd,space_cache=v2"))
@end lisp

@node 映射的设备
@section 映射的设备

@cindex device mapping
@cindex mapped devices
The Linux kernel has a notion of @dfn{device mapping}: a block device, such
as a hard disk partition, can be @dfn{mapped} into another device, usually
in @code{/dev/mapper/}, with additional processing over the data that flows
through it@footnote{Note that the GNU@tie{}Hurd makes no difference between
the concept of a ``mapped device'' and that of a file system: both boil down
to @emph{translating} input/output operations made on a file to operations
on its backing store.  Thus, the Hurd implements mapped devices, like file
systems, using the generic @dfn{translator} mechanism (@pxref{Translators,,,
hurd, The GNU Hurd Reference Manual}).}.  A typical example is encryption
device mapping: all writes to the mapped device are encrypted, and all reads
are deciphered, transparently.  Guix extends this notion by considering any
device or set of devices that are @dfn{transformed} in some way to create a
new device; for instance, RAID devices are obtained by @dfn{assembling}
several other devices, such as hard disks or partitions, into a new one that
behaves as one partition.

Mapped devices are declared using the @code{mapped-device} form, defined as
follows; for examples, see below.

@deftp {Data Type} mapped-device
Objects of this type represent device mappings that will be made when the
system boots up.

@table @code
@item source
This is either a string specifying the name of the block device to be
mapped, such as @code{"/dev/sda3"}, or a list of such strings when several
devices need to be assembled for creating a new one.  In case of LVM this is
a string specifying name of the volume group to be mapped.

@item target
This string specifies the name of the resulting mapped device.  For kernel
mappers such as encrypted devices of type @code{luks-device-mapping},
specifying @code{"my-partition"} leads to the creation of the
@code{"/dev/mapper/my-partition"} device.  For RAID devices of type
@code{raid-device-mapping}, the full device name such as @code{"/dev/md0"}
needs to be given.  LVM logical volumes of type @code{lvm-device-mapping}
need to be specified as @code{"VGNAME-LVNAME"}.

@item targets
This list of strings specifies names of the resulting mapped devices in case
there are several.  The format is identical to @var{target}.

@item type
This must be a @code{mapped-device-kind} object, which specifies how
@var{source} is mapped to @var{target}.
@end table
@end deftp

@defvr {Scheme Variable} luks-device-mapping
This defines LUKS block device encryption using the @command{cryptsetup}
command from the package with the same name.  It relies on the
@code{dm-crypt} Linux kernel module.
@end defvr

@defvr {Scheme Variable} raid-device-mapping
This defines a RAID device, which is assembled using the @code{mdadm}
command from the package with the same name.  It requires a Linux kernel
module for the appropriate RAID level to be loaded, such as @code{raid456}
for RAID-4, RAID-5 or RAID-6, or @code{raid10} for RAID-10.
@end defvr

@cindex LVM, logical volume manager
@defvr {Scheme Variable} lvm-device-mapping
This defines one or more logical volumes for the Linux
@uref{https://www.sourceware.org/lvm2/, Logical Volume Manager (LVM)}.  The
volume group is activated by the @command{vgchange} command from the
@code{lvm2} package.
@end defvr

@cindex disk encryption
@cindex LUKS
The following example specifies a mapping from @file{/dev/sda3} to
@file{/dev/mapper/home} using LUKS---the
@url{https://gitlab.com/cryptsetup/cryptsetup,Linux Unified Key Setup}, a
standard mechanism for disk encryption.  The @file{/dev/mapper/home} device
can then be used as the @code{device} of a @code{file-system} declaration
(@pxref{文件系统}).

@lisp
(mapped-device
  (source "/dev/sda3")
  (target "home")
  (type luks-device-mapping))
@end lisp

Alternatively, to become independent of device numbering, one may obtain the
LUKS UUID (@dfn{unique identifier}) of the source device by a command like:

@example
cryptsetup luksUUID /dev/sda3
@end example

and use it as follows:

@lisp
(mapped-device
  (source (uuid "cb67fc72-0d54-4c88-9d4b-b225f30b0f44"))
  (target "home")
  (type luks-device-mapping))
@end lisp

@cindex swap encryption
It is also desirable to encrypt swap space, since swap space may contain
sensitive data.  One way to accomplish that is to use a swap file in a file
system on a device mapped via LUKS encryption.  In this way, the swap file
is encrypted because the entire device is encrypted.  @xref{准备安装,,Disk Partitioning}, for an example.

A RAID device formed of the partitions @file{/dev/sda1} and @file{/dev/sdb1}
may be declared as follows:

@lisp
(mapped-device
  (source (list "/dev/sda1" "/dev/sdb1"))
  (target "/dev/md0")
  (type raid-device-mapping))
@end lisp

The @file{/dev/md0} device can then be used as the @code{device} of a
@code{file-system} declaration (@pxref{文件系统}).  Note that the RAID
level need not be given; it is chosen during the initial creation and
formatting of the RAID device and is determined automatically later.

LVM logical volumes ``alpha'' and ``beta'' from volume group ``vg0'' can be
declared as follows:

@lisp
(mapped-device
  (source "vg0")
  (targets (list "vg0-alpha" "vg0-beta"))
  (type lvm-device-mapping))
@end lisp

Devices @file{/dev/mapper/vg0-alpha} and @file{/dev/mapper/vg0-beta} can
then be used as the @code{device} of a @code{file-system} declaration
(@pxref{文件系统}).

@node 用户帐号
@section 用户帐号

@cindex users
@cindex accounts
@cindex user accounts
User accounts and groups are entirely managed through the
@code{operating-system} declaration.  They are specified with the
@code{user-account} and @code{user-group} forms:

@lisp
(user-account
  (name "alice")
  (group "users")
  (supplementary-groups '("wheel"   ;allow use of sudo, etc.
                          "audio"   ;sound card
                          "video"   ;video devices such as webcams
                          "cdrom")) ;the good ol' CD-ROM
  (comment "Bob's sister"))
@end lisp

Here's a user account that uses a different shell and a custom home
directory (the default would be @file{"/home/bob"}):

@lisp
(user-account
  (name "bob")
  (group "users")
  (comment "Alice's bro")
  (shell (file-append zsh "/bin/zsh"))
  (home-directory "/home/robert"))
@end lisp

When booting or upon completion of @command{guix system reconfigure}, the
system ensures that only the user accounts and groups specified in the
@code{operating-system} declaration exist, and with the specified
properties.  Thus, account or group creations or modifications made by
directly invoking commands such as @command{useradd} are lost upon
reconfiguration or reboot.  This ensures that the system remains exactly as
declared.

@deftp {Data Type} user-account
Objects of this type represent user accounts.  The following members may be
specified:

@table @asis
@item @code{名字}
The name of the user account.

@item @code{group}
@cindex groups
This is the name (a string) or identifier (a number) of the user group this
account belongs to.

@item @code{supplementary-groups} (default: @code{'()})
Optionally, this can be defined as a list of group names that this account
belongs to.

@item @code{uid} (default: @code{#f})
This is the user ID for this account (a number), or @code{#f}.  In the
latter case, a number is automatically chosen by the system when the account
is created.

@item @code{comment} (default: @code{""})
A comment about the account, such as the account owner's full name.

@item @code{home-directory}
This is the name of the home directory for the account.

@item @code{create-home-directory?} (default: @code{#t})
Indicates whether the home directory of this account should be created if it
does not exist yet.

@item @code{shell} (default: Bash)
This is a G-expression denoting the file name of a program to be used as the
shell (@pxref{G-表达式}).  For example, you would refer to the Bash
executable like this:

@lisp
(file-append bash "/bin/bash")
@end lisp

@noindent
... and to the Zsh executable like that:

@lisp
(file-append zsh "/bin/zsh")
@end lisp

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the account is a ``system'' account.
System accounts are sometimes treated specially; for instance, graphical
login managers do not list them.

@anchor{user-account-password}
@cindex password, for user accounts
@item @code{password} (default: @code{#f})
You would normally leave this field to @code{#f}, initialize user passwords
as @code{root} with the @command{passwd} command, and then let users change
it with @command{passwd}.  Passwords set with @command{passwd} are of course
preserved across reboot and reconfiguration.

If you @emph{do} want to set an initial password for an account, then this
field must contain the encrypted password, as a string.  You can use the
@code{crypt} procedure for this purpose:

@lisp
(user-account
  (name "charlie")
  (group "users")

  ;; Specify a SHA-512-hashed initial password.
  (password (crypt "InitialPassword!" "$6$abc")))
@end lisp

@quotation 注
The hash of this initial password will be available in a file in
@file{/gnu/store}, readable by all the users, so this method must be used
with care.
@end quotation

@xref{Passphrase Storage,,, libc, The GNU C Library Reference Manual}, for
more information on password encryption, and @ref{Encryption,,, guile, GNU
Guile Reference Manual}, for information on Guile's @code{crypt} procedure.

@end table
@end deftp

@cindex groups
User group declarations are even simpler:

@lisp
(user-group (name "students"))
@end lisp

@deftp {Data Type} user-group
This type is for, well, user groups.  There are just a few fields:

@table @asis
@item @code{名字}
The name of the group.

@item @code{id} (default: @code{#f})
The group identifier (a number).  If @code{#f}, a new number is
automatically allocated when the group is created.

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the group is a ``system'' group.
System groups have low numerical IDs.

@item @code{password} (default: @code{#f})
What, user groups can have a password? Well, apparently yes.  Unless
@code{#f}, this field specifies the password of the group.

@end table
@end deftp

For convenience, a variable lists all the basic user groups one may expect:

@defvr {Scheme Variable} %base-groups
This is the list of basic user groups that users and/or packages expect to
be present on the system.  This includes groups such as ``root'', ``wheel'',
and ``users'', as well as groups used to control access to specific devices
such as ``audio'', ``disk'', and ``cdrom''.
@end defvr

@defvr {Scheme Variable} %base-user-accounts
This is the list of basic system accounts that programs may expect to find
on a GNU/Linux system, such as the ``nobody'' account.

Note that the ``root'' account is not included here.  It is a special-case
and is automatically added whether or not it is specified.
@end defvr

@node 键盘布局
@section 键盘布局

@cindex keyboard layout
@cindex keymap
To specify what each key of your keyboard does, you need to tell the
operating system what @dfn{keyboard layout} you want to use.  The default,
when nothing is specified, is the US English QWERTY layout for 105-key PC
keyboards.  However, German speakers will usually prefer the German QWERTZ
layout, French speakers will want the AZERTY layout, and so on; hackers
might prefer Dvorak or bépo, and they might even want to further customize
the effect of some of the keys.  This section explains how to get that done.

@cindex keyboard layout, definition
There are three components that will want to know about your keyboard
layout:

@itemize
@item
The @emph{bootloader} may want to know what keyboard layout you want to use
(@pxref{引导设置, @code{keyboard-layout}}).  This is useful
if you want, for instance, to make sure that you can type the passphrase of
your encrypted root partition using the right layout.

@item
The @emph{operating system kernel}, Linux, will need that so that the
console is properly configured (@pxref{操作系统参考,
@code{keyboard-layout}}).

@item
The @emph{graphical display server}, usually Xorg, also has its own idea of
the keyboard layout (@pxref{X窗口, @code{keyboard-layout}}).
@end itemize

Guix allows you to configure all three separately but, fortunately, it
allows you to share the same keyboard layout for all three components.

@cindex XKB, keyboard layouts
Keyboard layouts are represented by records created by the
@code{keyboard-layout} procedure of @code{(gnu system keyboard)}.  Following
the X Keyboard extension (XKB), each layout has four attributes: a name
(often a language code such as ``fi'' for Finnish or ``jp'' for Japanese),
an optional variant name, an optional keyboard model name, and a possibly
empty list of additional options.  In most cases the layout name is all you
care about.

@deffn {Scheme Procedure} keyboard-layout @var{name} [@var{variant}] @
                [#:model] [#:options '()] Return a new keyboard layout with the given
@var{name} and @var{variant}.

@var{name} must be a string such as @code{"fr"}; @var{variant} must be a
string such as @code{"bepo"} or @code{"nodeadkeys"}.  See the
@code{xkeyboard-config} package for valid options.
@end deffn

Here are a few examples:

@lisp
;; The German QWERTZ layout.  Here we assume a standard
;; "pc105" keyboard model.
(keyboard-layout "de")

;; The bépo variant of the French layout.
(keyboard-layout "fr" "bepo")

;; The Catalan layout.
(keyboard-layout "es" "cat")

;; Arabic layout with "Alt-Shift" to switch to US layout.
(keyboard-layout "ar,us" #:options '("grp:alt_shift_toggle"))

;; The Latin American Spanish layout.  In addition, the
;; "Caps Lock" key is used as an additional "Ctrl" key,
;; and the "Menu" key is used as a "Compose" key to enter
;; accented letters.
(keyboard-layout "latam"
                 #:options '("ctrl:nocaps" "compose:menu"))

;; The Russian layout for a ThinkPad keyboard.
(keyboard-layout "ru" #:model "thinkpad")

;; The "US international" layout, which is the US layout plus
;; dead keys to enter accented characters.  This is for an
;; Apple MacBook keyboard.
(keyboard-layout "us" "intl" #:model "macbook78")
@end lisp

See the @file{share/X11/xkb} directory of the @code{xkeyboard-config}
package for a complete list of supported layouts, variants, and models.

@cindex keyboard layout, configuration
Let's say you want your system to use the Turkish keyboard layout throughout
your system---bootloader, console, and Xorg.  Here's what your system
configuration would look like:

@findex set-xorg-configuration
@lisp
;; Using the Turkish layout for the bootloader, the console,
;; and for Xorg.

(operating-system
  ;; ...
  (keyboard-layout (keyboard-layout "tr"))  ;for the console
  (bootloader (bootloader-configuration
                (bootloader grub-efi-bootloader)
                (target "/boot/efi")
                (keyboard-layout keyboard-layout))) ;for GRUB
  (services (cons (set-xorg-configuration
                    (xorg-configuration             ;for Xorg
                      (keyboard-layout keyboard-layout)))
                  %desktop-services)))
@end lisp

In the example above, for GRUB and for Xorg, we just refer to the
@code{keyboard-layout} field defined above, but we could just as well refer
to a different layout.  The @code{set-xorg-configuration} procedure
communicates the desired Xorg configuration to the graphical log-in manager,
by default GDM.

We've discussed how to specify the @emph{default} keyboard layout of your
system when it starts, but you can also adjust it at run time:

@itemize
@item
If you're using GNOME, its settings panel has a ``Region & Language'' entry
where you can select one or more keyboard layouts.

@item
Under Xorg, the @command{setxkbmap} command (from the same-named package)
allows you to change the current layout.  For example, this is how you would
change the layout to US Dvorak:

@example
setxkbmap us dvorak
@end example

@item
The @code{loadkeys} command changes the keyboard layout in effect in the
Linux console.  However, note that @code{loadkeys} does @emph{not} use the
XKB keyboard layout categorization described above.  The command below loads
the French bépo layout:

@example
loadkeys fr-bepo
@end example
@end itemize

@node 区域
@section 区域

@cindex locale
A @dfn{locale} defines cultural conventions for a particular language and
region of the world (@pxref{区域,,, libc, The GNU C Library Reference
Manual}).  Each locale has a name that typically has the form
@code{@var{language}_@var{territory}.@var{codeset}}---e.g.,
@code{fr_LU.utf8} designates the locale for the French language, with
cultural conventions from Luxembourg, and using the UTF-8 encoding.

@cindex locale definition
Usually, you will want to specify the default locale for the machine using
the @code{locale} field of the @code{operating-system} declaration
(@pxref{操作系统参考, @code{locale}}).

The selected locale is automatically added to the @dfn{locale definitions}
known to the system if needed, with its codeset inferred from its
name---e.g., @code{bo_CN.utf8} will be assumed to use the @code{UTF-8}
codeset.  Additional locale definitions can be specified in the
@code{locale-definitions} slot of @code{operating-system}---this is useful,
for instance, if the codeset could not be inferred from the locale name.
The default set of locale definitions includes some widely used locales, but
not all the available locales, in order to save space.

For instance, to add the North Frisian locale for Germany, the value of that
field may be:

@lisp
(cons (locale-definition
        (name "fy_DE.utf8") (source "fy_DE"))
      %default-locale-definitions)
@end lisp

Likewise, to save space, one might want @code{locale-definitions} to list
only the locales that are actually used, as in:

@lisp
(list (locale-definition
        (name "ja_JP.eucjp") (source "ja_JP")
        (charset "EUC-JP")))
@end lisp

@vindex LOCPATH
The compiled locale definitions are available at
@file{/run/current-system/locale/X.Y}, where @code{X.Y} is the libc version,
which is the default location where the GNU@tie{}libc provided by Guix looks
for locale data.  This can be overridden using the @env{LOCPATH} environment
variable (@pxref{locales-and-locpath, @env{LOCPATH} and locale packages}).

The @code{locale-definition} form is provided by the @code{(gnu system
locale)} module.  Details are given below.

@deftp {Data Type} locale-definition
This is the data type of a locale definition.

@table @asis

@item @code{名字}
The name of the locale.  @xref{Locale Names,,, libc, The GNU C Library
Reference Manual}, for more information on locale names.

@item @code{source}
The name of the source for that locale.  This is typically the
@code{@var{language}_@var{territory}} part of the locale name.

@item @code{charset} (default: @code{"UTF-8"})
The ``character set'' or ``code set'' for that locale,
@uref{https://www.iana.org/assignments/character-sets, as defined by IANA}.

@end table
@end deftp

@defvr {Scheme Variable} %default-locale-definitions
A list of commonly used UTF-8 locales, used as the default value of the
@code{locale-definitions} field of @code{operating-system} declarations.

@cindex locale name
@cindex normalized codeset in locale names
These locale definitions use the @dfn{normalized codeset} for the part that
follows the dot in the name (@pxref{Using gettextized software, normalized
codeset,, libc, The GNU C Library Reference Manual}).  So for instance it
has @code{uk_UA.utf8} but @emph{not}, say, @code{uk_UA.UTF-8}.
@end defvr

@subsection Locale Data Compatibility Considerations

@cindex incompatibility, of locale data
@code{operating-system} declarations provide a @code{locale-libcs} field to
specify the GNU@tie{}libc packages that are used to compile locale
declarations (@pxref{操作系统参考}).  ``Why would I care?'',
you may ask.  Well, it turns out that the binary format of locale data is
occasionally incompatible from one libc version to another.

@c See <https://sourceware.org/ml/libc-alpha/2015-09/msg00575.html>
@c and <https://lists.gnu.org/archive/html/guix-devel/2015-08/msg00737.html>.
For instance, a program linked against libc version 2.21 is unable to read
locale data produced with libc 2.22; worse, that program @emph{aborts}
instead of simply ignoring the incompatible locale data@footnote{Versions
2.23 and later of GNU@tie{}libc will simply skip the incompatible locale
data, which is already an improvement.}.  Similarly, a program linked
against libc 2.22 can read most, but not all, of the locale data from libc
2.21 (specifically, @env{LC_COLLATE} data is incompatible); thus calls to
@code{setlocale} may fail, but programs will not abort.

The ``problem'' with Guix is that users have a lot of freedom: They can
choose whether and when to upgrade software in their profiles, and might be
using a libc version different from the one the system administrator used to
build the system-wide locale data.

Fortunately, unprivileged users can also install their own locale data and
define @env{GUIX_LOCPATH} accordingly (@pxref{locales-and-locpath,
@env{GUIX_LOCPATH} and locale packages}).

Still, it is best if the system-wide locale data at
@file{/run/current-system/locale} is built for all the libc versions
actually in use on the system, so that all the programs can access it---this
is especially crucial on a multi-user system.  To do that, the administrator
can specify several libc packages in the @code{locale-libcs} field of
@code{operating-system}:

@lisp
(use-package-modules base)

(operating-system
  ;; @dots{}
  (locale-libcs (list glibc-2.21 (canonical-package glibc))))
@end lisp

This example would lead to a system containing locale definitions for both
libc 2.21 and the current version of libc in
@file{/run/current-system/locale}.


@node 服务
@section 服务

@cindex system services
An important part of preparing an @code{operating-system} declaration is
listing @dfn{system services} and their configuration (@pxref{使用配置系统}).  System services are typically daemons launched when
the system boots, or other actions needed at that time---e.g., configuring
network access.

Guix has a broad definition of ``service'' (@pxref{合成服务}),
but many services are managed by the GNU@tie{}Shepherd (@pxref{Shepherd服务}).  On a running system, the @command{herd} command allows you to
list the available services, show their status, start and stop them, or do
other specific operations (@pxref{Jump Start,,, shepherd, The GNU Shepherd
Manual}).  For example:

@example
# herd status
@end example

The above command, run as @code{root}, lists the currently defined
services.  The @command{herd doc} command shows a synopsis of the given
service and its associated actions:

@example
# herd doc nscd
Run libc's name service cache daemon (nscd).

# herd doc nscd action invalidate
invalidate: Invalidate the given cache--e.g., 'hosts' for host name lookups.
@end example

The @command{start}, @command{stop}, and @command{restart} sub-commands have
the effect you would expect.  For instance, the commands below stop the nscd
service and restart the Xorg display server:

@example
# herd stop nscd
Service nscd has been stopped.
# herd restart xorg-server
Service xorg-server has been stopped.
Service xorg-server has been started.
@end example

The following sections document the available services, starting with the
core services, that may be used in an @code{operating-system} declaration.

@menu
* 基础服务::             必要的系统服务。
* 执行计划任务::       mcron服务。
* 日志轮替::             rottlog服务。
* 网络服务::             网络设置，SSH后台进程，等
* Unattended Upgrades::      Automated system upgrades.
* X窗口::                  图形显示器。
* 打印服务::             本地和远程打印机的支持。
* 桌面服务::             D-Bus和桌面服务。
* 声音服务::             ALSA和Pulseaudio服务。
* 数据库服务::          SQL数据库，键值仓库，等
* 邮件服务::             IMAP，POP3，SMTP，等
* 消息服务::             消息服务。
* 电话服务::             电话服务。
* File-Sharing Services::    File-sharing services.
* 监控服务::             监控服务。
* Kerberos服务::           Kerberos服务。
* LDAP Services::            LDAP services.
* Web服务::                Web服务。
* 证书服务::             Let's Encrypt TLS证书。
* DNS服务::                DNS后台进程。
* VPN服务::                VPN后台进程。
* 网络文件系统::       网络文件系统相关的服务。
* 持续集成::             Cuirass and Laminar services.
* 电源管理服务::       延长电池寿命。
* 音频服务::             MPD。
* 虚拟化服务::          虚拟化服务。
* 版本控制服务::       远程访问Git仓库。
* 游戏服务::             游戏服务器。
* PAM Mount Service::        Service to mount volumes when logging in.
* Guix Services::            Services relating specifically to Guix.
* Linux Services::           Services tied to the Linux kernel.
* Hurd Services::            Services specific for a Hurd System.
* 其它各种服务::       其它服务。
@end menu

@node 基础服务
@subsection 基础服务

The @code{(gnu services base)} module provides definitions for the basic
services that one expects from the system.  The services exported by this
module are listed below.

@defvr {Scheme Variable} %base-services
This variable contains a list of basic services (@pxref{服务类型和服务}, for more information on service objects) one would expect from
the system: a login service (mingetty) on each tty, syslogd, the libc name
service cache daemon (nscd), the udev device manager, and more.

This is the default value of the @code{services} field of
@code{operating-system} declarations.  Usually, when customizing a system,
you will want to append services to @code{%base-services}, like this:

@lisp
(append (list (service avahi-service-type)
              (service openssh-service-type))
        %base-services)
@end lisp
@end defvr

@defvr {Scheme Variable} special-files-service-type
This is the service that sets up ``special files'' such as @file{/bin/sh};
an instance of it is part of @code{%base-services}.

The value associated with @code{special-files-service-type} services must be
a list of tuples where the first element is the ``special file'' and the
second element is its target.  By default it is:

@cindex @file{/bin/sh}
@cindex @file{sh}, in @file{/bin}
@lisp
`(("/bin/sh" ,(file-append bash "/bin/sh")))
@end lisp

@cindex @file{/usr/bin/env}
@cindex @file{env}, in @file{/usr/bin}
If you want to add, say, @code{/usr/bin/env} to your system, you can change
it to:

@lisp
`(("/bin/sh" ,(file-append bash "/bin/sh"))
  ("/usr/bin/env" ,(file-append coreutils "/bin/env")))
@end lisp

Since this is part of @code{%base-services}, you can use
@code{modify-services} to customize the set of special files (@pxref{服务参考, @code{modify-services}}).  But the simple way to add a special
file is @i{via} the @code{extra-special-file} procedure (see below).
@end defvr

@deffn {Scheme Procedure} extra-special-file @var{file} @var{target}
Use @var{target} as the ``special file'' @var{file}.

For example, adding the following lines to the @code{services} field of your
operating system declaration leads to a @file{/usr/bin/env} symlink:

@lisp
(extra-special-file "/usr/bin/env"
                    (file-append coreutils "/bin/env"))
@end lisp
@end deffn

@deffn {Scheme Procedure} host-name-service @var{name}
Return a service that sets the host name to @var{name}.
@end deffn

@defvr {Scheme Variable} console-font-service-type
Install the given fonts on the specified ttys (fonts are per virtual console
on the kernel Linux).  The value of this service is a list of tty/font
pairs.  The font can be the name of a font provided by the @code{kbd}
package or any valid argument to @command{setfont}, as in this example:

@lisp
`(("tty1" . "LatGrkCyr-8x16")
  ("tty2" . ,(file-append
                font-tamzen
                "/share/kbd/consolefonts/TamzenForPowerline10x20.psf"))
  ("tty3" . ,(file-append
                font-terminus
                "/share/consolefonts/ter-132n"))) ; for HDPI
@end lisp
@end defvr

@deffn {Scheme Procedure} login-service @var{config}
Return a service to run login according to @var{config}, a
@code{<login-configuration>} object, which specifies the message of the day,
among other things.
@end deffn

@deftp {Data Type} login-configuration
This is the data type representing the configuration of login.

@table @asis

@item @code{motd}
@cindex message of the day
A file-like object containing the ``message of the day''.

@item @code{allow-empty-passwords?} (default: @code{#t})
Allow empty passwords by default so that first-time users can log in when
the 'root' account has just been created.

@end table
@end deftp

@deffn {Scheme Procedure} mingetty-service @var{config}
Return a service to run mingetty according to @var{config}, a
@code{<mingetty-configuration>} object, which specifies the tty to run,
among other things.
@end deffn

@deftp {Data Type} mingetty-configuration
This is the data type representing the configuration of Mingetty, which
provides the default implementation of virtual console log-in.

@table @asis

@item @code{tty}
The name of the console this Mingetty runs on---e.g., @code{"tty1"}.

@item @code{auto-login} (default: @code{#f})
When true, this field must be a string denoting the user name under which
the system automatically logs in.  When it is @code{#f}, a user name and
password must be entered to log in.

@item @code{login-program} (default: @code{#f})
This must be either @code{#f}, in which case the default log-in program is
used (@command{login} from the Shadow tool suite), or a gexp denoting the
name of the log-in program.

@item @code{login-pause?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{auto-login}, the user will
have to press a key before the log-in shell is launched.

@item @code{clear-on-logout?} (default: @code{#t})
When set to @code{#t}, the screen will be cleared after logout.

@item @code{mingetty} (default: @var{mingetty})
The Mingetty package to use.

@end table
@end deftp

@deffn {Scheme Procedure} agetty-service @var{config}
Return a service to run agetty according to @var{config}, an
@code{<agetty-configuration>} object, which specifies the tty to run, among
other things.
@end deffn

@deftp {Data Type} agetty-configuration
This is the data type representing the configuration of agetty, which
implements virtual and serial console log-in.  See the @code{agetty(8)} man
page for more information.

@table @asis

@item @code{tty}
The name of the console this agetty runs on, as a string---e.g.,
@code{"ttyS0"}.  This argument is optional, it will default to a reasonable
default serial port used by the kernel Linux.

For this, if there is a value for an option @code{agetty.tty} in the kernel
command line, agetty will extract the device name of the serial port from it
and use that.

If not and if there is a value for an option @code{console} with a tty in
the Linux command line, agetty will extract the device name of the serial
port from it and use that.

In both cases, agetty will leave the other serial device settings (baud rate
etc.)@: alone---in the hope that Linux pinned them to the correct values.

@item @code{baud-rate} (default: @code{#f})
A string containing a comma-separated list of one or more baud rates, in
descending order.

@item @code{term} (default: @code{#f})
A string containing the value used for the @env{TERM} environment variable.

@item @code{eight-bits?} (default: @code{#f})
When @code{#t}, the tty is assumed to be 8-bit clean, and parity detection
is disabled.

@item @code{auto-login} (default: @code{#f})
When passed a login name, as a string, the specified user will be logged in
automatically without prompting for their login name or password.

@item @code{no-reset?} (default: @code{#f})
When @code{#t}, don't reset terminal cflags (control modes).

@item @code{host} (default: @code{#f})
This accepts a string containing the ``login_host'', which will be written
into the @file{/var/run/utmpx} file.

@item @code{remote?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{host}, this will add an
@code{-r} fakehost option to the command line of the login program specified
in @var{login-program}.

@item @code{flow-control?} (default: @code{#f})
When set to @code{#t}, enable hardware (RTS/CTS) flow control.

@item @code{no-issue?} (default: @code{#f})
When set to @code{#t}, the contents of the @file{/etc/issue} file will not
be displayed before presenting the login prompt.

@item @code{init-string} (default: @code{#f})
This accepts a string that will be sent to the tty or modem before sending
anything else.  It can be used to initialize a modem.

@item @code{no-clear?} (default: @code{#f})
When set to @code{#t}, agetty will not clear the screen before showing the
login prompt.

@item @code{login-program} (default: (file-append shadow "/bin/login"))
This must be either a gexp denoting the name of a log-in program, or unset,
in which case the default value is the @command{login} from the Shadow tool
suite.

@item @code{local-line} (default: @code{#f})
Control the CLOCAL line flag.  This accepts one of three symbols as
arguments, @code{'auto}, @code{'always}, or @code{'never}.  If @code{#f},
the default value chosen by agetty is @code{'auto}.

@item @code{extract-baud?} (default: @code{#f})
When set to @code{#t}, instruct agetty to try to extract the baud rate from
the status messages produced by certain types of modems.

@item @code{skip-login?} (default: @code{#f})
When set to @code{#t}, do not prompt the user for a login name.  This can be
used with @var{login-program} field to use non-standard login systems.

@item @code{no-newline?} (default: @code{#f})
When set to @code{#t}, do not print a newline before printing the
@file{/etc/issue} file.

@c Is this dangerous only when used with login-program, or always?
@item @code{login-options} (default: @code{#f})
This option accepts a string containing options that are passed to the login
program.  When used with the @var{login-program}, be aware that a malicious
user could try to enter a login name containing embedded options that could
be parsed by the login program.

@item @code{login-pause} (default: @code{#f})
When set to @code{#t}, wait for any key before showing the login prompt.
This can be used in conjunction with @var{auto-login} to save memory by
lazily spawning shells.

@item @code{chroot} (default: @code{#f})
Change root to the specified directory.  This option accepts a directory
path as a string.

@item @code{hangup?} (default: @code{#f})
Use the Linux system call @code{vhangup} to do a virtual hangup of the
specified terminal.

@item @code{keep-baud?} (default: @code{#f})
When set to @code{#t}, try to keep the existing baud rate.  The baud rates
from @var{baud-rate} are used when agetty receives a @key{BREAK} character.

@item @code{timeout} (default: @code{#f})
When set to an integer value, terminate if no user name could be read within
@var{timeout} seconds.

@item @code{detect-case?} (default: @code{#f})
When set to @code{#t}, turn on support for detecting an uppercase-only
terminal.  This setting will detect a login name containing only uppercase
letters as indicating an uppercase-only terminal and turn on some
upper-to-lower case conversions.  Note that this will not support Unicode
characters.

@item @code{wait-cr?} (default: @code{#f})
When set to @code{#t}, wait for the user or modem to send a carriage-return
or linefeed character before displaying @file{/etc/issue} or login prompt.
This is typically used with the @var{init-string} option.

@item @code{no-hints?} (default: @code{#f})
When set to @code{#t}, do not print hints about Num, Caps, and Scroll locks.

@item @code{no-hostname?} (default: @code{#f})
By default, the hostname is printed.  When this option is set to @code{#t},
no hostname will be shown at all.

@item @code{long-hostname?} (default: @code{#f})
By default, the hostname is only printed until the first dot.  When this
option is set to @code{#t}, the fully qualified hostname by
@code{gethostname} or @code{getaddrinfo} is shown.

@item @code{erase-characters} (default: @code{#f})
This option accepts a string of additional characters that should be
interpreted as backspace when the user types their login name.

@item @code{kill-characters} (default: @code{#f})
This option accepts a string that should be interpreted to mean ``ignore all
previous characters'' (also called a ``kill'' character) when the user types
their login name.

@item @code{chdir} (default: @code{#f})
This option accepts, as a string, a directory path that will be changed to
before login.

@item @code{delay} (default: @code{#f})
This options accepts, as an integer, the number of seconds to sleep before
opening the tty and displaying the login prompt.

@item @code{nice} (default: @code{#f})
This option accepts, as an integer, the nice value with which to run the
@command{login} program.

@item @code{extra-options} (default: @code{'()})
This option provides an ``escape hatch'' for the user to provide arbitrary
command-line arguments to @command{agetty} as a list of strings.

@end table
@end deftp

@deffn {Scheme Procedure} kmscon-service-type @var{config}
Return a service to run
@uref{https://www.freedesktop.org/wiki/Software/kmscon,kmscon} according to
@var{config}, a @code{<kmscon-configuration>} object, which specifies the
tty to run, among other things.
@end deffn

@deftp {Data Type} kmscon-configuration
This is the data type representing the configuration of Kmscon, which
implements virtual console log-in.

@table @asis

@item @code{virtual-terminal}
The name of the console this Kmscon runs on---e.g., @code{"tty1"}.

@item @code{login-program} (default: @code{#~(string-append #$shadow "/bin/login")})
A gexp denoting the name of the log-in program.  The default log-in program
is @command{login} from the Shadow tool suite.

@item @code{login-arguments} (default: @code{'("-p")})
A list of arguments to pass to @command{login}.

@item @code{auto-login} (default: @code{#f})
When passed a login name, as a string, the specified user will be logged in
automatically without prompting for their login name or password.

@item @code{hardware-acceleration?} (default: #f)
Whether to use hardware acceleration.

@item @code{font-engine} (default: @code{"pango"})
Font engine used in Kmscon.

@item @code{font-size} (default: @code{12})
Font size used in Kmscon.

@item @code{kmscon} (default: @var{kmscon})
The Kmscon package to use.

@end table
@end deftp

@cindex name service cache daemon
@cindex nscd
@deffn {Scheme Procedure} nscd-service [@var{config}] [#:glibc glibc] @
                [#:name-services '()] Return a service that runs the libc name service cache
daemon (nscd) with the given @var{config}---an @code{<nscd-configuration>}
object.  @xref{Name Service Switch}, for an example.

For convenience, the Shepherd service for nscd provides the following
actions:

@table @code
@item invalidate
@cindex cache invalidation, nscd
@cindex nscd, cache invalidation
This invalidate the given cache.  For instance, running:

@example
herd invalidate nscd hosts
@end example

@noindent
invalidates the host name lookup cache of nscd.

@item statistics
Running @command{herd statistics nscd} displays information about nscd usage
and caches.
@end table

@end deffn

@defvr {Scheme Variable} %nscd-default-configuration
This is the default @code{<nscd-configuration>} value (see below) used by
@code{nscd-service}.  It uses the caches defined by
@code{%nscd-default-caches}; see below.
@end defvr

@deftp {Data Type} nscd-configuration
This is the data type representing the name service cache daemon (nscd)
configuration.

@table @asis

@item @code{name-services} (default: @code{'()})
List of packages denoting @dfn{name services} that must be visible to the
nscd---e.g., @code{(list @var{nss-mdns})}.

@item @code{glibc} (default: @var{glibc})
Package object denoting the GNU C Library providing the @command{nscd}
command.

@item @code{log-file} (default: @code{"/var/log/nscd.log"})
Name of the nscd log file.  This is where debugging output goes when
@code{debug-level} is strictly positive.

@item @code{debug-level} (default: @code{0})
Integer denoting the debugging levels.  Higher numbers mean that more
debugging output is logged.

@item @code{caches} (default: @code{%nscd-default-caches})
List of @code{<nscd-cache>} objects denoting things to be cached; see below.

@end table
@end deftp

@deftp {Data Type} nscd-cache
Data type representing a cache database of nscd and its parameters.

@table @asis

@item @code{database}
This is a symbol representing the name of the database to be cached.  Valid
values are @code{passwd}, @code{group}, @code{hosts}, and @code{services},
which designate the corresponding NSS database (@pxref{NSS Basics,,, libc,
The GNU C Library Reference Manual}).

@item @code{positive-time-to-live}
@itemx @code{negative-time-to-live} (default: @code{20})
A number representing the number of seconds during which a positive or
negative lookup result remains in cache.

@item @code{check-files?} (default: @code{#t})
Whether to check for updates of the files corresponding to @var{database}.

For instance, when @var{database} is @code{hosts}, setting this flag
instructs nscd to check for updates in @file{/etc/hosts} and to take them
into account.

@item @code{persistent?} (default: @code{#t})
Whether the cache should be stored persistently on disk.

@item @code{shared?} (default: @code{#t})
Whether the cache should be shared among users.

@item @code{max-database-size} (default: 32@tie{}MiB)
Maximum size in bytes of the database cache.

@c XXX: 'suggested-size' and 'auto-propagate?' seem to be expert
@c settings, so leave them out.

@end table
@end deftp

@defvr {Scheme Variable} %nscd-default-caches
List of @code{<nscd-cache>} objects used by default by
@code{nscd-configuration} (see above).

It enables persistent and aggressive caching of service and host name
lookups.  The latter provides better host name lookup performance,
resilience in the face of unreliable name servers, and also better
privacy---often the result of host name lookups is in local cache, so
external name servers do not even need to be queried.
@end defvr

@anchor{syslog-configuration-type}
@cindex syslog
@cindex logging
@deftp {Data Type} syslog-configuration
This data type represents the configuration of the syslog daemon.

@table @asis
@item @code{syslogd} (default: @code{#~(string-append #$inetutils "/libexec/syslogd")})
The syslog daemon to use.

@item @code{config-file} (default: @code{%default-syslog.conf})
The syslog configuration file to use.

@end table
@end deftp

@anchor{syslog-service}
@cindex syslog
@deffn {Scheme Procedure} syslog-service @var{config}
Return a service that runs a syslog daemon according to @var{config}.

@xref{syslogd invocation,,, inetutils, GNU Inetutils}, for more information
on the configuration file syntax.
@end deffn

@defvr {Scheme Variable} guix-service-type
This is the type of the service that runs the build daemon,
@command{guix-daemon} (@pxref{调用guix-daemon}).  Its value must be a
@code{guix-configuration} record as described below.
@end defvr

@anchor{guix-configuration-type}
@deftp {Data Type} guix-configuration
This data type represents the configuration of the Guix build daemon.
@xref{调用guix-daemon}, for more information.

@table @asis
@item @code{guix} (default: @var{guix})
The Guix package to use.

@item @code{build-group} (default: @code{"guixbuild"})
Name of the group for build user accounts.

@item @code{build-accounts} (default: @code{10})
Number of build user accounts to create.

@item @code{authorize-key?} (default: @code{#t})
@cindex substitutes，对其授权
Whether to authorize the substitute keys listed in
@code{authorized-keys}---by default that of @code{@value{SUBSTITUTE-SERVER}}
(@pxref{substitutes}).

When @code{authorize-key?} is true, @file{/etc/guix/acl} cannot be changed
by invoking @command{guix archive --authorize}.  You must instead adjust
@code{guix-configuration} as you wish and reconfigure the system.  This
ensures that your operating system configuration file is self-contained.

@quotation 注
When booting or reconfiguring to a system where @code{authorize-key?} is
true, the existing @file{/etc/guix/acl} file is backed up as
@file{/etc/guix/acl.bak} if it was determined to be a manually modified
file.  This is to facilitate migration from earlier versions, which allowed
for in-place modifications to @file{/etc/guix/acl}.
@end quotation

@vindex %default-authorized-guix-keys
@item @code{authorized-keys} (default: @code{%default-authorized-guix-keys})
The list of authorized key files for archive imports, as a list of
string-valued gexps (@pxref{调用guix archive}).  By default, it
contains that of @code{@value{SUBSTITUTE-SERVER}} (@pxref{substitutes}).
See @code{substitute-urls} below for an example on how to change it.

@item @code{use-substitutes?} (default: @code{#t})
Whether to use substitutes.

@item @code{substitute-urls} (default: @code{%default-substitute-urls})
The list of URLs where to look for substitutes by default.

Suppose you would like to fetch substitutes from @code{guix.example.org} in
addition to @code{@value{SUBSTITUTE-SERVER}}.  You will need to do two
things: (1) add @code{guix.example.org} to @code{substitute-urls}, and (2)
authorize its signing key, having done appropriate checks (@pxref{授权substitute服务器。}).  The configuration below does exactly that:

@lisp
(guix-configuration
  (substitute-urls
   (append (list "https://guix.example.org")
           %default-substitute-urls))
  (authorized-keys
   (append (list (local-file "./guix.example.org-key.pub"))
           %default-authorized-guix-keys)))
@end lisp

This example assumes that the file @file{./guix.example.org-key.pub}
contains the public key that @code{guix.example.org} uses to sign
substitutes.

@item @code{max-silent-time} (default: @code{0})
@itemx @code{timeout} (default: @code{0})
The number of seconds of silence and the number of seconds of activity,
respectively, after which a build process times out.  A value of zero
disables the timeout.

@item @code{log-compression} (default: @code{'bzip2})
The type of compression used for build logs---one of @code{gzip},
@code{bzip2}, or @code{none}.

@item @code{discover?} (default: @code{#f})
Whether to discover substitute servers on the local network using mDNS and
DNS-SD.

@item @code{extra-options} (default: @code{'()})
List of extra command-line options for @command{guix-daemon}.

@item @code{log-file} (default: @code{"/var/log/guix-daemon.log"})
File where @command{guix-daemon}'s standard output and standard error are
written.

@cindex HTTP proxy, for @code{guix-daemon}
@cindex proxy, for @code{guix-daemon} HTTP access
@item @code{http-proxy} (default: @code{#f})
The URL of the HTTP and HTTPS proxy used for downloading fixed-output
derivations and substitutes.

It is also possible to change the daemon's proxy at run time through the
@code{set-http-proxy} action, which restarts it:

@example
herd set-http-proxy guix-daemon http://localhost:8118
@end example

To clear the proxy settings, run:

@example
herd set-http-proxy guix-daemon
@end example

@item @code{tmpdir} (default: @code{#f})
A directory path where the @command{guix-daemon} will perform builds.

@end table
@end deftp

@deffn {Scheme Procedure} udev-service [#:udev @var{eudev} #:rules @code{'()}]
Run @var{udev}, which populates the @file{/dev} directory dynamically.  udev
rules can be provided as a list of files through the @var{rules} variable.
The procedures @code{udev-rule}, @code{udev-rules-service} and
@code{file->udev-rule} from @code{(gnu services base)} simplify the creation
of such rule files.

The @command{herd rules udev} command, as root, returns the name of the
directory containing all the active udev rules.
@end deffn

@deffn {Scheme Procedure} udev-rule [@var{file-name} @var{contents}]
Return a udev-rule file named @var{file-name} containing the rules defined
by the @var{contents} literal.

In the following example, a rule for a USB device is defined to be stored in
the file @file{90-usb-thing.rules}.  The rule runs a script upon detecting a
USB device with a given product identifier.

@lisp
(define %example-udev-rule
  (udev-rule
    "90-usb-thing.rules"
    (string-append "ACTION==\"add\", SUBSYSTEM==\"usb\", "
                   "ATTR@{product@}==\"Example\", "
                   "RUN+=\"/path/to/script\"")))
@end lisp
@end deffn

@deffn {Scheme Procedure} udev-rules-service [@var{name} @var{rules}] @
               [#:groups @var{groups}] Return a service that extends
@code{udev-service-type } with @var{rules} and @code{account-service-type}
with @var{groups} as system groups.  This works by creating a singleton
service type @code{@var{name}-udev-rules}, of which the returned service is
an instance.

Here we show how it can be used to extend @code{udev-service-type} with the
previously defined rule @code{%example-udev-rule}.

@lisp
(operating-system
 ;; @dots{}
 (services
   (cons (udev-rules-service 'usb-thing %example-udev-rule)
         %desktop-services)))
@end lisp
@end deffn

@deffn {Scheme Procedure} file->udev-rule [@var{file-name} @var{file}]
Return a udev file named @var{file-name} containing the rules defined within
@var{file}, a file-like object.

The following example showcases how we can use an existing rule file.

@lisp
(use-modules (guix download)     ;for url-fetch
             (guix packages)     ;for origin
             @dots{})

(define %android-udev-rules
  (file->udev-rule
    "51-android-udev.rules"
    (let ((version "20170910"))
      (origin
       (method url-fetch)
       (uri (string-append "https://raw.githubusercontent.com/M0Rf30/"
                           "android-udev-rules/" version "/51-android.rules"))
       (sha256
        (base32 "0lmmagpyb6xsq6zcr2w1cyx9qmjqmajkvrdbhjx32gqf1d9is003"))))))
@end lisp
@end deffn

Additionally, Guix package definitions can be included in @var{rules} in
order to extend the udev rules with the definitions found under their
@file{lib/udev/rules.d} sub-directory.  In lieu of the previous
@var{file->udev-rule} example, we could have used the
@var{android-udev-rules} package which exists in Guix in the @code{(gnu
packages android)} module.

The following example shows how to use the @var{android-udev-rules} package
so that the Android tool @command{adb} can detect devices without root
privileges.  It also details how to create the @code{adbusers} group, which
is required for the proper functioning of the rules defined within the
@code{android-udev-rules} package.  To create such a group, we must define
it both as part of the @code{supplementary-groups} of our
@code{user-account} declaration, as well as in the @var{groups} of the
@code{udev-rules-service} procedure.

@lisp
(use-modules (gnu packages android)  ;for android-udev-rules
             (gnu system shadow)     ;for user-group
             @dots{})

(operating-system
  ;; @dots{}
  (users (cons (user-account
                ;; @dots{}
                (supplementary-groups
                 '("adbusers"   ;for adb
                   "wheel" "netdev" "audio" "video")))))
  ;; @dots{}
  (services
    (cons (udev-rules-service 'android android-udev-rules
                              #:groups '("adbusers"))
          %desktop-services)))
@end lisp

@defvr {Scheme Variable} urandom-seed-service-type
Save some entropy in @code{%random-seed-file} to seed @file{/dev/urandom}
when rebooting.  It also tries to seed @file{/dev/urandom} from
@file{/dev/hwrng} while booting, if @file{/dev/hwrng} exists and is
readable.
@end defvr

@defvr {Scheme Variable} %random-seed-file
This is the name of the file where some random bytes are saved by
@var{urandom-seed-service} to seed @file{/dev/urandom} when rebooting.  It
defaults to @file{/var/lib/random-seed}.
@end defvr

@cindex mouse
@cindex gpm
@defvr {Scheme Variable} gpm-service-type
This is the type of the service that runs GPM, the @dfn{general-purpose
mouse daemon}, which provides mouse support to the Linux console.  GPM
allows users to use the mouse in the console, notably to select, copy, and
paste text.

The value for services of this type must be a @code{gpm-configuration} (see
below).  This service is not part of @code{%base-services}.
@end defvr

@deftp {Data Type} gpm-configuration
Data type representing the configuration of GPM.

@table @asis
@item @code{options} (default: @code{%default-gpm-options})
Command-line options passed to @command{gpm}.  The default set of options
instruct @command{gpm} to listen to mouse events on @file{/dev/input/mice}.
@xref{Command Line,,, gpm, gpm manual}, for more information.

@item @code{gpm} (default: @code{gpm})
The GPM package to use.

@end table
@end deftp

@anchor{guix-publish-service-type}
@deffn {Scheme Variable} guix-publish-service-type
This is the service type for @command{guix publish} (@pxref{调用guix publish}).  Its value must be a @code{guix-publish-configuration} object, as
described below.

This assumes that @file{/etc/guix} already contains a signing key pair as
created by @command{guix archive --generate-key} (@pxref{调用guix archive}).  If that is not the case, the service will fail to start.
@end deffn

@deftp {Data Type} guix-publish-configuration
Data type representing the configuration of the @code{guix publish} service.

@table @asis
@item @code{guix} (default: @code{guix})
The Guix package to use.

@item @code{port} (default: @code{80})
The TCP port to listen for connections.

@item @code{host} (default: @code{"localhost"})
The host (and thus, network interface) to listen to.  Use @code{"0.0.0.0"}
to listen on all the network interfaces.

@item @code{advertise?} (default: @code{#f})
When true, advertise the service on the local network @i{via} the DNS-SD
protocol, using Avahi.

This allows neighboring Guix devices with discovery on (see
@code{guix-configuration} above) to discover this @command{guix publish}
instance and to automatically download substitutes from it.

@item @code{compression} (default: @code{'(("gzip" 3) ("zstd" 3))})
This is a list of compression method/level tuple used when compressing
substitutes.  For example, to compress all substitutes with @emph{both} lzip
at level 7 and gzip at level 9, write:

@lisp
'(("lzip" 7) ("gzip" 9))
@end lisp

Level 9 achieves the best compression ratio at the expense of increased CPU
usage, whereas level 1 achieves fast compression.  @xref{调用guix publish}, for more information on the available compression methods and the
tradeoffs involved.

An empty list disables compression altogether.

@item @code{nar-path} (default: @code{"nar"})
The URL path at which ``nars'' can be fetched.  @xref{调用guix publish,
@option{--nar-path}}, for details.

@item @code{cache} (default: @code{#f})
When it is @code{#f}, disable caching and instead generate archives on
demand.  Otherwise, this should be the name of a directory---e.g.,
@code{"/var/cache/guix/publish"}---where @command{guix publish} caches
archives and meta-data ready to be sent.  @xref{调用guix publish,
@option{--cache}}, for more information on the tradeoffs involved.

@item @code{workers} (default: @code{#f})
When it is an integer, this is the number of worker threads used for
caching; when @code{#f}, the number of processors is used.  @xref{调用guix publish, @option{--workers}}, for more information.

@item @code{cache-bypass-threshold} (default: 10 MiB)
When @code{cache} is true, this is the maximum size in bytes of a store item
for which @command{guix publish} may bypass its cache in case of a cache
miss.  @xref{调用guix publish, @option{--cache-bypass-threshold}}, for
more information.

@item @code{ttl} (default: @code{#f})
When it is an integer, this denotes the @dfn{time-to-live} in seconds of the
published archives.  @xref{调用guix publish, @option{--ttl}}, for more
information.
@end table
@end deftp

@anchor{rngd-service}
@deffn {Scheme Procedure} rngd-service [#:rng-tools @var{rng-tools}] @
            [#:device "/dev/hwrng"] Return a service that runs the @command{rngd}
program from @var{rng-tools} to add @var{device} to the kernel's entropy
pool.  The service will fail if @var{device} does not exist.
@end deffn

@anchor{pam-limits-service}
@cindex session limits
@cindex ulimit
@cindex priority
@cindex realtime
@cindex jackd
@cindex nofile
@cindex open file descriptors
@deffn {Scheme Procedure} pam-limits-service [#:limits @code{'()}]

Return a service that installs a configuration file for the
@uref{http://linux-pam.org/Linux-PAM-html/sag-pam_limits.html,
@code{pam_limits} module}.  The procedure optionally takes a list of
@code{pam-limits-entry} values, which can be used to specify @code{ulimit}
limits and @code{nice} priority limits to user sessions.

The following limits definition sets two hard and soft limits for all login
sessions of users in the @code{realtime} group:

@lisp
(pam-limits-service
 (list
  (pam-limits-entry "@@realtime" 'both 'rtprio 99)
  (pam-limits-entry "@@realtime" 'both 'memlock 'unlimited)))
@end lisp

The first entry increases the maximum realtime priority for non-privileged
processes; the second entry lifts any restriction of the maximum address
space that can be locked in memory.  These settings are commonly used for
real-time audio systems.

Another useful example is raising the maximum number of open file
descriptors that can be used:

@lisp
(pam-limits-service
 (list
  (pam-limits-entry "*" 'both 'nofile 100000)))
@end lisp

In the above example, the asterisk means the limit should apply to any
user.  It is important to ensure the chosen value doesn't exceed the maximum
system value visible in the @file{/proc/sys/fs/file-max} file, else the
users would be prevented from login in.  For more information about the
Pluggable Authentication Module (PAM) limits, refer to the @samp{pam_limits}
man page from the @code{linux-pam} package.
@end deffn

@node 执行计划任务
@subsection 执行计划任务

@cindex cron
@cindex mcron
@cindex scheduling jobs
The @code{(gnu services mcron)} module provides an interface to
GNU@tie{}mcron, a daemon to run jobs at scheduled times (@pxref{Top,,,
mcron, GNU@tie{}mcron}).  GNU@tie{}mcron is similar to the traditional Unix
@command{cron} daemon; the main difference is that it is implemented in
Guile Scheme, which provides a lot of flexibility when specifying the
scheduling of jobs and their actions.

The example below defines an operating system that runs the
@command{updatedb} (@pxref{Invoking updatedb,,, find, Finding Files})  and
the @command{guix gc} commands (@pxref{调用guix gc}) daily, as well as
the @command{mkid} command on behalf of an unprivileged user (@pxref{mkid
invocation,,, idutils, ID Database Utilities}).  It uses gexps to introduce
job definitions that are passed to mcron (@pxref{G-表达式}).

@lisp
(use-modules (guix) (gnu) (gnu services mcron))
(use-package-modules base idutils)

(define updatedb-job
  ;; Run 'updatedb' at 3AM every day.  Here we write the
  ;; job's action as a Scheme procedure.
  #~(job '(next-hour '(3))
         (lambda ()
           (execl (string-append #$findutils "/bin/updatedb")
                  "updatedb"
                  "--prunepaths=/tmp /var/tmp /gnu/store"))))

(define garbage-collector-job
  ;; Collect garbage 5 minutes after midnight every day.
  ;; The job's action is a shell command.
  #~(job "5 0 * * *"            ;Vixie cron syntax
         "guix gc -F 1G"))

(define idutils-job
  ;; Update the index database as user "charlie" at 12:15PM
  ;; and 19:15PM.  This runs from the user's home directory.
  #~(job '(next-minute-from (next-hour '(12 19)) '(15))
         (string-append #$idutils "/bin/mkid src")
         #:user "charlie"))

(operating-system
  ;; @dots{}

  ;; %BASE-SERVICES already includes an instance of
  ;; 'mcron-service-type', which we extend with additional
  ;; jobs using 'simple-service'.
  (services (cons (simple-service 'my-cron-jobs
                                   mcron-service-type
                                   (list garbage-collector-job
                                         updatedb-job
                                         idutils-job))
                  %base-services)))
@end lisp

For more complex jobs defined in Scheme where you need control over the top
level, for instance to introduce a @code{use-modules} form, you can move
your code to a separate program using the @code{program-file} procedure of
the @code{(guix gexp)} module (@pxref{G-表达式}).  The example below
illustrates that.

@lisp
(define %battery-alert-job
  ;; Beep when the battery percentage falls below %MIN-LEVEL.
  #~(job
     '(next-minute (range 0 60 1))
     #$(program-file
        "battery-alert.scm"
        (with-imported-modules (source-module-closure
                                '((guix build utils)))
          #~(begin
              (use-modules (guix build utils)
                           (ice-9 popen)
                           (ice-9 regex)
                           (ice-9 textual-ports)
                           (srfi srfi-2))

              (define %min-level 20)

              (setenv "LC_ALL" "C")     ;ensure English output
              (and-let* ((input-pipe (open-pipe*
                                      OPEN_READ
                                      #$(file-append acpi "/bin/acpi")))
                         (output (get-string-all input-pipe))
                         (m (string-match "Discharging, ([0-9]+)%" output))
                         (level (string->number (match:substring m 1)))
                         ((< level %min-level)))
                (format #t "warning: Battery level is low (~a%)~%" level)
                (invoke #$(file-append beep "/bin/beep") "-r5")))))))
@end lisp

@xref{Guile Syntax, mcron job specifications,, mcron, GNU@tie{}mcron}, for
more information on mcron job specifications.  Below is the reference of the
mcron service.

On a running system, you can use the @code{schedule} action of the service
to visualize the mcron jobs that will be executed next:

@example
# herd schedule mcron
@end example

@noindent
The example above lists the next five tasks that will be executed, but you
can also specify the number of tasks to display:

@example
# herd schedule mcron 10
@end example

@defvr {Scheme Variable} mcron-service-type
This is the type of the @code{mcron} service, whose value is an
@code{mcron-configuration} object.

This service type can be the target of a service extension that provides it
additional job specifications (@pxref{合成服务}).  In other
words, it is possible to define services that provide additional mcron jobs
to run.
@end defvr

@deftp {Data Type} mcron-configuration
Data type representing the configuration of mcron.

@table @asis
@item @code{mcron} (default: @var{mcron})
The mcron package to use.

@item @code{jobs}
This is a list of gexps (@pxref{G-表达式}), where each gexp corresponds
to an mcron job specification (@pxref{Syntax, mcron job specifications,,
mcron, GNU@tie{}mcron}).
@end table
@end deftp


@node 日志轮替
@subsection 日志轮替

@cindex rottlog
@cindex log rotation
@cindex logging
Log files such as those found in @file{/var/log} tend to grow endlessly, so
it's a good idea to @dfn{rotate} them once in a while---i.e., archive their
contents in separate files, possibly compressed.  The @code{(gnu services
admin)} module provides an interface to GNU@tie{}Rot[t]log, a log rotation
tool (@pxref{Top,,, rottlog, GNU Rot[t]log Manual}).

This service is part of @code{%base-services}, and thus enabled by default,
with the default settings, for commonly encountered log files.  The example
below shows how to extend it with an additional @dfn{rotation}, should you
need to do that (usually, services that produce log files already take care
of that):

@lisp
(use-modules (guix) (gnu))
(use-service-modules admin)

(define my-log-files
  ;; Log files that I want to rotate.
  '("/var/log/something.log" "/var/log/another.log"))

(operating-system
  ;; @dots{}
  (services (cons (simple-service 'rotate-my-stuff
                                  rottlog-service-type
                                  (list (log-rotation
                                         (frequency 'daily)
                                         (files my-log-files))))
                  %base-services)))
@end lisp

@defvr {Scheme Variable} rottlog-service-type
This is the type of the Rottlog service, whose value is a
@code{rottlog-configuration} object.

Other services can extend this one with new @code{log-rotation} objects (see
below), thereby augmenting the set of files to be rotated.

This service type can define mcron jobs (@pxref{执行计划任务}) to
run the rottlog service.
@end defvr

@deftp {Data Type} rottlog-configuration
Data type representing the configuration of rottlog.

@table @asis
@item @code{rottlog} (default: @code{rottlog})
The Rottlog package to use.

@item @code{rc-file} (default: @code{(file-append rottlog "/etc/rc")})
The Rottlog configuration file to use (@pxref{Mandatory RC Variables,,,
rottlog, GNU Rot[t]log Manual}).

@item @code{rotations} (default: @code{%default-rotations})
A list of @code{log-rotation} objects as defined below.

@item @code{jobs}
This is a list of gexps where each gexp corresponds to an mcron job
specification (@pxref{执行计划任务}).
@end table
@end deftp

@deftp {Data Type} log-rotation
Data type representing the rotation of a group of log files.

Taking an example from the Rottlog manual (@pxref{Period Related File
Examples,,, rottlog, GNU Rot[t]log Manual}), a log rotation might be defined
like this:

@lisp
(log-rotation
  (frequency 'daily)
  (files '("/var/log/apache/*"))
  (options '("storedir apache-archives"
             "rotate 6"
             "notifempty"
             "nocompress")))
@end lisp

The list of fields is as follows:

@table @asis
@item @code{frequency} (default: @code{'weekly})
The log rotation frequency, a symbol.

@item @code{files}
The list of files or file glob patterns to rotate.

@item @code{options} (default: @code{'()})
The list of rottlog options for this rotation (@pxref{Configuration
parameters,,, rottlog, GNU Rot[t]lg Manual}).

@item @code{post-rotate} (default: @code{#f})
Either @code{#f} or a gexp to execute once the rotation has completed.
@end table
@end deftp

@defvr {Scheme Variable} %default-rotations
Specifies weekly rotation of @code{%rotated-files} and of
@file{/var/log/guix-daemon.log}.
@end defvr

@defvr {Scheme Variable} %rotated-files
The list of syslog-controlled files to be rotated.  By default it is:
@code{'("/var/log/messages" "/var/log/secure" "/var/log/debug" \ 
"/var/log/maillog")}.
@end defvr

@node 网络服务
@subsection 网络服务

The @code{(gnu services networking)} module provides services to configure
the network interface.

@cindex DHCP, networking service
@defvr {Scheme Variable} dhcp-client-service-type
This is the type of services that run @var{dhcp}, a Dynamic Host
Configuration Protocol (DHCP) client, on all the non-loopback network
interfaces.  Its value is the DHCP client package to use, @code{isc-dhcp} by
default.
@end defvr

@deffn {Scheme Procedure} dhcpd-service-type
This type defines a service that runs a DHCP daemon.  To create a service of
this type, you must supply a @code{<dhcpd-configuration>}.  For example:

@lisp
(service dhcpd-service-type
         (dhcpd-configuration
          (config-file (local-file "my-dhcpd.conf"))
          (interfaces '("enp0s25"))))
@end lisp
@end deffn

@deftp {Data Type} dhcpd-configuration
@table @asis
@item @code{package} (default: @code{isc-dhcp})
The package that provides the DHCP daemon.  This package is expected to
provide the daemon at @file{sbin/dhcpd} relative to its output directory.
The default package is the @uref{https://www.isc.org/products/DHCP, ISC's
DHCP server}.
@item @code{config-file} (default: @code{#f})
The configuration file to use.  This is required.  It will be passed to
@code{dhcpd} via its @code{-cf} option.  This may be any ``file-like''
object (@pxref{G-表达式, file-like objects}).  See @code{man
dhcpd.conf} for details on the configuration file syntax.
@item @code{version} (default: @code{"4"})
The DHCP version to use.  The ISC DHCP server supports the values ``4'',
``6'', and ``4o6''.  These correspond to the @code{dhcpd} program options
@code{-4}, @code{-6}, and @code{-4o6}.  See @code{man dhcpd} for details.
@item @code{run-directory} (default: @code{"/run/dhcpd"})
The run directory to use.  At service activation time, this directory will
be created if it does not exist.
@item @code{pid-file} (default: @code{"/run/dhcpd/dhcpd.pid"})
The PID file to use.  This corresponds to the @code{-pf} option of
@code{dhcpd}.  See @code{man dhcpd} for details.
@item @code{interfaces} (default: @code{'()})
The names of the network interfaces on which dhcpd should listen for
broadcasts.  If this list is not empty, then its elements (which must be
strings) will be appended to the @code{dhcpd} invocation when starting the
daemon.  It may not be necessary to explicitly specify any interfaces here;
see @code{man dhcpd} for details.
@end table
@end deftp

@defvr {Scheme Variable} static-networking-service-type
@c TODO Document <static-networking> data structures.
This is the type for statically-configured network interfaces.
@end defvr

@deffn {Scheme Procedure} static-networking-service @var{interface} @var{ip} @
       [#:netmask #f] [#:gateway #f] [#:name-servers @code{'()}] @ [#:requirement
@code{'(udev)}] Return a service that starts @var{interface} with address
@var{ip}.  If @var{netmask} is true, use it as the network mask.  If
@var{gateway} is true, it must be a string specifying the default network
gateway.  @var{requirement} can be used to declare a dependency on another
service before configuring the interface.

This procedure can be called several times, one for each network interface
of interest.  Behind the scenes what it does is extend
@code{static-networking-service-type} with additional network interfaces to
handle.

For example:

@lisp
(static-networking-service "eno1" "192.168.1.82"
                           #:gateway "192.168.1.2"
                           #:name-servers '("192.168.1.2"))
@end lisp
@end deffn

@cindex wicd
@cindex wireless
@cindex WiFi
@cindex network management
@deffn {Scheme Procedure} wicd-service [#:wicd @var{wicd}]
Return a service that runs @url{https://launchpad.net/wicd,Wicd}, a network
management daemon that aims to simplify wired and wireless networking.

This service adds the @var{wicd} package to the global profile, providing
several commands to interact with the daemon and configure networking:
@command{wicd-client}, a graphical user interface, and the
@command{wicd-cli} and @command{wicd-curses} user interfaces.
@end deffn

@cindex ModemManager

@defvr {Scheme Variable} modem-manager-service-type
This is the service type for the
@uref{https://wiki.gnome.org/Projects/ModemManager, ModemManager} service.
The value for this service type is a @code{modem-manager-configuration}
record.

This service is part of @code{%desktop-services} (@pxref{桌面服务}).
@end defvr

@deftp {Data Type} modem-manager-configuration
Data type representing the configuration of ModemManager.

@table @asis
@item @code{modem-manager} (default: @code{modem-manager})
The ModemManager package to use.

@end table
@end deftp

@cindex USB_ModeSwitch
@cindex Modeswitching

@defvr {Scheme Variable} usb-modeswitch-service-type
This is the service type for the
@uref{https://www.draisberghof.de/usb_modeswitch/, USB_ModeSwitch} service.
The value for this service type is a @code{usb-modeswitch-configuration}
record.

When plugged in, some USB modems (and other USB devices) initially present
themselves as a read-only storage medium and not as a modem.  They need to
be @dfn{modeswitched} before they are usable.  The USB_ModeSwitch service
type installs udev rules to automatically modeswitch these devices when they
are plugged in.

This service is part of @code{%desktop-services} (@pxref{桌面服务}).
@end defvr

@deftp {Data Type} usb-modeswitch-configuration
Data type representing the configuration of USB_ModeSwitch.

@table @asis
@item @code{usb-modeswitch} (default: @code{usb-modeswitch})
The USB_ModeSwitch package providing the binaries for modeswitching.

@item @code{usb-modeswitch-data} (default: @code{usb-modeswitch-data})
The package providing the device data and udev rules file used by
USB_ModeSwitch.

@item @code{config-file} (default: @code{#~(string-append #$usb-modeswitch:dispatcher "/etc/usb_modeswitch.conf")})
Which config file to use for the USB_ModeSwitch dispatcher.  By default the
config file shipped with USB_ModeSwitch is used which disables logging to
@file{/var/log} among other default settings.  If set to @code{#f}, no
config file is used.

@end table
@end deftp

@cindex NetworkManager

@defvr {Scheme Variable} network-manager-service-type
This is the service type for the
@uref{https://wiki.gnome.org/Projects/NetworkManager, NetworkManager}
service. The value for this service type is a
@code{network-manager-configuration} record.

This service is part of @code{%desktop-services} (@pxref{桌面服务}).
@end defvr

@deftp {Data Type} network-manager-configuration
Data type representing the configuration of NetworkManager.

@table @asis
@item @code{network-manager} (default: @code{network-manager})
The NetworkManager package to use.

@item @code{dns} (default: @code{"default"})
Processing mode for DNS, which affects how NetworkManager uses the
@code{resolv.conf} configuration file.

@table @samp
@item default
NetworkManager will update @code{resolv.conf} to reflect the nameservers
provided by currently active connections.

@item dnsmasq
NetworkManager will run @code{dnsmasq} as a local caching nameserver, using
a @dfn{conditional forwarding} configuration if you are connected to a VPN,
and then update @code{resolv.conf} to point to the local nameserver.

With this setting, you can share your network connection.  For example when
you want to share your network connection to another laptop @i{via} an
Ethernet cable, you can open @command{nm-connection-editor} and configure
the Wired connection's method for IPv4 and IPv6 to be ``Shared to other
computers'' and reestablish the connection (or reboot).

You can also set up a @dfn{host-to-guest connection} to QEMU VMs
(@pxref{在虚拟机里安装 Guix}).  With a host-to-guest connection, you can
e.g.@: access a Web server running on the VM (@pxref{Web服务}) from a
Web browser on your host system, or connect to the VM @i{via} SSH
(@pxref{网络服务, @code{openssh-service-type}}).  To set up a
host-to-guest connection, run this command once:

@example
nmcli connection add type tun \
 connection.interface-name tap0 \
 tun.mode tap tun.owner $(id -u) \
 ipv4.method shared \
 ipv4.addresses 172.28.112.1/24
@end example

Then each time you launch your QEMU VM (@pxref{在虚拟机里运行Guix}), pass
@option{-nic tap,ifname=tap0,script=no,downscript=no} to
@command{qemu-system-...}.

@item none
NetworkManager will not modify @code{resolv.conf}.
@end table

@item @code{vpn-plugins} (default: @code{'()})
This is the list of available plugins for virtual private networks (VPNs).
An example of this is the @code{network-manager-openvpn} package, which
allows NetworkManager to manage VPNs @i{via} OpenVPN.

@end table
@end deftp

@cindex Connman
@deffn {Scheme Variable} connman-service-type
This is the service type to run @url{https://01.org/connman,Connman}, a
network connection manager.

Its value must be an @code{connman-configuration} record as in this example:

@lisp
(service connman-service-type
         (connman-configuration
           (disable-vpn? #t)))
@end lisp

See below for details about @code{connman-configuration}.
@end deffn

@deftp {Data Type} connman-configuration
Data Type representing the configuration of connman.

@table @asis
@item @code{connman} (default: @var{connman})
The connman package to use.

@item @code{disable-vpn?} (default: @code{#f})
When true, disable connman's vpn plugin.
@end table
@end deftp

@cindex WPA Supplicant
@defvr {Scheme Variable} wpa-supplicant-service-type
This is the service type to run @url{https://w1.fi/wpa_supplicant/,WPA
supplicant}, an authentication daemon required to authenticate against
encrypted WiFi or ethernet networks.
@end defvr

@deftp {Data Type} wpa-supplicant-configuration
Data type representing the configuration of WPA Supplicant.

It takes the following parameters:

@table @asis
@item @code{wpa-supplicant} (default: @code{wpa-supplicant})
The WPA Supplicant package to use.

@item @code{requirement} (default: @code{'(user-processes loopback syslogd)}
List of services that should be started before WPA Supplicant starts.

@item @code{dbus?} (default: @code{#t})
Whether to listen for requests on D-Bus.

@item @code{pid-file} (default: @code{"/var/run/wpa_supplicant.pid"})
Where to store the PID file.

@item @code{interface} (default: @code{#f})
If this is set, it must specify the name of a network interface that WPA
supplicant will control.

@item @code{config-file} (default: @code{#f})
Optional configuration file to use.

@item @code{extra-options} (default: @code{'()})
List of additional command-line arguments to pass to the daemon.
@end table
@end deftp

@cindex hostapd service, for Wi-Fi access points
@cindex Wi-Fi access points, hostapd service
@defvr {Scheme Variable} hostapd-service-type
This is the service type to run the @uref{https://w1.fi/hostapd/, hostapd}
daemon to set up WiFi (IEEE 802.11) access points and authentication
servers.  Its associated value must be a @code{hostapd-configuration} as
shown below:

@lisp
;; Use wlan1 to run the access point for "My Network".
(service hostapd-service-type
         (hostapd-configuration
          (interface "wlan1")
          (ssid "My Network")
          (channel 12)))
@end lisp
@end defvr

@deftp {Data Type} hostapd-configuration
This data type represents the configuration of the hostapd service, with the
following fields:

@table @asis
@item @code{package} (default: @code{hostapd})
The hostapd package to use.

@item @code{interface} (default: @code{"wlan0"})
The network interface to run the WiFi access point.

@item @code{ssid}
The SSID (@dfn{service set identifier}), a string that identifies this
network.

@item @code{broadcast-ssid?} (default: @code{#t})
Whether to broadcast this SSID.

@item @code{channel} (default: @code{1})
The WiFi channel to use.

@item @code{driver} (default: @code{"nl80211"})
The driver interface type.  @code{"nl80211"} is used with all Linux mac80211
drivers.  Use @code{"none"} if building hostapd as a standalone RADIUS
server that does # not control any wireless/wired driver.

@item @code{extra-settings} (default: @code{""})
Extra settings to append as-is to the hostapd configuration file.  See
@uref{https://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf} for the
configuration file reference.
@end table
@end deftp

@defvr {Scheme Variable} simulated-wifi-service-type
This is the type of a service to simulate WiFi networking, which can be
useful in virtual machines for testing purposes.  The service loads the
Linux kernel
@uref{https://www.kernel.org/doc/html/latest/networking/mac80211_hwsim/mac80211_hwsim.html,
@code{mac80211_hwsim} module} and starts hostapd to create a pseudo WiFi
network that can be seen on @code{wlan0}, by default.

The service's value is a @code{hostapd-configuration} record.
@end defvr

@cindex iptables
@defvr {Scheme Variable} iptables-service-type
This is the service type to set up an iptables configuration.  iptables is a
packet filtering framework supported by the Linux kernel.  This service
supports configuring iptables for both IPv4 and IPv6.  A simple example
configuration rejecting all incoming connections except those to the ssh
port 22 is shown below.

@lisp
(service iptables-service-type
         (iptables-configuration
          (ipv4-rules (plain-file "iptables.rules" "*filter
:INPUT ACCEPT
:FORWARD ACCEPT
:OUTPUT ACCEPT
-A INPUT -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-port-unreachable
COMMIT
"))
          (ipv6-rules (plain-file "ip6tables.rules" "*filter
:INPUT ACCEPT
:FORWARD ACCEPT
:OUTPUT ACCEPT
-A INPUT -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp6-port-unreachable
COMMIT
"))))
@end lisp
@end defvr

@deftp {Data Type} iptables-configuration
The data type representing the configuration of iptables.

@table @asis
@item @code{iptables} (default: @code{iptables})
The iptables package that provides @code{iptables-restore} and
@code{ip6tables-restore}.
@item @code{ipv4-rules} (default: @code{%iptables-accept-all-rules})
The iptables rules to use.  It will be passed to @code{iptables-restore}.
This may be any ``file-like'' object (@pxref{G-表达式, file-like
objects}).
@item @code{ipv6-rules} (default: @code{%iptables-accept-all-rules})
The ip6tables rules to use.  It will be passed to @code{ip6tables-restore}.
This may be any ``file-like'' object (@pxref{G-表达式, file-like
objects}).
@end table
@end deftp

@cindex nftables
@defvr {Scheme Variable} nftables-service-type
This is the service type to set up a nftables configuration.  nftables is a
netfilter project that aims to replace the existing iptables, ip6tables,
arptables and ebtables framework.  It provides a new packet filtering
framework, a new user-space utility @command{nft}, and a compatibility layer
for iptables.  This service comes with a default ruleset
@code{%default-nftables-ruleset} that rejecting all incoming connections
except those to the ssh port 22.  To use it, simply write:

@lisp
(service nftables-service-type)
@end lisp
@end defvr

@deftp {Data Type} nftables-configuration
The data type representing the configuration of nftables.

@table @asis
@item @code{package} (default: @code{nftables})
The nftables package that provides @command{nft}.
@item @code{ruleset} (default: @code{%default-nftables-ruleset})
The nftables ruleset to use.  This may be any ``file-like'' object
(@pxref{G-表达式, file-like objects}).
@end table
@end deftp

@cindex NTP (Network Time Protocol), service
@cindex ntpd, service for the Network Time Protocol daemon
@cindex real time clock
@defvr {Scheme Variable} ntp-service-type
This is the type of the service running the @uref{https://www.ntp.org,
Network Time Protocol (NTP)} daemon, @command{ntpd}.  The daemon will keep
the system clock synchronized with that of the specified NTP servers.

The value of this service is an @code{ntpd-configuration} object, as
described below.
@end defvr

@deftp {Data Type} ntp-configuration
This is the data type for the NTP service configuration.

@table @asis
@item @code{servers} (default: @code{%ntp-servers})
This is the list of servers (@code{<ntp-server>} records) with which
@command{ntpd} will be synchronized.  See the @code{ntp-server} data type
definition below.

@item @code{allow-large-adjustment?} (default: @code{#t})
This determines whether @command{ntpd} is allowed to make an initial
adjustment of more than 1,000 seconds.

@item @code{ntp} (default: @code{ntp})
The NTP package to use.
@end table
@end deftp

@defvr {Scheme Variable} %ntp-servers
List of host names used as the default NTP servers.  These are servers of
the @uref{https://www.ntppool.org/en/, NTP Pool Project}.
@end defvr

@deftp {Data Type} ntp-server
The data type representing the configuration of a NTP server.

@table @asis
@item @code{type} (default: @code{'server})
The type of the NTP server, given as a symbol.  One of @code{'pool},
@code{'server}, @code{'peer}, @code{'broadcast} or @code{'manycastclient}.

@item @code{address}
The address of the server, as a string.

@item @code{options}
NTPD options to use with that specific server, given as a list of option
names and/or of option names and values tuples.  The following example
define a server to use with the options @option{iburst} and @option{prefer},
as well as @option{version} 3 and a @option{maxpoll} time of 16 seconds.

@example
(ntp-server
 (type 'server)
 (address "some.ntp.server.org")
 (options `(iburst (version 3) (maxpoll 16) prefer))))
@end example
@end table
@end deftp

@cindex OpenNTPD
@deffn {Scheme Procedure} openntpd-service-type
Run the @command{ntpd}, the Network Time Protocol (NTP) daemon, as
implemented by @uref{http://www.openntpd.org, OpenNTPD}.  The daemon will
keep the system clock synchronized with that of the given servers.

@lisp
(service
 openntpd-service-type
 (openntpd-configuration
  (listen-on '("127.0.0.1" "::1"))
  (sensor '("udcf0 correction 70000"))
  (constraint-from '("www.gnu.org"))
  (constraints-from '("https://www.google.com/"))))

@end lisp
@end deffn

@defvr {Scheme Variable} %openntpd-servers
This variable is a list of the server addresses defined in
@code{%ntp-servers}.
@end defvr

@deftp {Data Type} openntpd-configuration
@table @asis
@item @code{openntpd} (default: @code{(file-append openntpd "/sbin/ntpd")})
The openntpd executable to use.
@item @code{listen-on} (default: @code{'("127.0.0.1" "::1")})
A list of local IP addresses or hostnames the ntpd daemon should listen on.
@item @code{query-from} (default: @code{'()})
A list of local IP address the ntpd daemon should use for outgoing queries.
@item @code{sensor} (default: @code{'()})
Specify a list of timedelta sensor devices ntpd should use.  @code{ntpd}
will listen to each sensor that actually exists and ignore non-existent
ones.  See @uref{https://man.openbsd.org/ntpd.conf, upstream documentation}
for more information.
@item @code{server} (default: @code{'()})
Specify a list of IP addresses or hostnames of NTP servers to synchronize
to.
@item @code{servers} (default: @code{%openntp-servers})
Specify a list of IP addresses or hostnames of NTP pools to synchronize to.
@item @code{constraint-from} (default: @code{'()})
@code{ntpd} can be configured to query the ‘Date’ from trusted HTTPS servers
via TLS.  This time information is not used for precision but acts as an
authenticated constraint, thereby reducing the impact of unauthenticated NTP
man-in-the-middle attacks.  Specify a list of URLs, IP addresses or
hostnames of HTTPS servers to provide a constraint.
@item @code{constraints-from} (default: @code{'()})
As with constraint from, specify a list of URLs, IP addresses or hostnames
of HTTPS servers to provide a constraint.  Should the hostname resolve to
multiple IP addresses, @code{ntpd} will calculate a median constraint from
all of them.
@end table
@end deftp

@cindex inetd
@deffn {Scheme variable} inetd-service-type
This service runs the @command{inetd} (@pxref{inetd invocation,,, inetutils,
GNU Inetutils}) daemon.  @command{inetd} listens for connections on internet
sockets, and lazily starts the specified server program when a connection is
made on one of these sockets.

The value of this service is an @code{inetd-configuration} object.  The
following example configures the @command{inetd} daemon to provide the
built-in @command{echo} service, as well as an smtp service which forwards
smtp traffic over ssh to a server @code{smtp-server} behind a gateway
@code{hostname}:

@lisp
(service
 inetd-service-type
 (inetd-configuration
  (entries (list
            (inetd-entry
             (name "echo")
             (socket-type 'stream)
             (protocol "tcp")
             (wait? #f)
             (user "root"))
            (inetd-entry
             (node "127.0.0.1")
             (name "smtp")
             (socket-type 'stream)
             (protocol "tcp")
             (wait? #f)
             (user "root")
             (program (file-append openssh "/bin/ssh"))
             (arguments
              '("ssh" "-qT" "-i" "/path/to/ssh_key"
                "-W" "smtp-server:25" "user@@hostname")))))))
@end lisp

See below for more details about @code{inetd-configuration}.
@end deffn

@deftp {Data Type} inetd-configuration
Data type representing the configuration of @command{inetd}.

@table @asis
@item @code{program} (default: @code{(file-append inetutils "/libexec/inetd")})
The @command{inetd} executable to use.

@item @code{entries} (default: @code{'()})
A list of @command{inetd} service entries.  Each entry should be created by
the @code{inetd-entry} constructor.
@end table
@end deftp

@deftp {Data Type} inetd-entry
Data type representing an entry in the @command{inetd} configuration.  Each
entry corresponds to a socket where @command{inetd} will listen for
requests.

@table @asis
@item @code{node} (default: @code{#f})
Optional string, a comma-separated list of local addresses @command{inetd}
should use when listening for this service.  @xref{Configuration file,,,
inetutils, GNU Inetutils} for a complete description of all options.
@item @code{名字}
A string, the name must correspond to an entry in @code{/etc/services}.
@item @code{socket-type}
One of @code{'stream}, @code{'dgram}, @code{'raw}, @code{'rdm} or
@code{'seqpacket}.
@item @code{protocol}
A string, must correspond to an entry in @code{/etc/protocols}.
@item @code{wait?} (default: @code{#t})
Whether @command{inetd} should wait for the server to exit before listening
to new service requests.
@item @code{用户}
A string containing the user (and, optionally, group) name of the user as
whom the server should run.  The group name can be specified in a suffix,
separated by a colon or period, i.e.@: @code{"user"}, @code{"user:group"} or
@code{"user.group"}.
@item @code{program} (default: @code{"internal"})
The server program which will serve the requests, or @code{"internal"} if
@command{inetd} should use a built-in service.
@item @code{arguments} (default: @code{'()})
A list strings or file-like objects, which are the server program's
arguments, starting with the zeroth argument, i.e.@: the name of the program
itself.  For @command{inetd}'s internal services, this entry must be
@code{'()} or @code{'("internal")}.
@end table

@xref{Configuration file,,, inetutils, GNU Inetutils} for a more detailed
discussion of each configuration field.
@end deftp

@cindex Tor
@defvr {Scheme Variable} tor-service-type
This is the type for a service that runs the @uref{https://torproject.org,
Tor} anonymous networking daemon.  The service is configured using a
@code{<tor-configuration>} record.  By default, the Tor daemon runs as the
@code{tor} unprivileged user, which is a member of the @code{tor} group.

@end defvr

@deftp {Data Type} tor-configuration
@table @asis
@item @code{tor} (default: @code{tor})
The package that provides the Tor daemon.  This package is expected to
provide the daemon at @file{bin/tor} relative to its output directory.  The
default package is the @uref{https://www.torproject.org, Tor Project's}
implementation.

@item @code{config-file} (default: @code{(plain-file "empty" "")})
The configuration file to use.  It will be appended to a default
configuration file, and the final configuration file will be passed to
@code{tor} via its @code{-f} option.  This may be any ``file-like'' object
(@pxref{G-表达式, file-like objects}).  See @code{man tor} for details
on the configuration file syntax.

@item @code{hidden-services} (default: @code{'()})
The list of @code{<hidden-service>} records to use.  For any hidden service
you include in this list, appropriate configuration to enable the hidden
service will be automatically added to the default configuration file.  You
may conveniently create @code{<hidden-service>} records using the
@code{tor-hidden-service} procedure described below.

@item @code{socks-socket-type} (default: @code{'tcp})
The default socket type that Tor should use for its SOCKS socket.  This must
be either @code{'tcp} or @code{'unix}.  If it is @code{'tcp}, then by
default Tor will listen on TCP port 9050 on the loopback interface (i.e.,
localhost).  If it is @code{'unix}, then Tor will listen on the UNIX domain
socket @file{/var/run/tor/socks-sock}, which will be made writable by
members of the @code{tor} group.

If you want to customize the SOCKS socket in more detail, leave
@code{socks-socket-type} at its default value of @code{'tcp} and use
@code{config-file} to override the default by providing your own
@code{SocksPort} option.

@item @code{control-socket?} (default: @code{#f})
Whether or not to provide a ``control socket'' by which Tor can be
controlled to, for instance, dynamically instantiate tor onion services.  If
@code{#t}, Tor will listen for control commands on the UNIX domain socket
@file{/var/run/tor/control-sock}, which will be made writable by members of
the @code{tor} group.

@end table
@end deftp

@cindex hidden service
@deffn {Scheme Procedure} tor-hidden-service @var{name} @var{mapping}
Define a new Tor @dfn{hidden service} called @var{name} and implementing
@var{mapping}.  @var{mapping} is a list of port/host tuples, such as:

@example
 '((22 "127.0.0.1:22")
   (80 "127.0.0.1:8080"))
@end example

In this example, port 22 of the hidden service is mapped to local port 22,
and port 80 is mapped to local port 8080.

This creates a @file{/var/lib/tor/hidden-services/@var{name}} directory,
where the @file{hostname} file contains the @code{.onion} host name for the
hidden service.

See @uref{https://www.torproject.org/docs/tor-hidden-service.html.en, the
Tor project's documentation} for more information.
@end deffn

The @code{(gnu services rsync)} module provides the following services:

You might want an rsync daemon if you have files that you want available so
anyone (or just yourself) can download existing files or upload new files.

@deffn {Scheme Variable} rsync-service-type
This is the service type for the @uref{https://rsync.samba.org, rsync}
daemon, The value for this service type is a @command{rsync-configuration}
record as in this example:

@lisp
(service rsync-service-type)
@end lisp

See below for details about @code{rsync-configuration}.
@end deffn

@deftp {Data Type} rsync-configuration
Data type representing the configuration for @code{rsync-service}.

@table @asis
@item @code{package} (default: @var{rsync})
@code{rsync} package to use.

@item @code{port-number} (default: @code{873})
TCP port on which @command{rsync} listens for incoming connections.  If port
is less than @code{1024} @command{rsync} needs to be started as the
@code{root} user and group.

@item @code{pid-file} (default: @code{"/var/run/rsyncd/rsyncd.pid"})
Name of the file where @command{rsync} writes its PID.

@item @code{lock-file} (default: @code{"/var/run/rsyncd/rsyncd.lock"})
Name of the file where @command{rsync} writes its lock file.

@item @code{log-file} (default: @code{"/var/log/rsyncd.log"})
Name of the file where @command{rsync} writes its log file.

@item @code{use-chroot?} (default: @var{#t})
Whether to use chroot for @command{rsync} shared directory.

@item @code{share-path} (default: @file{/srv/rsync})
Location of the @command{rsync} shared directory.

@item @code{share-comment} (default: @code{"Rsync share"})
Comment of the @command{rsync} shared directory.

@item @code{read-only?} (default: @var{#f})
Read-write permissions to shared directory.

@item @code{timeout} (default: @code{300})
I/O timeout in seconds.

@item @code{user} (default: @var{"root"})
Owner of the @code{rsync} process.

@item @code{group} (default: @var{"root"})
Group of the @code{rsync} process.

@item @code{uid} (default: @var{"rsyncd"})
User name or user ID that file transfers to and from that module should take
place as when the daemon was run as @code{root}.

@item @code{gid} (default: @var{"rsyncd"})
Group name or group ID that will be used when accessing the module.

@end table
@end deftp

The @code{(gnu services syncthing)} module provides the following services:
@cindex syncthing

You might want a syncthing daemon if you have files between two or more
computers and want to sync them in real time, safely protected from prying
eyes.

@deffn {Scheme Variable} syncthing-service-type
This is the service type for the @uref{https://syncthing.net/, syncthing}
daemon, The value for this service type is a
@command{syncthing-configuration} record as in this example:

@lisp
(service syncthing-service-type
         (syncthing-configuration (user "alice")))
@end lisp

See below for details about @code{syncthing-configuration}.

@deftp {Data Type} syncthing-configuration
Data type representing the configuration for @code{syncthing-service-type}.

@table @asis
@item @code{syncthing} (default: @var{syncthing})
@code{syncthing} package to use.

@item @code{arguments} (default: @var{'()})
List of command-line arguments passing to @code{syncthing} binary.

@item @code{logflags} (default: @var{0})
Sum of logging flags, see
@uref{https://docs.syncthing.net/users/syncthing.html#cmdoption-logflags,
Syncthing documentation logflags}.

@item @code{user} (default: @var{#f})
The user as which the Syncthing service is to be run.  This assumes that the
specified user exists.

@item @code{group} (default: @var{"users"})
The group as which the Syncthing service is to be run.  This assumes that
the specified group exists.

@item @code{home} (default: @var{#f})
Common configuration and data directory.  The default configuration
directory is @file{$HOME} of the specified Syncthing @code{user}.

@end table
@end deftp
@end deffn

Furthermore, @code{(gnu services ssh)} provides the following services.
@cindex SSH
@cindex SSH server

@deffn {Scheme Procedure} lsh-service [#:host-key "/etc/lsh/host-key"] @
       [#:daemonic? #t] [#:interfaces '()] [#:port-number 22] @
[#:allow-empty-passwords? #f] [#:root-login? #f] @ [#:syslog-output? #t]
[#:x11-forwarding? #t] @ [#:tcp/ip-forwarding? #t]
[#:password-authentication? #t] @ [#:public-key-authentication? #t]
[#:initialize? #t] Run the @command{lshd} program from @var{lsh} to listen
on port @var{port-number}.  @var{host-key} must designate a file containing
the host key, and readable only by root.

When @var{daemonic?} is true, @command{lshd} will detach from the
controlling terminal and log its output to syslogd, unless one sets
@var{syslog-output?} to false.  Obviously, it also makes lsh-service depend
on existence of syslogd service.  When @var{pid-file?} is true,
@command{lshd} writes its PID to the file called @var{pid-file}.

When @var{initialize?} is true, automatically create the seed and host key
upon service activation if they do not exist yet.  This may take long and
require interaction.

When @var{initialize?} is false, it is up to the user to initialize the
randomness generator (@pxref{lsh-make-seed,,, lsh, LSH Manual}), and to
create a key pair with the private key stored in file @var{host-key}
(@pxref{lshd basics,,, lsh, LSH Manual}).

When @var{interfaces} is empty, lshd listens for connections on all the
network interfaces; otherwise, @var{interfaces} must be a list of host names
or addresses.

@var{allow-empty-passwords?} specifies whether to accept log-ins with empty
passwords, and @var{root-login?} specifies whether to accept log-ins as
root.

The other options should be self-descriptive.
@end deffn

@cindex SSH
@cindex SSH server
@deffn {Scheme Variable} openssh-service-type
This is the type for the @uref{http://www.openssh.org, OpenSSH} secure shell
daemon, @command{sshd}.  Its value must be an @code{openssh-configuration}
record as in this example:

@lisp
(service openssh-service-type
         (openssh-configuration
           (x11-forwarding? #t)
           (permit-root-login 'without-password)
           (authorized-keys
             `(("alice" ,(local-file "alice.pub"))
               ("bob" ,(local-file "bob.pub"))))))
@end lisp

See below for details about @code{openssh-configuration}.

This service can be extended with extra authorized keys, as in this example:

@lisp
(service-extension openssh-service-type
                   (const `(("charlie"
                             ,(local-file "charlie.pub")))))
@end lisp
@end deffn

@deftp {Data Type} openssh-configuration
This is the configuration record for OpenSSH's @command{sshd}.

@table @asis
@item @code{openssh} (default @var{openssh})
The Openssh package to use.

@item @code{pid-file} (default: @code{"/var/run/sshd.pid"})
Name of the file where @command{sshd} writes its PID.

@item @code{port-number} (default: @code{22})
TCP port on which @command{sshd} listens for incoming connections.

@item @code{permit-root-login} (default: @code{#f})
This field determines whether and when to allow logins as root.  If
@code{#f}, root logins are disallowed; if @code{#t}, they are allowed.  If
it's the symbol @code{'without-password}, then root logins are permitted but
not with password-based authentication.

@item @code{allow-empty-passwords?} (default: @code{#f})
When true, users with empty passwords may log in.  When false, they may not.

@item @code{password-authentication?} (default: @code{#t})
When true, users may log in with their password.  When false, they have
other authentication methods.

@item @code{public-key-authentication?} (default: @code{#t})
When true, users may log in using public key authentication.  When false,
users have to use other authentication method.

Authorized public keys are stored in @file{~/.ssh/authorized_keys}.  This is
used only by protocol version 2.

@item @code{x11-forwarding?} (default: @code{#f})
When true, forwarding of X11 graphical client connections is enabled---in
other words, @command{ssh} options @option{-X} and @option{-Y} will work.

@item @code{allow-agent-forwarding?} (default: @code{#t})
Whether to allow agent forwarding.

@item @code{allow-tcp-forwarding?} (default: @code{#t})
Whether to allow TCP forwarding.

@item @code{gateway-ports?} (default: @code{#f})
Whether to allow gateway ports.

@item @code{challenge-response-authentication?} (default: @code{#f})
Specifies whether challenge response authentication is allowed (e.g.@: via
PAM).

@item @code{use-pam?} (default: @code{#t})
Enables the Pluggable Authentication Module interface.  If set to @code{#t},
this will enable PAM authentication using
@code{challenge-response-authentication?} and
@code{password-authentication?}, in addition to PAM account and session
module processing for all authentication types.

Because PAM challenge response authentication usually serves an equivalent
role to password authentication, you should disable either
@code{challenge-response-authentication?} or
@code{password-authentication?}.

@item @code{print-last-log?} (default: @code{#t})
Specifies whether @command{sshd} should print the date and time of the last
user login when a user logs in interactively.

@item @code{subsystems} (default: @code{'(("sftp" "internal-sftp"))})
Configures external subsystems (e.g.@: file transfer daemon).

This is a list of two-element lists, each of which containing the subsystem
name and a command (with optional arguments) to execute upon subsystem
request.

The command @command{internal-sftp} implements an in-process SFTP server.
Alternatively, one can specify the @command{sftp-server} command:
@lisp
(service openssh-service-type
         (openssh-configuration
          (subsystems
           `(("sftp" ,(file-append openssh "/libexec/sftp-server"))))))
@end lisp

@item @code{accepted-environment} (default: @code{'()})
List of strings describing which environment variables may be exported.

Each string gets on its own line.  See the @code{AcceptEnv} option in
@code{man sshd_config}.

This example allows ssh-clients to export the @env{COLORTERM} variable.  It
is set by terminal emulators, which support colors.  You can use it in your
shell's resource file to enable colors for the prompt and commands if this
variable is set.

@lisp
(service openssh-service-type
         (openssh-configuration
           (accepted-environment '("COLORTERM"))))
@end lisp

@item @code{authorized-keys} (default: @code{'()})
@cindex authorized keys, SSH
@cindex SSH authorized keys
This is the list of authorized keys.  Each element of the list is a user
name followed by one or more file-like objects that represent SSH public
keys.  For example:

@lisp
(openssh-configuration
  (authorized-keys
    `(("rekado" ,(local-file "rekado.pub"))
      ("chris" ,(local-file "chris.pub"))
      ("root" ,(local-file "rekado.pub") ,(local-file "chris.pub")))))
@end lisp

@noindent
registers the specified public keys for user accounts @code{rekado},
@code{chris}, and @code{root}.

Additional authorized keys can be specified @i{via}
@code{service-extension}.

Note that this does @emph{not} interfere with the use of
@file{~/.ssh/authorized_keys}.

@item @code{log-level} (default: @code{'info})
This is a symbol specifying the logging level: @code{quiet}, @code{fatal},
@code{error}, @code{info}, @code{verbose}, @code{debug}, etc.  See the man
page for @file{sshd_config} for the full list of level names.

@item @code{extra-content} (default: @code{""})
This field can be used to append arbitrary text to the configuration file.
It is especially useful for elaborate configurations that cannot be
expressed otherwise.  This configuration, for example, would generally
disable root logins, but permit them from one specific IP address:

@lisp
(openssh-configuration
  (extra-content "\
Match Address 192.168.0.1
  PermitRootLogin yes"))
@end lisp

@end table
@end deftp

@deffn {Scheme Procedure} dropbear-service [@var{config}]
Run the @uref{https://matt.ucc.asn.au/dropbear/dropbear.html,Dropbear SSH
daemon} with the given @var{config}, a @code{<dropbear-configuration>}
object.

For example, to specify a Dropbear service listening on port 1234, add this
call to the operating system's @code{services} field:

@lisp
(dropbear-service (dropbear-configuration
                    (port-number 1234)))
@end lisp
@end deffn

@deftp {Data Type} dropbear-configuration
This data type represents the configuration of a Dropbear SSH daemon.

@table @asis
@item @code{dropbear} (default: @var{dropbear})
The Dropbear package to use.

@item @code{port-number} (default: 22)
The TCP port where the daemon waits for incoming connections.

@item @code{syslog-output?} (default: @code{#t})
Whether to enable syslog output.

@item @code{pid-file} (default: @code{"/var/run/dropbear.pid"})
File name of the daemon's PID file.

@item @code{root-login?} (default: @code{#f})
Whether to allow @code{root} logins.

@item @code{allow-empty-passwords?} (default: @code{#f})
Whether to allow empty passwords.

@item @code{password-authentication?} (default: @code{#t})
Whether to enable password-based authentication.
@end table
@end deftp

@cindex AutoSSH
@deffn {Scheme Variable} autossh-service-type
This is the type for the @uref{https://www.harding.motd.ca/autossh, AutoSSH}
program that runs a copy of @command{ssh} and monitors it, restarting it as
necessary should it die or stop passing traffic.  AutoSSH can be run
manually from the command-line by passing arguments to the binary
@command{autossh} from the package @code{autossh}, but it can also be run as
a Guix service.  This latter use case is documented here.

AutoSSH can be used to forward local traffic to a remote machine using an
SSH tunnel, and it respects the @file{~/.ssh/config} of the user it is run
as.

For example, to specify a service running autossh as the user @code{pino}
and forwarding all local connections to port @code{8081} to
@code{remote:8081} using an SSH tunnel, add this call to the operating
system's @code{services} field:

@lisp
(service autossh-service-type
         (autossh-configuration
          (user "pino")
          (ssh-options (list "-T" "-N" "-L" "8081:localhost:8081" "remote.net"))))
@end lisp
@end deffn

@deftp {Data Type} autossh-configuration
This data type represents the configuration of an AutoSSH service.

@table @asis

@item @code{user} (default @code{"autossh"})
The user as which the AutoSSH service is to be run.  This assumes that the
specified user exists.

@item @code{poll} (default @code{600})
Specifies the connection poll time in seconds.

@item @code{first-poll} (default @code{#f})
Specifies how many seconds AutoSSH waits before the first connection test.
After this first test, polling is resumed at the pace defined in
@code{poll}.  When set to @code{#f}, the first poll is not treated specially
and will also use the connection poll specified in @code{poll}.

@item @code{gate-time} (default @code{30})
Specifies how many seconds an SSH connection must be active before it is
considered successful.

@item @code{log-level} (default @code{1})
The log level, corresponding to the levels used by syslog---so @code{0} is
the most silent while @code{7} is the chattiest.

@item @code{max-start} (default @code{#f})
The maximum number of times SSH may be (re)started before AutoSSH exits.
When set to @code{#f}, no maximum is configured and AutoSSH may restart
indefinitely.

@item @code{message} (default @code{""})
The message to append to the echo message sent when testing connections.

@item @code{port} (default @code{"0"})
The ports used for monitoring the connection.  When set to @code{"0"},
monitoring is disabled.  When set to @code{"@var{n}"} where @var{n} is a
positive integer, ports @var{n} and @var{n}+1 are used for monitoring the
connection, such that port @var{n} is the base monitoring port and
@code{n+1} is the echo port.  When set to @code{"@var{n}:@var{m}"} where
@var{n} and @var{m} are positive integers, the ports @var{n} and @var{m} are
used for monitoring the connection, such that port @var{n} is the base
monitoring port and @var{m} is the echo port.

@item @code{ssh-options} (default @code{'()})
The list of command-line arguments to pass to @command{ssh} when it is run.
Options @option{-f} and @option{-M} are reserved for AutoSSH and may cause
undefined behaviour.

@end table
@end deftp

@cindex WebSSH
@deffn {Scheme Variable} webssh-service-type
This is the type for the @uref{https://webssh.huashengdun.org/, WebSSH}
program that runs a web SSH client.  WebSSH can be run manually from the
command-line by passing arguments to the binary @command{wssh} from the
package @code{webssh}, but it can also be run as a Guix service.  This
latter use case is documented here.

For example, to specify a service running WebSSH on loopback interface on
port @code{8888} with reject policy with a list of allowed to connection
hosts, and NGINX as a reverse-proxy to this service listening for HTTPS
connection, add this call to the operating system's @code{services} field:

@lisp
(service webssh-service-type
  (webssh-configuration (address "127.0.0.1")
                        (port 8888)
                        (policy 'reject)
                        (known-hosts '("localhost ecdsa-sha2-nistp256 AAAA…"
                                       "127.0.0.1 ecdsa-sha2-nistp256 AAAA…"))))

(service nginx-service-type
         (nginx-configuration
          (server-blocks
           (list
            (nginx-server-configuration
             (inherit %webssh-configuration-nginx)
             (server-name '("webssh.example.com"))
             (listen '("443 ssl"))
             (ssl-certificate (letsencrypt-certificate "webssh.example.com"))
             (ssl-certificate-key (letsencrypt-key "webssh.example.com"))
             (locations
              (cons (nginx-location-configuration
                     (uri "/.well-known")
                     (body '("root /var/www;")))
                    (nginx-server-configuration-locations %webssh-configuration-nginx))))))))
@end lisp
@end deffn

@deftp {Data Type} webssh-configuration
Data type representing the configuration for @code{webssh-service}.

@table @asis
@item @code{package} (default: @var{webssh})
@code{webssh} package to use.

@item @code{user-name} (default: @var{"webssh"})
User name or user ID that file transfers to and from that module should take
place.

@item @code{group-name} (default: @var{"webssh"})
Group name or group ID that will be used when accessing the module.

@item @code{address} (default: @var{#f})
IP address on which @command{webssh} listens for incoming connections.

@item @code{port} (default: @var{8888})
TCP port on which @command{webssh} listens for incoming connections.

@item @code{policy} (default: @var{#f})
Connection policy.  @var{reject} policy requires to specify
@var{known-hosts}.

@item @code{known-hosts} (default: @var{'()})
List of hosts which allowed for SSH connection from @command{webssh}.

@item @code{log-file} (default: @file{"/var/log/webssh.log"})
Name of the file where @command{webssh} writes its log file.

@item @code{log-level} (default: @var{#f})
Logging level.

@end table
@end deftp

@defvr {Scheme Variable} %facebook-host-aliases
This variable contains a string for use in @file{/etc/hosts} (@pxref{Host
Names,,, libc, The GNU C Library Reference Manual}).  Each line contains a
entry that maps a known server name of the Facebook on-line service---e.g.,
@code{www.facebook.com}---to the local host---@code{127.0.0.1} or its IPv6
equivalent, @code{::1}.

This variable is typically used in the @code{hosts-file} field of an
@code{operating-system} declaration (@pxref{操作系统参考,
@file{/etc/hosts}}):

@lisp
(use-modules (gnu) (guix))

(operating-system
  (host-name "mymachine")
  ;; ...
  (hosts-file
    ;; Create a /etc/hosts file with aliases for "localhost"
    ;; and "mymachine", as well as for Facebook servers.
    (plain-file "hosts"
                (string-append (local-host-aliases host-name)
                               %facebook-host-aliases))))
@end lisp

This mechanism can prevent programs running locally, such as Web browsers,
from accessing Facebook.
@end defvr

The @code{(gnu services avahi)} provides the following definition.

@defvr {Scheme Variable} avahi-service-type
This is the service that runs @command{avahi-daemon}, a system-wide
mDNS/DNS-SD responder that allows for service discovery and
``zero-configuration'' host name lookups (see @uref{https://avahi.org/}).
Its value must be an @code{avahi-configuration} record---see below.

This service extends the name service cache daemon (nscd) so that it can
resolve @code{.local} host names using
@uref{https://0pointer.de/lennart/projects/nss-mdns/, nss-mdns}.  @xref{Name Service Switch}, for information on host name resolution.

Additionally, add the @var{avahi} package to the system profile so that
commands such as @command{avahi-browse} are directly usable.
@end defvr

@deftp {Data Type} avahi-configuration
Data type representation the configuration for Avahi.

@table @asis

@item @code{host-name} (default: @code{#f})
If different from @code{#f}, use that as the host name to publish for this
machine; otherwise, use the machine's actual host name.

@item @code{publish?} (default: @code{#t})
When true, allow host names and services to be published (broadcast) over
the network.

@item @code{publish-workstation?} (default: @code{#t})
When true, @command{avahi-daemon} publishes the machine's host name and IP
address via mDNS on the local network.  To view the host names published on
your local network, you can run:

@example
avahi-browse _workstation._tcp
@end example

@item @code{wide-area?} (default: @code{#f})
When true, DNS-SD over unicast DNS is enabled.

@item @code{ipv4?} (default: @code{#t})
@itemx @code{ipv6?} (default: @code{#t})
These fields determine whether to use IPv4/IPv6 sockets.

@item @code{domains-to-browse} (default: @code{'()})
This is a list of domains to browse.
@end table
@end deftp

@deffn {Scheme Variable} openvswitch-service-type
This is the type of the @uref{https://www.openvswitch.org, Open vSwitch}
service, whose value should be an @code{openvswitch-configuration} object.
@end deffn

@deftp {Data Type} openvswitch-configuration
Data type representing the configuration of Open vSwitch, a multilayer
virtual switch which is designed to enable massive network automation
through programmatic extension.

@table @asis
@item @code{package} (default: @var{openvswitch})
Package object of the Open vSwitch.

@end table
@end deftp

@defvr {Scheme Variable} pagekite-service-type
This is the service type for the @uref{https://pagekite.net, PageKite}
service, a tunneling solution for making localhost servers publicly visible,
even from behind restrictive firewalls or NAT without forwarded ports.  The
value for this service type is a @code{pagekite-configuration} record.

Here's an example exposing the local HTTP and SSH daemons:

@lisp
(service pagekite-service-type
         (pagekite-configuration
           (kites '("http:@@kitename:localhost:80:@@kitesecret"
                    "raw/22:@@kitename:localhost:22:@@kitesecret"))
           (extra-file "/etc/pagekite.rc")))
@end lisp
@end defvr

@deftp {Data Type} pagekite-configuration
Data type representing the configuration of PageKite.

@table @asis
@item @code{package} (default: @var{pagekite})
Package object of PageKite.

@item @code{kitename} (default: @code{#f})
PageKite name for authenticating to the frontend server.

@item @code{kitesecret} (default: @code{#f})
Shared secret for authenticating to the frontend server.  You should
probably put this inside @code{extra-file} instead.

@item @code{frontend} (default: @code{#f})
Connect to the named PageKite frontend server instead of the
@uref{https://pagekite.net,,pagekite.net} service.

@item @code{kites} (default: @code{'("http:@@kitename:localhost:80:@@kitesecret")})
List of service kites to use.  Exposes HTTP on port 80 by default.  The
format is @code{proto:kitename:host:port:secret}.

@item @code{extra-file} (default: @code{#f})
Extra configuration file to read, which you are expected to create
manually.  Use this to add additional options and manage shared secrets
out-of-band.

@end table
@end deftp

@defvr {Scheme Variable} yggdrasil-service-type
The service type for connecting to the
@uref{https://yggdrasil-network.github.io/, Yggdrasil network}, an
early-stage implementation of a fully end-to-end encrypted IPv6 network.

@quotation
Yggdrasil provides name-independent routing with cryptographically generated
addresses.  Static addressing means you can keep the same address as long as
you want, even if you move to a new location, or generate a new address (by
generating new keys) whenever you want.
@uref{https://yggdrasil-network.github.io/2018/07/28/addressing.html}
@end quotation

Pass it a value of @code{yggdrasil-configuration} to connect it to public
peers and/or local peers.

Here is an example using public peers and a static address.  The static
signing and encryption keys are defined in
@file{/etc/yggdrasil-private.conf} (the default value for
@code{config-file}).

@lisp
;; part of the operating-system declaration
(service yggdrasil-service-type
              (yggdrasil-configuration
               (autoconf? #f) ;; use only the public peers
               (json-config
               ;; choose one from
               ;; https://github.com/yggdrasil-network/public-peers
                '((peers . #("tcp://1.2.3.4:1337"))))
               ;; /etc/yggdrasil-private.conf is the default value for config-file
               ))
@end lisp
@example
# sample content for /etc/yggdrasil-private.conf
@{
  # Your public encryption key. Your peers may ask you for this to put
  # into their AllowedEncryptionPublicKeys configuration.
  EncryptionPublicKey: 378dc5...

  # Your private encryption key. DO NOT share this with anyone!
  EncryptionPrivateKey: 0777...

  # Your public signing key. You should not ordinarily need to share
  # this with anyone.
  SigningPublicKey: e1664...

  # Your private signing key. DO NOT share this with anyone!
  SigningPrivateKey: 0589d...
@}
@end example
@end defvr

@deftp {Data Type} yggdrasil-configuration
Data type representing the configuration of Yggdrasil.

@table @asis
@item @code{package} (default: @code{yggdrasil})
Package object of Yggdrasil.

@item @code{json-config} (default: @code{'()})
Contents of @file{/etc/yggdrasil.conf}.  Will be merged with
@file{/etc/yggdrasil-private.conf}.  Note that these settings are stored in
the Guix store, which is readable to all users. @strong{Do not store your
private keys in it}.  See the output of @code{yggdrasil -genconf} for a
quick overview of valid keys and their default values.

@item @code{autoconf?} (default: @code{#f})
Whether to use automatic mode.  Enabling it makes Yggdrasil use adynamic IP
and peer with IPv6 neighbors.

@item @code{log-level} (default: @code{'info})
How much detail to include in logs.  Use @code{'debug} for more detail.

@item @code{log-to} (default: @code{'stdout})
Where to send logs.  By default, the service logs standard output to
@file{/var/log/yggdrasil.log}.  The alternative is @code{'syslog}, which
sends output to the running syslog service.

@item @code{config-file} (default: @code{"/etc/yggdrasil-private.conf"})
What HJSON file to load sensitive data from.  This is where private keys
should be stored, which are necessary to specify if you don't want a
randomized address after each restart.  Use @code{#f} to disable.  Options
defined in this file take precedence over @code{json-config}.  Use the
output of @code{yggdrasil -genconf} as a starting point.  To configure a
static address, delete everything except these options:

@itemize
@item @code{EncryptionPublicKey}
@item @code{EncryptionPrivateKey}
@item @code{SigningPublicKey}
@item @code{SigningPrivateKey}
@end itemize
@end table
@end deftp

@cindex IPFS
@defvr {Scheme Variable} ipfs-service-type
The service type for connecting to the @uref{https://ipfs.io,IPFS network},
a global, versioned, peer-to-peer file system. Pass it a
@code{ipfs-configuration} to change the ports used for the gateway and API.

Here's an example configuration, using some non-standard ports:

@lisp
(service ipfs-service-type
         (ipfs-configuration
          (gateway "/ip4/127.0.0.1/tcp/8880")
          (api "/ip4/127.0.0.1/tcp/8881")))
@end lisp
@end defvr

@deftp {Data Type} ipfs-configuration
Data type representing the configuration of IPFS.

@table @asis
@item @code{package} (default: @code{go-ipfs})
Package object of IPFS.

@item @code{gateway} (default: @code{"/ip4/127.0.0.1/tcp/8082"})
Address of the gateway, in ‘multiaddress’ format.

@item @code{api} (default: @code{"/ip4/127.0.0.1/tcp/5001"})
Address of the API endpoint, in ‘multiaddress’ format.
@end table
@end deftp

@cindex keepalived
@deffn {Scheme Variable} keepalived-service-type
This is the type for the @uref{https://www.keepalived.org/, Keepalived}
routing software, @command{keepalived}.  Its value must be an
@code{keepalived-configuration} record as in this example for master
machine:

@lisp
(service keepalived-service-type
         (keepalived-configuration
           (config-file (local-file "keepalived-master.conf"))))
@end lisp

where @file{keepalived-master.conf}:

@example
vrrp_instance my-group @{
  state MASTER
  interface enp9s0
  virtual_router_id 100
  priority 100
  unicast_peer @{ 10.0.0.2 @}
  virtual_ipaddress @{
    10.0.0.4/24
  @}
@}
@end example

and for backup machine:

@lisp
(service keepalived-service-type
         (keepalived-configuration
          (config-file (local-file "keepalived-backup.conf"))))
@end lisp

where @file{keepalived-backup.conf}:

@example
vrrp_instance my-group @{
  state BACKUP
  interface enp9s0
  virtual_router_id 100
  priority 99
  unicast_peer @{ 10.0.0.3 @}
  virtual_ipaddress @{
    10.0.0.4/24
  @}
@}
@end example
@end deffn

@node Unattended Upgrades
@subsection Unattended Upgrades

@cindex unattended upgrades
@cindex upgrades, unattended
Guix provides a service to perform @emph{unattended upgrades}: periodically,
the system automatically reconfigures itself from the latest Guix.  Guix
System has several properties that make unattended upgrades safe:

@itemize
@item
upgrades are transactional (either the upgrade succeeds or it fails, but you
cannot end up with an ``in-between'' system state);
@item
the upgrade log is kept---you can view it with @command{guix system
list-generations}---and you can roll back to any previous generation, should
the upgraded system fail to behave as intended;
@item
channel code is authenticated so you know you can only run genuine code
(@pxref{通道});
@item
@command{guix system reconfigure} prevents downgrades, which makes it immune
to @dfn{downgrade attacks}.
@end itemize

To set up unattended upgrades, add an instance of
@code{unattended-upgrade-service-type} like the one below to the list of
your operating system services:

@lisp
(service unattended-upgrade-service-type)
@end lisp

The defaults above set up weekly upgrades: every Sunday at midnight.  You do
not need to provide the operating system configuration file: it uses
@file{/run/current-system/configuration.scm}, which ensures it always uses
your latest configuration---@pxref{provenance-service-type}, for more
information about this file.

There are several things that can be configured, in particular the
periodicity and services (daemons) to be restarted upon completion.  When
the upgrade is successful, the service takes care of deleting system
generations older that some threshold, as per @command{guix system
delete-generations}.  See the reference below for details.

To ensure that upgrades are actually happening, you can run @command{guix
system describe}.  To investigate upgrade failures, visit the unattended
upgrade log file (see below).

@defvr {Scheme Variable} unattended-upgrade-service-type
This is the service type for unattended upgrades.  It sets up an mcron job
(@pxref{执行计划任务}) that runs @command{guix system
reconfigure} from the latest version of the specified channels.

Its value must be a @code{unattended-upgrade-configuration} record (see
below).
@end defvr

@deftp {Data Type} unattended-upgrade-configuration
This data type represents the configuration of the unattended upgrade
service.  The following fields are available:

@table @asis
@item @code{schedule} (default: @code{"30 01 * * 0"})
This is the schedule of upgrades, expressed as a gexp containing an mcron
job schedule (@pxref{Guile Syntax, mcron job specifications,, mcron,
GNU@tie{}mcron}).

@item @code{channels} (default: @code{#~%default-channels})
This gexp specifies the channels to use for the upgrade (@pxref{通道}).
By default, the tip of the official @code{guix} channel is used.

@item @code{operating-system-file} (default: @code{"/run/current-system/configuration.scm"})
This field specifies the operating system configuration file to use.  The
default is to reuse the config file of the current configuration.

There are cases, though, where referring to
@file{/run/current-system/configuration.scm} is not enough, for instance
because that file refers to extra files (SSH public keys, extra
configuration files, etc.) @i{via} @code{local-file} and similar
constructs.  For those cases, we recommend something along these lines:

@lisp
(unattended-upgrade-configuration
  (operating-system-file
    (file-append (local-file "." "config-dir" #:recursive? #t)
                 "/config.scm")))
@end lisp

The effect here is to import all of the current directory into the store,
and to refer to @file{config.scm} within that directory.  Therefore, uses of
@code{local-file} within @file{config.scm} will work as expected.
@xref{G-表达式}, for information about @code{local-file} and
@code{file-append}.

@item @code{services-to-restart} (default: @code{'(mcron)})
This field specifies the Shepherd services to restart when the upgrade
completes.

Those services are restarted right away upon completion, as with
@command{herd restart}, which ensures that the latest version is
running---remember that by default @command{guix system reconfigure} only
restarts services that are not currently running, which is conservative: it
minimizes disruption but leaves outdated services running.

Use @command{herd status} to find out candidates for restarting.
@xref{服务}, for general information about services.  Common services to
restart would include @code{ntpd} and @code{ssh-daemon}.

By default, the @code{mcron} service is restarted.  This ensures that the
latest version of the unattended upgrade job will be used next time.

@item @code{system-expiration} (default: @code{(* 3 30 24 3600)})
This is the expiration time in seconds for system generations.  System
generations older that this amount of time are deleted with @command{guix
system delete-generations} when an upgrade completes.

@quotation 注
The unattended upgrade service does not run the garbage collector.  You will
probably want to set up your own mcron job to run @command{guix gc}
periodically.
@end quotation

@item @code{maximum-duration} (default: @code{3600})
Maximum duration in seconds for the upgrade; past that time, the upgrade
aborts.

This is primarily useful to ensure the upgrade does not end up rebuilding or
re-downloading ``the world''.

@item @code{log-file} (default: @code{"/var/log/unattended-upgrade.log"})
File where unattended upgrades are logged.
@end table
@end deftp

@node X窗口
@subsection X窗口

@cindex X11
@cindex X Window System
@cindex login manager
Support for the X Window graphical display system---specifically Xorg---is
provided by the @code{(gnu services xorg)} module.  Note that there is no
@code{xorg-service} procedure.  Instead, the X server is started by the
@dfn{login manager}, by default the GNOME Display Manager (GDM).

@cindex GDM
@cindex GNOME, login manager
GDM of course allows users to log in into window managers and desktop
environments other than GNOME; for those using GNOME, GDM is required for
features such as automatic screen locking.

@cindex window manager
To use X11, you must install at least one @dfn{window manager}---for example
the @code{windowmaker} or @code{openbox} packages---preferably by adding it
to the @code{packages} field of your operating system definition
(@pxref{操作系统参考, system-wide packages}).

@defvr {Scheme Variable} gdm-service-type
This is the type for the @uref{https://wiki.gnome.org/Projects/GDM/, GNOME
Desktop Manager} (GDM), a program that manages graphical display servers and
handles graphical user logins.  Its value must be a @code{gdm-configuration}
(see below).

@cindex session types (X11)
@cindex X11 session types
GDM looks for @dfn{session types} described by the @file{.desktop} files in
@file{/run/current-system/profile/share/xsessions} and allows users to
choose a session from the log-in screen.  Packages such as @code{gnome},
@code{xfce}, and @code{i3} provide @file{.desktop} files; adding them to the
system-wide set of packages automatically makes them available at the log-in
screen.

In addition, @file{~/.xsession} files are honored.  When available,
@file{~/.xsession} must be an executable that starts a window manager and/or
other X clients.
@end defvr

@deftp {Data Type} gdm-configuration
@table @asis
@item @code{auto-login?} (default: @code{#f})
@itemx @code{default-user} (default: @code{#f})
When @code{auto-login?} is false, GDM presents a log-in screen.

When @code{auto-login?} is true, GDM logs in directly as
@code{default-user}.

@item @code{debug?} (default: @code{#f})
When true, GDM writes debug messages to its log.

@item @code{gnome-shell-assets} (default: ...)
List of GNOME Shell assets needed by GDM: icon theme, fonts, etc.

@item @code{xorg-configuration} (default: @code{(xorg-configuration)})
Configuration of the Xorg graphical server.

@item @code{xsession} (default: @code{(xinitrc)})
Script to run before starting a X session.

@item @code{dbus-daemon} (default: @code{dbus-daemon-wrapper})
File name of the @code{dbus-daemon} executable.

@item @code{gdm} (default: @code{gdm})
The GDM package to use.
@end table
@end deftp

@defvr {Scheme Variable} slim-service-type
This is the type for the SLiM graphical login manager for X11.

Like GDM, SLiM looks for session types described by @file{.desktop} files
and allows users to choose a session from the log-in screen using @kbd{F1}.
It also honors @file{~/.xsession} files.

Unlike GDM, SLiM does not spawn the user session on a different VT after
logging in, which means that you can only start one graphical session.  If
you want to be able to run multiple graphical sessions at the same time you
have to add multiple SLiM services to your system services.  The following
example shows how to replace the default GDM service with two SLiM services
on tty7 and tty8.

@lisp
(use-modules (gnu services)
             (gnu services desktop)
             (gnu services xorg)
             (srfi srfi-1))  ;for 'remove'

(operating-system
  ;; ...
  (services (cons* (service slim-service-type (slim-configuration
                                               (display ":0")
                                               (vt "vt7")))
                   (service slim-service-type (slim-configuration
                                               (display ":1")
                                               (vt "vt8")))
                   (modify-services %desktop-services
                     (delete gdm-service-type)))))
@end lisp

@end defvr

@deftp {Data Type} slim-configuration
Data type representing the configuration of @code{slim-service-type}.

@table @asis
@item @code{allow-empty-passwords?} (default: @code{#t})
Whether to allow logins with empty passwords.

@item @code{auto-login?} (default: @code{#f})
@itemx @code{default-user} (default: @code{""})
When @code{auto-login?} is false, SLiM presents a log-in screen.

When @code{auto-login?} is true, SLiM logs in directly as
@code{default-user}.

@item @code{theme} (default: @code{%default-slim-theme})
@itemx @code{theme-name} (default: @code{%default-slim-theme-name})
The graphical theme to use and its name.

@item @code{auto-login-session} (default: @code{#f})
If true, this must be the name of the executable to start as the default
session---e.g., @code{(file-append windowmaker "/bin/windowmaker")}.

If false, a session described by one of the available @file{.desktop} files
in @code{/run/current-system/profile} and @code{~/.guix-profile} will be
used.

@quotation 注
You must install at least one window manager in the system profile or in
your user profile.  Failing to do that, if @code{auto-login-session} is
false, you will be unable to log in.
@end quotation

@item @code{xorg-configuration} (default @code{(xorg-configuration)})
Configuration of the Xorg graphical server.

@item @code{display}（默认值：@code{":0"}）
The display on which to start the Xorg graphical server.

@item @code{vt}（默认值：@code{"vt7"}）
The VT on which to start the Xorg graphical server.

@item @code{xauth} (default: @code{xauth})
The XAuth package to use.

@item @code{shepherd} (default: @code{shepherd})
The Shepherd package used when invoking @command{halt} and @command{reboot}.

@item @code{sessreg} (default: @code{sessreg})
The sessreg package used in order to register the session.

@item @code{slim} (default: @code{slim})
The SLiM package to use.
@end table
@end deftp

@defvr {Scheme Variable} %default-theme
@defvrx {Scheme Variable} %default-theme-name
The default SLiM theme and its name.
@end defvr


@deftp {Data Type} sddm-configuration
This is the data type representing the SDDM service configuration.

@table @asis
@item @code{display-server} (default: "x11")
Select display server to use for the greeter.  Valid values are @samp{"x11"}
or @samp{"wayland"}.

@item @code{numlock} (default: "on")
Valid values are @samp{"on"}, @samp{"off"} or @samp{"none"}.

@item @code{halt-command} (default @code{#~(string-apppend #$shepherd "/sbin/halt")})
Command to run when halting.

@item @code{reboot-command} (default @code{#~(string-append #$shepherd "/sbin/reboot")})
Command to run when rebooting.

@item @code{theme} (default "maldives")
Theme to use.  Default themes provided by SDDM are @samp{"elarun"},
@samp{"maldives"} or @samp{"maya"}.

@item @code{themes-directory} (default "/run/current-system/profile/share/sddm/themes")
Directory to look for themes.

@item @code{faces-directory} (default "/run/current-system/profile/share/sddm/faces")
Directory to look for faces.

@item @code{default-path} (default "/run/current-system/profile/bin")
Default PATH to use.

@item @code{minimum-uid} (default: 1000)
Minimum UID displayed in SDDM and allowed for log-in.

@item @code{maximum-uid} (default: 2000)
Maximum UID to display in SDDM.

@item @code{remember-last-user?} (default #t)
Remember last user.

@item @code{remember-last-session?} (default #t)
Remember last session.

@item @code{hide-users} (default "")
Usernames to hide from SDDM greeter.

@item @code{hide-shells} (default @code{#~(string-append #$shadow "/sbin/nologin")})
Users with shells listed will be hidden from the SDDM greeter.

@item @code{session-command} (default @code{#~(string-append #$sddm "/share/sddm/scripts/wayland-session")})
Script to run before starting a wayland session.

@item @code{sessions-directory} (default "/run/current-system/profile/share/wayland-sessions")
Directory to look for desktop files starting wayland sessions.

@item @code{xorg-configuration} (default @code{(xorg-configuration)})
Configuration of the Xorg graphical server.

@item @code{xauth-path} (default @code{#~(string-append #$xauth "/bin/xauth")})
Path to xauth.

@item @code{xephyr-path} (default @code{#~(string-append #$xorg-server "/bin/Xephyr")})
Path to Xephyr.

@item @code{xdisplay-start} (default @code{#~(string-append #$sddm "/share/sddm/scripts/Xsetup")})
Script to run after starting xorg-server.

@item @code{xdisplay-stop} (default @code{#~(string-append #$sddm "/share/sddm/scripts/Xstop")})
Script to run before stopping xorg-server.

@item @code{xsession-command} (default: @code{xinitrc})
Script to run before starting a X session.

@item @code{xsessions-directory} (default: "/run/current-system/profile/share/xsessions")
Directory to look for desktop files starting X sessions.

@item @code{minimum-vt} (default: 7)
Minimum VT to use.

@item @code{auto-login-user} (default "")
User to use for auto-login.

@item @code{auto-login-session} (default "")
Desktop file to use for auto-login.

@item @code{relogin?} (default #f)
Relogin after logout.

@end table
@end deftp

@cindex login manager
@cindex X11 login
@defvr {Scheme Variable} sddm-service-type
This is the type of the service to run the
@uref{https://github.com/sddm/sddm,SDDM display manager}.  Its value must be
a @code{sddm-configuration} record (see below).

Here's an example use:

@lisp
(service sddm-service-type
         (sddm-configuration
           (auto-login-user "alice")
           (auto-login-session "xfce.desktop")))
@end lisp
@end defvr

@deftp {Data Type} sddm-configuration
This data type represents the configuration of the SDDM login manager.  The
available fields are:

@table @asis
@item @code{sddm} (default: @code{sddm})
The SDDM package to use.

@item @code{display-server} (default: @code{"x11"})
This must be either @code{"x11"} or @code{"wayland"}.

@c FIXME: Add more fields.

@item @code{auto-login-user} (default: @code{""})
If non-empty, this is the user account under which to log in automatically.

@item @code{auto-login-session} (default: @code{""})
If non-empty, this is the @file{.desktop} file name to use as the auto-login
session.
@end table
@end deftp

@cindex Xorg, configuration
@deftp {Data Type} xorg-configuration
This data type represents the configuration of the Xorg graphical display
server.  Note that there is no Xorg service; instead, the X server is
started by a ``display manager'' such as GDM, SDDM, and SLiM@.  Thus, the
configuration of these display managers aggregates an
@code{xorg-configuration} record.

@table @asis
@item @code{modules} (default: @code{%default-xorg-modules})
This is a list of @dfn{module packages} loaded by the Xorg server---e.g.,
@code{xf86-video-vesa}, @code{xf86-input-keyboard}, and so on.

@item @code{fonts} (default: @code{%default-xorg-fonts})
This is a list of font directories to add to the server's @dfn{font path}.

@item @code{drivers} (default: @code{'()})
This must be either the empty list, in which case Xorg chooses a graphics
driver automatically, or a list of driver names that will be tried in this
order---e.g., @code{("modesetting" "vesa")}.

@item @code{resolutions} (default: @code{'()})
When @code{resolutions} is the empty list, Xorg chooses an appropriate
screen resolution.  Otherwise, it must be a list of resolutions---e.g.,
@code{((1024 768) (640 480))}.

@cindex keyboard layout, for Xorg
@cindex keymap, for Xorg
@item @code{keyboard-layout} (default: @code{#f})
If this is @code{#f}, Xorg uses the default keyboard layout---usually US
English (``qwerty'') for a 105-key PC keyboard.

Otherwise this must be a @code{keyboard-layout} object specifying the
keyboard layout in use when Xorg is running.  @xref{键盘布局}, for
more information on how to specify the keyboard layout.

@item @code{extra-config} (default: @code{'()})
This is a list of strings or objects appended to the configuration file.  It
is used to pass extra text to be added verbatim to the configuration file.

@item @code{server} (default: @code{xorg-server})
This is the package providing the Xorg server.

@item @code{server-arguments} (default: @code{%default-xorg-server-arguments})
This is the list of command-line arguments to pass to the X server.  The
default is @code{-nolisten tcp}.
@end table
@end deftp

@deffn {Scheme Procedure} set-xorg-configuration @var{config} @
  [@var{login-manager-service-type}] Tell the log-in manager (of type
@var{login-manager-service-type}) to use @var{config}, an
@code{<xorg-configuration>} record.

Since the Xorg configuration is embedded in the log-in manager's
configuration---e.g., @code{gdm-configuration}---this procedure provides a
shorthand to set the Xorg configuration.
@end deffn

@deffn {Scheme Procedure} xorg-start-command [@var{config}]
Return a @code{startx} script in which the modules, fonts, etc. specified in
@var{config}, are available.  The result should be used in place of
@code{startx}.

Usually the X server is started by a login manager.
@end deffn


@deffn {Scheme Procedure} screen-locker-service @var{package} [@var{program}]
Add @var{package}, a package for a screen locker or screen saver whose
command is @var{program}, to the set of setuid programs and add a PAM entry
for it.  For example:

@lisp
(screen-locker-service xlockmore "xlock")
@end lisp

makes the good ol' XlockMore usable.
@end deffn


@node 打印服务
@subsection 打印服务

@cindex printer support with CUPS
The @code{(gnu services cups)} module provides a Guix service definition for
the CUPS printing service.  To add printer support to a Guix system, add a
@code{cups-service} to the operating system definition:

@deffn {Scheme Variable} cups-service-type
The service type for the CUPS print server.  Its value should be a valid
CUPS configuration (see below).  To use the default settings, simply write:
@lisp
(service cups-service-type)
@end lisp
@end deffn

The CUPS configuration controls the basic things about your CUPS
installation: what interfaces it listens on, what to do if a print job
fails, how much logging to do, and so on.  To actually add a printer, you
have to visit the @url{http://localhost:631} URL, or use a tool such as
GNOME's printer configuration services.  By default, configuring a CUPS
service will generate a self-signed certificate if needed, for secure
connections to the print server.

Suppose you want to enable the Web interface of CUPS and also add support
for Epson printers @i{via} the @code{epson-inkjet-printer-escpr} package and
for HP printers @i{via} the @code{hplip-minimal} package.  You can do that
directly, like this (you need to use the @code{(gnu packages cups)} module):

@lisp
(service cups-service-type
         (cups-configuration
           (web-interface? #t)
           (extensions
             (list cups-filters epson-inkjet-printer-escpr hplip-minimal))))
@end lisp

Note: If you wish to use the Qt5 based GUI which comes with the hplip
package then it is suggested that you install the @code{hplip} package,
either in your OS configuration file or as your user.

The available configuration parameters follow.  Each parameter definition is
preceded by its type; for example, @samp{string-list foo} indicates that the
@code{foo} parameter should be specified as a list of strings.  There is
also a way to specify the configuration as a string, if you have an old
@code{cupsd.conf} file that you want to port over from some other system;
see the end for more details.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services cups).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as CUPS updates.


Available @code{cups-configuration} fields are:

@deftypevr {@code{cups-configuration} parameter} package cups
The CUPS package.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} package-list extensions (default: @code{(list brlaser cups-filters epson-inkjet-printer-escpr foomatic-filters hplip-minimal splix)})
Drivers and other extensions to the CUPS package.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} files-configuration files-configuration
Configuration of where to write logs, what directories to use for print
spools, and related privileged configuration parameters.

Available @code{files-configuration} fields are:

@deftypevr {@code{files-configuration} parameter} log-location access-log
Defines the access log filename.  Specifying a blank filename disables
access log generation.  The value @code{stderr} causes log entries to be
sent to the standard error file when the scheduler is running in the
foreground, or to the system log daemon when run in the background.  The
value @code{syslog} causes log entries to be sent to the system log daemon.
The server name may be included in filenames using the string @code{%s}, as
in @code{/var/log/cups/%s-access_log}.

Defaults to @samp{"/var/log/cups/access_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name cache-dir
Where CUPS should cache data.

Defaults to @samp{"/var/cache/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string config-file-perm
Specifies the permissions for all configuration files that the scheduler
writes.

Note that the permissions for the printers.conf file are currently masked to
only allow access from the scheduler user (typically root).  This is done
because printer device URIs sometimes contain sensitive authentication
information that should not be generally known on the system.  There is no
way to disable this security feature.

Defaults to @samp{"0640"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} log-location error-log
Defines the error log filename.  Specifying a blank filename disables error
log generation.  The value @code{stderr} causes log entries to be sent to
the standard error file when the scheduler is running in the foreground, or
to the system log daemon when run in the background.  The value
@code{syslog} causes log entries to be sent to the system log daemon.  The
server name may be included in filenames using the string @code{%s}, as in
@code{/var/log/cups/%s-error_log}.

Defaults to @samp{"/var/log/cups/error_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string fatal-errors
Specifies which errors are fatal, causing the scheduler to exit.  The kind
strings are:

@table @code
@item none
No errors are fatal.

@item all
All of the errors below are fatal.

@item browse
Browsing initialization errors are fatal, for example failed connections to
the DNS-SD daemon.

@item config
Configuration file syntax errors are fatal.

@item listen
Listen or Port errors are fatal, except for IPv6 failures on the loopback or
@code{any} addresses.

@item log
Log file creation or write errors are fatal.

@item permissions
Bad startup file permissions are fatal, for example shared TLS certificate
and key files with world-read permissions.
@end table

Defaults to @samp{"all -browse"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} boolean file-device?
Specifies whether the file pseudo-device can be used for new printer
queues.  The URI @uref{file:///dev/null} is always allowed.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string group
Specifies the group name or ID that will be used when executing external
programs.

Defaults to @samp{"lp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string log-file-perm
Specifies the permissions for all log files that the scheduler writes.

Defaults to @samp{"0644"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} log-location page-log
Defines the page log filename.  Specifying a blank filename disables page
log generation.  The value @code{stderr} causes log entries to be sent to
the standard error file when the scheduler is running in the foreground, or
to the system log daemon when run in the background.  The value
@code{syslog} causes log entries to be sent to the system log daemon.  The
server name may be included in filenames using the string @code{%s}, as in
@code{/var/log/cups/%s-page_log}.

Defaults to @samp{"/var/log/cups/page_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string remote-root
Specifies the username that is associated with unauthenticated accesses by
clients claiming to be the root user.  The default is @code{remroot}.

Defaults to @samp{"remroot"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name request-root
Specifies the directory that contains print jobs and other HTTP request
data.

Defaults to @samp{"/var/spool/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} sandboxing sandboxing
Specifies the level of security sandboxing that is applied to print filters,
backends, and other child processes of the scheduler; either @code{relaxed}
or @code{strict}.  This directive is currently only used/supported on macOS.

Defaults to @samp{strict}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name server-keychain
Specifies the location of TLS certificates and private keys.  CUPS will look
for public and private keys in this directory: @file{.crt} files for
PEM-encoded certificates and corresponding @file{.key} files for PEM-encoded
private keys.

Defaults to @samp{"/etc/cups/ssl"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name server-root
Specifies the directory containing the server configuration files.

Defaults to @samp{"/etc/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} boolean sync-on-close?
Specifies whether the scheduler calls fsync(2) after writing configuration
or state files.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} space-separated-string-list system-group
Specifies the group(s) to use for @code{@@SYSTEM} group authentication.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name temp-dir
Specifies the directory where temporary files are stored.

Defaults to @samp{"/var/spool/cups/tmp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string user
Specifies the user name or ID that is used when running external programs.

Defaults to @samp{"lp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string set-env
Set the specified environment variable to be passed to child processes.

Defaults to @samp{"variable value"}.
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} access-log-level access-log-level
Specifies the logging level for the AccessLog file.  The @code{config} level
logs when printers and classes are added, deleted, or modified and when
configuration files are accessed or updated.  The @code{actions} level logs
when print jobs are submitted, held, released, modified, or canceled, and
any of the conditions for @code{config}.  The @code{all} level logs all
requests.

Defaults to @samp{actions}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean auto-purge-jobs?
Specifies whether to purge job history data automatically when it is no
longer required for quotas.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} comma-separated-string-list browse-dns-sd-sub-types
Specifies a list of DNS-SD sub-types to advertise for each shared printer.
For example, @samp{"_cups" "_print"} will tell network clients that both
CUPS sharing and IPP Everywhere are supported.

Defaults to @samp{"_cups"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} browse-local-protocols browse-local-protocols
Specifies which protocols to use for local printer sharing.

Defaults to @samp{dnssd}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean browse-web-if?
Specifies whether the CUPS web interface is advertised.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean browsing?
Specifies whether shared printers are advertised.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string classification
Specifies the security classification of the server.  Any valid banner name
can be used, including @samp{"classified"}, @samp{"confidential"},
@samp{"secret"}, @samp{"topsecret"}, and @samp{"unclassified"}, or the
banner can be omitted to disable secure printing functions.

Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean classify-override?
Specifies whether users may override the classification (cover page) of
individual print jobs using the @code{job-sheets} option.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} default-auth-type default-auth-type
Specifies the default type of authentication to use.

Defaults to @samp{Basic}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} default-encryption default-encryption
Specifies whether encryption will be used for authenticated requests.

Defaults to @samp{Required}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-language
Specifies the default language to use for text and web content.

Defaults to @samp{"en"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-paper-size
Specifies the default paper size for new print queues.  @samp{"Auto"} uses a
locale-specific default, while @samp{"None"} specifies there is no default
paper size.  Specific size names are typically @samp{"Letter"} or
@samp{"A4"}.

Defaults to @samp{"Auto"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-policy
Specifies the default access policy to use.

Defaults to @samp{"default"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean default-shared?
Specifies whether local printers are shared by default.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer dirty-clean-interval
Specifies the delay for updating of configuration and state files, in
seconds.  A value of 0 causes the update to happen as soon as possible,
typically within a few milliseconds.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} error-policy error-policy
Specifies what to do when an error occurs.  Possible values are
@code{abort-job}, which will discard the failed print job; @code{retry-job},
which will retry the job at a later time; @code{retry-current-job}, which
retries the failed job immediately; and @code{stop-printer}, which stops the
printer.

Defaults to @samp{stop-printer}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer filter-limit
Specifies the maximum cost of filters that are run concurrently, which can
be used to minimize disk, memory, and CPU resource problems.  A limit of 0
disables filter limiting.  An average print to a non-PostScript printer
needs a filter limit of about 200.  A PostScript printer needs about half
that (100).  Setting the limit below these thresholds will effectively limit
the scheduler to printing a single job at any time.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer filter-nice
Specifies the scheduling priority of filters that are run to print a job.
The nice value ranges from 0, the highest priority, to 19, the lowest
priority.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} host-name-lookups host-name-lookups
Specifies whether to do reverse lookups on connecting clients.  The
@code{double} setting causes @code{cupsd} to verify that the hostname
resolved from the address matches one of the addresses returned for that
hostname.  Double lookups also prevent clients with unregistered addresses
from connecting to your server.  Only set this option to @code{#t} or
@code{double} if absolutely required.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-kill-delay
Specifies the number of seconds to wait before killing the filters and
backend associated with a canceled or held job.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-retry-interval
Specifies the interval between retries of jobs in seconds.  This is
typically used for fax queues but can also be used with normal print queues
whose error policy is @code{retry-job} or @code{retry-current-job}.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-retry-limit
Specifies the number of retries that are done for jobs.  This is typically
used for fax queues but can also be used with normal print queues whose
error policy is @code{retry-job} or @code{retry-current-job}.

Defaults to @samp{5}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean keep-alive?
Specifies whether to support HTTP keep-alive connections.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer keep-alive-timeout
Specifies how long an idle client connection remains open, in seconds.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer limit-request-body
Specifies the maximum size of print files, IPP requests, and HTML form
data.  A limit of 0 disables the limit check.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} multiline-string-list listen
Listens on the specified interfaces for connections.  Valid values are of
the form @var{address}:@var{port}, where @var{address} is either an IPv6
address enclosed in brackets, an IPv4 address, or @code{*} to indicate all
addresses.  Values can also be file names of local UNIX domain sockets.  The
Listen directive is similar to the Port directive but allows you to restrict
access to specific interfaces or networks.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer listen-back-log
Specifies the number of pending connections that will be allowed.  This
normally only affects very busy servers that have reached the MaxClients
limit, but can also be triggered by large numbers of simultaneous
connections.  When the limit is reached, the operating system will refuse
additional connections until the scheduler can accept the pending ones.

Defaults to @samp{128}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} location-access-control-list location-access-controls
Specifies a set of additional access controls.

Available @code{location-access-controls} fields are:

@deftypevr {@code{location-access-controls} parameter} file-name path
Specifies the URI path to which the access control applies.
@end deftypevr

@deftypevr {@code{location-access-controls} parameter} access-control-list access-controls
Access controls for all access to this path, in the same format as the
@code{access-controls} of @code{operation-access-control}.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{location-access-controls} parameter} method-access-control-list method-access-controls
Access controls for method-specific access to this path.

Defaults to @samp{()}.

Available @code{method-access-controls} fields are:

@deftypevr {@code{method-access-controls} parameter} boolean reverse?
If @code{#t}, apply access controls to all methods except the listed
methods.  Otherwise apply to only the listed methods.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{method-access-controls} parameter} method-list methods
Methods to which this access control applies.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{method-access-controls} parameter} access-control-list access-controls
Access control directives, as a list of strings.  Each string should be one
directive, such as @samp{"Order allow,deny"}.

Defaults to @samp{()}.
@end deftypevr
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer log-debug-history
Specifies the number of debugging messages that are retained for logging if
an error occurs in a print job.  Debug messages are logged regardless of the
LogLevel setting.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} log-level log-level
Specifies the level of logging for the ErrorLog file.  The value @code{none}
stops all logging while @code{debug2} logs everything.

Defaults to @samp{info}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} log-time-format log-time-format
Specifies the format of the date and time in the log files.  The value
@code{standard} logs whole seconds while @code{usecs} logs microseconds.

Defaults to @samp{standard}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-clients
Specifies the maximum number of simultaneous clients that are allowed by the
scheduler.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-clients-per-host
Specifies the maximum number of simultaneous clients that are allowed from a
single address.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-copies
Specifies the maximum number of copies that a user can print of each job.

Defaults to @samp{9999}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-hold-time
Specifies the maximum time a job may remain in the @code{indefinite} hold
state before it is canceled.  A value of 0 disables cancellation of held
jobs.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs
Specifies the maximum number of simultaneous jobs that are allowed.  Set to
0 to allow an unlimited number of jobs.

Defaults to @samp{500}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs-per-printer
Specifies the maximum number of simultaneous jobs that are allowed per
printer.  A value of 0 allows up to MaxJobs jobs per printer.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs-per-user
Specifies the maximum number of simultaneous jobs that are allowed per
user.  A value of 0 allows up to MaxJobs jobs per user.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-job-time
Specifies the maximum time a job may take to print before it is canceled, in
seconds.  Set to 0 to disable cancellation of ``stuck'' jobs.

Defaults to @samp{10800}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-log-size
Specifies the maximum size of the log files before they are rotated, in
bytes.  The value 0 disables log rotation.

Defaults to @samp{1048576}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer multiple-operation-timeout
Specifies the maximum amount of time to allow between files in a multiple
file print job, in seconds.

Defaults to @samp{300}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string page-log-format
Specifies the format of PageLog lines.  Sequences beginning with percent
(@samp{%}) characters are replaced with the corresponding information, while
all other characters are copied literally.  The following percent sequences
are recognized:

@table @samp
@item %%
insert a single percent character

@item %@{name@}
insert the value of the specified IPP attribute

@item %C
insert the number of copies for the current page

@item %P
insert the current page number

@item %T
insert the current date and time in common log format

@item %j
insert the job ID

@item %p
insert the printer name

@item %u
insert the username
@end table

A value of the empty string disables page logging.  The string @code{%p %u
%j %T %P %C %@{job-billing@} %@{job-originating-host-name@} %@{job-name@}
%@{media@} %@{sides@}} creates a page log with the standard items.

Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} environment-variables environment-variables
Passes the specified environment variable(s) to child processes; a list of
strings.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} policy-configuration-list policies
Specifies named access control policies.

Available @code{policy-configuration} fields are:

@deftypevr {@code{policy-configuration} parameter} string name
Name of the policy.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string job-private-access
Specifies an access list for a job's private values.  @code{@@ACL} maps to
the printer's requesting-user-name-allowed or requesting-user-name-denied
values.  @code{@@OWNER} maps to the job's owner.  @code{@@SYSTEM} maps to
the groups listed for the @code{system-group} field of the
@code{files-config} configuration, which is reified into the
@code{cups-files.conf(5)} file.  Other possible elements of the access list
include specific user names, and @code{@@@var{group}} to indicate members of
a specific group.  The access list may also be simply @code{all} or
@code{default}.

Defaults to @samp{"@@OWNER @@SYSTEM"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string job-private-values
Specifies the list of job values to make private, or @code{all},
@code{default}, or @code{none}.

Defaults to @samp{"job-name job-originating-host-name
job-originating-user-name phone"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string subscription-private-access
Specifies an access list for a subscription's private values.  @code{@@ACL}
maps to the printer's requesting-user-name-allowed or
requesting-user-name-denied values.  @code{@@OWNER} maps to the job's
owner.  @code{@@SYSTEM} maps to the groups listed for the
@code{system-group} field of the @code{files-config} configuration, which is
reified into the @code{cups-files.conf(5)} file.  Other possible elements of
the access list include specific user names, and @code{@@@var{group}} to
indicate members of a specific group.  The access list may also be simply
@code{all} or @code{default}.

Defaults to @samp{"@@OWNER @@SYSTEM"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string subscription-private-values
Specifies the list of job values to make private, or @code{all},
@code{default}, or @code{none}.

Defaults to @samp{"notify-events notify-pull-method notify-recipient-uri
notify-subscriber-user-name notify-user-data"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} operation-access-control-list access-controls
Access control by IPP operation.

Defaults to @samp{()}.
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean-or-non-negative-integer preserve-job-files
Specifies whether job files (documents) are preserved after a job is
printed.  If a numeric value is specified, job files are preserved for the
indicated number of seconds after printing.  Otherwise a boolean value
applies indefinitely.

Defaults to @samp{86400}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean-or-non-negative-integer preserve-job-history
Specifies whether the job history is preserved after a job is printed.  If a
numeric value is specified, the job history is preserved for the indicated
number of seconds after printing.  If @code{#t}, the job history is
preserved until the MaxJobs limit is reached.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer reload-timeout
Specifies the amount of time to wait for job completion before restarting
the scheduler.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string rip-cache
Specifies the maximum amount of memory to use when converting documents into
bitmaps for a printer.

Defaults to @samp{"128m"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string server-admin
Specifies the email address of the server administrator.

Defaults to @samp{"root@@localhost.localdomain"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} host-name-list-or-* server-alias
The ServerAlias directive is used for HTTP Host header validation when
clients connect to the scheduler from external interfaces.  Using the
special name @code{*} can expose your system to known browser-based DNS
rebinding attacks, even when accessing sites through a firewall.  If the
auto-discovery of alternate names does not work, we recommend listing each
alternate name with a ServerAlias directive instead of using @code{*}.

Defaults to @samp{*}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string server-name
Specifies the fully-qualified host name of the server.

Defaults to @samp{"localhost"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} server-tokens server-tokens
Specifies what information is included in the Server header of HTTP
responses.  @code{None} disables the Server header.  @code{ProductOnly}
reports @code{CUPS}.  @code{Major} reports @code{CUPS 2}.  @code{Minor}
reports @code{CUPS 2.0}.  @code{Minimal} reports @code{CUPS 2.0.0}.
@code{OS} reports @code{CUPS 2.0.0 (@var{uname})} where @var{uname} is the
output of the @code{uname} command.  @code{Full} reports @code{CUPS 2.0.0
(@var{uname}) IPP/2.0}.

Defaults to @samp{Minimal}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} multiline-string-list ssl-listen
Listens on the specified interfaces for encrypted connections.  Valid values
are of the form @var{address}:@var{port}, where @var{address} is either an
IPv6 address enclosed in brackets, an IPv4 address, or @code{*} to indicate
all addresses.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} ssl-options ssl-options
Sets encryption options.  By default, CUPS only supports encryption using
TLS v1.0 or higher using known secure cipher suites.  Security is reduced
when @code{Allow} options are used, and enhanced when @code{Deny} options
are used.  The @code{AllowRC4} option enables the 128-bit RC4 cipher suites,
which are required for some older clients.  The @code{AllowSSL3} option
enables SSL v3.0, which is required for some older clients that do not
support TLS v1.0.  The @code{DenyCBC} option disables all CBC cipher
suites.  The @code{DenyTLS1.0} option disables TLS v1.0 support - this sets
the minimum protocol version to TLS v1.1.

Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean strict-conformance?
Specifies whether the scheduler requires clients to strictly adhere to the
IPP specifications.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer timeout
Specifies the HTTP request timeout, in seconds.

Defaults to @samp{300}.

@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean web-interface?
Specifies whether the web interface is enabled.

Defaults to @samp{#f}.
@end deftypevr

At this point you're probably thinking ``oh dear, Guix manual, I like you
but you can stop already with the configuration options''.  Indeed.
However, one more point: it could be that you have an existing
@code{cupsd.conf} that you want to use.  In that case, you can pass an
@code{opaque-cups-configuration} as the configuration of a
@code{cups-service-type}.

Available @code{opaque-cups-configuration} fields are:

@deftypevr {@code{opaque-cups-configuration} parameter} package cups
The CUPS package.
@end deftypevr

@deftypevr {@code{opaque-cups-configuration} parameter} string cupsd.conf
The contents of the @code{cupsd.conf}, as a string.
@end deftypevr

@deftypevr {@code{opaque-cups-configuration} parameter} string cups-files.conf
The contents of the @code{cups-files.conf} file, as a string.
@end deftypevr

For example, if your @code{cupsd.conf} and @code{cups-files.conf} are in
strings of the same name, you could instantiate a CUPS service like this:

@lisp
(service cups-service-type
         (opaque-cups-configuration
           (cupsd.conf cupsd.conf)
           (cups-files.conf cups-files.conf)))
@end lisp


@node 桌面服务
@subsection 桌面服务

The @code{(gnu services desktop)} module provides services that are usually
useful in the context of a ``desktop'' setup---that is, on a machine running
a graphical display server, possibly with graphical user interfaces, etc.
It also defines services that provide specific desktop environments like
GNOME, Xfce or MATE.

To simplify things, the module defines a variable containing the set of
services that users typically expect on a machine with a graphical
environment and networking:

@defvr {Scheme Variable} %desktop-services
This is a list of services that builds upon @code{%base-services} and adds
or adjusts services for a typical ``desktop'' setup.

In particular, it adds a graphical login manager (@pxref{X窗口,
@code{gdm-service-type}}), screen lockers, a network management tool
(@pxref{网络服务, @code{network-manager-service-type}}) with
modem support (@pxref{网络服务,
@code{modem-manager-service-type}}), energy and color management services,
the @code{elogind} login and seat manager, the Polkit privilege service, the
GeoClue location service, the AccountsService daemon that allows authorized
users change system passwords, an NTP client (@pxref{网络服务}),
the Avahi daemon, and has the name service switch service configured to be
able to use @code{nss-mdns} (@pxref{Name Service Switch, mDNS}).
@end defvr

The @code{%desktop-services} variable can be used as the @code{services}
field of an @code{operating-system} declaration (@pxref{操作系统参考, @code{services}}).

Additionally, the @code{gnome-desktop-service-type},
@code{xfce-desktop-service}, @code{mate-desktop-service-type},
@code{lxqt-desktop-service-type} and
@code{enlightenment-desktop-service-type} procedures can add GNOME, Xfce,
MATE and/or Enlightenment to a system.  To ``add GNOME'' means that
system-level services like the backlight adjustment helpers and the power
management utilities are added to the system, extending @code{polkit} and
@code{dbus} appropriately, allowing GNOME to operate with elevated
privileges on a limited number of special-purpose system interfaces.
Additionally, adding a service made by @code{gnome-desktop-service-type}
adds the GNOME metapackage to the system profile.  Likewise, adding the Xfce
service not only adds the @code{xfce} metapackage to the system profile, but
it also gives the Thunar file manager the ability to open a ``root-mode''
file management window, if the user authenticates using the administrator's
password via the standard polkit graphical interface.  To ``add MATE'' means
that @code{polkit} and @code{dbus} are extended appropriately, allowing MATE
to operate with elevated privileges on a limited number of special-purpose
system interfaces.  Additionally, adding a service of type
@code{mate-desktop-service-type} adds the MATE metapackage to the system
profile.  ``Adding Enlightenment'' means that @code{dbus} is extended
appropriately, and several of Enlightenment's binaries are set as setuid,
allowing Enlightenment's screen locker and other functionality to work as
expected.

The desktop environments in Guix use the Xorg display server by default.  If
you'd like to use the newer display server protocol called Wayland, you need
to use the @code{sddm-service} instead of GDM as the graphical login
manager.  You should then select the ``GNOME (Wayland)'' session in SDDM@.
Alternatively you can also try starting GNOME on Wayland manually from a TTY
with the command ``XDG_SESSION_TYPE=wayland exec dbus-run-session
gnome-session``.  Currently only GNOME has support for Wayland.

@defvr {Scheme Variable} gnome-desktop-service-type
This is the type of the service that adds the @uref{https://www.gnome.org,
GNOME} desktop environment.  Its value is a
@code{gnome-desktop-configuration} object (see below).

This service adds the @code{gnome} package to the system profile, and
extends polkit with the actions from @code{gnome-settings-daemon}.
@end defvr

@deftp {Data Type} gnome-desktop-configuration
Configuration record for the GNOME desktop environment.

@table @asis
@item @code{gnome}（默认值：@code{gnome}）
The GNOME package to use.
@end table
@end deftp

@defvr {Scheme Variable} xfce-desktop-service-type
This is the type of a service to run the @uref{Xfce, https://xfce.org/}
desktop environment.  Its value is an @code{xfce-desktop-configuration}
object (see below).

This service adds the @code{xfce} package to the system profile, and extends
polkit with the ability for @code{thunar} to manipulate the file system as
root from within a user session, after the user has authenticated with the
administrator's password.

Note that @code{xfce4-panel} and its plugin packages should be installed in
the same profile to ensure compatibility.  When using this service, you
should add extra plugins (@code{xfce4-whiskermenu-plugin},
@code{xfce4-weather-plugin}, etc.) to the @code{packages} field of your
@code{operating-system}.
@end defvr

@deftp {Data Type} xfce-desktop-configuration
Configuration record for the Xfce desktop environment.

@table @asis
@item @code{xfce}（默认值：@code{xfce}）
The Xfce package to use.
@end table
@end deftp

@deffn {Scheme Variable} mate-desktop-service-type
This is the type of the service that runs the
@uref{https://mate-desktop.org/, MATE desktop environment}.  Its value is a
@code{mate-desktop-configuration} object (see below).

This service adds the @code{mate} package to the system profile, and extends
polkit with the actions from @code{mate-settings-daemon}.
@end deffn

@deftp {Data Type} mate-desktop-configuration
Configuration record for the MATE desktop environment.

@table @asis
@item @code{mate}（默认值：@code{mate}）
The MATE package to use.
@end table
@end deftp

@deffn {Scheme Variable} lxqt-desktop-service-type
This is the type of the service that runs the @uref{https://lxqt.github.io,
LXQt desktop environment}.  Its value is a @code{lxqt-desktop-configuration}
object (see below).

This service adds the @code{lxqt} package to the system profile.
@end deffn

@deftp {Data Type} lxqt-desktop-configuration
Configuration record for the LXQt desktop environment.

@table @asis
@item @code{lxqt} (default: @code{lxqt})
The LXQT package to use.
@end table
@end deftp

@deffn {Scheme Variable} enlightenment-desktop-service-type
Return a service that adds the @code{enlightenment} package to the system
profile, and extends dbus with actions from @code{efl}.
@end deffn

@deftp {Data Type} enlightenment-desktop-service-configuration
@table @asis
@item @code{enlightenment}（默认值：@code{enlightenment}）
The enlightenment package to use.
@end table
@end deftp

Because the GNOME, Xfce and MATE desktop services pull in so many packages,
the default @code{%desktop-services} variable doesn't include any of them by
default.  To add GNOME, Xfce or MATE, just @code{cons} them onto
@code{%desktop-services} in the @code{services} field of your
@code{operating-system}:

@lisp
(use-modules (gnu))
(use-service-modules desktop)
(operating-system
  ...
  ;; cons* adds items to the list given as its last argument.
  (services (cons* (service gnome-desktop-service-type)
                   (service xfce-desktop-service)
                   %desktop-services))
  ...)
@end lisp

These desktop environments will then be available as options in the
graphical login window.

The actual service definitions included in @code{%desktop-services} and
provided by @code{(gnu services dbus)} and @code{(gnu services desktop)} are
described below.

@deffn {Scheme Procedure} dbus-service [#:dbus @var{dbus}] [#:services '()]
Return a service that runs the ``system bus'', using @var{dbus}, with
support for @var{services}.

@uref{https://dbus.freedesktop.org/, D-Bus} is an inter-process
communication facility.  Its system bus is used to allow system services to
communicate and to be notified of system-wide events.

@var{services} must be a list of packages that provide an
@file{etc/dbus-1/system.d} directory containing additional D-Bus
configuration and policy files.  For example, to allow avahi-daemon to use
the system bus, @var{services} must be equal to @code{(list avahi)}.
@end deffn

@deffn {Scheme Procedure} elogind-service [#:config @var{config}]
Return a service that runs the @code{elogind} login and seat management
daemon.  @uref{https://github.com/elogind/elogind, Elogind} exposes a D-Bus
interface that can be used to know which users are logged in, know what kind
of sessions they have open, suspend the system, inhibit system suspend,
reboot the system, and other tasks.

Elogind handles most system-level power events for a computer, for example
suspending the system when a lid is closed, or shutting it down when the
power button is pressed.

The @var{config} keyword argument specifies the configuration for elogind,
and should be the result of an @code{(elogind-configuration (@var{parameter}
@var{value})...)} invocation.  Available parameters and their default values
are:

@table @code
@item kill-user-processes?
@code{#f}
@item kill-only-users
@code{()}
@item kill-exclude-users
@code{("root")}
@item inhibit-delay-max-seconds
@code{5}
@item handle-power-key
@code{poweroff}
@item handle-suspend-key
@code{suspend}
@item handle-hibernate-key
@code{hibernate}
@item handle-lid-switch
@code{suspend}
@item handle-lid-switch-docked
@code{ignore}
@item handle-lid-switch-external-power
@code{ignore}
@item power-key-ignore-inhibited?
@code{#f}
@item suspend-key-ignore-inhibited?
@code{#f}
@item hibernate-key-ignore-inhibited?
@code{#f}
@item lid-switch-ignore-inhibited?
@code{#t}
@item holdoff-timeout-seconds
@code{30}
@item idle-action
@code{ignore}
@item idle-action-seconds
@code{(* 30 60)}
@item runtime-directory-size-percent
@code{10}
@item runtime-directory-size
@code{#f}
@item remove-ipc?
@code{#t}
@item suspend-state
@code{("mem" "standby" "freeze")}
@item suspend-mode
@code{()}
@item hibernate-state
@code{("disk")}
@item hibernate-mode
@code{("platform" "shutdown")}
@item hybrid-sleep-state
@code{("disk")}
@item hybrid-sleep-mode
@code{("suspend" "platform" "shutdown")}
@end table
@end deffn

@deffn {Scheme Procedure} accountsservice-service @
       [#:accountsservice @var{accountsservice}] Return a service that runs
AccountsService, a system service that can list available accounts, change
their passwords, and so on.  AccountsService integrates with PolicyKit to
enable unprivileged users to acquire the capability to modify their system
configuration.
@uref{https://www.freedesktop.org/wiki/Software/AccountsService/, the
accountsservice web site} for more information.

The @var{accountsservice} keyword argument is the @code{accountsservice}
package to expose as a service.
@end deffn

@deffn {Scheme Procedure} polkit-service @
                         [#:polkit @var{polkit}] Return a service that runs the
@uref{https://www.freedesktop.org/wiki/Software/polkit/, Polkit privilege
management service}, which allows system administrators to grant access to
privileged operations in a structured way.  By querying the Polkit service,
a privileged system component can know when it should grant additional
capabilities to ordinary users.  For example, an ordinary user can be
granted the capability to suspend the system if the user is logged in
locally.
@end deffn

@defvr {Scheme Variable} polkit-wheel-service
Service that adds the @code{wheel} group as admins to the Polkit service.
This makes it so that users in the @code{wheel} group are queried for their
own passwords when performing administrative actions instead of
@code{root}'s, similar to the behaviour used by @code{sudo}.
@end defvr

@defvr {Scheme Variable} upower-service-type
Service that runs @uref{https://upower.freedesktop.org/, @command{upowerd}},
a system-wide monitor for power consumption and battery levels, with the
given configuration settings.

It implements the @code{org.freedesktop.UPower} D-Bus interface, and is
notably used by GNOME.
@end defvr

@deftp {Data Type} upower-configuration
Data type representation the configuration for UPower.

@table @asis

@item @code{upower} (default: @var{upower})
Package to use for @code{upower}.

@item @code{watts-up-pro?} (default: @code{#f})
Enable the Watts Up Pro device.

@item @code{poll-batteries?} (default: @code{#t})
Enable polling the kernel for battery level changes.

@item @code{ignore-lid?} (default: @code{#f})
Ignore the lid state, this can be useful if it's incorrect on a device.

@item @code{use-percentage-for-policy?} (default: @code{#f})
Whether battery percentage based policy should be used.  The default is to
use the time left, change to @code{#t} to use the percentage.

@item @code{percentage-low} (default: @code{10})
When @code{use-percentage-for-policy?} is @code{#t}, this sets the
percentage at which the battery is considered low.

@item @code{percentage-critical} (default: @code{3})
When @code{use-percentage-for-policy?} is @code{#t}, this sets the
percentage at which the battery is considered critical.

@item @code{percentage-action} (default: @code{2})
When @code{use-percentage-for-policy?} is @code{#t}, this sets the
percentage at which action will be taken.

@item @code{time-low} (default: @code{1200})
When @code{use-time-for-policy?} is @code{#f}, this sets the time remaining
in seconds at which the battery is considered low.

@item @code{time-critical} (default: @code{300})
When @code{use-time-for-policy?} is @code{#f}, this sets the time remaining
in seconds at which the battery is considered critical.

@item @code{time-action} (default: @code{120})
When @code{use-time-for-policy?} is @code{#f}, this sets the time remaining
in seconds at which action will be taken.

@item @code{critical-power-action} (default: @code{'hybrid-sleep})
The action taken when @code{percentage-action} or @code{time-action} is
reached (depending on the configuration of
@code{use-percentage-for-policy?}).

Possible values are:

@itemize @bullet
@item
@code{'power-off}

@item
@code{'hibernate}

@item
@code{'hybrid-sleep}.
@end itemize

@end table
@end deftp

@deffn {Scheme Procedure} udisks-service [#:udisks @var{udisks}]
Return a service for @uref{https://udisks.freedesktop.org/docs/latest/,
UDisks}, a @dfn{disk management} daemon that provides user interfaces with
notifications and ways to mount/unmount disks.  Programs that talk to UDisks
include the @command{udisksctl} command, part of UDisks, and GNOME Disks.
Note that Udisks relies on the @command{mount} command, so it will only be
able to use the file-system utilities installed in the system profile.  For
example if you want to be able to mount NTFS file-systems in read and write
fashion, you'll need to have @code{ntfs-3g} installed system-wide.
@end deffn

@deffn {Scheme Variable} colord-service-type
This is the type of the service that runs @command{colord}, a system service
with a D-Bus interface to manage the color profiles of input and output
devices such as screens and scanners.  It is notably used by the GNOME Color
Manager graphical tool.  See
@uref{https://www.freedesktop.org/software/colord/, the colord web site} for
more information.
@end deffn

@cindex scanner access
@defvr {Scheme Variable} sane-service-type
This service provides access to scanners @i{via}
@uref{http://www.sane-project.org, SANE} by installing the necessary udev
rules.  It is included in @code{%desktop-services} (@pxref{桌面服务}) and relies by default on @code{sane-backends-minimal} package
(see below) for hardware support.
@end defvr

@defvr {Scheme Variable} sane-backends-minimal
The default package which the @code{sane-service-type} installs.  It
supports many recent scanners.
@end defvr

@defvr {Scheme Variable} sane-backends
This package includes support for all scanners that
@code{sane-backends-minimal} supports, plus older Hewlett-Packard scanners
supported by @code{hplip} package.  In order to use this on a system which
relies on @code{%desktop-services}, you may use @code{modify-services}
(@pxref{服务参考, @code{modify-services}}) as illustrated below:

@lisp
(use-modules (gnu))
(use-service-modules
  @dots{}
  desktop)
(use-package-modules
  @dots{}
  scanner)

(define %my-desktop-services
  ;; List of desktop services that supports a broader range of scanners.
  (modify-services %desktop-services
    (sane-service-type _ => sane-backends)))

(operating-system
  @dots{}
  (services %my-desktop-services)
@end lisp
@end defvr

@deffn {Scheme Procedure} geoclue-application name [#:allowed? #t] [#:system? #f] [#:users '()]
Return a configuration allowing an application to access GeoClue location
data.  @var{name} is the Desktop ID of the application, without the
@code{.desktop} part.  If @var{allowed?} is true, the application will have
access to location information by default.  The boolean @var{system?} value
indicates whether an application is a system component or not.  Finally
@var{users} is a list of UIDs of all users for which this application is
allowed location info access.  An empty users list means that all users are
allowed.
@end deffn

@defvr {Scheme Variable} %standard-geoclue-applications
The standard list of well-known GeoClue application configurations, granting
authority to the GNOME date-and-time utility to ask for the current location
in order to set the time zone, and allowing the IceCat and Epiphany web
browsers to request location information.  IceCat and Epiphany both query
the user before allowing a web page to know the user's location.
@end defvr

@deffn {Scheme Procedure} geoclue-service [#:colord @var{colord}] @
                         [#:whitelist '()] @ [#:wifi-geolocation-url
"https://location.services.mozilla.com/v1/geolocate?key=geoclue"] @
[#:submit-data? #f] [#:wifi-submission-url
"https://location.services.mozilla.com/v1/submit?key=geoclue"] @
[#:submission-nick "geoclue"] @ [#:applications
%standard-geoclue-applications] Return a service that runs the GeoClue
location service.  This service provides a D-Bus interface to allow
applications to request access to a user's physical location, and optionally
to add information to online location databases.  See
@uref{https://wiki.freedesktop.org/www/Software/GeoClue/, the GeoClue web
site} for more information.
@end deffn

@deffn {Scheme Procedure} bluetooth-service [#:bluez @var{bluez}] @
       [@w{#:auto-enable? #f}] Return a service that runs the @command{bluetoothd}
daemon, which manages all the Bluetooth devices and provides a number of
D-Bus interfaces.  When AUTO-ENABLE? is true, the bluetooth controller is
powered automatically at boot, which can be useful when using a bluetooth
keyboard or mouse.

Users need to be in the @code{lp} group to access the D-Bus service.
@end deffn

@defvr {Scheme Variable} gnome-keyring-service-type
This is the type of the service that adds the
@uref{https://wiki.gnome.org/Projects/GnomeKeyring, GNOME Keyring}.  Its
value is a @code{gnome-keyring-configuration} object (see below).

This service adds the @code{gnome-keyring} package to the system profile and
extends PAM with entries using @code{pam_gnome_keyring.so}, unlocking a
user's login keyring when they log in or setting its password with passwd.
@end defvr

@deftp {Data Type} gnome-keyring-configuration
Configuration record for the GNOME Keyring service.

@table @asis
@item @code{keyring} (default: @code{gnome-keyring})
The GNOME keyring package to use.

@item @code{pam-services}
A list of @code{(@var{service} . @var{kind})} pairs denoting PAM services to
extend, where @var{service} is the name of an existing service to extend and
@var{kind} is one of @code{login} or @code{passwd}.

If @code{login} is given, it adds an optional @code{pam_gnome_keyring.so} to
the auth block without arguments and to the session block with
@code{auto_start}.  If @code{passwd} is given, it adds an optional
@code{pam_gnome_keyring.so} to the password block without arguments.

By default, this field contains ``gdm-password'' with the value @code{login}
and ``passwd'' is with the value @code{passwd}.
@end table
@end deftp


@node 声音服务
@subsection 声音服务

@cindex sound support
@cindex ALSA
@cindex PulseAudio, sound support

The @code{(gnu services sound)} module provides a service to configure the
Advanced Linux Sound Architecture (ALSA) system, which makes PulseAudio the
preferred ALSA output driver.

@deffn {Scheme Variable} alsa-service-type
This is the type for the @uref{https://alsa-project.org/, Advanced Linux
Sound Architecture} (ALSA) system, which generates the
@file{/etc/asound.conf} configuration file.  The value for this type is a
@command{alsa-configuration} record as in this example:

@lisp
(service alsa-service-type)
@end lisp

See below for details about @code{alsa-configuration}.
@end deffn

@deftp {Data Type} alsa-configuration
Data type representing the configuration for @code{alsa-service}.

@table @asis
@item @code{alsa-plugins} (default: @var{alsa-plugins})
@code{alsa-plugins} package to use.

@item @code{pulseaudio?} (default: @var{#t})
Whether ALSA applications should transparently be made to use the
@uref{https://www.pulseaudio.org/, PulseAudio} sound server.

Using PulseAudio allows you to run several sound-producing applications at
the same time and to individual control them @i{via} @command{pavucontrol},
among other things.

@item @code{extra-options} (default: @var{""})
String to append to the @file{/etc/asound.conf} file.

@end table
@end deftp

Individual users who want to override the system configuration of ALSA can
do it with the @file{~/.asoundrc} file:

@example
# In guix, we have to specify the absolute path for plugins.
pcm_type.jack @{
  lib "/home/alice/.guix-profile/lib/alsa-lib/libasound_module_pcm_jack.so"
@}

# Routing ALSA to jack:
# <http://jackaudio.org/faq/routing_alsa.html>.
pcm.rawjack @{
  type jack
  playback_ports @{
    0 system:playback_1
    1 system:playback_2
  @}

  capture_ports @{
    0 system:capture_1
    1 system:capture_2
  @}
@}

pcm.!default @{
  type plug
  slave @{
    pcm "rawjack"
  @}
@}
@end example

See @uref{https://www.alsa-project.org/main/index.php/Asoundrc} for the
details.

@deffn {Scheme Variable} pulseaudio-service-type
This is the type for the @uref{https://www.pulseaudio.org/, PulseAudio}
sound server.  It exists to allow system overrides of the default settings
via @code{pulseaudio-configuration}, see below.

@quotation Warning
This service overrides per-user configuration files.  If you want PulseAudio
to honor configuration files in @file{~/.config/pulse} you have to unset the
environment variables @env{PULSE_CONFIG} and @env{PULSE_CLIENTCONFIG} in
your @file{~/.bash_profile}.
@end quotation

@quotation Warning
This service on its own does not ensure, that the @code{pulseaudio} package
exists on your machine.  It merely adds configuration files for it, as
detailed below.  In the (admittedly unlikely) case, that you find yourself
without a @code{pulseaudio} package, consider enabling it through the
@code{alsa-service-type} above.
@end quotation
@end deffn

@deftp {Data Type} pulseaudio-configuration
Data type representing the configuration for @code{pulseaudio-service}.

@table @asis
@item @code{client-conf} (default: @code{'()})
List of settings to set in @file{client.conf}.  Accepts a list of strings or
a symbol-value pairs.  A string will be inserted as-is with a newline
added.  A pair will be formatted as ``key = value'', again with a newline
added.

@item @code{daemon-conf} (default: @code{'((flat-volumes . no))})
List of settings to set in @file{daemon.conf}, formatted just like
@var{client-conf}.

@item @code{script-file} (default: @code{(file-append pulseaudio "/etc/pulse/default.pa")})
Script file to use as @file{default.pa}.

@item @code{system-script-file} (default: @code{(file-append pulseaudio "/etc/pulse/system.pa")})
Script file to use as @file{system.pa}.
@end table
@end deftp

@deffn {Scheme Variable} ladspa-service-type
This service sets the @var{LADSPA_PATH} variable, so that programs, which
respect it, e.g. PulseAudio, can load LADSPA plugins.

The following example will setup the service to enable modules from the
@code{swh-plugins} package:

@lisp
(service ladspa-service-type
         (ladspa-configuration (plugins (list swh-plugins))))
@end lisp

See @uref{http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html} for the
details.

@end deffn

@node 数据库服务
@subsection 数据库服务

@cindex database
@cindex SQL
The @code{(gnu services databases)} module provides the following services.

@subsubheading PostgreSQL

The following example describes a PostgreSQL service with the default
configuration.

@lisp
(service postgresql-service-type
         (postgresql-configuration
          (postgresql postgresql-10)))
@end lisp

If the services fails to start, it may be due to an incompatible cluster
already present in @var{data-directory}.  Adjust it (or, if you don't need
the cluster anymore, delete @var{data-directory}), then restart the service.

Peer authentication is used by default and the @code{postgres} user account
has no shell, which prevents the direct execution of @code{psql} commands as
this user.  To use @code{psql}, you can temporarily log in as
@code{postgres} using a shell, create a PostgreSQL superuser with the same
name as one of the system users and then create the associated database.

@example
sudo -u postgres -s /bin/sh
createuser --interactive
createdb $MY_USER_LOGIN      # Replace appropriately.
@end example

@deftp {Data Type} postgresql-configuration
Data type representing the configuration for the
@code{postgresql-service-type}.

@table @asis
@item @code{postgresql}
PostgreSQL package to use for the service.

@item @code{port} (default: @code{5432})
Port on which PostgreSQL should listen.

@item @code{locale} (default: @code{"en_US.utf8"})
Locale to use as the default when creating the database cluster.

@item @code{config-file} (default: @code{(postgresql-config-file)})
The configuration file to use when running PostgreSQL@.  The default
behaviour uses the postgresql-config-file record with the default values for
the fields.

@item @code{log-directory} (default: @code{"/var/log/postgresql"})
The directory where @command{pg_ctl} output will be written in a file named
@code{"pg_ctl.log"}.  This file can be useful to debug PostgreSQL
configuration errors for instance.

@item @code{data-directory} (default: @code{"/var/lib/postgresql/data"})
Directory in which to store the data.

@item @code{extension-packages} (default: @code{'()})
@cindex postgresql extension-packages
Additional extensions are loaded from packages listed in
@var{extension-packages}.  Extensions are available at runtime.  For
instance, to create a geographic database using the @code{postgis}
extension, a user can configure the postgresql-service as in this example:

@cindex postgis
@lisp
(use-package-modules databases geo)

(operating-system
  ...
  ;; postgresql is required to run `psql' but postgis is not required for
  ;; proper operation.
  (packages (cons* postgresql %base-packages))
  (services
    (cons*
      (service postgresql-service-type
               (postgresql-configuration
                (postgresql postgresql-10)
                (extension-packages (list postgis))))
      %base-services)))
@end lisp

Then the extension becomes visible and you can initialise an empty
geographic database in this way:

@example
psql -U postgres
> create database postgistest;
> \connect postgistest;
> create extension postgis;
> create extension postgis_topology;
@end example

There is no need to add this field for contrib extensions such as hstore or
dblink as they are already loadable by postgresql.  This field is only
required to add extensions provided by other packages.

@end table
@end deftp

@deftp {Data Type} postgresql-config-file
Data type representing the PostgreSQL configuration file.  As shown in the
following example, this can be used to customize the configuration of
PostgreSQL@.  Note that you can use any G-expression or filename in place of
this record, if you already have a configuration file you'd like to use for
example.

@lisp
(service postgresql-service-type
         (postgresql-configuration
          (config-file
           (postgresql-config-file
            (log-destination "stderr")
            (hba-file
             (plain-file "pg_hba.conf"
                         "
local	all	all			trust
host	all	all	127.0.0.1/32 	md5
host	all	all	::1/128 	md5"))
            (extra-config
             '(("session_preload_libraries"     "auto_explain")
               ("random_page_cost"              2)
               ("auto_explain.log_min_duration" "100 ms")
               ("work_mem"                      "500 MB")
               ("logging_collector"             #t)
               ("log_directory"                 "/var/log/postgresql")))))))
@end lisp

@table @asis
@item @code{log-destination} (default: @code{"syslog"})
The logging method to use for PostgreSQL@.  Multiple values are accepted,
separated by commas.

@item @code{hba-file} (default: @code{%default-postgres-hba})
Filename or G-expression for the host-based authentication configuration.

@item @code{ident-file} (default: @code{%default-postgres-ident})
Filename or G-expression for the user name mapping configuration.

@item @code{socket-directory} (default: @code{#false})
Specifies the directory of the Unix-domain socket(s) on which PostgreSQL is
to listen for connections from client applications. If set to @code{""}
PostgreSQL does not listen on any Unix-domain sockets, in which case only
TCP/IP sockets can be used to connect to the server.

By default, the @code{#false} value means the PostgreSQL default value will
be used, which is currently @samp{/tmp}.

@item @code{extra-config} (default: @code{'()})
List of additional keys and values to include in the PostgreSQL config
file.  Each entry in the list should be a list where the first element is
the key, and the remaining elements are the values.

The values can be numbers, booleans or strings and will be mapped to
PostgreSQL parameters types @code{Boolean}, @code{String}, @code{Numeric},
@code{Numeric with Unit} and @code{Enumerated} described
@uref{https://www.postgresql.org/docs/current/config-setting.html, here}.

@end table
@end deftp

@deffn {Scheme Variable} postgresql-role-service-type
This service allows to create PostgreSQL roles and databases after
PostgreSQL service start.  Here is an example of its use.

@lisp
(service postgresql-role-service-type
            (postgresql-role-configuration
             (roles
              (list (postgresql-role
                     (name "test")
                     (create-database? #t))))))
@end lisp

This service can be extended with extra roles, as in this example:

@lisp
(service-extension postgresql-role-service-type
                   (const (postgresql-role
                           (name "alice")
                           (create-database? #t))))
@end lisp
@end deffn

@deftp {Data Type} postgresql-role
PostgreSQL manages database access permissions using the concept of roles.
A role can be thought of as either a database user, or a group of database
users, depending on how the role is set up.  Roles can own database objects
(for example, tables) and can assign privileges on those objects to other
roles to control who has access to which objects.

@table @asis
@item @code{名字}
The role name.

@item @code{permissions} (default: @code{'(createdb login)})
The role permissions list.  Supported permissions are @code{bypassrls},
@code{createdb}, @code{createrole}, @code{login}, @code{replication} and
@code{superuser}.

@item @code{create-database?} (default: @code{#f})
Whether to create a database with the same name as the role.

@end table
@end deftp

@deftp {Data Type} postgresql-role-configuration
Data type representing the configuration of
@var{postgresql-role-service-type}.

@table @asis
@item @code{host} (default: @code{"/var/run/postgresql"})
The PostgreSQL host to connect to.

@item @code{log} (default: @code{"/var/log/postgresql_roles.log"})
File name of the log file.

@item @code{roles} (default: @code{'()})
The initial PostgreSQL roles to create.
@end table
@end deftp

@subsubheading MariaDB/MySQL

@defvr {Scheme Variable} mysql-service-type
This is the service type for a MySQL or MariaDB database server.  Its value
is a @code{mysql-configuration} object that specifies which package to use,
as well as various settings for the @command{mysqld} daemon.
@end defvr

@deftp {Data Type} mysql-configuration
Data type representing the configuration of @var{mysql-service-type}.

@table @asis
@item @code{mysql} (default: @var{mariadb})
Package object of the MySQL database server, can be either @var{mariadb} or
@var{mysql}.

For MySQL, a temporary root password will be displayed at activation time.
For MariaDB, the root password is empty.

@item @code{bind-address} (default: @code{"127.0.0.1"})
The IP on which to listen for network connections.  Use @code{"0.0.0.0"} to
bind to all available network interfaces.

@item @code{port} (default: @code{3306})
TCP port on which the database server listens for incoming connections.

@item @code{socket} (default: @code{"/run/mysqld/mysqld.sock"})
Socket file to use for local (non-network) connections.

@item @code{extra-content} (default: @code{""})
Additional settings for the @file{my.cnf} configuration file.

@item @code{auto-upgrade?} (default: @code{#t})
Whether to automatically run @command{mysql_upgrade} after starting the
service.  This is necessary to upgrade the @dfn{system schema} after
``major'' updates (such as switching from MariaDB 10.4 to 10.5), but can be
disabled if you would rather do that manually.

@end table
@end deftp

@subsubheading Memcached

@defvr {Scheme Variable} memcached-service-type
This is the service type for the @uref{https://memcached.org/, Memcached}
service, which provides a distributed in memory cache.  The value for the
service type is a @code{memcached-configuration} object.
@end defvr

@lisp
(service memcached-service-type)
@end lisp

@deftp {Data Type} memcached-configuration
Data type representing the configuration of memcached.

@table @asis
@item @code{memcached} (default: @code{memcached})
The Memcached package to use.

@item @code{interfaces} (default: @code{'("0.0.0.0")})
Network interfaces on which to listen.

@item @code{tcp-port} (default: @code{11211})
Port on which to accept connections.

@item @code{udp-port} (default: @code{11211})
Port on which to accept UDP connections on, a value of 0 will disable
listening on a UDP socket.

@item @code{additional-options} (default: @code{'()})
Additional command line options to pass to @code{memcached}.
@end table
@end deftp

@subsubheading Redis

@defvr {Scheme Variable} redis-service-type
This is the service type for the @uref{https://redis.io/, Redis} key/value
store, whose value is a @code{redis-configuration} object.
@end defvr

@deftp {Data Type} redis-configuration
Data type representing the configuration of redis.

@table @asis
@item @code{redis} (default: @code{redis})
The Redis package to use.

@item @code{bind} (default: @code{"127.0.0.1"})
Network interface on which to listen.

@item @code{port} (default: @code{6379})
Port on which to accept connections on, a value of 0 will disable listening
on a TCP socket.

@item @code{working-directory} (default: @code{"/var/lib/redis"})
Directory in which to store the database and related files.
@end table
@end deftp

@node 邮件服务
@subsection 邮件服务

@cindex mail
@cindex email
The @code{(gnu services mail)} module provides Guix service definitions for
email services: IMAP, POP3, and LMTP servers, as well as mail transport
agents (MTAs).  Lots of acronyms! These services are detailed in the
subsections below.

@subsubheading Dovecot Service

@deffn {Scheme Procedure} dovecot-service [#:config (dovecot-configuration)]
Return a service that runs the Dovecot IMAP/POP3/LMTP mail server.
@end deffn

By default, Dovecot does not need much configuration; the default
configuration object created by @code{(dovecot-configuration)} will suffice
if your mail is delivered to @code{~/Maildir}.  A self-signed certificate
will be generated for TLS-protected connections, though Dovecot will also
listen on cleartext ports by default.  There are a number of options,
though, which mail administrators might need to change, and as is the case
with other services, Guix allows the system administrator to specify these
parameters via a uniform Scheme interface.

For example, to specify that mail is located at @code{maildir~/.mail}, one
would instantiate the Dovecot service like this:

@lisp
(dovecot-service #:config
                 (dovecot-configuration
                  (mail-location "maildir:~/.mail")))
@end lisp

The available configuration parameters follow.  Each parameter definition is
preceded by its type; for example, @samp{string-list foo} indicates that the
@code{foo} parameter should be specified as a list of strings.  There is
also a way to specify the configuration as a string, if you have an old
@code{dovecot.conf} file that you want to port over from some other system;
see the end for more details.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services mail).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as dovecot updates.

Available @code{dovecot-configuration} fields are:

@deftypevr {@code{dovecot-configuration} parameter} package dovecot
The dovecot package.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} comma-separated-string-list listen
A list of IPs or hosts where to listen for connections.  @samp{*} listens on
all IPv4 interfaces, @samp{::} listens on all IPv6 interfaces.  If you want
to specify non-default ports or anything more complex, customize the address
and port fields of the @samp{inet-listener} of the specific services you are
interested in.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} protocol-configuration-list protocols
List of protocols we want to serve.  Available protocols include
@samp{imap}, @samp{pop3}, and @samp{lmtp}.

Available @code{protocol-configuration} fields are:

@deftypevr {@code{protocol-configuration} parameter} string name
The name of the protocol.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} string auth-socket-path
UNIX socket path to the master authentication server to find users.  This is
used by imap (for shared users) and lda.  It defaults to
@samp{"/var/run/dovecot/auth-userdb"}.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} space-separated-string-list mail-plugins
Space separated list of plugins to load.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} non-negative-integer mail-max-userip-connections
Maximum number of IMAP connections allowed for a user from each IP address.
NOTE: The username is compared case-sensitively.  Defaults to @samp{10}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} service-configuration-list services
List of services to enable.  Available services include @samp{imap},
@samp{imap-login}, @samp{pop3}, @samp{pop3-login}, @samp{auth}, and
@samp{lmtp}.

Available @code{service-configuration} fields are:

@deftypevr {@code{service-configuration} parameter} string kind
The service kind.  Valid values include @code{director}, @code{imap-login},
@code{pop3-login}, @code{lmtp}, @code{imap}, @code{pop3}, @code{auth},
@code{auth-worker}, @code{dict}, @code{tcpwrap}, @code{quota-warning}, or
anything else.
@end deftypevr

@deftypevr {@code{service-configuration} parameter} listener-configuration-list listeners
Listeners for the service.  A listener is either a
@code{unix-listener-configuration}, a @code{fifo-listener-configuration}, or
an @code{inet-listener-configuration}.  Defaults to @samp{()}.

Available @code{unix-listener-configuration} fields are:

@deftypevr {@code{unix-listener-configuration} parameter} string path
Path to the file, relative to @code{base-dir} field.  This is also used as
the section name.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string mode
The access mode for the socket.  Defaults to @samp{"0600"}.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string user
The user to own the socket.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string group
The group to own the socket.  Defaults to @samp{""}.
@end deftypevr


Available @code{fifo-listener-configuration} fields are:

@deftypevr {@code{fifo-listener-configuration} parameter} string path
Path to the file, relative to @code{base-dir} field.  This is also used as
the section name.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string mode
The access mode for the socket.  Defaults to @samp{"0600"}.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string user
The user to own the socket.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string group
The group to own the socket.  Defaults to @samp{""}.
@end deftypevr


Available @code{inet-listener-configuration} fields are:

@deftypevr {@code{inet-listener-configuration} parameter} string protocol
The protocol to listen for.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} string address
The address on which to listen, or empty for all addresses.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} non-negative-integer port
The port on which to listen.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} boolean ssl?
Whether to use SSL for this service; @samp{yes}, @samp{no}, or
@samp{required}.  Defaults to @samp{#t}.
@end deftypevr

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer client-limit
Maximum number of simultaneous client connections per process.  Once this
number of connections is received, the next incoming connection will prompt
Dovecot to spawn another process.  If set to 0, @code{default-client-limit}
is used instead.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer service-count
Number of connections to handle before starting a new process.  Typically
the only useful values are 0 (unlimited) or 1.  1 is more secure, but 0 is
faster.  <doc/wiki/LoginProcess.txt>.  Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer process-limit
Maximum number of processes that can exist for this service.  If set to 0,
@code{default-process-limit} is used instead.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer process-min-avail
Number of processes to always keep waiting for more connections.  Defaults
to @samp{0}.
@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer vsz-limit
If you set @samp{service-count 0}, you probably need to grow this.  Defaults
to @samp{256000000}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} dict-configuration dict
Dict configuration, as created by the @code{dict-configuration} constructor.

Available @code{dict-configuration} fields are:

@deftypevr {@code{dict-configuration} parameter} free-form-fields entries
A list of key-value pairs that this dict should hold.  Defaults to
@samp{()}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} passdb-configuration-list passdbs
A list of passdb configurations, each one created by the
@code{passdb-configuration} constructor.

Available @code{passdb-configuration} fields are:

@deftypevr {@code{passdb-configuration} parameter} string driver
The driver that the passdb should use.  Valid values include @samp{pam},
@samp{passwd}, @samp{shadow}, @samp{bsdauth}, and @samp{static}.  Defaults
to @samp{"pam"}.
@end deftypevr

@deftypevr {@code{passdb-configuration} parameter} space-separated-string-list args
Space separated list of arguments to the passdb driver.  Defaults to
@samp{""}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} userdb-configuration-list userdbs
List of userdb configurations, each one created by the
@code{userdb-configuration} constructor.

Available @code{userdb-configuration} fields are:

@deftypevr {@code{userdb-configuration} parameter} string driver
The driver that the userdb should use.  Valid values include @samp{passwd}
and @samp{static}.  Defaults to @samp{"passwd"}.
@end deftypevr

@deftypevr {@code{userdb-configuration} parameter} space-separated-string-list args
Space separated list of arguments to the userdb driver.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{userdb-configuration} parameter} free-form-args override-fields
Override fields from passwd.  Defaults to @samp{()}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} plugin-configuration plugin-configuration
Plug-in configuration, created by the @code{plugin-configuration}
constructor.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} list-of-namespace-configuration namespaces
List of namespaces.  Each item in the list is created by the
@code{namespace-configuration} constructor.

Available @code{namespace-configuration} fields are:

@deftypevr {@code{namespace-configuration} parameter} string name
Name for this namespace.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string type
Namespace type: @samp{private}, @samp{shared} or @samp{public}.  Defaults to
@samp{"private"}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string separator
Hierarchy separator to use.  You should use the same separator for all
namespaces or some clients get confused.  @samp{/} is usually a good one.
The default however depends on the underlying mail storage format.  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string prefix
Prefix required to access this namespace.  This needs to be different for
all namespaces.  For example @samp{Public/}.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string location
Physical location of the mailbox. This is in the same format as
mail_location, which is also the default for it.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean inbox?
There can be only one INBOX, and this setting defines which namespace has
it.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean hidden?
If namespace is hidden, it's not advertised to clients via NAMESPACE
extension.  You'll most likely also want to set @samp{list? #f}.  This is
mostly useful when converting from another server with different namespaces
which you want to deprecate but still keep working.  For example you can
create hidden namespaces with prefixes @samp{~/mail/}, @samp{~%u/mail/} and
@samp{mail/}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean list?
Show the mailboxes under this namespace with the LIST command.  This makes
the namespace visible for clients that do not support the NAMESPACE
extension.  The special @code{children} value lists child mailboxes, but
hides the namespace prefix.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean subscriptions?
Namespace handles its own subscriptions.  If set to @code{#f}, the parent
namespace handles them.  The empty prefix should always have this as
@code{#t}).  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} mailbox-configuration-list mailboxes
List of predefined mailboxes in this namespace.  Defaults to @samp{()}.

Available @code{mailbox-configuration} fields are:

@deftypevr {@code{mailbox-configuration} parameter} string name
Name for this mailbox.
@end deftypevr

@deftypevr {@code{mailbox-configuration} parameter} string auto
@samp{create} will automatically create this mailbox.  @samp{subscribe} will
both create and subscribe to the mailbox.  Defaults to @samp{"no"}.
@end deftypevr

@deftypevr {@code{mailbox-configuration} parameter} space-separated-string-list special-use
List of IMAP @code{SPECIAL-USE} attributes as specified by RFC 6154.  Valid
values are @code{\All}, @code{\Archive}, @code{\Drafts}, @code{\Flagged},
@code{\Junk}, @code{\Sent}, and @code{\Trash}.  Defaults to @samp{()}.
@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name base-dir
Base directory where to store runtime data.  Defaults to
@samp{"/var/run/dovecot/"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string login-greeting
Greeting message for clients.  Defaults to @samp{"Dovecot ready."}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-trusted-networks
List of trusted network ranges.  Connections from these IPs are allowed to
override their IP addresses and ports (for logging and for authentication
checks).  @samp{disable-plaintext-auth} is also ignored for these networks.
Typically you would specify your IMAP proxy servers here.  Defaults to
@samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-access-sockets
List of login access check sockets (e.g.@: tcpwrap).  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean verbose-proctitle?
Show more verbose process titles (in ps).  Currently shows user name and IP
address.  Useful for seeing who is actually using the IMAP processes (e.g.@:
shared mailboxes or if the same uid is used for multiple accounts).
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean shutdown-clients?
Should all processes be killed when Dovecot master process shuts down.
Setting this to @code{#f} means that Dovecot can be upgraded without forcing
existing client connections to close (although that could also be a problem
if the upgrade is e.g.@: due to a security fix).  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer doveadm-worker-count
If non-zero, run mail commands via this many connections to doveadm server,
instead of running them directly in the same process.  Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string doveadm-socket-path
UNIX socket or host:port used for connecting to doveadm server.  Defaults to
@samp{"doveadm-server"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list import-environment
List of environment variables that are preserved on Dovecot startup and
passed down to all of its child processes.  You can also give key=value
pairs to always set specific settings.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean disable-plaintext-auth?
Disable LOGIN command and all other plaintext authentications unless SSL/TLS
is used (LOGINDISABLED capability).  Note that if the remote IP matches the
local IP (i.e.@: you're connecting from the same computer), the connection
is considered secure and plaintext authentication is allowed.  See also
ssl=required setting.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer auth-cache-size
Authentication cache size (e.g.@: @samp{#e10e6}).  0 means it's disabled.
Note that bsdauth, PAM and vpopmail require @samp{cache-key} to be set for
caching to be used.  Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-cache-ttl
Time to live for cached data.  After TTL expires the cached record is no
longer used, *except* if the main database lookup returns internal failure.
We also try to handle password changes automatically: If user's previous
authentication was successful, but this one wasn't, the cache isn't used.
For now this works only with plaintext authentication.  Defaults to @samp{"1
hour"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-cache-negative-ttl
TTL for negative hits (user not found, password mismatch).  0 disables
caching them completely.  Defaults to @samp{"1 hour"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list auth-realms
List of realms for SASL authentication mechanisms that need them.  You can
leave it empty if you don't want to support multiple realms.  Many clients
simply use the first one listed here, so keep the default realm first.
Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-default-realm
Default realm/domain to use if none was specified.  This is used for both
SASL realms and appending @@domain to username in plaintext logins.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-chars
List of allowed characters in username.  If the user-given username contains
a character not listed in here, the login automatically fails.  This is just
an extra check to make sure user can't exploit any potential quote escaping
vulnerabilities with SQL/LDAP databases.  If you want to allow all
characters, set this value to empty.  Defaults to
@samp{"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@@"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-translation
Username character translations before it's looked up from databases.  The
value contains series of from -> to characters.  For example @samp{#@@/@@}
means that @samp{#} and @samp{/} characters are translated to @samp{@@}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-format
Username formatting before it's looked up from databases.  You can use the
standard variables here, e.g.@: %Lu would lowercase the username, %n would
drop away the domain if it was given, or @samp{%n-AT-%d} would change the
@samp{@@} into @samp{-AT-}.  This translation is done after
@samp{auth-username-translation} changes.  Defaults to @samp{"%Lu"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-master-user-separator
If you want to allow master users to log in by specifying the master
username within the normal username string (i.e.@: not using SASL
mechanism's support for it), you can specify the separator character here.
The format is then <username><separator><master username>.  UW-IMAP uses
@samp{*} as the separator, so that could be a good choice.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-anonymous-username
Username to use for users logging in with ANONYMOUS SASL mechanism.
Defaults to @samp{"anonymous"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer auth-worker-max-count
Maximum number of dovecot-auth worker processes.  They're used to execute
blocking passdb and userdb queries (e.g.@: MySQL and PAM).  They're
automatically created and destroyed as needed.  Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-gssapi-hostname
Host name to use in GSSAPI principal names.  The default is to use the name
returned by gethostname().  Use @samp{$ALL} (with quotes) to allow all
keytab entries.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-krb5-keytab
Kerberos keytab to use for the GSSAPI mechanism.  Will use the system
default (usually @file{/etc/krb5.keytab}) if not specified.  You may need to
change the auth service to run as root to be able to read this file.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-use-winbind?
Do NTLM and GSS-SPNEGO authentication using Samba's winbind daemon and
@samp{ntlm-auth} helper.  <doc/wiki/Authentication/Mechanisms/Winbind.txt>.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name auth-winbind-helper-path
Path for Samba's @samp{ntlm-auth} helper binary.  Defaults to
@samp{"/usr/bin/ntlm_auth"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-failure-delay
Time to delay before replying to failed authentications.  Defaults to
@samp{"2 secs"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-ssl-require-client-cert?
Require a valid SSL client certificate or the authentication fails.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-ssl-username-from-cert?
Take the username from client's SSL certificate, using
@code{X509_NAME_get_text_by_NID()} which returns the subject's DN's
CommonName.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list auth-mechanisms
List of wanted authentication mechanisms.  Supported mechanisms are:
@samp{plain}, @samp{login}, @samp{digest-md5}, @samp{cram-md5}, @samp{ntlm},
@samp{rpa}, @samp{apop}, @samp{anonymous}, @samp{gssapi}, @samp{otp},
@samp{skey}, and @samp{gss-spnego}.  NOTE: See also
@samp{disable-plaintext-auth} setting.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list director-servers
List of IPs or hostnames to all director servers, including ourself.  Ports
can be specified as ip:port.  The default port is the same as what director
service's @samp{inet-listener} is using.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list director-mail-servers
List of IPs or hostnames to all backend mail servers.  Ranges are allowed
too, like 10.0.0.10-10.0.0.30.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string director-user-expire
How long to redirect users to a specific server after it no longer has any
connections.  Defaults to @samp{"15 min"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string director-username-hash
How the username is translated before being hashed.  Useful values include
%Ln if user can log in with or without @@domain, %Ld if mailboxes are shared
within domain.  Defaults to @samp{"%Lu"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string log-path
Log file to use for error messages.  @samp{syslog} logs to syslog,
@samp{/dev/stderr} logs to stderr.  Defaults to @samp{"syslog"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string info-log-path
Log file to use for informational messages.  Defaults to @samp{log-path}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string debug-log-path
Log file to use for debug messages.  Defaults to @samp{info-log-path}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string syslog-facility
Syslog facility to use if you're logging to syslog.  Usually if you don't
want to use @samp{mail}, you'll use local0..local7.  Also other standard
facilities are supported.  Defaults to @samp{"mail"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-verbose?
Log unsuccessful authentication attempts and the reasons why they failed.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-verbose-passwords
In case of password mismatches, log the attempted password.  Valid values
are no, plain and sha1.  sha1 can be useful for detecting brute force
password attempts vs.  user simply trying the same password over and over
again.  You can also truncate the value to n chars by appending ":n" (e.g.@:
sha1:6).  Defaults to @samp{"no"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-debug?
Even more verbose logging for debugging purposes.  Shows for example SQL
queries.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-debug-passwords?
In case of password mismatches, log the passwords and used scheme so the
problem can be debugged.  Enabling this also enables @samp{auth-debug}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-debug?
Enable mail process debugging.  This can help you figure out why Dovecot
isn't finding your mails.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean verbose-ssl?
Show protocol level SSL errors.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string log-timestamp
Prefix for each line written to log file.  % codes are in strftime(3)
format.  Defaults to @samp{"\"%b %d %H:%M:%S \""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-log-format-elements
List of elements we want to log.  The elements which have a non-empty
variable value are joined together to form a comma-separated string.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string login-log-format
Login log format.  %s contains @samp{login-log-format-elements} string, %$
contains the data we want to log.  Defaults to @samp{"%$: %s"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-log-prefix
Log prefix for mail processes.  See doc/wiki/Variables.txt for list of
possible variables you can use.  Defaults to
@samp{"\"%s(%u)<%@{pid@}><%@{session@}>: \""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string deliver-log-format
Format to use for logging mail deliveries.  You can use variables:
@table @code
@item %$
Delivery status message (e.g.@: @samp{saved to INBOX})
@item %m
Message-ID
@item %s
Subject
@item %f
From address
@item %p
Physical size
@item %w
Virtual size.
@end table
Defaults to @samp{"msgid=%m: %$"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-location
Location for users' mailboxes.  The default is empty, which means that
Dovecot tries to find the mailboxes automatically.  This won't work if the
user doesn't yet have any mail, so you should explicitly tell Dovecot the
full location.

If you're using mbox, giving a path to the INBOX file (e.g.@:
@file{/var/mail/%u}) isn't enough.  You'll also need to tell Dovecot where
the other mailboxes are kept.  This is called the @emph{root mail
directory}, and it must be the first path given in the @samp{mail-location}
setting.

There are a few special variables you can use, e.g.:

@table @samp
@item %u
username
@item %n
user part in user@@domain, same as %u if there's no domain
@item %d
domain part in user@@domain, empty if there's no domain
@item %h
home director
@end table

See doc/wiki/Variables.txt for full list.  Some examples:
@table @samp
@item maildir:~/Maildir
@item mbox:~/mail:INBOX=/var/mail/%u
@item mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%
@end table
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-uid
System user and group used to access mails.  If you use multiple, userdb can
override these by returning uid or gid fields.  You can use either numbers
or names.  <doc/wiki/UserIds.txt>.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-gid

Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-privileged-group
Group to enable temporarily for privileged operations.  Currently this is
used only with INBOX when either its initial creation or dotlocking fails.
Typically this is set to @samp{"mail"} to give access to @file{/var/mail}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-access-groups
Grant access to these supplementary groups for mail processes.  Typically
these are used to set up access to shared mailboxes.  Note that it may be
dangerous to set these if users can create symlinks (e.g.@: if @samp{mail}
group is set here, @code{ln -s /var/mail ~/mail/var} could allow a user to
delete others' mailboxes, or @code{ln -s /secret/shared/box ~/mail/mybox}
would allow reading it).  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-full-filesystem-access?
Allow full file system access to clients.  There's no access checks other
than what the operating system does for the active UID/GID@.  It works with
both maildir and mboxes, allowing you to prefix mailboxes names with e.g.@:
@file{/path/} or @file{~user/}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mmap-disable?
Don't use @code{mmap()} at all.  This is required if you store indexes to
shared file systems (NFS or clustered file system).  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean dotlock-use-excl?
Rely on @samp{O_EXCL} to work when creating dotlock files.  NFS supports
@samp{O_EXCL} since version 3, so this should be safe to use nowadays by
default.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-fsync
When to use fsync() or fdatasync() calls:
@table @code
@item optimized
Whenever necessary to avoid losing important data
@item always
Useful with e.g.@: NFS when @code{write()}s are delayed
@item never
Never use it (best performance, but crashes can lose data).
@end table
Defaults to @samp{"optimized"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-nfs-storage?
Mail storage exists in NFS@.  Set this to yes to make Dovecot flush NFS
caches whenever needed.  If you're using only a single mail server this
isn't needed.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-nfs-index?
Mail index files also exist in NFS@.  Setting this to yes requires
@samp{mmap-disable? #t} and @samp{fsync-disable? #f}.  Defaults to
@samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string lock-method
Locking method for index files.  Alternatives are fcntl, flock and dotlock.
Dotlocking uses some tricks which may create more disk I/O than other
locking methods.  NFS users: flock doesn't work, remember to change
@samp{mmap-disable}.  Defaults to @samp{"fcntl"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name mail-temp-dir
Directory in which LDA/LMTP temporarily stores incoming mails >128 kB.
Defaults to @samp{"/tmp"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer first-valid-uid
Valid UID range for users.  This is mostly to make sure that users can't log
in as daemons or other system users.  Note that denying root logins is
hardcoded to dovecot binary and can't be done even if @samp{first-valid-uid}
is set to 0.  Defaults to @samp{500}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer last-valid-uid

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer first-valid-gid
Valid GID range for users.  Users having non-valid GID as primary group ID
aren't allowed to log in.  If user belongs to supplementary groups with
non-valid GIDs, those groups are not set.  Defaults to @samp{1}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer last-valid-gid

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-max-keyword-length
Maximum allowed length for mail keyword name.  It's only forced when trying
to create new keywords.  Defaults to @samp{50}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} colon-separated-file-name-list valid-chroot-dirs
List of directories under which chrooting is allowed for mail processes
(i.e.@: @file{/var/mail} will allow chrooting to @file{/var/mail/foo/bar}
too).  This setting doesn't affect @samp{login-chroot} @samp{mail-chroot} or
auth chroot settings.  If this setting is empty, @samp{/./} in home dirs are
ignored.  WARNING: Never add directories here which local users can modify,
that may lead to root exploit.  Usually this should be done only if you
don't allow shell access for users.  <doc/wiki/Chrooting.txt>.  Defaults to
@samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-chroot
Default chroot directory for mail processes.  This can be overridden for
specific users in user database by giving @samp{/./} in user's home
directory (e.g.@: @samp{/home/./user} chroots into @file{/home}).  Note that
usually there is no real need to do chrooting, Dovecot doesn't allow users
to access files outside their mail directory anyway.  If your home
directories are prefixed with the chroot directory, append @samp{/.} to
@samp{mail-chroot}.  <doc/wiki/Chrooting.txt>.  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name auth-socket-path
UNIX socket path to master authentication server to find users.  This is
used by imap (for shared users) and lda.  Defaults to
@samp{"/var/run/dovecot/auth-userdb"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name mail-plugin-dir
Directory where to look up mail plugins.  Defaults to
@samp{"/usr/lib/dovecot"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mail-plugins
List of plugins to load for all services.  Plugins specific to IMAP, LDA,
etc.@: are added to this list in their own .conf files.  Defaults to
@samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-cache-min-mail-count
The minimum number of mails in a mailbox before updates are done to cache
file.  This allows optimizing Dovecot's behavior to do less disk writes at
the cost of more disk reads.  Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mailbox-idle-check-interval
When IDLE command is running, mailbox is checked once in a while to see if
there are any new mails or other changes.  This setting defines the minimum
time to wait between those checks.  Dovecot can also use dnotify, inotify
and kqueue to find out immediately when changes occur.  Defaults to
@samp{"30 secs"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-save-crlf?
Save mails with CR+LF instead of plain LF@.  This makes sending those mails
take less CPU, especially with sendfile() syscall with Linux and FreeBSD@.
But it also creates a bit more disk I/O which may just make it slower.  Also
note that if other software reads the mboxes/maildirs, they may handle the
extra CRs wrong and cause problems.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-stat-dirs?
By default LIST command returns all entries in maildir beginning with a
dot.  Enabling this option makes Dovecot return only entries which are
directories.  This is done by stat()ing each entry, so it causes more disk
I/O.  (For systems setting struct @samp{dirent->d_type} this check is free
and it's done always regardless of this setting).  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-copy-with-hardlinks?
When copying a message, do it with hard links whenever possible.  This makes
the performance much better, and it's unlikely to have any side effects.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-very-dirty-syncs?
Assume Dovecot is the only MUA accessing Maildir: Scan cur/ directory only
when its mtime changes unexpectedly or when we can't find the mail
otherwise.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mbox-read-locks
Which locking methods to use for locking mbox.  There are four available:

@table @code
@item dotlock
Create <mailbox>.lock file.  This is the oldest and most NFS-safe solution.
If you want to use /var/mail/ like directory, the users will need write
access to that directory.
@item dotlock-try
Same as dotlock, but if it fails because of permissions or because there
isn't enough disk space, just skip it.
@item fcntl
Use this if possible.  Works with NFS too if lockd is used.
@item flock
May not exist in all systems.  Doesn't work with NFS.
@item lockf
May not exist in all systems.  Doesn't work with NFS.
@end table

You can use multiple locking methods; if you do the order they're declared
in is important to avoid deadlocks if other MTAs/MUAs are using multiple
locking methods as well.  Some operating systems don't allow using some of
them simultaneously.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mbox-write-locks

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mbox-lock-timeout
Maximum time to wait for lock (all of them) before aborting.  Defaults to
@samp{"5 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mbox-dotlock-change-timeout
If dotlock exists but the mailbox isn't modified in any way, override the
lock file after this much time.  Defaults to @samp{"2 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-dirty-syncs?
When mbox changes unexpectedly we have to fully read it to find out what
changed.  If the mbox is large this can take a long time.  Since the change
is usually just a newly appended mail, it'd be faster to simply read the new
mails.  If this setting is enabled, Dovecot does this but still safely
fallbacks to re-reading the whole mbox file whenever something in mbox isn't
how it's expected to be.  The only real downside to this setting is that if
some other MUA changes message flags, Dovecot doesn't notice it
immediately.  Note that a full sync is done with SELECT, EXAMINE, EXPUNGE
and CHECK commands.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-very-dirty-syncs?
Like @samp{mbox-dirty-syncs}, but don't do full syncs even with SELECT,
EXAMINE, EXPUNGE or CHECK commands.  If this is set, @samp{mbox-dirty-syncs}
is ignored.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-lazy-writes?
Delay writing mbox headers until doing a full write sync (EXPUNGE and CHECK
commands and when closing the mailbox).  This is especially useful for POP3
where clients often delete all mails.  The downside is that our changes
aren't immediately visible to other MUAs.  Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mbox-min-index-size
If mbox size is smaller than this (e.g.@: 100k), don't write index files.
If an index file already exists it's still read, just not updated.  Defaults
to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mdbox-rotate-size
Maximum dbox file size until it's rotated.  Defaults to @samp{10000000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mdbox-rotate-interval
Maximum dbox file age until it's rotated.  Typically in days.  Day begins
from midnight, so 1d = today, 2d = yesterday, etc.  0 = check disabled.
Defaults to @samp{"1d"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mdbox-preallocate-space?
When creating new mdbox files, immediately preallocate their size to
@samp{mdbox-rotate-size}.  This setting currently works only in Linux with
some file systems (ext4, xfs).  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-dir
sdbox and mdbox support saving mail attachments to external files, which
also allows single instance storage for them.  Other backends don't support
this for now.

WARNING: This feature hasn't been tested much yet.  Use at your own risk.

Directory root where to store mail attachments.  Disabled, if empty.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-attachment-min-size
Attachments smaller than this aren't saved externally.  It's also possible
to write a plugin to disable saving specific attachments externally.
Defaults to @samp{128000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-fs
File system backend to use for saving attachments:
@table @code
@item posix
No SiS done by Dovecot (but this might help FS's own deduplication)
@item sis posix
SiS with immediate byte-by-byte comparison during saving
@item sis-queue posix
SiS with delayed comparison and deduplication.
@end table
Defaults to @samp{"sis posix"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-hash
Hash format to use in attachment filenames.  You can add any text and
variables: @code{%@{md4@}}, @code{%@{md5@}}, @code{%@{sha1@}},
@code{%@{sha256@}}, @code{%@{sha512@}}, @code{%@{size@}}.  Variables can be
truncated, e.g.@: @code{%@{sha256:80@}} returns only first 80 bits.
Defaults to @samp{"%@{sha1@}"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-process-limit

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-client-limit

Defaults to @samp{1000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-vsz-limit
Default VSZ (virtual memory size) limit for service processes.  This is
mainly intended to catch and kill processes that leak memory before they eat
up everything.  Defaults to @samp{256000000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string default-login-user
Login user is internally used by login processes.  This is the most
untrusted user in Dovecot system.  It shouldn't have access to anything at
all.  Defaults to @samp{"dovenull"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string default-internal-user
Internal user is used by unprivileged processes.  It should be separate from
login user, so that login processes can't disturb other processes.  Defaults
to @samp{"dovecot"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl?
SSL/TLS support: yes, no, required.  <doc/wiki/SSL.txt>.  Defaults to
@samp{"required"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cert
PEM encoded X.509 SSL/TLS certificate (public key).  Defaults to
@samp{"</etc/dovecot/default.pem"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-key
PEM encoded SSL/TLS private key.  The key is opened before dropping root
privileges, so keep the key file unreadable by anyone but root.  Defaults to
@samp{"</etc/dovecot/private/default.pem"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-key-password
If key file is password protected, give the password here.  Alternatively
give it when starting dovecot with -p parameter.  Since this file is often
world-readable, you may want to place this setting instead to a different.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-ca
PEM encoded trusted certificate authority.  Set this only if you intend to
use @samp{ssl-verify-client-cert? #t}.  The file should contain the CA
certificate(s) followed by the matching CRL(s).  (e.g.@: @samp{ssl-ca
</etc/ssl/certs/ca.pem}).  Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean ssl-require-crl?
Require that CRL check succeeds for client certificates.  Defaults to
@samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean ssl-verify-client-cert?
Request client to send a certificate.  If you also want to require it, set
@samp{auth-ssl-require-client-cert? #t} in auth section.  Defaults to
@samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cert-username-field
Which field from certificate to use for username.  commonName and
x500UniqueIdentifier are the usual choices.  You'll also need to set
@samp{auth-ssl-username-from-cert? #t}.  Defaults to @samp{"commonName"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-min-protocol
Minimum SSL protocol version to accept.  Defaults to @samp{"TLSv1"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cipher-list
SSL ciphers to use.  Defaults to
@samp{"ALL:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW@@STRENGTH"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-crypto-device
SSL crypto device to use, for valid values run "openssl engine".  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string postmaster-address
Address to use when sending rejection mails.  %d expands to recipient
domain.  Defaults to @samp{"postmaster@@%d"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string hostname
Hostname to use in various parts of sent mails (e.g.@: in Message-Id)  and
in LMTP replies.  Default is the system's real hostname@@domain.  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean quota-full-tempfail?
If user is over quota, return with temporary failure instead of bouncing the
mail.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name sendmail-path
Binary to use for sending mails.  Defaults to @samp{"/usr/sbin/sendmail"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string submission-host
If non-empty, send mails via this SMTP host[:port] instead of sendmail.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string rejection-subject
Subject: header to use for rejection mails.  You can use the same variables
as for @samp{rejection-reason} below.  Defaults to @samp{"Rejected: %s"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string rejection-reason
Human readable error message for rejection mails.  You can use variables:

@table @code
@item %n
CRLF
@item %r
reason
@item %s
original subject
@item %t
recipient
@end table
Defaults to @samp{"Your message to <%t> was automatically rejected:%n%r"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string recipient-delimiter
Delimiter character between local-part and detail in email address.
Defaults to @samp{"+"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string lda-original-recipient-header
Header where the original recipient address (SMTP's RCPT TO: address) is
taken from if not available elsewhere.  With dovecot-lda -a parameter
overrides this.  A commonly used header for this is X-Original-To.  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean lda-mailbox-autocreate?
Should saving a mail to a nonexistent mailbox automatically create it?.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean lda-mailbox-autosubscribe?
Should automatically created mailboxes be also automatically subscribed?.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer imap-max-line-length
Maximum IMAP command line length.  Some clients generate very long command
lines with huge mailboxes, so you may need to raise this if you get "Too
long argument" or "IMAP command line too large" errors often.  Defaults to
@samp{64000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-logout-format
IMAP logout format string:
@table @code
@item %i
total number of bytes read from client
@item %o
total number of bytes sent to client.
@end table
See @file{doc/wiki/Variables.txt} for a list of all the variables you can
use.  Defaults to @samp{"in=%i out=%o deleted=%@{deleted@}
expunged=%@{expunged@} trashed=%@{trashed@} hdr_count=%@{fetch_hdr_count@}
hdr_bytes=%@{fetch_hdr_bytes@} body_count=%@{fetch_body_count@}
body_bytes=%@{fetch_body_bytes@}"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-capability
Override the IMAP CAPABILITY response.  If the value begins with '+', add
the given capabilities on top of the defaults (e.g.@: +XFOO XBAR).  Defaults
to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-idle-notify-interval
How long to wait between "OK Still here" notifications when client is
IDLEing.  Defaults to @samp{"2 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-id-send
ID field names and values to send to clients.  Using * as the value makes
Dovecot use the default value.  The following fields have default values
currently: name, version, os, os-version, support-url, support-email.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-id-log
ID fields sent by client to log.  * means everything.  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list imap-client-workarounds
Workarounds for various client bugs:

@table @code
@item delay-newmail
Send EXISTS/RECENT new mail notifications only when replying to NOOP and
CHECK commands.  Some clients ignore them otherwise, for example OSX Mail
(<v2.1).  Outlook Express breaks more badly though, without this it may show
user "Message no longer in server" errors.  Note that OE6 still breaks even
with this workaround if synchronization is set to "Headers Only".

@item tb-extra-mailbox-sep
Thunderbird gets somehow confused with LAYOUT=fs (mbox and dbox) and adds
extra @samp{/} suffixes to mailbox names.  This option causes Dovecot to
ignore the extra @samp{/} instead of treating it as invalid mailbox name.

@item tb-lsub-flags
Show \Noselect flags for LSUB replies with LAYOUT=fs (e.g.@: mbox).  This
makes Thunderbird realize they aren't selectable and show them greyed out,
instead of only later giving "not selectable" popup error.
@end table
Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-urlauth-host
Host allowed in URLAUTH URLs sent by client.  "*" allows all.  Defaults to
@samp{""}.
@end deftypevr


Whew! Lots of configuration options.  The nice thing about it though is that
Guix has a complete interface to Dovecot's configuration language.  This
allows not only a nice way to declare configurations, but also offers
reflective capabilities as well: users can write code to inspect and
transform configurations from within Scheme.

However, it could be that you just want to get a @code{dovecot.conf} up and
running.  In that case, you can pass an @code{opaque-dovecot-configuration}
as the @code{#:config} parameter to @code{dovecot-service}.  As its name
indicates, an opaque configuration does not have easy reflective
capabilities.

Available @code{opaque-dovecot-configuration} fields are:

@deftypevr {@code{opaque-dovecot-configuration} parameter} package dovecot
The dovecot package.
@end deftypevr

@deftypevr {@code{opaque-dovecot-configuration} parameter} string string
The contents of the @code{dovecot.conf}, as a string.
@end deftypevr

For example, if your @code{dovecot.conf} is just the empty string, you could
instantiate a dovecot service like this:

@lisp
(dovecot-service #:config
                 (opaque-dovecot-configuration
                  (string "")))
@end lisp

@subsubheading OpenSMTPD Service

@deffn {Scheme Variable} opensmtpd-service-type
This is the type of the @uref{https://www.opensmtpd.org, OpenSMTPD} service,
whose value should be an @code{opensmtpd-configuration} object as in this
example:

@lisp
(service opensmtpd-service-type
         (opensmtpd-configuration
           (config-file (local-file "./my-smtpd.conf"))))
@end lisp
@end deffn

@deftp {Data Type} opensmtpd-configuration
Data type representing the configuration of opensmtpd.

@table @asis
@item @code{package} (default: @var{opensmtpd})
Package object of the OpenSMTPD SMTP server.

@item @code{config-file} (default: @code{%default-opensmtpd-file})
File-like object of the OpenSMTPD configuration file to use.  By default it
listens on the loopback network interface, and allows for mail from users
and daemons on the local machine, as well as permitting email to remote
servers.  Run @command{man smtpd.conf} for more information.

@end table
@end deftp

@subsubheading Exim Service

@cindex mail transfer agent (MTA)
@cindex MTA (mail transfer agent)
@cindex SMTP

@deffn {Scheme Variable} exim-service-type
This is the type of the @uref{https://exim.org, Exim} mail transfer agent
(MTA), whose value should be an @code{exim-configuration} object as in this
example:

@lisp
(service exim-service-type
         (exim-configuration
           (config-file (local-file "./my-exim.conf"))))
@end lisp
@end deffn

In order to use an @code{exim-service-type} service you must also have a
@code{mail-aliases-service-type} service present in your
@code{operating-system} (even if it has no aliases).

@deftp {Data Type} exim-configuration
Data type representing the configuration of exim.

@table @asis
@item @code{package} (default: @var{exim})
Package object of the Exim server.

@item @code{config-file} (default: @code{#f})
File-like object of the Exim configuration file to use.  If its value is
@code{#f} then use the default configuration file from the package provided
in @code{package}.  The resulting configuration file is loaded after setting
the @code{exim_user} and @code{exim_group} configuration variables.

@end table
@end deftp

@subsubheading Getmail service

@cindex IMAP
@cindex POP

@deffn {Scheme Variable} getmail-service-type
This is the type of the @uref{http://pyropus.ca/software/getmail/, Getmail}
mail retriever, whose value should be an @code{getmail-configuration}.
@end deffn

Available @code{getmail-configuration} fields are:

@deftypevr {@code{getmail-configuration} parameter} symbol name
A symbol to identify the getmail service.

Defaults to @samp{"unset"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} package package
The getmail package to use.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} string user
The user to run getmail as.

Defaults to @samp{"getmail"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} string group
The group to run getmail as.

Defaults to @samp{"getmail"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} string directory
The getmail directory to use.

Defaults to @samp{"/var/lib/getmail/default"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} getmail-configuration-file rcfile
The getmail configuration file to use.

Available @code{getmail-configuration-file} fields are:

@deftypevr {@code{getmail-configuration-file} parameter} getmail-retriever-configuration retriever
What mail account to retrieve mail from, and how to access that account.

Available @code{getmail-retriever-configuration} fields are:

@deftypevr {@code{getmail-retriever-configuration} parameter} string type
The type of mail retriever to use.  Valid values include @samp{passwd} and
@samp{static}.

Defaults to @samp{"SimpleIMAPSSLRetriever"}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string server
Username to login to the mail server with.

Defaults to @samp{unset}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string username
Username to login to the mail server with.

Defaults to @samp{unset}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} non-negative-integer port
Port number to connect to.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string password
Override fields from passwd.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} list password-command
Override fields from passwd.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string keyfile
PEM-formatted key file to use for the TLS negotiation.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string certfile
PEM-formatted certificate file to use for the TLS negotiation.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string ca-certs
CA certificates to use.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} parameter-alist extra-parameters
Extra retriever parameters.

Defaults to @samp{()}.

@end deftypevr

@end deftypevr

@deftypevr {@code{getmail-configuration-file} parameter} getmail-destination-configuration destination
What to do with retrieved messages.

Available @code{getmail-destination-configuration} fields are:

@deftypevr {@code{getmail-destination-configuration} parameter} string type
The type of mail destination.  Valid values include @samp{Maildir},
@samp{Mboxrd} and @samp{MDA_external}.

Defaults to @samp{unset}.

@end deftypevr

@deftypevr {@code{getmail-destination-configuration} parameter} string-or-filelike path
The path option for the mail destination.  The behaviour depends on the
chosen type.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-destination-configuration} parameter} parameter-alist extra-parameters
Extra destination parameters

Defaults to @samp{()}.

@end deftypevr

@end deftypevr

@deftypevr {@code{getmail-configuration-file} parameter} getmail-options-configuration options
Configure getmail.

Available @code{getmail-options-configuration} fields are:

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer verbose
If set to @samp{0}, getmail will only print warnings and errors.  A value of
@samp{1} means that messages will be printed about retrieving and deleting
messages.  If set to @samp{2}, getmail will print messages about each of
it's actions.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean read-all
If true, getmail will retrieve all available messages.  Otherwise it will
only retrieve messages it hasn't seen previously.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean delete
If set to true, messages will be deleted from the server after retrieving
and successfully delivering them.  Otherwise, messages will be left on the
server.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer delete-after
Getmail will delete messages this number of days after seeing them, if they
have been delivered.  This means messages will be left on the server this
number of days after delivering them.  A value of @samp{0} disabled this
feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer delete-bigger-than
Delete messages larger than this of bytes after retrieving them, even if the
delete and delete-after options are disabled.  A value of @samp{0} disables
this feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer max-bytes-per-session
Retrieve messages totalling up to this number of bytes before closing the
session with the server.  A value of @samp{0} disables this feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer max-message-size
Don't retrieve messages larger than this number of bytes.  A value of
@samp{0} disables this feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean delivered-to
If true, getmail will add a Delivered-To header to messages.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean received
If set, getmail adds a Received header to the messages.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} string message-log
Getmail will record a log of its actions to the named file.  A value of
@samp{""} disables this feature.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean message-log-syslog
If true, getmail will record a log of its actions using the system logger.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean message-log-verbose
If true, getmail will log information about messages not retrieved and the
reason for not retrieving them, as well as starting and ending information
lines.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} parameter-alist extra-parameters
Extra options to include.

Defaults to @samp{()}.

@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} list idle
A list of mailboxes that getmail should wait on the server for new mail
notifications.  This depends on the server supporting the IDLE extension.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} list environment-variables
Environment variables to set for getmail.

Defaults to @samp{()}.

@end deftypevr

@subsubheading Mail Aliases Service

@cindex email aliases
@cindex aliases, for email addresses

@deffn {Scheme Variable} mail-aliases-service-type
This is the type of the service which provides @code{/etc/aliases},
specifying how to deliver mail to users on this system.

@lisp
(service mail-aliases-service-type
         '(("postmaster" "bob")
           ("bob" "bob@@example.com" "bob@@example2.com")))
@end lisp
@end deffn

The configuration for a @code{mail-aliases-service-type} service is an
association list denoting how to deliver mail that comes to this system.
Each entry is of the form @code{(alias addresses ...)}, with @code{alias}
specifying the local alias and @code{addresses} specifying where to deliver
this user's mail.

The aliases aren't required to exist as users on the local system.  In the
above example, there doesn't need to be a @code{postmaster} entry in the
@code{operating-system}'s @code{user-accounts} in order to deliver the
@code{postmaster} mail to @code{bob} (which subsequently would deliver mail
to @code{bob@@example.com} and @code{bob@@example2.com}).

@subsubheading GNU Mailutils IMAP4 Daemon
@cindex GNU Mailutils IMAP4 Daemon

@deffn {Scheme Variable} imap4d-service-type
This is the type of the GNU Mailutils IMAP4 Daemon (@pxref{imap4d,,,
mailutils, GNU Mailutils Manual}), whose value should be an
@code{imap4d-configuration} object as in this example:

@lisp
(service imap4d-service-type
         (imap4d-configuration
           (config-file (local-file "imap4d.conf"))))
@end lisp
@end deffn

@deftp {Data Type} imap4d-configuration
Data type representing the configuration of @command{imap4d}.

@table @asis
@item @code{package} (default: @code{mailutils})
The package that provides @command{imap4d}.

@item @code{config-file} (default: @code{%default-imap4d-config-file})
File-like object of the configuration file to use, by default it will listen
on TCP port 143 of @code{localhost}.  @xref{Conf-imap4d,,, mailutils, GNU
Mailutils Manual}, for details.

@end table
@end deftp

@subsubheading Radicale Service
@cindex CalDAV
@cindex CardDAV

@deffn {Scheme Variable} radicale-service-type
This is the type of the @uref{https://radicale.org, Radicale} CalDAV/CardDAV
server whose value should be a @code{radicale-configuration}.
@end deffn

@deftp {Data Type} radicale-configuration
Data type representing the configuration of @command{radicale}.

@table @asis
@item @code{package} (default: @code{radicale})
The package that provides @command{radicale}.

@item @code{config-file} (default: @code{%default-radicale-config-file})
File-like object of the configuration file to use, by default it will listen
on TCP port 5232 of @code{localhost} and use the @code{htpasswd} file at
@file{/var/lib/radicale/users} with no (@code{plain}) encryption.

@end table
@end deftp

@node 消息服务
@subsection 消息服务

@cindex messaging
@cindex jabber
@cindex XMPP
The @code{(gnu services messaging)} module provides Guix service definitions
for messaging services.  Currently it provides the following services:

@subsubheading Prosody Service

@deffn {Scheme Variable} prosody-service-type
This is the type for the @uref{https://prosody.im, Prosody XMPP
communication server}.  Its value must be a @code{prosody-configuration}
record as in this example:

@lisp
(service prosody-service-type
         (prosody-configuration
          (modules-enabled (cons* "groups" "mam" %default-modules-enabled))
          (int-components
           (list
            (int-component-configuration
             (hostname "conference.example.net")
             (plugin "muc")
             (mod-muc (mod-muc-configuration)))))
          (virtualhosts
           (list
            (virtualhost-configuration
             (domain "example.net"))))))
@end lisp

See below for details about @code{prosody-configuration}.

@end deffn

By default, Prosody does not need much configuration.  Only one
@code{virtualhosts} field is needed: it specifies the domain you wish
Prosody to serve.

You can perform various sanity checks on the generated configuration with
the @code{prosodyctl check} command.

Prosodyctl will also help you to import certificates from the
@code{letsencrypt} directory so that the @code{prosody} user can access
them.  See @url{https://prosody.im/doc/letsencrypt}.

@example
prosodyctl --root cert import /etc/letsencrypt/live
@end example

The available configuration parameters follow.  Each parameter definition is
preceded by its type; for example, @samp{string-list foo} indicates that the
@code{foo} parameter should be specified as a list of strings.  Types
starting with @code{maybe-} denote parameters that won't show up in
@code{prosody.cfg.lua} when their value is @code{'disabled}.

There is also a way to specify the configuration as a string, if you have an
old @code{prosody.cfg.lua} file that you want to port over from some other
system; see the end for more details.

The @code{file-object} type designates either a file-like object
(@pxref{G-表达式, file-like objects}) or a file name.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services messaging).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as Prosody updates.

Available @code{prosody-configuration} fields are:

@deftypevr {@code{prosody-configuration} parameter} package prosody
The Prosody package.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name data-path
Location of the Prosody data storage directory.  See
@url{https://prosody.im/doc/configure}.  Defaults to
@samp{"/var/lib/prosody"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-object-list plugin-paths
Additional plugin directories.  They are searched in all the specified paths
in order.  See @url{https://prosody.im/doc/plugins_directory}.  Defaults to
@samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name certificates
Every virtual host and component needs a certificate so that clients and
servers can securely verify its identity.  Prosody will automatically load
certificates/keys from the directory specified here.  Defaults to
@samp{"/etc/prosody/certs"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list admins
This is a list of accounts that are admins for the server.  Note that you
must create the accounts separately.  See
@url{https://prosody.im/doc/admins} and
@url{https://prosody.im/doc/creating_accounts}.  Example: @code{(admins
'("user1@@example.com" "user2@@example.net"))} Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean use-libevent?
Enable use of libevent for better performance under high load.  See
@url{https://prosody.im/doc/libevent}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} module-list modules-enabled
This is the list of modules Prosody will load on startup.  It looks for
@code{mod_modulename.lua} in the plugins folder, so make sure that exists
too.  Documentation on modules can be found at:
@url{https://prosody.im/doc/modules}.  Defaults to @samp{("roster"
"saslauth" "tls" "dialback" "disco" "carbons" "private" "blocklist" "vcard"
"version" "uptime" "time" "ping" "pep" "register" "admin_adhoc")}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list modules-disabled
@samp{"offline"}, @samp{"c2s"} and @samp{"s2s"} are auto-loaded, but should
you want to disable them then add them to this list.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-object groups-file
Path to a text file where the shared groups are defined.  If this path is
empty then @samp{mod_groups} does nothing.  See
@url{https://prosody.im/doc/modules/mod_groups}.  Defaults to
@samp{"/var/lib/prosody/sharedgroups.txt"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean allow-registration?
Disable account creation by default, for security.  See
@url{https://prosody.im/doc/creating_accounts}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-ssl-configuration ssl
These are the SSL/TLS-related settings.  Most of them are disabled so to use
Prosody's defaults.  If you do not completely understand these options, do
not add them to your config, it is easy to lower the security of your server
using them.  See @url{https://prosody.im/doc/advanced_ssl_config}.

Available @code{ssl-configuration} fields are:

@deftypevr {@code{ssl-configuration} parameter} maybe-string protocol
This determines what handshake to use.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name key
Path to your private key file.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name certificate
Path to your certificate file.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} file-object capath
Path to directory containing root certificates that you wish Prosody to
trust when verifying the certificates of remote servers.  Defaults to
@samp{"/etc/ssl/certs"}.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-object cafile
Path to a file containing root certificates that you wish Prosody to trust.
Similar to @code{capath} but with all certificates concatenated together.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list verify
A list of verification options (these mostly map to OpenSSL's
@code{set_verify()} flags).
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list options
A list of general options relating to SSL/TLS@.  These map to OpenSSL's
@code{set_options()}.  For a full list of options available in LuaSec, see
the LuaSec source.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-non-negative-integer depth
How long a chain of certificate authorities to check when looking for a
trusted root certificate.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string ciphers
An OpenSSL cipher string.  This selects what ciphers Prosody will offer to
clients, and in what order.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name dhparam
A path to a file containing parameters for Diffie-Hellman key exchange.  You
can create such a file with: @code{openssl dhparam -out
/etc/prosody/certs/dh-2048.pem 2048}
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string curve
Curve for Elliptic curve Diffie-Hellman.  Prosody's default is
@samp{"secp384r1"}.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list verifyext
A list of ``extra'' verification options.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string password
Password for encrypted private keys.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean c2s-require-encryption?
Whether to force all client-to-server connections to be encrypted or not.
See @url{https://prosody.im/doc/modules/mod_tls}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list disable-sasl-mechanisms
Set of mechanisms that will never be offered.  See
@url{https://prosody.im/doc/modules/mod_saslauth}.  Defaults to
@samp{("DIGEST-MD5")}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean s2s-require-encryption?
Whether to force all server-to-server connections to be encrypted or not.
See @url{https://prosody.im/doc/modules/mod_tls}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean s2s-secure-auth?
Whether to require encryption and certificate authentication.  This provides
ideal security, but requires servers you communicate with to support
encryption AND present valid, trusted certificates.  See
@url{https://prosody.im/doc/s2s#security}.  Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list s2s-insecure-domains
Many servers don't support encryption or have invalid or self-signed
certificates.  You can list domains here that will not be required to
authenticate using certificates.  They will be authenticated using DNS@.
See @url{https://prosody.im/doc/s2s#security}.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list s2s-secure-domains
Even if you leave @code{s2s-secure-auth?} disabled, you can still require
valid certificates for some domains by specifying a list here.  See
@url{https://prosody.im/doc/s2s#security}.  Defaults to @samp{()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string authentication
Select the authentication backend to use.  The default provider stores
passwords in plaintext and uses Prosody's configured data storage to store
the authentication data.  If you do not trust your server please see
@url{https://prosody.im/doc/modules/mod_auth_internal_hashed} for
information about using the hashed backend.  See also
@url{https://prosody.im/doc/authentication} Defaults to
@samp{"internal_plain"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-string log
Set logging options.  Advanced logging configuration is not yet supported by
the Prosody service.  See @url{https://prosody.im/doc/logging}.  Defaults to
@samp{"*syslog"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name pidfile
File to write pid in.  See @url{https://prosody.im/doc/modules/mod_posix}.
Defaults to @samp{"/var/run/prosody/prosody.pid"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-non-negative-integer http-max-content-size
Maximum allowed size of the HTTP body (in bytes).
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-string http-external-url
Some modules expose their own URL in various ways.  This URL is built from
the protocol, host and port used.  If Prosody sits behind a proxy, the
public URL will be @code{http-external-url} instead.  See
@url{https://prosody.im/doc/http#external_url}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} virtualhost-configuration-list virtualhosts
A host in Prosody is a domain on which user accounts can be created.  For
example if you want your users to have addresses like
@samp{"john.smith@@example.com"} then you need to add a host
@samp{"example.com"}.  All options in this list will apply only to this
host.

Note: the name @emph{virtual} host is used in configuration to avoid
confusion with the actual physical host that Prosody is installed on.  A
single Prosody instance can serve many domains, each one defined as a
VirtualHost entry in Prosody's configuration.  Conversely a server that
hosts a single domain would have just one VirtualHost entry.

See @url{https://prosody.im/doc/configure#virtual_host_settings}.

Available @code{virtualhost-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins},
@code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled},
@code{groups-file}, @code{allow-registration?}, @code{ssl},
@code{c2s-require-encryption?}, @code{disable-sasl-mechanisms},
@code{s2s-require-encryption?}, @code{s2s-secure-auth?},
@code{s2s-insecure-domains}, @code{s2s-secure-domains},
@code{authentication}, @code{log}, @code{http-max-content-size},
@code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{virtualhost-configuration} parameter} string domain
Domain you wish Prosody to serve.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} int-component-configuration-list int-components
Components are extra services on a server which are available to clients,
usually on a subdomain of the main server (such as
@samp{"mycomponent.example.com"}).  Example components might be chatroom
servers, user directories, or gateways to other protocols.

Internal components are implemented with Prosody-specific plugins.  To add
an internal component, you simply fill the hostname field, and the plugin
you wish to use for the component.

See @url{https://prosody.im/doc/components}.  Defaults to @samp{()}.

Available @code{int-component-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins},
@code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled},
@code{groups-file}, @code{allow-registration?}, @code{ssl},
@code{c2s-require-encryption?}, @code{disable-sasl-mechanisms},
@code{s2s-require-encryption?}, @code{s2s-secure-auth?},
@code{s2s-insecure-domains}, @code{s2s-secure-domains},
@code{authentication}, @code{log}, @code{http-max-content-size},
@code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{int-component-configuration} parameter} string hostname
Hostname of the component.
@end deftypevr

@deftypevr {@code{int-component-configuration} parameter} string plugin
Plugin you wish to use for the component.
@end deftypevr

@deftypevr {@code{int-component-configuration} parameter} maybe-mod-muc-configuration mod-muc
Multi-user chat (MUC) is Prosody's module for allowing you to create hosted
chatrooms/conferences for XMPP users.

General information on setting up and using multi-user chatrooms can be
found in the ``Chatrooms'' documentation
(@url{https://prosody.im/doc/chatrooms}), which you should read if you are
new to XMPP chatrooms.

See also @url{https://prosody.im/doc/modules/mod_muc}.

Available @code{mod-muc-configuration} fields are:

@deftypevr {@code{mod-muc-configuration} parameter} string name
The name to return in service discovery responses.  Defaults to
@samp{"Prosody Chatrooms"}.
@end deftypevr

@deftypevr {@code{mod-muc-configuration} parameter} string-or-boolean restrict-room-creation
If @samp{#t}, this will only allow admins to create new chatrooms.
Otherwise anyone can create a room.  The value @samp{"local"} restricts room
creation to users on the service's parent domain.  E.g.@:
@samp{user@@example.com} can create rooms on @samp{rooms.example.com}.  The
value @samp{"admin"} restricts to service administrators only.  Defaults to
@samp{#f}.
@end deftypevr

@deftypevr {@code{mod-muc-configuration} parameter} non-negative-integer max-history-messages
Maximum number of history messages that will be sent to the member that has
just joined the room.  Defaults to @samp{20}.
@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} ext-component-configuration-list ext-components
External components use XEP-0114, which most standalone components support.
To add an external component, you simply fill the hostname field.  See
@url{https://prosody.im/doc/components}.  Defaults to @samp{()}.

Available @code{ext-component-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins},
@code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled},
@code{groups-file}, @code{allow-registration?}, @code{ssl},
@code{c2s-require-encryption?}, @code{disable-sasl-mechanisms},
@code{s2s-require-encryption?}, @code{s2s-secure-auth?},
@code{s2s-insecure-domains}, @code{s2s-secure-domains},
@code{authentication}, @code{log}, @code{http-max-content-size},
@code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{ext-component-configuration} parameter} string component-secret
Password which the component will use to log in.
@end deftypevr

@deftypevr {@code{ext-component-configuration} parameter} string hostname
Hostname of the component.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} non-negative-integer-list component-ports
Port(s) Prosody listens on for component connections.  Defaults to
@samp{(5347)}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string component-interface
Interface Prosody listens on for component connections.  Defaults to
@samp{"127.0.0.1"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-raw-content raw-content
Raw content that will be added to the configuration file.
@end deftypevr

It could be that you just want to get a @code{prosody.cfg.lua} up and
running.  In that case, you can pass an @code{opaque-prosody-configuration}
record as the value of @code{prosody-service-type}.  As its name indicates,
an opaque configuration does not have easy reflective capabilities.
Available @code{opaque-prosody-configuration} fields are:

@deftypevr {@code{opaque-prosody-configuration} parameter} package prosody
The prosody package.
@end deftypevr

@deftypevr {@code{opaque-prosody-configuration} parameter} string prosody.cfg.lua
The contents of the @code{prosody.cfg.lua} to use.
@end deftypevr

For example, if your @code{prosody.cfg.lua} is just the empty string, you
could instantiate a prosody service like this:

@lisp
(service prosody-service-type
         (opaque-prosody-configuration
          (prosody.cfg.lua "")))
@end lisp

@c end of Prosody auto-generated documentation

@subsubheading BitlBee Service

@cindex IRC (Internet Relay Chat)
@cindex IRC gateway
@url{https://bitlbee.org,BitlBee} is a gateway that provides an IRC
interface to a variety of messaging protocols such as XMPP.

@defvr {Scheme Variable} bitlbee-service-type
This is the service type for the @url{https://bitlbee.org,BitlBee} IRC
gateway daemon.  Its value is a @code{bitlbee-configuration} (see below).

To have BitlBee listen on port 6667 on localhost, add this line to your
services:

@lisp
(service bitlbee-service-type)
@end lisp
@end defvr

@deftp {Data Type} bitlbee-configuration
This is the configuration for BitlBee, with the following fields:

@table @asis
@item @code{interface} (default: @code{"127.0.0.1"})
@itemx @code{port} (default: @code{6667})
Listen on the network interface corresponding to the IP address specified in
@var{interface}, on @var{port}.

When @var{interface} is @code{127.0.0.1}, only local clients can connect;
when it is @code{0.0.0.0}, connections can come from any networking
interface.

@item @code{bitlbee} (default: @code{bitlbee})
The BitlBee package to use.

@item @code{plugins} (default: @code{'()})
List of plugin packages to use---e.g., @code{bitlbee-discord}.

@item @code{extra-settings} (default: @code{""})
Configuration snippet added as-is to the BitlBee configuration file.
@end table
@end deftp

@subsubheading Quassel Service

@cindex IRC (Internet Relay Chat)
@url{https://quassel-irc.org/,Quassel} is a distributed IRC client, meaning
that one or more clients can attach to and detach from the central core.

@defvr {Scheme Variable} quassel-service-type
This is the service type for the @url{https://quassel-irc.org/,Quassel} IRC
backend daemon.  Its value is a @code{quassel-configuration} (see below).
@end defvr

@deftp {Data Type} quassel-configuration
This is the configuration for Quassel, with the following fields:

@table @asis
@item @code{quassel} (default: @code{quassel})
The Quassel package to use.

@item @code{interface} (default: @code{"::,0.0.0.0"})
@item @code{port} (default: @code{4242})
Listen on the network interface(s) corresponding to the IPv4 or IPv6
interfaces specified in the comma delimited @var{interface}, on @var{port}.

@item @code{loglevel} (default: @code{"Info"})
The level of logging desired.  Accepted values are Debug, Info, Warning and
Error.
@end table
@end deftp

@node 电话服务
@subsection 电话服务

@cindex Murmur (VoIP server)
@cindex VoIP server
This section describes how to set up and run a Murmur server.  Murmur is the
server of the @uref{https://mumble.info, Mumble} voice-over-IP (VoIP) suite.

@deftp {Data Type} murmur-configuration
The service type for the Murmur server.  An example configuration can look
like this:

@lisp
(service murmur-service-type
         (murmur-configuration
          (welcome-text
            "Welcome to this Mumble server running on Guix!")
          (cert-required? #t) ;disallow text password logins
          (ssl-cert "/etc/letsencrypt/live/mumble.example.com/fullchain.pem")
          (ssl-key "/etc/letsencrypt/live/mumble.example.com/privkey.pem")))
@end lisp

After reconfiguring your system, you can manually set the murmur
@code{SuperUser} password with the command that is printed during the
activation phase.

It is recommended to register a normal Mumble user account and grant it
admin or moderator rights.  You can use the @code{mumble} client to login as
new normal user, register yourself, and log out.  For the next step login
with the name @code{SuperUser} use the @code{SuperUser} password that you
set previously, and grant your newly registered mumble user administrator or
moderator rights and create some channels.

Available @code{murmur-configuration} fields are:

@table @asis
@item @code{package} (default: @code{mumble})
Package that contains @code{bin/murmurd}.

@item @code{user} (default: @code{"murmur"})
User who will run the Murmur server.

@item @code{group} (default: @code{"murmur"})
Group of the user who will run the murmur server.

@item @code{port} (default: @code{64738})
Port on which the server will listen.

@item @code{welcome-text} (default: @code{""})
Welcome text sent to clients when they connect.

@item @code{server-password} (default: @code{""})
Password the clients have to enter in order to connect.

@item @code{max-users} (default: @code{100})
Maximum of users that can be connected to the server at once.

@item @code{max-user-bandwidth} (default: @code{#f})
Maximum voice traffic a user can send per second.

@item @code{database-file} (default: @code{"/var/lib/murmur/db.sqlite"})
File name of the sqlite database.  The service's user will become the owner
of the directory.

@item @code{log-file} (default: @code{"/var/log/murmur/murmur.log"})
File name of the log file.  The service's user will become the owner of the
directory.

@item @code{autoban-attempts} (default: @code{10})
Maximum number of logins a user can make in @code{autoban-timeframe} without
getting auto banned for @code{autoban-time}.

@item @code{autoban-timeframe} (default: @code{120})
Timeframe for autoban in seconds.

@item @code{autoban-time} (default: @code{300})
Amount of time in seconds for which a client gets banned when violating the
autoban limits.

@item @code{opus-threshold} (default: @code{100})
Percentage of clients that need to support opus before switching over to
opus audio codec.

@item @code{channel-nesting-limit} (default: @code{10})
How deep channels can be nested at maximum.

@item @code{channelname-regex} (default: @code{#f})
A string in form of a Qt regular expression that channel names must conform
to.

@item @code{username-regex} (default: @code{#f})
A string in form of a Qt regular expression that user names must conform to.

@item @code{text-message-length} (default: @code{5000})
Maximum size in bytes that a user can send in one text chat message.

@item @code{image-message-length} (default: @code{(* 128 1024)})
Maximum size in bytes that a user can send in one image message.

@item @code{cert-required?} (default: @code{#f})
If it is set to @code{#t} clients that use weak password authentication will
not be accepted.  Users must have completed the certificate wizard to join.

@item @code{remember-channel?} (default: @code{#f})
Should murmur remember the last channel each user was in when they
disconnected and put them into the remembered channel when they rejoin.

@item @code{allow-html?} (default: @code{#f})
Should html be allowed in text messages, user comments, and channel
descriptions.

@item @code{allow-ping?} (default: @code{#f})
Setting to true exposes the current user count, the maximum user count, and
the server's maximum bandwidth per client to unauthenticated users.  In the
Mumble client, this information is shown in the Connect dialog.

Disabling this setting will prevent public listing of the server.

@item @code{bonjour?} (default: @code{#f})
Should the server advertise itself in the local network through the bonjour
protocol.

@item @code{send-version?} (default: @code{#f})
Should the murmur server version be exposed in ping requests.

@item @code{log-days} (default: @code{31})
Murmur also stores logs in the database, which are accessible via RPC.  The
default is 31 days of months, but you can set this setting to 0 to keep logs
forever, or -1 to disable logging to the database.

@item @code{obfuscate-ips?} (default: @code{#t})
Should logged ips be obfuscated to protect the privacy of users.

@item @code{ssl-cert} (default: @code{#f})
File name of the SSL/TLS certificate used for encrypted connections.

@lisp
(ssl-cert "/etc/letsencrypt/live/example.com/fullchain.pem")
@end lisp
@item @code{ssl-key} (default: @code{#f})
Filepath to the ssl private key used for encrypted connections.
@lisp
(ssl-key "/etc/letsencrypt/live/example.com/privkey.pem")
@end lisp

@item @code{ssl-dh-params} (default: @code{#f})
File name of a PEM-encoded file with Diffie-Hellman parameters for the
SSL/TLS encryption.  Alternatively you set it to @code{"@@ffdhe2048"},
@code{"@@ffdhe3072"}, @code{"@@ffdhe4096"}, @code{"@@ffdhe6144"} or
@code{"@@ffdhe8192"} to use bundled parameters from RFC 7919.

@item @code{ssl-ciphers} (default: @code{#f})
The @code{ssl-ciphers} option chooses the cipher suites to make available
for use in SSL/TLS.

This option is specified using
@uref{https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT,
OpenSSL cipher list notation}.

It is recommended that you try your cipher string using 'openssl ciphers
<string>' before setting it here, to get a feel for which cipher suites you
will get.  After setting this option, it is recommend that you inspect your
Murmur log to ensure that Murmur is using the cipher suites that you
expected it to.

Note: Changing this option may impact the backwards compatibility of your
Murmur server, and can remove the ability for older Mumble clients to be
able to connect to it.

@item @code{public-registration} (default: @code{#f})
Must be a @code{<murmur-public-registration-configuration>} record or
@code{#f}.

You can optionally register your server in the public server list that the
@code{mumble} client shows on startup.  You cannot register your server if
you have set a @code{server-password}, or set @code{allow-ping} to
@code{#f}.

It might take a few hours until it shows up in the public list.

@item @code{file} (default: @code{#f})
Optional alternative override for this configuration.
@end table
@end deftp

@deftp {Data Type} murmur-public-registration-configuration
Configuration for public registration of a murmur service.

@table @asis
@item @code{名字}
This is a display name for your server.  Not to be confused with the
hostname.

@item @code{password}
A password to identify your registration.  Subsequent updates will need the
same password.  Don't lose your password.

@item @code{url}
This should be a @code{http://} or @code{https://} link to your web site.

@item @code{hostname} (default: @code{#f})
By default your server will be listed by its IP address.  If it is set your
server will be linked by this host name instead.
@end table
@end deftp



@node File-Sharing Services
@subsection File-Sharing Services

The @code{(gnu services file-sharing)} module provides services that assist
with transferring files over peer-to-peer file-sharing networks.

@subsubheading Transmission Daemon Service

@uref{https://transmissionbt.com/, Transmission} is a flexible BitTorrent
client that offers a variety of graphical and command-line interfaces.  A
@code{transmission-daemon-service-type} service provides Transmission's
headless variant, @command{transmission-daemon}, as a system service,
allowing users to share files via BitTorrent even when they are not logged
in.

@deffn {Scheme Variable} transmission-daemon-service-type
The service type for the Transmission Daemon BitTorrent client. Its value
must be a @code{transmission-daemon-configuration} object as in this
example:

@lisp
(service transmission-daemon-service-type
         (transmission-daemon-configuration
          ;; Restrict access to the RPC ("control") interface
          (rpc-authentication-required? #t)
          (rpc-username "transmission")
          (rpc-password
           (transmission-password-hash
            "transmission" ; desired password
            "uKd1uMs9"))   ; arbitrary salt value

          ;; Accept requests from this and other hosts on the
          ;; local network
          (rpc-whitelist-enabled? #t)
          (rpc-whitelist '("::1" "127.0.0.1" "192.168.0.*"))

          ;; Limit bandwidth use during work hours
          (alt-speed-down (* 1024 2)) ;   2 MB/s
          (alt-speed-up 512)          ; 512 kB/s

          (alt-speed-time-enabled? #t)
          (alt-speed-time-day 'weekdays)
          (alt-speed-time-begin
           (+ (* 60 8) 30))           ; 8:30 am
          (alt-speed-time-end
           (+ (* 60 (+ 12 5)) 30))))  ; 5:30 pm
@end lisp
@end deffn

Once the service is started, users can interact with the daemon through its
Web interface (at @code{http://localhost:9091/}) or by using the
@command{transmission-remote} command-line tool, available in the
@code{transmission} package.  (Emacs users may want to also consider the
@code{emacs-transmission} package.)  Both communicate with the daemon
through its remote procedure call (RPC) interface, which by default is
available to all users on the system; you may wish to change this by
assigning values to the @code{rpc-authentication-required?},
@code{rpc-username} and @code{rpc-password} settings, as shown in the
example above and documented further below.

The value for @code{rpc-password} must be a password hash of the type
generated and used by Transmission clients.  This can be copied verbatim
from an existing @file{settings.json} file, if another Transmission client
is already being used.  Otherwise, the @code{transmission-password-hash} and
@code{transmission-random-salt} procedures provided by this module can be
used to obtain a suitable hash value.

@deffn {Scheme Procedure} transmission-password-hash @var{password} @var{salt}
Returns a string containing the result of hashing @var{password} together
with @var{salt}, in the format recognized by Transmission clients for their
@code{rpc-password} configuration setting.

@var{salt} must be an eight-character string.  The
@code{transmission-random-salt} procedure can be used to generate a suitable
salt value at random.
@end deffn

@deffn {Scheme Procedure} transmission-random-salt
Returns a string containing a random, eight-character salt value of the type
generated and used by Transmission clients, suitable for passing to the
@code{transmission-password-hash} procedure.
@end deffn

These procedures are accessible from within a Guile REPL started with the
@command{guix repl} command (@pxref{调用guix repl}).  This is useful
for obtaining a random salt value to provide as the second parameter to
`transmission-password-hash`, as in this example session:

@example
$ guix repl
scheme@@(guix-user)> ,use (gnu services file-sharing)
scheme@@(guix-user)> (transmission-random-salt)
$1 = "uKd1uMs9"
@end example

Alternatively, a complete password hash can generated in a single step:

@example
scheme@@(guix-user)> (transmission-password-hash "transmission"
(transmission-random-salt))
$2 = "@{c8bbc6d1740cd8dc819a6e25563b67812c1c19c9VtFPfdsX"
@end example

The resulting string can be used as-is for the value of @code{rpc-password},
allowing the password to be kept hidden even in the operating-system
configuration.

Torrent files downloaded by the daemon are directly accessible only to users
in the ``transmission'' user group, who receive read-only access to the
directory specified by the @code{download-dir} configuration setting (and
also the directory specified by @code{incomplete-dir}, if
@code{incomplete-dir-enabled?} is @code{#t}).  Downloaded files can be moved
to another directory or deleted altogether using
@command{transmission-remote} with its @code{--move} and
@code{--remove-and-delete} options.

If the @code{watch-dir-enabled?} setting is set to @code{#t}, users in the
``transmission'' group are able also to place @file{.torrent} files in the
directory specified by @code{watch-dir} to have the corresponding torrents
added by the daemon.  (The @code{trash-original-torrent-files?} setting
controls whether the daemon deletes these files after processing them.)

Some of the daemon's configuration settings can be changed temporarily by
@command{transmission-remote} and similar tools. To undo these changes, use
the service's @code{reload} action to have the daemon reload its settings
from disk:

@example
# herd reload transmission-daemon
@end example

The full set of available configuration settings is defined by the
@code{transmission-daemon-configuration} data type.

@deftp {Data Type} transmission-daemon-configuration
The data type representing configuration settings for Transmission Daemon.
These correspond directly to the settings recognized by Transmission clients
in their @file{settings.json} file.
@end deftp

@c The following documentation was initially generated by
@c (generate-transmission-daemon-documentation) in (gnu services
@c file-sharing).  Manually maintained documentation is better, so we
@c shouldn't hesitate to edit below as needed.  However if the change
@c you want to make to this documentation can be done in an automated
@c way, it's probably easier to change (generate-documentation) than to
@c make it below and have to deal with the churn as Transmission Daemon
@c updates.

@c %start of fragment

Available @code{transmission-daemon-configuration} fields are:

@deftypevr {@code{transmission-daemon-configuration} parameter} package transmission
The Transmission package to use.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer stop-wait-period
The period, in seconds, to wait when stopping the service for
@command{transmission-daemon} to exit before killing its process.  This
allows the daemon time to complete its housekeeping and send a final update
to trackers as it shuts down.  On slow hosts, or hosts with a slow network
connection, this value may need to be increased.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string download-dir
The directory to which torrent files are downloaded.

Defaults to @samp{"/var/lib/transmission-daemon/downloads"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean incomplete-dir-enabled?
If @code{#t}, files will be held in @code{incomplete-dir} while their
torrent is being downloaded, then moved to @code{download-dir} once the
torrent is complete.  Otherwise, files for all torrents (including those
still being downloaded) will be placed in @code{download-dir}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string incomplete-dir
The directory in which files from incompletely downloaded torrents will be
held when @code{incomplete-dir-enabled?} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} umask umask
The file mode creation mask used for downloaded files.  (See the
@command{umask} man page for more information.)

Defaults to @samp{18}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rename-partial-files?
When @code{#t}, ``.part'' is appended to the name of partially downloaded
files.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} preallocation-mode preallocation
The mode by which space should be preallocated for downloaded files, one of
@code{none}, @code{fast} (or @code{sparse}) and @code{full}.  Specifying
@code{full} will minimize disk fragmentation at a cost to file-creation
speed.

Defaults to @samp{fast}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean watch-dir-enabled?
If @code{#t}, the directory specified by @code{watch-dir} will be watched
for new @file{.torrent} files and the torrents they describe added
automatically (and the original files removed, if
@code{trash-original-torrent-files?} is @code{#t}).

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string watch-dir
The directory to be watched for @file{.torrent} files indicating new
torrents to be added, when @code{watch-dir-enabled} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean trash-original-torrent-files?
When @code{#t}, @file{.torrent} files will be deleted from the watch
directory once their torrent has been added (see
@code{watch-directory-enabled?}).

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean speed-limit-down-enabled?
When @code{#t}, the daemon's download speed will be limited to the rate
specified by @code{speed-limit-down}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer speed-limit-down
The default global-maximum download speed, in kilobytes per second.

Defaults to @samp{100}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean speed-limit-up-enabled?
When @code{#t}, the daemon's upload speed will be limited to the rate
specified by @code{speed-limit-up}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer speed-limit-up
The default global-maximum upload speed, in kilobytes per second.

Defaults to @samp{100}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean alt-speed-enabled?
When @code{#t}, the alternate speed limits @code{alt-speed-down} and
@code{alt-speed-up} are used (in place of @code{speed-limit-down} and
@code{speed-limit-up}, if they are enabled) to constrain the daemon's
bandwidth usage.  This can be scheduled to occur automatically at certain
times during the week; see @code{alt-speed-time-enabled?}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-down
The alternate global-maximum download speed, in kilobytes per second.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-up
The alternate global-maximum upload speed, in kilobytes per second.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean alt-speed-time-enabled?
When @code{#t}, the alternate speed limits @code{alt-speed-down} and
@code{alt-speed-up} will be enabled automatically during the periods
specified by @code{alt-speed-time-day}, @code{alt-speed-time-begin} and
@code{alt-time-speed-end}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} day-list alt-speed-time-day
The days of the week on which the alternate-speed schedule should be used,
specified either as a list of days (@code{sunday}, @code{monday}, and so on)
or using one of the symbols @code{weekdays}, @code{weekends} or @code{all}.

Defaults to @samp{all}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-time-begin
The time of day at which to enable the alternate speed limits, expressed as
a number of minutes since midnight.

Defaults to @samp{540}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-time-end
The time of day at which to disable the alternate speed limits, expressed as
a number of minutes since midnight.

Defaults to @samp{1020}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string bind-address-ipv4
The IP address at which to listen for peer connections, or ``0.0.0.0'' to
listen at all available IP addresses.

Defaults to @samp{"0.0.0.0"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string bind-address-ipv6
The IPv6 address at which to listen for peer connections, or ``::'' to
listen at all available IPv6 addresses.

Defaults to @samp{"::"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean peer-port-random-on-start?
If @code{#t}, when the daemon starts it will select a port at random on
which to listen for peer connections, from the range specified (inclusively)
by @code{peer-port-random-low} and @code{peer-port-random-high}.  Otherwise,
it listens on the port specified by @code{peer-port}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number peer-port-random-low
The lowest selectable port number when @code{peer-port-random-on-start?} is
@code{#t}.

Defaults to @samp{49152}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number peer-port-random-high
The highest selectable port number when @code{peer-port-random-on-start} is
@code{#t}.

Defaults to @samp{65535}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number peer-port
The port on which to listen for peer connections when
@code{peer-port-random-on-start?} is @code{#f}.

Defaults to @samp{51413}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean port-forwarding-enabled?
If @code{#t}, the daemon will attempt to configure port-forwarding on an
upstream gateway automatically using @acronym{UPnP} and @acronym{NAT-PMP}.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} encryption-mode encryption
The encryption preference for peer connections, one of
@code{prefer-unencrypted-connections}, @code{prefer-encrypted-connections}
or @code{require-encrypted-connections}.

Defaults to @samp{prefer-encrypted-connections}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string peer-congestion-algorithm
The TCP congestion-control algorithm to use for peer connections, specified
using a string recognized by the operating system in calls to
@code{setsockopt} (or set to @code{disabled}, in which case the
operating-system default is used).

Note that on GNU/Linux systems, the kernel must be configured to allow
processes to use a congestion-control algorithm not in the default set;
otherwise, it will deny these requests with ``Operation not permitted''.  To
see which algorithms are available on your system and which are currently
permitted for use, look at the contents of the files
@file{tcp_available_congestion_control} and
@file{tcp_allowed_congestion_control} in the @file{/proc/sys/net/ipv4}
directory.

As an example, to have Transmission Daemon use
@uref{http://www-ece.rice.edu/networks/TCP-LP/,the TCP Low Priority
congestion-control algorithm}, you'll need to modify your kernel
configuration to build in support for the algorithm, then update your
operating-system configuration to allow its use by adding a
@code{sysctl-service-type} service (or updating the existing one's
configuration) with lines like the following:

@lisp
(service sysctl-service-type
         (sysctl-configuration
          (settings
           ("net.ipv4.tcp_allowed_congestion_control" .
            "reno cubic lp"))))
@end lisp

The Transmission Daemon configuration can then be updated with

@lisp
(peer-congestion-algorithm "lp")
@end lisp

and the system reconfigured to have the changes take effect.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} tcp-type-of-service peer-socket-tos
The type of service to request in outgoing @acronym{TCP} packets, one of
@code{default}, @code{low-cost}, @code{throughput}, @code{low-delay} and
@code{reliability}.

Defaults to @samp{default}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer peer-limit-global
The global limit on the number of connected peers.

Defaults to @samp{200}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer peer-limit-per-torrent
The per-torrent limit on the number of connected peers.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer upload-slots-per-torrent
The maximum number of peers to which the daemon will upload data
simultaneously for each torrent.

Defaults to @samp{14}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer peer-id-ttl-hours
The maximum lifespan, in hours, of the peer ID associated with each public
torrent before it is regenerated.

Defaults to @samp{6}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean blocklist-enabled?
When @code{#t}, the daemon will ignore peers mentioned in the blocklist it
has most recently downloaded from @code{blocklist-url}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string blocklist-url
The URL of a peer blocklist (in @acronym{P2P}-plaintext or eMule @file{.dat}
format) to be periodically downloaded and applied when
@code{blocklist-enabled?} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean download-queue-enabled?
If @code{#t}, the daemon will be limited to downloading at most
@code{download-queue-size} non-stalled torrents simultaneously.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer download-queue-size
The size of the daemon's download queue, which limits the number of
non-stalled torrents it will download at any one time when
@code{download-queue-enabled?} is @code{#t}.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean seed-queue-enabled?
If @code{#t}, the daemon will be limited to seeding at most
@code{seed-queue-size} non-stalled torrents simultaneously.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer seed-queue-size
The size of the daemon's seed queue, which limits the number of non-stalled
torrents it will seed at any one time when @code{seed-queue-enabled?} is
@code{#t}.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean queue-stalled-enabled?
When @code{#t}, the daemon will consider torrents for which it has not
shared data in the past @code{queue-stalled-minutes} minutes to be stalled
and not count them against its @code{download-queue-size} and
@code{seed-queue-size} limits.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer queue-stalled-minutes
The maximum period, in minutes, a torrent may be idle before it is
considered to be stalled, when @code{queue-stalled-enabled?} is @code{#t}.

Defaults to @samp{30}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean ratio-limit-enabled?
When @code{#t}, a torrent being seeded will automatically be paused once it
reaches the ratio specified by @code{ratio-limit}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-rational ratio-limit
The ratio at which a torrent being seeded will be paused, when
@code{ratio-limit-enabled?} is @code{#t}.

Defaults to @samp{2.0}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean idle-seeding-limit-enabled?
When @code{#t}, a torrent being seeded will automatically be paused once it
has been idle for @code{idle-seeding-limit} minutes.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer idle-seeding-limit
The maximum period, in minutes, a torrent being seeded may be idle before it
is paused, when @code{idle-seeding-limit-enabled?} is @code{#t}.

Defaults to @samp{30}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean dht-enabled?
Enable @uref{http://bittorrent.org/beps/bep_0005.html,the distributed hash
table (@acronym{DHT}) protocol}, which supports the use of trackerless
torrents.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean lpd-enabled?
Enable @uref{https://en.wikipedia.org/wiki/Local_Peer_Discovery,local peer
discovery} (@acronym{LPD}), which allows the discovery of peers on the local
network and may reduce the amount of data sent over the public Internet.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean pex-enabled?
Enable @uref{https://en.wikipedia.org/wiki/Peer_exchange,peer exchange}
(@acronym{PEX}), which reduces the daemon's reliance on external trackers
and may improve its performance.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean utp-enabled?
Enable @uref{http://bittorrent.org/beps/bep_0029.html,the micro transport
protocol} (@acronym{uTP}), which aims to reduce the impact of BitTorrent
traffic on other users of the local network while maintaining full
utilization of the available bandwidth.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-enabled?
If @code{#t}, enable the remote procedure call (@acronym{RPC})  interface,
which allows remote control of the daemon via its Web interface, the
@command{transmission-remote} command-line client, and similar tools.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string rpc-bind-address
The IP address at which to listen for @acronym{RPC} connections, or
``0.0.0.0'' to listen at all available IP addresses.

Defaults to @samp{"0.0.0.0"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number rpc-port
The port on which to listen for @acronym{RPC} connections.

Defaults to @samp{9091}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string rpc-url
The path prefix to use in the @acronym{RPC}-endpoint @acronym{URL}.

Defaults to @samp{"/transmission/"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-authentication-required?
When @code{#t}, clients must authenticate (see @code{rpc-username} and
@code{rpc-password}) when using the @acronym{RPC} interface.  Note this has
the side effect of disabling host-name whitelisting (see
@code{rpc-host-whitelist-enabled?}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string rpc-username
The username required by clients to access the @acronym{RPC} interface when
@code{rpc-authentication-required?} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-transmission-password-hash rpc-password
The password required by clients to access the @acronym{RPC} interface when
@code{rpc-authentication-required?} is @code{#t}.  This must be specified
using a password hash in the format recognized by Transmission clients,
either copied from an existing @file{settings.json} file or generated using
the @code{transmission-password-hash} procedure.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-whitelist-enabled?
When @code{#t}, @acronym{RPC} requests will be accepted only when they
originate from an address specified in @code{rpc-whitelist}.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string-list rpc-whitelist
The list of IP and IPv6 addresses from which @acronym{RPC} requests will be
accepted when @code{rpc-whitelist-enabled?} is @code{#t}.  Wildcards may be
specified using @samp{*}.

Defaults to @samp{("127.0.0.1" "::1")}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-host-whitelist-enabled?
When @code{#t}, @acronym{RPC} requests will be accepted only when they are
addressed to a host named in @code{rpc-host-whitelist}.  Note that requests
to ``localhost'' or ``localhost.'', or to a numeric address, are always
accepted regardless of these settings.

Note also this functionality is disabled when
@code{rpc-authentication-required?} is @code{#t}.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string-list rpc-host-whitelist
The list of host names recognized by the @acronym{RPC} server when
@code{rpc-host-whitelist-enabled?} is @code{#t}.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} message-level message-level
The minimum severity level of messages to be logged (to
@file{/var/log/transmission.log}) by the daemon, one of @code{none} (no
logging), @code{error}, @code{info} and @code{debug}.

Defaults to @samp{info}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean start-added-torrents?
When @code{#t}, torrents are started as soon as they are added; otherwise,
they are added in ``paused'' state.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean script-torrent-done-enabled?
When @code{#t}, the script specified by @code{script-torrent-done-filename}
will be invoked each time a torrent completes.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-file-object script-torrent-done-filename
A file name or file-like object specifying a script to run each time a
torrent completes, when @code{script-torrent-done-enabled?} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean scrape-paused-torrents-enabled?
When @code{#t}, the daemon will scrape trackers for a torrent even when the
torrent is paused.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer cache-size-mb
The amount of memory, in megabytes, to allocate for the daemon's in-memory
cache.  A larger value may increase performance by reducing the frequency of
disk I/O.

Defaults to @samp{4}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean prefetch-enabled?
When @code{#t}, the daemon will try to improve I/O performance by hinting to
the operating system which data is likely to be read next from disk to
satisfy requests from peers.

Defaults to @samp{#t}.

@end deftypevr


@c %end of fragment



@node 监控服务
@subsection 监控服务

@subsubheading Tailon Service

@uref{https://tailon.readthedocs.io/, Tailon} is a web application for
viewing and searching log files.

The following example will configure the service with default values.  By
default, Tailon can be accessed on port 8080 (@code{http://localhost:8080}).

@lisp
(service tailon-service-type)
@end lisp

The following example customises more of the Tailon configuration, adding
@command{sed} to the list of allowed commands.

@lisp
(service tailon-service-type
         (tailon-configuration
           (config-file
             (tailon-configuration-file
               (allowed-commands '("tail" "grep" "awk" "sed"))))))
@end lisp


@deftp {Data Type} tailon-configuration
Data type representing the configuration of Tailon.  This type has the
following parameters:

@table @asis
@item @code{config-file} (default: @code{(tailon-configuration-file)})
The configuration file to use for Tailon.  This can be set to a
@dfn{tailon-configuration-file} record value, or any gexp
(@pxref{G-表达式}).

For example, to instead use a local file, the @code{local-file} function can
be used:

@lisp
(service tailon-service-type
         (tailon-configuration
           (config-file (local-file "./my-tailon.conf"))))
@end lisp

@item @code{package} (default: @code{tailon})
The tailon package to use.

@end table
@end deftp

@deftp {Data Type} tailon-configuration-file
Data type representing the configuration options for Tailon.  This type has
the following parameters:

@table @asis
@item @code{files} (default: @code{(list "/var/log")})
List of files to display.  The list can include strings for a single file or
directory, or a list, where the first item is the name of a subsection, and
the remaining items are the files or directories in that subsection.

@item @code{bind} (default: @code{"localhost:8080"})
Address and port to which Tailon should bind on.

@item @code{relative-root} (default: @code{#f})
URL path to use for Tailon, set to @code{#f} to not use a path.

@item @code{allow-transfers?} (default: @code{#t})
Allow downloading the log files in the web interface.

@item @code{follow-names?} (default: @code{#t})
Allow tailing of not-yet existent files.

@item @code{tail-lines} (default: @code{200})
Number of lines to read initially from each file.

@item @code{allowed-commands} (default: @code{(list "tail" "grep" "awk")})
Commands to allow running.  By default, @code{sed} is disabled.

@item @code{debug?} (default: @code{#f})
Set @code{debug?} to @code{#t} to show debug messages.

@item @code{wrap-lines} (default: @code{#t})
Initial line wrapping state in the web interface.  Set to @code{#t} to
initially wrap lines (the default), or to @code{#f} to initially not wrap
lines.

@item @code{http-auth} (default: @code{#f})
HTTP authentication type to use.  Set to @code{#f} to disable authentication
(the default).  Supported values are @code{"digest"} or @code{"basic"}.

@item @code{users} (default: @code{#f})
If HTTP authentication is enabled (see @code{http-auth}), access will be
restricted to the credentials provided here.  To configure users, use a list
of pairs, where the first element of the pair is the username, and the 2nd
element of the pair is the password.

@lisp
(tailon-configuration-file
  (http-auth "basic")
  (users     '(("user1" . "password1")
               ("user2" . "password2"))))
@end lisp

@end table
@end deftp


@subsubheading Darkstat Service
@cindex darkstat
Darkstat is a packet sniffer that captures network traffic, calculates
statistics about usage, and serves reports over HTTP.

@defvar {Scheme Variable} darkstat-service-type
This is the service type for the @uref{https://unix4lyfe.org/darkstat/,
darkstat} service, its value must be a @code{darkstat-configuration} record
as in this example:

@lisp
(service darkstat-service-type
         (darkstat-configuration
           (interface "eno1")))
@end lisp
@end defvar

@deftp {Data Type} darkstat-configuration
Data type representing the configuration of @command{darkstat}.

@table @asis
@item @code{package} (default: @code{darkstat})
The darkstat package to use.

@item @code{interface}
Capture traffic on the specified network interface.

@item @code{port} (default: @code{"667"})
Bind the web interface to the specified port.

@item @code{bind-address} (default: @code{"127.0.0.1"})
Bind the web interface to the specified address.

@item @code{base} (default: @code{"/"})
Specify the path of the base URL@.  This can be useful if @command{darkstat}
is accessed via a reverse proxy.

@end table
@end deftp

@subsubheading Prometheus Node Exporter Service

@cindex prometheus-node-exporter
The Prometheus ``node exporter'' makes hardware and operating system
statistics provided by the Linux kernel available for the Prometheus
monitoring system.  This service should be deployed on all physical nodes
and virtual machines, where monitoring these statistics is desirable.

@defvar {Scheme variable} prometheus-node-exporter-service-type
This is the service type for the
@uref{https://github.com/prometheus/node_exporter/,
prometheus-node-exporter} service, its value must be a
@code{prometheus-node-exporter-configuration}.

@lisp
(service prometheus-node-exporter-service-type)
@end lisp
@end defvar

@deftp {Data Type} prometheus-node-exporter-configuration
Data type representing the configuration of @command{node_exporter}.

@table @asis
@item @code{package} (default: @code{go-github-com-prometheus-node-exporter})
The prometheus-node-exporter package to use.

@item @code{web-listen-address} (default: @code{":9100"})
Bind the web interface to the specified address.

@item @code{textfile-directory} (default: @code{"/var/lib/prometheus/node-exporter"})
This directory can be used to export metrics specific to this machine.
Files containing metrics in the text format, with the filename ending in
@code{.prom} should be placed in this directory.

@item @code{extra-options} (default: @code{'()})
Extra options to pass to the Prometheus node exporter.

@end table
@end deftp

@subsubheading Zabbix server
@cindex zabbix zabbix-server
Zabbix provides monitoring metrics, among others network utilization, CPU
load and disk space consumption:

@itemize
@item High performance, high capacity (able to monitor hundreds of thousands of devices).
@item Auto-discovery of servers and network devices and interfaces.
@item Low-level discovery, allows to automatically start monitoring new items, file systems or network interfaces among others.
@item Distributed monitoring with centralized web administration.
@item Native high performance agents.
@item SLA, and ITIL KPI metrics on reporting.
@item High-level (business) view of monitored resources through user-defined visual console screens and dashboards.
@item Remote command execution through Zabbix proxies.
@end itemize

@c %start of fragment

Available @code{zabbix-server-configuration} fields are:

@deftypevr {@code{zabbix-server-configuration} parameter} package zabbix-server
The zabbix-server package.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string user
User who will run the Zabbix server.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} group group
Group who will run the Zabbix server.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string db-host
Database host name.

Defaults to @samp{"127.0.0.1"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string db-name
Database name.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string db-user
Database user.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string db-password
Database password.  Please, use @code{include-files} with
@code{DBPassword=SECRET} inside a specified file instead.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} number db-port
Database port.

Defaults to @samp{5432}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string log-type
Specifies where log messages are written to:

@itemize @bullet
@item
@code{system} - syslog.

@item
@code{file} - file specified with @code{log-file} parameter.

@item
@code{console} - standard output.

@end itemize

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string log-file
Log file name for @code{log-type} @code{file} parameter.

Defaults to @samp{"/var/log/zabbix/server.log"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string pid-file
Name of PID file.

Defaults to @samp{"/var/run/zabbix/zabbix_server.pid"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string ssl-ca-location
The location of certificate authority (CA) files for SSL server certificate
verification.

Defaults to @samp{"/etc/ssl/certs/ca-certificates.crt"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string ssl-cert-location
Location of SSL client certificates.

Defaults to @samp{"/etc/ssl/certs"}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} string extra-options
Extra options will be appended to Zabbix server configuration file.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-server-configuration} parameter} include-files include-files
You may include individual files or all files in a directory in the
configuration file.

Defaults to @samp{()}.

@end deftypevr

@c %end of fragment

@subsubheading Zabbix agent
@cindex zabbix zabbix-agent

Zabbix agent gathers information for Zabbix server.

@c %start of fragment

Available @code{zabbix-agent-configuration} fields are:

@deftypevr {@code{zabbix-agent-configuration} parameter} package zabbix-agent
The zabbix-agent package.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} string user
User who will run the Zabbix agent.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} group group
Group who will run the Zabbix agent.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} string hostname
Unique, case sensitive hostname which is required for active checks and must
match hostname as configured on the server.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} string log-type
Specifies where log messages are written to:

@itemize @bullet
@item
@code{system} - syslog.

@item
@code{file} - file specified with @code{log-file} parameter.

@item
@code{console} - standard output.

@end itemize

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} string log-file
Log file name for @code{log-type} @code{file} parameter.

Defaults to @samp{"/var/log/zabbix/agent.log"}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} string pid-file
Name of PID file.

Defaults to @samp{"/var/run/zabbix/zabbix_agent.pid"}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} list server
List of IP addresses, optionally in CIDR notation, or hostnames of Zabbix
servers and Zabbix proxies.  Incoming connections will be accepted only from
the hosts listed here.

Defaults to @samp{("127.0.0.1")}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} list server-active
List of IP:port (or hostname:port) pairs of Zabbix servers and Zabbix
proxies for active checks.  If port is not specified, default port is used.
If this parameter is not specified, active checks are disabled.

Defaults to @samp{("127.0.0.1")}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} string extra-options
Extra options will be appended to Zabbix server configuration file.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-agent-configuration} parameter} include-files include-files
You may include individual files or all files in a directory in the
configuration file.

Defaults to @samp{()}.

@end deftypevr

@c %end of fragment

@subsubheading Zabbix front-end
@cindex zabbix zabbix-front-end

This service provides a WEB interface to Zabbix server.

@c %start of fragment

Available @code{zabbix-front-end-configuration} fields are:

@deftypevr {@code{zabbix-front-end-configuration} parameter} nginx-server-configuration-list nginx
NGINX configuration.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} string db-host
Database host name.

Defaults to @samp{"localhost"}.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} number db-port
Database port.

Defaults to @samp{5432}.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} string db-name
Database name.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} string db-user
Database user.

Defaults to @samp{"zabbix"}.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} string db-password
Database password.  Please, use @code{db-secret-file} instead.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} string db-secret-file
Secret file containing the credentials for the Zabbix front-end.  The value
must be a local file name, not a G-expression.  You are expected to create
this file manually.  Its contents will be copied into @file{zabbix.conf.php}
as the value of @code{$DB['PASSWORD']}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} string zabbix-host
Zabbix server hostname.

Defaults to @samp{"localhost"}.

@end deftypevr

@deftypevr {@code{zabbix-front-end-configuration} parameter} number zabbix-port
Zabbix server port.

Defaults to @samp{10051}.

@end deftypevr


@c %end of fragment

@node Kerberos服务
@subsection Kerberos服务
@cindex Kerberos

The @code{(gnu services kerberos)} module provides services relating to the
authentication protocol @dfn{Kerberos}.

@subsubheading Krb5 Service

Programs using a Kerberos client library normally expect a configuration
file in @file{/etc/krb5.conf}.  This service generates such a file from a
definition provided in the operating system declaration.  It does not cause
any daemon to be started.

No ``keytab'' files are provided by this service---you must explicitly
create them.  This service is known to work with the MIT client library,
@code{mit-krb5}.  Other implementations have not been tested.

@defvr {Scheme Variable} krb5-service-type
A service type for Kerberos 5 clients.
@end defvr

@noindent
Here is an example of its use:
@lisp
(service krb5-service-type
         (krb5-configuration
          (default-realm "EXAMPLE.COM")
          (allow-weak-crypto? #t)
          (realms (list
                   (krb5-realm
                    (name "EXAMPLE.COM")
                    (admin-server "groucho.example.com")
                    (kdc "karl.example.com"))
                   (krb5-realm
                    (name "ARGRX.EDU")
                    (admin-server "kerb-admin.argrx.edu")
                    (kdc "keys.argrx.edu"))))))
@end lisp

@noindent
This example provides a Kerberos@tie{}5 client configuration which:
@itemize
@item Recognizes two realms, @i{viz:} ``EXAMPLE.COM'' and ``ARGRX.EDU'', both
of which have distinct administration servers and key distribution centers;
@item Will default to the realm ``EXAMPLE.COM'' if the realm is not explicitly
specified by clients;
@item Accepts services which only support encryption types known to be weak.
@end itemize

The @code{krb5-realm} and @code{krb5-configuration} types have many fields.
Only the most commonly used ones are described here.  For a full list, and
more detailed explanation of each, see the MIT
@uref{https://web.mit.edu/kerberos/krb5-devel/doc/admin/conf_files/krb5_conf.html,,krb5.conf}
documentation.


@deftp {Data Type} krb5-realm
@cindex realm, kerberos
@table @asis
@item @code{名字}
This field is a string identifying the name of the realm.  A common
convention is to use the fully qualified DNS name of your organization,
converted to upper case.

@item @code{admin-server}
This field is a string identifying the host where the administration server
is running.

@item @code{kdc}
This field is a string identifying the key distribution center for the
realm.
@end table
@end deftp

@deftp {Data Type} krb5-configuration

@table @asis
@item @code{allow-weak-crypto?} (default: @code{#f})
If this flag is @code{#t} then services which only offer encryption
algorithms known to be weak will be accepted.

@item @code{default-realm} (default: @code{#f})
This field should be a string identifying the default Kerberos realm for the
client.  You should set this field to the name of your Kerberos realm.  If
this value is @code{#f} then a realm must be specified with every Kerberos
principal when invoking programs such as @command{kinit}.

@item @code{realms}
This should be a non-empty list of @code{krb5-realm} objects, which clients
may access.  Normally, one of them will have a @code{name} field matching
the @code{default-realm} field.
@end table
@end deftp


@subsubheading PAM krb5 Service
@cindex pam-krb5

The @code{pam-krb5} service allows for login authentication and password
management via Kerberos.  You will need this service if you want PAM enabled
applications to authenticate users using Kerberos.

@defvr {Scheme Variable} pam-krb5-service-type
A service type for the Kerberos 5 PAM module.
@end defvr

@deftp {Data Type} pam-krb5-configuration
Data type representing the configuration of the Kerberos 5 PAM module.  This
type has the following parameters:
@table @asis
@item @code{pam-krb5} (default: @code{pam-krb5})
The pam-krb5 package to use.

@item @code{minimum-uid} (default: @code{1000})
The smallest user ID for which Kerberos authentications should be
attempted.  Local accounts with lower values will silently fail to
authenticate.
@end table
@end deftp


@node LDAP Services
@subsection LDAP Services
@cindex LDAP
@cindex nslcd, LDAP service

The @code{(gnu services authentication)} module provides the
@code{nslcd-service-type}, which can be used to authenticate against an LDAP
server.  In addition to configuring the service itself, you may want to add
@code{ldap} as a name service to the Name Service Switch. @xref{Name Service Switch} for detailed information.

Here is a simple operating system declaration with a default configuration
of the @code{nslcd-service-type} and a Name Service Switch configuration
that consults the @code{ldap} name service last:

@lisp
(use-service-modules authentication)
(use-modules (gnu system nss))
...
(operating-system
  ...
  (services
    (cons*
      (service nslcd-service-type)
      (service dhcp-client-service-type)
      %base-services))
  (name-service-switch
   (let ((services (list (name-service (name "db"))
                         (name-service (name "files"))
                         (name-service (name "ldap")))))
     (name-service-switch
      (inherit %mdns-host-lookup-nss)
      (password services)
      (shadow   services)
      (group    services)
      (netgroup services)
      (gshadow  services)))))
@end lisp

@c %start of generated documentation for nslcd-configuration

Available @code{nslcd-configuration} fields are:

@deftypevr {@code{nslcd-configuration} parameter} package nss-pam-ldapd
The @code{nss-pam-ldapd} package to use.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number threads
The number of threads to start that can handle requests and perform LDAP
queries.  Each thread opens a separate connection to the LDAP server.  The
default is to start 5 threads.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} string uid
This specifies the user id with which the daemon should be run.

Defaults to @samp{"nslcd"}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} string gid
This specifies the group id with which the daemon should be run.

Defaults to @samp{"nslcd"}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} log-option log
This option controls the way logging is done via a list containing SCHEME
and LEVEL@.  The SCHEME argument may either be the symbols @samp{none} or
@samp{syslog}, or an absolute file name.  The LEVEL argument is optional and
specifies the log level.  The log level may be one of the following symbols:
@samp{crit}, @samp{error}, @samp{warning}, @samp{notice}, @samp{info} or
@samp{debug}.  All messages with the specified log level or higher are
logged.

Defaults to @samp{("/var/log/nslcd" info)}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list uri
The list of LDAP server URIs.  Normally, only the first server will be used
with the following servers as fall-back.

Defaults to @samp{("ldap://localhost:389/")}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string ldap-version
The version of the LDAP protocol to use.  The default is to use the maximum
version supported by the LDAP library.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string binddn
Specifies the distinguished name with which to bind to the directory server
for lookups.  The default is to bind anonymously.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string bindpw
Specifies the credentials with which to bind.  This option is only
applicable when used with binddn.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string rootpwmoddn
Specifies the distinguished name to use when the root user tries to modify a
user's password using the PAM module.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string rootpwmodpw
Specifies the credentials with which to bind if the root user tries to
change a user's password.  This option is only applicable when used with
rootpwmoddn

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-mech
Specifies the SASL mechanism to be used when performing SASL authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-realm
Specifies the SASL realm to be used when performing SASL authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-authcid
Specifies the authentication identity to be used when performing SASL
authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-authzid
Specifies the authorization identity to be used when performing SASL
authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean sasl-canonicalize?
Determines whether the LDAP server host name should be canonicalised.  If
this is enabled the LDAP library will do a reverse host name lookup.  By
default, it is left up to the LDAP library whether this check is performed
or not.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string krb5-ccname
Set the name for the GSS-API Kerberos credentials cache.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} string base
The directory search base.

Defaults to @samp{"dc=example,dc=com"}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} scope-option scope
Specifies the search scope (subtree, onelevel, base or children).  The
default scope is subtree; base scope is almost never useful for name service
lookups; children scope is not supported on all servers.

Defaults to @samp{(subtree)}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-deref-option deref
Specifies the policy for dereferencing aliases.  The default policy is to
never dereference aliases.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean referrals
Specifies whether automatic referral chasing should be enabled.  The default
behaviour is to chase referrals.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list-of-map-entries maps
This option allows for custom attributes to be looked up instead of the
default RFC 2307 attributes.  It is a list of maps, each consisting of the
name of a map, the RFC 2307 attribute to match and the query expression for
the attribute as it is available in the directory.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list-of-filter-entries filters
A list of filters consisting of the name of a map to which the filter
applies and an LDAP search filter expression.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number bind-timelimit
Specifies the time limit in seconds to use when connecting to the directory
server.  The default value is 10 seconds.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number timelimit
Specifies the time limit (in seconds) to wait for a response from the LDAP
server.  A value of zero, which is the default, is to wait indefinitely for
searches to be completed.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number idle-timelimit
Specifies the period if inactivity (in seconds) after which the con‐ nection
to the LDAP server will be closed.  The default is not to time out
connections.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number reconnect-sleeptime
Specifies the number of seconds to sleep when connecting to all LDAP servers
fails.  By default one second is waited between the first failure and the
first retry.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number reconnect-retrytime
Specifies the time after which the LDAP server is considered to be
permanently unavailable.  Once this time is reached retries will be done
only once per this time period.  The default value is 10 seconds.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-ssl-option ssl
Specifies whether to use SSL/TLS or not (the default is not to).  If
'start-tls is specified then StartTLS is used rather than raw LDAP over SSL.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-tls-reqcert-option tls-reqcert
Specifies what checks to perform on a server-supplied certificate.  The
meaning of the values is described in the ldap.conf(5) manual page.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-cacertdir
Specifies the directory containing X.509 certificates for peer authen‐
tication.  This parameter is ignored when using GnuTLS.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-cacertfile
Specifies the path to the X.509 certificate for peer authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-randfile
Specifies the path to an entropy source.  This parameter is ignored when
using GnuTLS.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-ciphers
Specifies the ciphers to use for TLS as a string.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-cert
Specifies the path to the file containing the local certificate for client
TLS authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-key
Specifies the path to the file containing the private key for client TLS
authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number pagesize
Set this to a number greater than 0 to request paged results from the LDAP
server in accordance with RFC2696.  The default (0) is to not request paged
results.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-ignore-users-option nss-initgroups-ignoreusers
This option prevents group membership lookups through LDAP for the specified
users.  Alternatively, the value 'all-local may be used.  With that value
nslcd builds a full list of non-LDAP users on startup.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number nss-min-uid
This option ensures that LDAP users with a numeric user id lower than the
specified value are ignored.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number nss-uid-offset
This option specifies an offset that is added to all LDAP numeric user ids.
This can be used to avoid user id collisions with local users.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number nss-gid-offset
This option specifies an offset that is added to all LDAP numeric group
ids.  This can be used to avoid user id collisions with local groups.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean nss-nested-groups
If this option is set, the member attribute of a group may point to another
group.  Members of nested groups are also returned in the higher level group
and parent groups are returned when finding groups for a specific user.  The
default is not to perform extra searches for nested groups.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean nss-getgrent-skipmembers
If this option is set, the group member list is not retrieved when looking
up groups.  Lookups for finding which groups a user belongs to will remain
functional so the user will likely still get the correct groups assigned on
login.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean nss-disable-enumeration
If this option is set, functions which cause all user/group entries to be
loaded from the directory will not succeed in doing so.  This can
dramatically reduce LDAP server load in situations where there are a great
number of users and/or groups.  This option is not recommended for most
configurations.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string validnames
This option can be used to specify how user and group names are verified
within the system.  This pattern is used to check all user and group names
that are requested and returned from LDAP.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean ignorecase
This specifies whether or not to perform searches using case-insensitive
matching.  Enabling this could open up the system to authorization bypass
vulnerabilities and introduce nscd cache poisoning vulnerabilities which
allow denial of service.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean pam-authc-ppolicy
This option specifies whether password policy controls are requested and
handled from the LDAP server when performing user authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string pam-authc-search
By default nslcd performs an LDAP search with the user's credentials after
BIND (authentication) to ensure that the BIND operation was successful.  The
default search is a simple check to see if the user's DN exists.  A search
filter can be specified that will be used instead.  It should return at
least one entry.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string pam-authz-search
This option allows flexible fine tuning of the authorisation check that
should be performed.  The search filter specified is executed and if any
entries match, access is granted, otherwise access is denied.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string pam-password-prohibit-message
If this option is set password modification using pam_ldap will be denied
and the specified message will be presented to the user instead.  The
message can be used to direct the user to an alternative means of changing
their password.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list pam-services
List of pam service names for which LDAP authentication should suffice.

Defaults to @samp{()}.

@end deftypevr

@c %end of generated documentation for nslcd-configuration


@node Web服务
@subsection Web服务

@cindex web
@cindex www
@cindex HTTP
The @code{(gnu services web)} module provides the Apache HTTP Server, the
nginx web server, and also a fastcgi wrapper daemon.

@subsubheading Apache HTTP Server

@deffn {Scheme Variable} httpd-service-type
Service type for the @uref{https://httpd.apache.org/,Apache HTTP} server
(@dfn{httpd}).  The value for this service type is a
@code{httpd-configuration} record.

A simple example configuration is given below.

@lisp
(service httpd-service-type
         (httpd-configuration
           (config
             (httpd-config-file
               (server-name "www.example.com")
               (document-root "/srv/http/www.example.com")))))
@end lisp

Other services can also extend the @code{httpd-service-type} to add to the
configuration.

@lisp
(simple-service 'www.example.com-server httpd-service-type
                (list
                  (httpd-virtualhost
                    "*:80"
                    (list (string-join '("ServerName www.example.com"
                                          "DocumentRoot /srv/http/www.example.com")
                                       "\n")))))
@end lisp
@end deffn

The details for the @code{httpd-configuration}, @code{httpd-module},
@code{httpd-config-file} and @code{httpd-virtualhost} record types are given
below.

@deffn {Data Type} httpd-configuration
This data type represents the configuration for the httpd service.

@table @asis
@item @code{package} (default: @code{httpd})
The httpd package to use.

@item @code{pid-file} (default: @code{"/var/run/httpd"})
The pid file used by the shepherd-service.

@item @code{config} (default: @code{(httpd-config-file)})
The configuration file to use with the httpd service.  The default value is
a @code{httpd-config-file} record, but this can also be a different
G-expression that generates a file, for example a @code{plain-file}.  A file
outside of the store can also be specified through a string.

@end table
@end deffn

@deffn {Data Type} httpd-module
This data type represents a module for the httpd service.

@table @asis
@item @code{名字}
The name of the module.

@item @code{file}
The file for the module.  This can be relative to the httpd package being
used, the absolute location of a file, or a G-expression for a file within
the store, for example @code{(file-append mod-wsgi "/modules/mod_wsgi.so")}.

@end table
@end deffn

@defvr {Scheme Variable} %default-httpd-modules
A default list of @code{httpd-module} objects.
@end defvr

@deffn {Data Type} httpd-config-file
This data type represents a configuration file for the httpd service.

@table @asis
@item @code{modules} (default: @code{%default-httpd-modules})
The modules to load.  Additional modules can be added here, or loaded by
additional configuration.

For example, in order to handle requests for PHP files, you can use Apache’s
@code{mod_proxy_fcgi} module along with @code{php-fpm-service-type}:

@lisp
(service httpd-service-type
         (httpd-configuration
          (config
           (httpd-config-file
            (modules (cons*
                      (httpd-module
                       (name "proxy_module")
                       (file "modules/mod_proxy.so"))
                      (httpd-module
                       (name "proxy_fcgi_module")
                       (file "modules/mod_proxy_fcgi.so"))
                      %default-httpd-modules))
            (extra-config (list "\
<FilesMatch \\.php$>
    SetHandler \"proxy:unix:/var/run/php-fpm.sock|fcgi://localhost/\"
</FilesMatch>"))))))
(service php-fpm-service-type
         (php-fpm-configuration
          (socket "/var/run/php-fpm.sock")
          (socket-group "httpd")))
@end lisp

@item @code{server-root} (default: @code{httpd})
The @code{ServerRoot} in the configuration file, defaults to the httpd
package.  Directives including @code{Include} and @code{LoadModule} are
taken as relative to the server root.

@item @code{server-name} (default: @code{#f})
The @code{ServerName} in the configuration file, used to specify the request
scheme, hostname and port that the server uses to identify itself.

This doesn't need to be set in the server config, and can be specified in
virtual hosts.  The default is @code{#f} to not specify a @code{ServerName}.

@item @code{document-root} (default: @code{"/srv/http"})
The @code{DocumentRoot} from which files will be served.

@item @code{listen} (default: @code{'("80")})
The list of values for the @code{Listen} directives in the config file.  The
value should be a list of strings, when each string can specify the port
number to listen on, and optionally the IP address and protocol to use.

@item @code{pid-file} (default: @code{"/var/run/httpd"})
The @code{PidFile} to use.  This should match the @code{pid-file} set in the
@code{httpd-configuration} so that the Shepherd service is configured
correctly.

@item @code{error-log} (default: @code{"/var/log/httpd/error_log"})
The @code{ErrorLog} to which the server will log errors.

@item @code{user} (default: @code{"httpd"})
The @code{User} which the server will answer requests as.

@item @code{group} (default: @code{"httpd"})
The @code{Group} which the server will answer requests as.

@item @code{extra-config} (default: @code{(list "TypesConfig etc/httpd/mime.types")})
A flat list of strings and G-expressions which will be added to the end of
the configuration file.

Any values which the service is extended with will be appended to this list.

@end table
@end deffn

@deffn {Data Type} httpd-virtualhost
This data type represents a virtualhost configuration block for the httpd
service.

These should be added to the extra-config for the httpd-service.

@lisp
(simple-service 'www.example.com-server httpd-service-type
                (list
                  (httpd-virtualhost
                    "*:80"
                    (list (string-join '("ServerName www.example.com"
                                          "DocumentRoot /srv/http/www.example.com")
                                       "\n")))))
@end lisp

@table @asis
@item @code{addresses-and-ports}
The addresses and ports for the @code{VirtualHost} directive.

@item @code{contents}
The contents of the @code{VirtualHost} directive, this should be a list of
strings and G-expressions.

@end table
@end deffn

@subsubheading NGINX

@deffn {Scheme Variable} nginx-service-type
Service type for the @uref{https://nginx.org/,NGinx} web server.  The value
for this service type is a @code{<nginx-configuration>} record.

A simple example configuration is given below.

@lisp
(service nginx-service-type
         (nginx-configuration
           (server-blocks
             (list (nginx-server-configuration
                     (server-name '("www.example.com"))
                     (root "/srv/http/www.example.com"))))))
@end lisp

In addition to adding server blocks to the service configuration directly,
this service can be extended by other services to add server blocks, as in
this example:

@lisp
(simple-service 'my-extra-server nginx-service-type
                (list (nginx-server-configuration
                        (root "/srv/http/extra-website")
                        (try-files (list "$uri" "$uri/index.html")))))
@end lisp
@end deffn

At startup, @command{nginx} has not yet read its configuration file, so it
uses a default file to log error messages.  If it fails to load its
configuration file, that is where error messages are logged.  After the
configuration file is loaded, the default error log file changes as per
configuration.  In our case, startup error messages can be found in
@file{/var/run/nginx/logs/error.log}, and after configuration in
@file{/var/log/nginx/error.log}.  The second location can be changed with
the @var{log-directory} configuration option.

@deffn {Data Type} nginx-configuration
This data type represents the configuration for NGinx.  Some configuration
can be done through this and the other provided record types, or
alternatively, a config file can be provided.

@table @asis
@item @code{nginx} (default: @code{nginx})
The nginx package to use.

@item @code{log-directory} (default: @code{"/var/log/nginx"})
The directory to which NGinx will write log files.

@item @code{run-directory} (default: @code{"/var/run/nginx"})
The directory in which NGinx will create a pid file, and write temporary
files.

@item @code{server-blocks} (default: @code{'()})
A list of @dfn{server blocks} to create in the generated configuration file,
the elements should be of type @code{<nginx-server-configuration>}.

The following example would setup NGinx to serve @code{www.example.com} from
the @code{/srv/http/www.example.com} directory, without using HTTPS.
@lisp
(service nginx-service-type
         (nginx-configuration
           (server-blocks
             (list (nginx-server-configuration
                     (server-name '("www.example.com"))
                     (root "/srv/http/www.example.com"))))))
@end lisp

@item @code{upstream-blocks} (default: @code{'()})
A list of @dfn{upstream blocks} to create in the generated configuration
file, the elements should be of type @code{<nginx-upstream-configuration>}.

Configuring upstreams through the @code{upstream-blocks} can be useful when
combined with @code{locations} in the @code{<nginx-server-configuration>}
records.  The following example creates a server configuration with one
location configuration, that will proxy requests to a upstream
configuration, which will handle requests with two servers.

@lisp
(service
  nginx-service-type
  (nginx-configuration
    (server-blocks
      (list (nginx-server-configuration
              (server-name '("www.example.com"))
              (root "/srv/http/www.example.com")
              (locations
                (list
                  (nginx-location-configuration
                  (uri "/path1")
                  (body '("proxy_pass http://server-proxy;"))))))))
    (upstream-blocks
      (list (nginx-upstream-configuration
              (name "server-proxy")
              (servers (list "server1.example.com"
                             "server2.example.com")))))))
@end lisp

@item @code{file} (default: @code{#f})
If a configuration @var{file} is provided, this will be used, rather than
generating a configuration file from the provided @code{log-directory},
@code{run-directory}, @code{server-blocks} and @code{upstream-blocks}.  For
proper operation, these arguments should match what is in @var{file} to
ensure that the directories are created when the service is activated.

This can be useful if you have an existing configuration file, or it's not
possible to do what is required through the other parts of the
nginx-configuration record.

@item @code{server-names-hash-bucket-size} (default: @code{#f})
Bucket size for the server names hash tables, defaults to @code{#f} to use
the size of the processors cache line.

@item @code{server-names-hash-bucket-max-size} (default: @code{#f})
Maximum bucket size for the server names hash tables.

@item @code{modules} (default: @code{'()})
List of nginx dynamic modules to load.  This should be a list of file names
of loadable modules, as in this example:

@lisp
(modules
 (list
  (file-append nginx-accept-language-module "\
/etc/nginx/modules/ngx_http_accept_language_module.so")
  (file-append nginx-lua-module "\
/etc/nginx/modules/ngx_http_lua_module.so")))
@end lisp

@item @code{lua-package-path} (default: @code{'()})
List of nginx lua packages to load.  This should be a list of package names
of loadable lua modules, as in this example:

@lisp
(lua-package-path (list lua-resty-core
                        lua-resty-lrucache
                        lua-resty-signal
                        lua-tablepool
                        lua-resty-shell))
@end lisp

@item @code{lua-package-cpath} (default: @code{'()})
List of nginx lua C packages to load.  This should be a list of package
names of loadable lua C modules, as in this example:

@lisp
(lua-package-cpath (list lua-resty-signal))
@end lisp

@item @code{global-directives} (default: @code{'((events . ()))})
Association list of global directives for the top level of the nginx
configuration.  Values may themselves be association lists.

@lisp
(global-directives
 `((worker_processes . 16)
   (pcre_jit . on)
   (events . ((worker_connections . 1024)))))
@end lisp

@item @code{extra-content} (default: @code{""})
Extra content for the @code{http} block.  Should be string or a string
valued G-expression.

@end table
@end deffn

@deftp {Data Type} nginx-server-configuration
Data type representing the configuration of an nginx server block.  This
type has the following parameters:

@table @asis
@item @code{listen} (default: @code{'("80" "443 ssl")})
Each @code{listen} directive sets the address and port for IP, or the path
for a UNIX-domain socket on which the server will accept requests.  Both
address and port, or only address or only port can be specified.  An address
may also be a hostname, for example:

@lisp
'("127.0.0.1:8000" "127.0.0.1" "8000" "*:8000" "localhost:8000")
@end lisp

@item @code{server-name} (default: @code{(list 'default)})
A list of server names this server represents. @code{'default} represents
the default server for connections matching no other server.

@item @code{root} (default: @code{"/srv/http"})
Root of the website nginx will serve.

@item @code{locations} (default: @code{'()})
A list of @dfn{nginx-location-configuration} or
@dfn{nginx-named-location-configuration} records to use within this server
block.

@item @code{index} (default: @code{(list "index.html")})
Index files to look for when clients ask for a directory.  If it cannot be
found, Nginx will send the list of files in the directory.

@item @code{try-files} (default: @code{'()})
A list of files whose existence is checked in the specified order.
@code{nginx} will use the first file it finds to process the request.

@item @code{ssl-certificate} (default: @code{#f})
Where to find the certificate for secure connections.  Set it to @code{#f}
if you don't have a certificate or you don't want to use HTTPS.

@item @code{ssl-certificate-key} (default: @code{#f})
Where to find the private key for secure connections.  Set it to @code{#f}
if you don't have a key or you don't want to use HTTPS.

@item @code{server-tokens?} (default: @code{#f})
Whether the server should add its configuration to response.

@item @code{raw-content} (default: @code{'()})
A list of raw lines added to the server block.

@end table
@end deftp

@deftp {Data Type} nginx-upstream-configuration
Data type representing the configuration of an nginx @code{upstream} block.
This type has the following parameters:

@table @asis
@item @code{名字}
Name for this group of servers.

@item @code{servers}
Specify the addresses of the servers in the group.  The address can be
specified as a IP address (e.g.@: @samp{127.0.0.1}), domain name (e.g.@:
@samp{backend1.example.com}) or a path to a UNIX socket using the prefix
@samp{unix:}.  For addresses using an IP address or domain name, the default
port is 80, and a different port can be specified explicitly.

@end table
@end deftp

@deftp {Data Type} nginx-location-configuration
Data type representing the configuration of an nginx @code{location} block.
This type has the following parameters:

@table @asis
@item @code{uri}
URI which this location block matches.

@anchor{nginx-location-configuration body}
@item @code{body}
Body of the location block, specified as a list of strings.  This can
contain many configuration directives.  For example, to pass requests to a
upstream server group defined using an @code{nginx-upstream-configuration}
block, the following directive would be specified in the body @samp{(list
"proxy_pass http://upstream-name;")}.

@end table
@end deftp

@deftp {Data Type} nginx-named-location-configuration
Data type representing the configuration of an nginx named location block.
Named location blocks are used for request redirection, and not used for
regular request processing.  This type has the following parameters:

@table @asis
@item @code{名字}
Name to identify this location block.

@item @code{body}
@xref{nginx-location-configuration body}, as the body for named location
blocks can be used in a similar way to the
@code{nginx-location-configuration body}.  One restriction is that the body
of a named location block cannot contain location blocks.

@end table
@end deftp

@subsubheading Varnish Cache
@cindex Varnish
Varnish is a fast cache server that sits in between web applications and end
users.  It proxies requests from clients and caches the accessed URLs such
that multiple requests for the same resource only creates one request to the
back-end.

@defvr {Scheme Variable} varnish-service-type
Service type for the Varnish daemon.
@end defvr

@deftp {Data Type} varnish-configuration
Data type representing the @code{varnish} service configuration.  This type
has the following parameters:

@table @asis
@item @code{package} (default: @code{varnish})
The Varnish package to use.

@item @code{name} (default: @code{"default"})
A name for this Varnish instance.  Varnish will create a directory in
@file{/var/varnish/} with this name and keep temporary files there.  If the
name starts with a forward slash, it is interpreted as an absolute directory
name.

Pass the @code{-n} argument to other Varnish programs to connect to the
named instance, e.g.@: @command{varnishncsa -n default}.

@item @code{backend} (default: @code{"localhost:8080"})
The backend to use.  This option has no effect if @code{vcl} is set.

@item @code{vcl} (default: #f)
The @dfn{VCL} (Varnish Configuration Language) program to run.  If this is
@code{#f}, Varnish will proxy @code{backend} using the default
configuration.  Otherwise this must be a file-like object with valid VCL
syntax.

@c Varnish does not support HTTPS, so keep this URL to avoid confusion.
For example, to mirror @url{https://www.gnu.org,www.gnu.org} with VCL you
can do something along these lines:

@lisp
(define %gnu-mirror
  (plain-file "gnu.vcl"
              "vcl 4.1;
backend gnu @{ .host = \"www.gnu.org\"; @}"))

(operating-system
  ;; @dots{}
  (services (cons (service varnish-service-type
                           (varnish-configuration
                            (listen '(":80"))
                            (vcl %gnu-mirror)))
                  %base-services)))
@end lisp

The configuration of an already running Varnish instance can be inspected
and changed using the @command{varnishadm} program.

Consult the @url{https://varnish-cache.org/docs/,Varnish User Guide} and
@url{https://book.varnish-software.com/4.0/,Varnish Book} for comprehensive
documentation on Varnish and its configuration language.

@item @code{listen} (default: @code{'("localhost:80")})
List of addresses Varnish will listen on.

@item @code{storage} (default: @code{'("malloc,128m")})
List of storage backends that will be available in VCL.

@item @code{parameters} (default: @code{'()})
List of run-time parameters in the form @code{'(("parameter" . "value"))}.

@item @code{extra-options} (default: @code{'()})
Additional arguments to pass to the @command{varnishd} process.

@end table
@end deftp

@subsubheading Patchwork
@cindex Patchwork
Patchwork is a patch tracking system.  It can collect patches sent to a
mailing list, and display them in a web interface.

@defvr {Scheme Variable} patchwork-service-type
Service type for Patchwork.
@end defvr

The following example is an example of a minimal service for Patchwork, for
the @code{patchwork.example.com} domain.

@lisp
(service patchwork-service-type
         (patchwork-configuration
          (domain "patchwork.example.com")
          (settings-module
           (patchwork-settings-module
            (allowed-hosts (list domain))
            (default-from-email "patchwork@@patchwork.example.com")))
          (getmail-retriever-config
           (getmail-retriever-configuration
            (type "SimpleIMAPSSLRetriever")
            (server "imap.example.com")
            (port 993)
            (username "patchwork")
            (password-command
             (list (file-append coreutils "/bin/cat")
                   "/etc/getmail-patchwork-imap-password"))
            (extra-parameters
            '((mailboxes . ("Patches"))))))))

@end lisp

There are three records for configuring the Patchwork service.  The
@code{<patchwork-configuration>} relates to the configuration for Patchwork
within the HTTPD service.

The @code{settings-module} field within the @code{<patchwork-configuration>}
record can be populated with the @code{<patchwork-settings-module>} record,
which describes a settings module that is generated within the Guix store.

For the @code{database-configuration} field within the
@code{<patchwork-settings-module>}, the
@code{<patchwork-database-configuration>} must be used.

@deftp {Data Type} patchwork-configuration
Data type representing the Patchwork service configuration.  This type has
the following parameters:

@table @asis
@item @code{patchwork} (default: @code{patchwork})
The Patchwork package to use.

@item @code{domain}
The domain to use for Patchwork, this is used in the HTTPD service virtual
host.

@item @code{settings-module}
The settings module to use for Patchwork.  As a Django application,
Patchwork is configured with a Python module containing the settings.  This
can either be an instance of the @code{<patchwork-settings-module>} record,
any other record that represents the settings in the store, or a directory
outside of the store.

@item @code{static-path}  (default: @code{"/static/"})
The path under which the HTTPD service should serve the static files.

@item @code{getmail-retriever-config}
The getmail-retriever-configuration record value to use with Patchwork.
Getmail will be configured with this value, the messages will be delivered
to Patchwork.

@end table
@end deftp

@deftp {Data Type} patchwork-settings-module
Data type representing a settings module for Patchwork.  Some of these
settings relate directly to Patchwork, but others relate to Django, the web
framework used by Patchwork, or the Django Rest Framework library.  This
type has the following parameters:

@table @asis
@item @code{database-configuration} (default: @code{(patchwork-database-configuration)})
The database connection settings used for Patchwork.  See the
@code{<patchwork-database-configuration>} record type for more information.

@item @code{secret-key-file} (default: @code{"/etc/patchwork/django-secret-key"})
Patchwork, as a Django web application uses a secret key for
cryptographically signing values.  This file should contain a unique
unpredictable value.

If this file does not exist, it will be created and populated with a random
value by the patchwork-setup shepherd service.

This setting relates to Django.

@item @code{allowed-hosts}
A list of valid hosts for this Patchwork service.  This should at least
include the domain specified in the @code{<patchwork-configuration>} record.

This is a Django setting.

@item @code{default-from-email}
The email address from which Patchwork should send email by default.

This is a Patchwork setting.

@item @code{static-url} (default: @code{#f})
The URL to use when serving static assets.  It can be part of a URL, or a
full URL, but must end in a @code{/}.

If the default value is used, the @code{static-path} value from the
@code{<patchwork-configuration>} record will be used.

This is a Django setting.

@item @code{admins} (default: @code{'()})
Email addresses to send the details of errors that occur.  Each value should
be a list containing two elements, the name and then the email address.

This is a Django setting.

@item @code{debug?} (default: @code{#f})
Whether to run Patchwork in debug mode.  If set to @code{#t}, detailed error
messages will be shown.

This is a Django setting.

@item @code{enable-rest-api?} (default: @code{#t})
Whether to enable the Patchwork REST API.

This is a Patchwork setting.

@item @code{enable-xmlrpc?} (default: @code{#t})
Whether to enable the XML RPC API.

This is a Patchwork setting.

@item @code{force-https-links?} (default: @code{#t})
Whether to use HTTPS links on Patchwork pages.

This is a Patchwork setting.

@item @code{extra-settings} (default: @code{""})
Extra code to place at the end of the Patchwork settings module.

@end table
@end deftp

@deftp {Data Type} patchwork-database-configuration
Data type representing the database configuration for Patchwork.

@table @asis
@item @code{engine} (default: @code{"django.db.backends.postgresql_psycopg2"})
The database engine to use.

@item @code{name} (default: @code{"patchwork"})
The name of the database to use.

@item @code{user} (default: @code{"httpd"})
The user to connect to the database as.

@item @code{password} (default: @code{""})
The password to use when connecting to the database.

@item @code{host} (default: @code{""})
The host to make the database connection to.

@item @code{port} (default: @code{""})
The port on which to connect to the database.

@end table
@end deftp

@subsubheading Mumi

@cindex Mumi, Debbugs Web interface
@cindex Debbugs, Mumi Web interface
@uref{https://git.elephly.net/gitweb.cgi?p=software/mumi.git, Mumi} is a Web
interface to the Debbugs bug tracker, by default for
@uref{https://bugs.gnu.org, the GNU instance}.  Mumi is a Web server, but it
also fetches and indexes mail retrieved from Debbugs.

@defvr {Scheme Variable} mumi-service-type
This is the service type for Mumi.
@end defvr

@deftp {Data Type} mumi-configuration
Data type representing the Mumi service configuration.  This type has the
following fields:

@table @asis
@item @code{mumi} (default: @code{mumi})
The Mumi package to use.

@item @code{mailer?} (default: @code{#true})
Whether to enable or disable the mailer component.

@item @code{mumi-configuration-sender}
The email address used as the sender for comments.

@item @code{mumi-configuration-smtp}
A URI to configure the SMTP settings for Mailutils.  This could be something
like @code{sendmail:///path/to/bin/msmtp} or any other URI supported by
Mailutils.  @xref{SMTP Mailboxes, SMTP Mailboxes,, mailutils,
GNU@tie{}Mailutils}.

@end table
@end deftp


@subsubheading FastCGI
@cindex fastcgi
@cindex fcgiwrap
FastCGI is an interface between the front-end and the back-end of a web
service.  It is a somewhat legacy facility; new web services should
generally just talk HTTP between the front-end and the back-end.  However
there are a number of back-end services such as PHP or the optimized HTTP
Git repository access that use FastCGI, so we have support for it in Guix.

To use FastCGI, you configure the front-end web server (e.g., nginx) to
dispatch some subset of its requests to the fastcgi backend, which listens
on a local TCP or UNIX socket.  There is an intermediary @code{fcgiwrap}
program that sits between the actual backend process and the web server.
The front-end indicates which backend program to run, passing that
information to the @code{fcgiwrap} process.

@defvr {Scheme Variable} fcgiwrap-service-type
A service type for the @code{fcgiwrap} FastCGI proxy.
@end defvr

@deftp {Data Type} fcgiwrap-configuration
Data type representing the configuration of the @code{fcgiwrap} service.
This type has the following parameters:
@table @asis
@item @code{package} (default: @code{fcgiwrap})
The fcgiwrap package to use.

@item @code{socket} (default: @code{tcp:127.0.0.1:9000})
The socket on which the @code{fcgiwrap} process should listen, as a string.
Valid @var{socket} values include @code{unix:@var{/path/to/unix/socket}},
@code{tcp:@var{dot.ted.qu.ad}:@var{port}} and
@code{tcp6:[@var{ipv6_addr}]:port}.

@item @code{user} (default: @code{fcgiwrap})
@itemx @code{group} (default: @code{fcgiwrap})
The user and group names, as strings, under which to run the @code{fcgiwrap}
process.  The @code{fastcgi} service will ensure that if the user asks for
the specific user or group names @code{fcgiwrap} that the corresponding user
and/or group is present on the system.

It is possible to configure a FastCGI-backed web service to pass HTTP
authentication information from the front-end to the back-end, and to allow
@code{fcgiwrap} to run the back-end process as a corresponding local user.
To enable this capability on the back-end, run @code{fcgiwrap} as the
@code{root} user and group.  Note that this capability also has to be
configured on the front-end as well.
@end table
@end deftp

@cindex php-fpm
PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI
implementation with some additional features useful for sites of any size.

These features include:
@itemize @bullet
@item Adaptive process spawning
@item Basic statistics (similar to Apache's mod_status)
@item Advanced process management with graceful stop/start
@item Ability to start workers with different uid/gid/chroot/environment
and different php.ini (replaces safe_mode)
@item Stdout & stderr logging
@item Emergency restart in case of accidental opcode cache destruction
@item Accelerated upload support
@item Support for a "slowlog"
@item Enhancements to FastCGI, such as fastcgi_finish_request() -
a special function to finish request & flush all data while continuing to do
something time-consuming (video converting, stats processing, etc.)
@end itemize
...@: and much more.

@defvr {Scheme Variable} php-fpm-service-type
A Service type for @code{php-fpm}.
@end defvr

@deftp {Data Type} php-fpm-configuration
Data Type for php-fpm service configuration.
@table @asis
@item @code{php} (default: @code{php})
The php package to use.
@item @code{socket} (default: @code{(string-append "/var/run/php" (version-major (package-version php)) "-fpm.sock")})
The address on which to accept FastCGI requests.  Valid syntaxes are:
@table @asis
@item @code{"ip.add.re.ss:port"}
Listen on a TCP socket to a specific address on a specific port.
@item @code{"port"}
Listen on a TCP socket to all addresses on a specific port.
@item @code{"/path/to/unix/socket"}
Listen on a unix socket.
@end table

@item @code{user} (default: @code{php-fpm})
User who will own the php worker processes.
@item @code{group} (default: @code{php-fpm})
Group of the worker processes.
@item @code{socket-user} (default: @code{php-fpm})
User who can speak to the php-fpm socket.
@item @code{socket-group} (default: @code{nginx})
Group that can speak to the php-fpm socket.
@item @code{pid-file} (default: @code{(string-append "/var/run/php" (version-major (package-version php)) "-fpm.pid")})
The process id of the php-fpm process is written to this file once the
service has started.
@item @code{log-file} (default: @code{(string-append "/var/log/php" (version-major (package-version php)) "-fpm.log")})
Log for the php-fpm master process.
@item @code{process-manager} (default: @code{(php-fpm-dynamic-process-manager-configuration)})
Detailed settings for the php-fpm process manager.  Must be one of:
@table @asis
@item @code{<php-fpm-dynamic-process-manager-configuration>}
@item @code{<php-fpm-static-process-manager-configuration>}
@item @code{<php-fpm-on-demand-process-manager-configuration>}
@end table
@item @code{display-errors} (default @code{#f})
Determines whether php errors and warning should be sent to clients and
displayed in their browsers.  This is useful for local php development, but
a security risk for public sites, as error messages can reveal passwords and
personal data.
@item @code{timezone} (default @code{#f})
Specifies @code{php_admin_value[date.timezone]} parameter.
@item @code{workers-logfile} (default @code{(string-append "/var/log/php" (version-major (package-version php)) "-fpm.www.log")})
This file will log the @code{stderr} outputs of php worker processes.  Can
be set to @code{#f} to disable logging.
@item @code{file} (default @code{#f})
An optional override of the whole configuration.  You can use the
@code{mixed-text-file} function or an absolute filepath for it.
@item @code{php-ini-file} (default @code{#f})
An optional override of the default php settings.  It may be any
``file-like'' object (@pxref{G-表达式, file-like objects}).  You can
use the @code{mixed-text-file} function or an absolute filepath for it.

For local development it is useful to set a higher timeout and memory limit
for spawned php processes.  This be accomplished with the following
operating system configuration snippet:
@lisp
(define %local-php-ini
  (plain-file "php.ini"
              "memory_limit = 2G
max_execution_time = 1800"))

(operating-system
  ;; @dots{}
  (services (cons (service php-fpm-service-type
                           (php-fpm-configuration
                            (php-ini-file %local-php-ini)))
                  %base-services)))
@end lisp

Consult the @url{https://www.php.net/manual/en/ini.core.php,core php.ini
directives} for comprehensive documentation on the acceptable @file{php.ini}
directives.
@end table
@end deftp

@deftp {Data type} php-fpm-dynamic-process-manager-configuration
Data Type for the @code{dynamic} php-fpm process manager.  With the
@code{dynamic} process manager, spare worker processes are kept around based
on it's configured limits.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@item @code{start-servers} (default: @code{2})
How many worker processes should be started on start-up.
@item @code{min-spare-servers} (default: @code{1})
How many spare worker processes should be kept around at minimum.
@item @code{max-spare-servers} (default: @code{3})
How many spare worker processes should be kept around at maximum.
@end table
@end deftp

@deftp {Data type} php-fpm-static-process-manager-configuration
Data Type for the @code{static} php-fpm process manager.  With the
@code{static} process manager, an unchanging number of worker processes are
created.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@end table
@end deftp

@deftp {Data type} php-fpm-on-demand-process-manager-configuration
Data Type for the @code{on-demand} php-fpm process manager.  With the
@code{on-demand} process manager, worker processes are only created as
requests arrive.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@item @code{process-idle-timeout} (default: @code{10})
The time in seconds after which a process with no requests is killed.
@end table
@end deftp


@deffn {Scheme Procedure} nginx-php-location @
       [#:nginx-package nginx] @ [socket (string-append "/var/run/php" @
(version-major (package-version php)) @ "-fpm.sock")] A helper function to
quickly add php to an @code{nginx-server-configuration}.
@end deffn

A simple services setup for nginx with php can look like this:
@lisp
(services (cons* (service dhcp-client-service-type)
                 (service php-fpm-service-type)
                 (service nginx-service-type
                          (nginx-server-configuration
                           (server-name '("example.com"))
                           (root "/srv/http/")
                           (locations
                            (list (nginx-php-location)))
                           (listen '("80"))
                           (ssl-certificate #f)
                           (ssl-certificate-key #f)))
                 %base-services))
@end lisp

@cindex cat-avatar-generator
The cat avatar generator is a simple service to demonstrate the use of
php-fpm in @code{Nginx}.  It is used to generate cat avatar from a seed, for
instance the hash of a user's email address.

@deffn {Scheme Procedure} cat-avatar-generator-service @
       [#:cache-dir "/var/cache/cat-avatar-generator"] @ [#:package
cat-avatar-generator] @ [#:configuration (nginx-server-configuration)]
Returns an nginx-server-configuration that inherits @code{configuration}.
It extends the nginx configuration to add a server block that serves
@code{package}, a version of cat-avatar-generator.  During execution,
cat-avatar-generator will be able to use @code{cache-dir} as its cache
directory.
@end deffn

A simple setup for cat-avatar-generator can look like this:
@lisp
(services (cons* (cat-avatar-generator-service
                  #:configuration
                  (nginx-server-configuration
                    (server-name '("example.com"))))
                 ...
                 %base-services))
@end lisp

@subsubheading Hpcguix-web

@cindex hpcguix-web
The @uref{https://github.com/UMCUGenetics/hpcguix-web/, hpcguix-web} program
is a customizable web interface to browse Guix packages, initially designed
for users of high-performance computing (HPC)  clusters.

@defvr {Scheme Variable} hpcguix-web-service-type
The service type for @code{hpcguix-web}.
@end defvr

@deftp {Data Type} hpcguix-web-configuration
Data type for the hpcguix-web service configuration.

@table @asis
@item @code{specs}
A gexp (@pxref{G-表达式}) specifying the hpcguix-web service
configuration.  The main items available in this spec are:

@table @asis
@item @code{title-prefix} (default: @code{"hpcguix | "})
The page title prefix.

@item @code{guix-command} (default: @code{"guix"})
The @command{guix} command.

@item @code{package-filter-proc} (default: @code{(const #t)})
A procedure specifying how to filter packages that are displayed.

@item @code{package-page-extension-proc} (default: @code{(const '())})
Extension package for @code{hpcguix-web}.

@item @code{menu} (default: @code{'()})
Additional entry in page @code{menu}.

@item @code{channels} (default: @code{%default-channels})
List of channels from which the package list is built (@pxref{通道}).

@item @code{package-list-expiration} (default: @code{(* 12 3600)})
The expiration time, in seconds, after which the package list is rebuilt
from the latest instances of the given channels.
@end table

See the hpcguix-web repository for a
@uref{https://github.com/UMCUGenetics/hpcguix-web/blob/master/hpcweb-configuration.scm,
complete example}.

@item @code{package} (default: @code{hpcguix-web})
The hpcguix-web package to use.
@end table
@end deftp

A typical hpcguix-web service declaration looks like this:

@lisp
(service hpcguix-web-service-type
         (hpcguix-web-configuration
          (specs
           #~(define site-config
               (hpcweb-configuration
                (title-prefix "Guix-HPC - ")
                (menu '(("/about" "ABOUT"))))))))
@end lisp

@quotation 注
The hpcguix-web service periodically updates the package list it publishes
by pulling channels from Git.  To that end, it needs to access X.509
certificates so that it can authenticate Git servers when communicating over
HTTPS, and it assumes that @file{/etc/ssl/certs} contains those
certificates.

Thus, make sure to add @code{nss-certs} or another certificate package to
the @code{packages} field of your configuration.  @ref{X.509证书},
for more information on X.509 certificates.
@end quotation

@subsubheading gmnisrv

@cindex gmnisrv
The @uref{https://git.sr.ht/~sircmpwn/gmnisrv, gmnisrv} program is a simple
@uref{https://gemini.circumlunar.space/, Gemini} protocol server.

@deffn {Scheme Variable} gmnisrv-service-type
This is the type of the gmnisrv service, whose value should be a
@code{gmnisrv-configuration} object, as in this example:

@lisp
(service gmnisrv-service-type
         (gmnisrv-configuration
           (config-file (local-file "./my-gmnisrv.ini"))))
@end lisp
@end deffn

@deftp {Data Type} gmnisrv-configuration
Data type representing the configuration of gmnisrv.

@table @asis
@item @code{package} (default: @var{gmnisrv})
Package object of the gmnisrv server.

@item @code{config-file} (default: @code{%default-gmnisrv-config-file})
File-like object of the gmnisrv configuration file to use.  The default
configuration listens on port 1965 and serves files from
@file{/srv/gemini}.  Certificates are stored in
@file{/var/lib/gemini/certs}.  For more information, run @command{man
gmnisrv} and @command{man gmnisrv.ini}.

@end table
@end deftp

@subsubheading Agate

@cindex agate
The @uref{gemini://qwertqwefsday.eu/agate.gmi, Agate}
(@uref{https://github.com/mbrubeck/agate, GitHub page over HTTPS})  program
is a simple @uref{https://gemini.circumlunar.space/, Gemini} protocol server
written in Rust.

@deffn {Scheme Variable} agate-service-type
This is the type of the agate service, whose value should be an
@code{agate-service-type} object, as in this example:

@lisp
(service agate-service-type
	 (agate-configuration
	   (content "/srv/gemini")
	   (cert "/srv/cert.pem")
	   (key "/srv/key.rsa")))
@end lisp

The example above represents the minimal tweaking necessary to get Agate up
and running.  Specifying the path to the certificate and key is always
necessary, as the Gemini protocol requires TLS by default.

To obtain a certificate and a key, you could, for example, use OpenSSL,
running a command similar to the following example:

@example
openssl req -x509 -newkey rsa:4096 -keyout key.rsa -out cert.pem \
    -days 3650 -nodes -subj "/CN=example.com"
@end example

Of course, you'll have to replace @i{example.com} with your own domain name,
and then point the Agate configuration towards the path of the generated key
and certificate.

@end deffn

@deftp {Data Type} agate-configuration
Data type representing the configuration of Agate.

@table @asis
@item @code{package} (default: @code{agate})
The package object of the Agate server.

@item @code{content} (default: @file{"/srv/gemini"})
The directory from which Agate will serve files.

@item @code{cert} (default: @code{#f})
The path to the TLS certificate PEM file to be used for encrypted
connections.  Must be filled in with a value from the user.

@item @code{key} (default: @code{#f})
The path to the PKCS8 private key file to be used for encrypted
connections.  Must be filled in with a value from the user.

@item @code{addr} (default: @code{'("0.0.0.0:1965" "[::]:1965")})
A list of the addresses to listen on.

@item @code{hostname} (default: @code{#f})
The domain name of this Gemini server.  Optional.

@item @code{lang} (default: @code{#f})
RFC 4646 language code(s) for text/gemini documents.  Optional.

@item @code{silent?} (default: @code{#f})
Set to @code{#t} to disable logging output.

@item @code{serve-secret?} (default: @code{#f})
Set to @code{#t} to serve secret files (files/directories starting with a
dot).

@item @code{log-ip?} (default: @code{#t})
Whether or not to output IP addresses when logging.

@item @code{user} (default: @code{"agate"})
Owner of the @code{agate} process.

@item @code{group} (default: @code{"agate"})
Owner's group of the @code{agate} process.

@item @code{log-file} (default: @file{"/var/log/agate.log"})
The file which should store the logging output of Agate.

@end table
@end deftp

@node 证书服务
@subsection 证书服务

@cindex Web
@cindex HTTP, HTTPS
@cindex Let's Encrypt
@cindex TLS certificates
The @code{(gnu services certbot)} module provides a service to automatically
obtain a valid TLS certificate from the Let's Encrypt certificate
authority.  These certificates can then be used to serve content securely
over HTTPS or other TLS-based protocols, with the knowledge that the client
will be able to verify the server's authenticity.

@url{https://letsencrypt.org/, Let's Encrypt} provides the @code{certbot}
tool to automate the certification process.  This tool first securely
generates a key on the server.  It then makes a request to the Let's Encrypt
certificate authority (CA) to sign the key.  The CA checks that the request
originates from the host in question by using a challenge-response protocol,
requiring the server to provide its response over HTTP@.  If that protocol
completes successfully, the CA signs the key, resulting in a certificate.
That certificate is valid for a limited period of time, and therefore to
continue to provide TLS services, the server needs to periodically ask the
CA to renew its signature.

The certbot service automates this process: the initial key generation, the
initial certification request to the Let's Encrypt service, the web server
challenge/response integration, writing the certificate to disk, the
automated periodic renewals, and the deployment tasks associated with the
renewal (e.g.@: reloading services, copying keys with different
permissions).

Certbot is run twice a day, at a random minute within the hour.  It won't do
anything until your certificates are due for renewal or revoked, but running
it regularly would give your service a chance of staying online in case a
Let's Encrypt-initiated revocation happened for some reason.

By using this service, you agree to the ACME Subscriber Agreement, which can
be found there: @url{https://acme-v01.api.letsencrypt.org/directory}.

@defvr {Scheme Variable} certbot-service-type
A service type for the @code{certbot} Let's Encrypt client.  Its value must
be a @code{certbot-configuration} record as in this example:

@lisp
(define %nginx-deploy-hook
  (program-file
   "nginx-deploy-hook"
   #~(let ((pid (call-with-input-file "/var/run/nginx/pid" read)))
       (kill pid SIGHUP))))

(service certbot-service-type
         (certbot-configuration
          (email "foo@@example.net")
          (certificates
           (list
            (certificate-configuration
             (domains '("example.net" "www.example.net"))
             (deploy-hook %nginx-deploy-hook))
            (certificate-configuration
             (domains '("bar.example.net")))))))
@end lisp

See below for details about @code{certbot-configuration}.
@end defvr

@deftp {Data Type} certbot-configuration
Data type representing the configuration of the @code{certbot} service.
This type has the following parameters:

@table @asis
@item @code{package} (default: @code{certbot})
The certbot package to use.

@item @code{webroot} (default: @code{/var/www})
The directory from which to serve the Let's Encrypt challenge/response
files.

@item @code{certificates} (default: @code{()})
A list of @code{certificates-configuration}s for which to generate
certificates and request signatures.  Each certificate has a @code{name} and
several @code{domains}.

@item @code{email} (default: @code{#f})
Optional email address used for registration and recovery contact.  Setting
this is encouraged as it allows you to receive important notifications about
the account and issued certificates.

@item @code{server} (default: @code{#f})
Optional URL of ACME server.  Setting this overrides certbot's default,
which is the Let's Encrypt server.

@item @code{rsa-key-size} (default: @code{2048})
Size of the RSA key.

@item @code{default-location} (default: @i{see below})
The default @code{nginx-location-configuration}.  Because @code{certbot}
needs to be able to serve challenges and responses, it needs to be able to
run a web server.  It does so by extending the @code{nginx} web service with
an @code{nginx-server-configuration} listening on the @var{domains} on port
80, and which has a @code{nginx-location-configuration} for the
@code{/.well-known/} URI path subspace used by Let's Encrypt.  @xref{Web服务}, for more on these nginx configuration data types.

Requests to other URL paths will be matched by the @code{default-location},
which if present is added to all @code{nginx-server-configuration}s.

By default, the @code{default-location} will issue a redirect from
@code{http://@var{domain}/...} to @code{https://@var{domain}/...}, leaving
you to define what to serve on your site via @code{https}.

Pass @code{#f} to not issue a default location.
@end table
@end deftp

@deftp {Data Type} certificate-configuration
Data type representing the configuration of a certificate.  This type has
the following parameters:

@table @asis
@item @code{name} (default: @i{see below})
This name is used by Certbot for housekeeping and in file paths; it doesn't
affect the content of the certificate itself.  To see certificate names, run
@code{certbot certificates}.

Its default is the first provided domain.

@item @code{domains} (default: @code{()})
The first domain provided will be the subject CN of the certificate, and all
domains will be Subject Alternative Names on the certificate.

@item @code{challenge}（默认值：@code{#f}）
The challenge type that has to be run by certbot.  If @code{#f} is
specified, default to the HTTP challenge.  If a value is specified, defaults
to the manual plugin (see @code{authentication-hook}, @code{cleanup-hook}
and the documentation at
@url{https://certbot.eff.org/docs/using.html#hooks}), and gives Let's
Encrypt permission to log the public IP address of the requesting machine.

@item @code{authentication-hook}（默认值：@code{#f}）
Command to be run in a shell once for each certificate challenge to be
answered.  For this command, the shell variable @code{$CERTBOT_DOMAIN} will
contain the domain being authenticated, @code{$CERTBOT_VALIDATION} contains
the validation string and @code{$CERTBOT_TOKEN} contains the file name of
the resource requested when performing an HTTP-01 challenge.

@item @code{cleanup-hook}（默认值：@code{#f}）
Command to be run in a shell once for each certificate challenge that have
been answered by the @code{auth-hook}.  For this command, the shell
variables available in the @code{auth-hook} script are still available, and
additionally @code{$CERTBOT_AUTH_OUTPUT} will contain the standard output of
the @code{auth-hook} script.

@item @code{deploy-hook} (default: @code{#f})
Command to be run in a shell once for each successfully issued certificate.
For this command, the shell variable @code{$RENEWED_LINEAGE} will point to
the config live subdirectory (for example,
@samp{"/etc/letsencrypt/live/example.com"}) containing the new certificates
and keys; the shell variable @code{$RENEWED_DOMAINS} will contain a
space-delimited list of renewed certificate domains (for example,
@samp{"example.com www.example.com"}.

@end table
@end deftp

For each @code{certificate-configuration}, the certificate is saved to
@code{/etc/letsencrypt/live/@var{name}/fullchain.pem} and the key is saved
to @code{/etc/letsencrypt/live/@var{name}/privkey.pem}.
@node DNS服务
@subsection DNS服务
@cindex DNS (domain name system)
@cindex domain name system (DNS)

The @code{(gnu services dns)} module provides services related to the
@dfn{domain name system} (DNS).  It provides a server service for hosting an
@emph{authoritative} DNS server for multiple zones, slave or master.  This
service uses @uref{https://www.knot-dns.cz/, Knot DNS}.  And also a caching
and forwarding DNS server for the LAN, which uses
@uref{http://www.thekelleys.org.uk/dnsmasq/doc.html, dnsmasq}.

@subsubheading Knot Service

An example configuration of an authoritative server for two zones, one
master and one slave, is:

@lisp
(define-zone-entries example.org.zone
;; Name TTL Class Type Data
  ("@@"  ""  "IN"  "A"  "127.0.0.1")
  ("@@"  ""  "IN"  "NS" "ns")
  ("ns" ""  "IN"  "A"  "127.0.0.1"))

(define master-zone
  (knot-zone-configuration
    (domain "example.org")
    (zone (zone-file
            (origin "example.org")
            (entries example.org.zone)))))

(define slave-zone
  (knot-zone-configuration
    (domain "plop.org")
    (dnssec-policy "default")
    (master (list "plop-master"))))

(define plop-master
  (knot-remote-configuration
    (id "plop-master")
    (address (list "208.76.58.171"))))

(operating-system
  ;; ...
  (services (cons* (service knot-service-type
                     (knot-configuration
                       (remotes (list plop-master))
                       (zones (list master-zone slave-zone))))
                   ;; ...
                   %base-services)))
@end lisp

@deffn {Scheme Variable} knot-service-type
This is the type for the Knot DNS server.

Knot DNS is an authoritative DNS server, meaning that it can serve multiple
zones, that is to say domain names you would buy from a registrar.  This
server is not a resolver, meaning that it can only resolve names for which
it is authoritative.  This server can be configured to serve zones as a
master server or a slave server as a per-zone basis.  Slave zones will get
their data from masters, and will serve it as an authoritative server.  From
the point of view of a resolver, there is no difference between master and
slave.

The following data types are used to configure the Knot DNS server:
@end deffn

@deftp {Data Type} knot-key-configuration
Data type representing a key.  This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this key.  IDs must
be unique and must not be empty.

@item @code{algorithm} (default: @code{#f})
The algorithm to use.  Choose between @code{#f}, @code{'hmac-md5},
@code{'hmac-sha1}, @code{'hmac-sha224}, @code{'hmac-sha256},
@code{'hmac-sha384} and @code{'hmac-sha512}.

@item @code{secret} (default: @code{""})
The secret key itself.

@end table
@end deftp

@deftp {Data Type} knot-acl-configuration
Data type representing an Access Control List (ACL) configuration.  This
type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this key.  IDs must
be unique and must not be empty.

@item @code{address} (default: @code{'()})
An ordered list of IP addresses, network subnets, or network ranges
represented with strings.  The query must match one of them.  Empty value
means that address match is not required.

@item @code{key} (default: @code{'()})
An ordered list of references to keys represented with strings.  The string
must match a key ID defined in a @code{knot-key-configuration}.  No key
means that a key is not require to match that ACL.

@item @code{action} (default: @code{'()})
An ordered list of actions that are permitted or forbidden by this ACL@.
Possible values are lists of zero or more elements from @code{'transfer},
@code{'notify} and @code{'update}.

@item @code{deny?} (default: @code{#f})
When true, the ACL defines restrictions.  Listed actions are forbidden.
When false, listed actions are allowed.

@end table
@end deftp

@deftp {Data Type} zone-entry
Data type representing a record entry in a zone file.  This type has the
following parameters:

@table @asis
@item @code{name} (default: @code{"@@"})
The name of the record.  @code{"@@"} refers to the origin of the zone.
Names are relative to the origin of the zone.  For example, in the
@code{example.org} zone, @code{"ns.example.org"} actually refers to
@code{ns.example.org.example.org}.  Names ending with a dot are absolute,
which means that @code{"ns.example.org."} refers to @code{ns.example.org}.

@item @code{ttl} (default: @code{""})
The Time-To-Live (TTL) of this record.  If not set, the default TTL is used.

@item @code{class} (default: @code{"IN"})
The class of the record.  Knot currently supports only @code{"IN"} and
partially @code{"CH"}.

@item @code{type} (default: @code{"A"})
The type of the record.  Common types include A (IPv4 address), AAAA (IPv6
address), NS (Name Server) and MX (Mail eXchange).  Many other types are
defined.

@item @code{data} (default: @code{""})
The data contained in the record.  For instance an IP address associated
with an A record, or a domain name associated with an NS record.  Remember
that domain names are relative to the origin unless they end with a dot.

@end table
@end deftp

@deftp {Data Type} zone-file
Data type representing the content of a zone file.  This type has the
following parameters:

@table @asis
@item @code{entries} (default: @code{'()})
The list of entries.  The SOA record is taken care of, so you don't need to
put it in the list of entries.  This list should probably contain an entry
for your primary authoritative DNS server.  Other than using a list of
entries directly, you can use @code{define-zone-entries} to define a object
containing the list of entries more easily, that you can later pass to the
@code{entries} field of the @code{zone-file}.

@item @code{origin} (default: @code{""})
The name of your zone.  This parameter cannot be empty.

@item @code{ns} (default: @code{"ns"})
The domain of your primary authoritative DNS server.  The name is relative
to the origin, unless it ends with a dot.  It is mandatory that this primary
DNS server corresponds to an NS record in the zone and that it is associated
to an IP address in the list of entries.

@item @code{mail} (default: @code{"hostmaster"})
An email address people can contact you at, as the owner of the zone.  This
is translated as @code{<mail>@@<origin>}.

@item @code{serial} (default: @code{1})
The serial number of the zone.  As this is used to keep track of changes by
both slaves and resolvers, it is mandatory that it @emph{never} decreases.
Always increment it when you make a change in your zone.

@item @code{refresh} (default: @code{(* 2 24 3600)})
The frequency at which slaves will do a zone transfer.  This value is a
number of seconds.  It can be computed by multiplications or with
@code{(string->duration)}.

@item @code{retry} (default: @code{(* 15 60)})
The period after which a slave will retry to contact its master when it
fails to do so a first time.

@item @code{expiry} (default: @code{(* 14 24 3600)})
Default TTL of records.  Existing records are considered correct for at most
this amount of time.  After this period, resolvers will invalidate their
cache and check again that it still exists.

@item @code{nx} (default: @code{3600})
Default TTL of inexistent records.  This delay is usually short because you
want your new domains to reach everyone quickly.

@end table
@end deftp

@deftp {Data Type} knot-remote-configuration
Data type representing a remote configuration.  This type has the following
parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this remote.  IDs
must be unique and must not be empty.

@item @code{address} (default: @code{'()})
An ordered list of destination IP addresses.  Addresses are tried in
sequence.  An optional port can be given with the @@ separator.  For
instance: @code{(list "1.2.3.4" "2.3.4.5@@53")}.  Default port is 53.

@item @code{via} (default: @code{'()})
An ordered list of source IP addresses.  An empty list will have Knot choose
an appropriate source IP@.  An optional port can be given with the @@
separator.  The default is to choose at random.

@item @code{key} (default: @code{#f})
A reference to a key, that is a string containing the identifier of a key
defined in a @code{knot-key-configuration} field.

@end table
@end deftp

@deftp {Data Type} knot-keystore-configuration
Data type representing a keystore to hold dnssec keys.  This type has the
following parameters:

@table @asis
@item @code{id} (default: @code{""})
The id of the keystore.  It must not be empty.

@item @code{backend} (default: @code{'pem})
The backend to store the keys in.  Can be @code{'pem} or @code{'pkcs11}.

@item @code{config} (default: @code{"/var/lib/knot/keys/keys"})
The configuration string of the backend.  An example for the PKCS#11 is:
@code{"pkcs11:token=knot;pin-value=1234
/gnu/store/.../lib/pkcs11/libsofthsm2.so"}.  For the pem backend, the string
represents a path in the file system.

@end table
@end deftp

@deftp {Data Type} knot-policy-configuration
Data type representing a dnssec policy.  Knot DNS is able to automatically
sign your zones.  It can either generate and manage your keys automatically
or use keys that you generate.

Dnssec is usually implemented using two keys: a Key Signing Key (KSK) that
is used to sign the second, and a Zone Signing Key (ZSK) that is used to
sign the zone.  In order to be trusted, the KSK needs to be present in the
parent zone (usually a top-level domain).  If your registrar supports
dnssec, you will have to send them your KSK's hash so they can add a DS
record in their zone.  This is not automated and need to be done each time
you change your KSK.

The policy also defines the lifetime of keys.  Usually, ZSK can be changed
easily and use weaker cryptographic functions (they use lower parameters) in
order to sign records quickly, so they are changed often.  The KSK however
requires manual interaction with the registrar, so they are changed less
often and use stronger parameters because they sign only one record.

This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
The id of the policy.  It must not be empty.

@item @code{keystore} (default: @code{"default"})
A reference to a keystore, that is a string containing the identifier of a
keystore defined in a @code{knot-keystore-configuration} field.  The
@code{"default"} identifier means the default keystore (a kasp database that
was setup by this service).

@item @code{manual?} (default: @code{#f})
Whether the key management is manual or automatic.

@item @code{single-type-signing?} (default: @code{#f})
When @code{#t}, use the Single-Type Signing Scheme.

@item @code{algorithm} (default: @code{"ecdsap256sha256"})
An algorithm of signing keys and issued signatures.

@item @code{ksk-size} (default: @code{256})
The length of the KSK@.  Note that this value is correct for the default
algorithm, but would be unsecure for other algorithms.

@item @code{zsk-size} (default: @code{256})
The length of the ZSK@.  Note that this value is correct for the default
algorithm, but would be unsecure for other algorithms.

@item @code{dnskey-ttl} (default: @code{'default})
The TTL value for DNSKEY records added into zone apex.  The special
@code{'default} value means same as the zone SOA TTL.

@item @code{zsk-lifetime} (default: @code{(* 30 24 3600)})
The period between ZSK publication and the next rollover initiation.

@item @code{propagation-delay} (default: @code{(* 24 3600)})
An extra delay added for each key rollover step.  This value should be high
enough to cover propagation of data from the master server to all slaves.

@item @code{rrsig-lifetime} (default: @code{(* 14 24 3600)})
A validity period of newly issued signatures.

@item @code{rrsig-refresh} (default: @code{(* 7 24 3600)})
A period how long before a signature expiration the signature will be
refreshed.

@item @code{nsec3?} (default: @code{#f})
When @code{#t}, NSEC3 will be used instead of NSEC.

@item @code{nsec3-iterations} (default: @code{5})
The number of additional times the hashing is performed.

@item @code{nsec3-salt-length} (default: @code{8})
The length of a salt field in octets, which is appended to the original
owner name before hashing.

@item @code{nsec3-salt-lifetime} (default: @code{(* 30 24 3600)})
The validity period of newly issued salt field.

@end table
@end deftp

@deftp {Data Type} knot-zone-configuration
Data type representing a zone served by Knot.  This type has the following
parameters:

@table @asis
@item @code{domain} (default: @code{""})
The domain served by this configuration.  It must not be empty.

@item @code{file} (default: @code{""})
The file where this zone is saved.  This parameter is ignored by master
zones.  Empty means default location that depends on the domain name.

@item @code{zone} (default: @code{(zone-file)})
The content of the zone file.  This parameter is ignored by slave zones.  It
must contain a zone-file record.

@item @code{master} (default: @code{'()})
A list of master remotes.  When empty, this zone is a master.  When set,
this zone is a slave.  This is a list of remotes identifiers.

@item @code{ddns-master} (default: @code{#f})
The main master.  When empty, it defaults to the first master in the list of
masters.

@item @code{notify} (default: @code{'()})
A list of slave remote identifiers.

@item @code{acl} (default: @code{'()})
A list of acl identifiers.

@item @code{semantic-checks?} (default: @code{#f})
When set, this adds more semantic checks to the zone.

@item @code{disable-any?} (default: @code{#f})
When set, this forbids queries of the ANY type.

@item @code{zonefile-sync} (default: @code{0})
The delay between a modification in memory and on disk.  0 means immediate
synchronization.

@item @code{zonefile-load}（默认值：@code{#f}）
The way the zone file contents are applied during zone load.  Possible
values are:

@itemize
@item @code{#f} for using the default value from Knot,
@item @code{'none} for not using the zone file at all,
@item @code{'difference} for computing the difference between already available
contents and zone contents and applying it to the current zone contents,
@item @code{'difference-no-serial} for the same as @code{'difference}, but
ignoring the SOA serial in the zone file, while the server takes care of it
automatically.
@item @code{'whole} for loading zone contents from the zone file.
@end itemize

@item @code{journal-content}（默认值：@code{#f}）
The way the journal is used to store zone and its changes.  Possible values
are @code{'none} to not use it at all, @code{'changes} to store changes and
@code{'all} to store contents.  @code{#f} does not set this option, so the
default value from Knot is used.

@item @code{max-journal-usage}（默认值：@code{#f}）
The maximum size for the journal on disk.  @code{#f} does not set this
option, so the default value from Knot is used.

@item @code{max-journal-depth}（默认值：@code{#f}）
The maximum size of the history.  @code{#f} does not set this option, so the
default value from Knot is used.

@item @code{max-zone-size}（默认值：@code{#f}）
The maximum size of the zone file.  This limit is enforced for incoming
transfer and updates.  @code{#f} does not set this option, so the default
value from Knot is used.

@item @code{dnssec-policy}（默认值：@code{#f}）
A reference to a @code{knot-policy-configuration} record, or the special
name @code{"default"}.  If the value is @code{#f}, there is no dnssec
signing on this zone.

@item @code{serial-policy} (default: @code{'increment})
A policy between @code{'increment} and @code{'unixtime}.

@end table
@end deftp

@deftp {Data Type} knot-configuration
Data type representing the Knot configuration.  This type has the following
parameters:

@table @asis
@item @code{knot} (default: @code{knot})
The Knot package.

@item @code{run-directory} (default: @code{"/var/run/knot"})
The run directory.  This directory will be used for pid file and sockets.

@item @code{includes}（默认值：@code{'()}）
A list of strings or file-like objects denoting other files that must be
included at the top of the configuration file.

@cindex 秘密，Knot服务。
This can be used to manage secrets out-of-band.  For example, secret keys
may be stored in an out-of-band file not managed by Guix, and thus not
visible in @file{/gnu/store}---e.g., you could store secret key
configuration in @file{/etc/knot/secrets.conf} and add this file to the
@code{includes} list.

One can generate a secret tsig key (for nsupdate and zone transfers with the
keymgr command from the knot package.  Note that the package is not
automatically installed by the service.  The following example shows how to
generate a new tsig key:

@example
keymgr -t mysecret > /etc/knot/secrets.conf
chmod 600 /etc/knot/secrets.conf
@end example

Also note that the generated key will be named @var{mysecret}, so it is the
name that needs to be used in the @var{key} field of the
@code{knot-acl-configuration} record and in other places that need to refer
to that key.

It can also be used to add configuration not supported by this interface.

@item @code{listen-v4} (default: @code{"0.0.0.0"})
An ip address on which to listen.

@item @code{listen-v6} (default: @code{"::"})
An ip address on which to listen.

@item @code{listen-port} (default: @code{53})
A port on which to listen.

@item @code{keys} (default: @code{'()})
The list of knot-key-configuration used by this configuration.

@item @code{acls} (default: @code{'()})
The list of knot-acl-configuration used by this configuration.

@item @code{remotes} (default: @code{'()})
The list of knot-remote-configuration used by this configuration.

@item @code{zones} (default: @code{'()})
The list of knot-zone-configuration used by this configuration.

@end table
@end deftp

@subsubheading Knot Resolver Service

@deffn {Scheme Variable} knot-resolver-service-type
This is the type of the knot resolver service, whose value should be an
@code{knot-resolver-configuration} object as in this example:

@lisp
(service knot-resolver-service-type
         (knot-resolver-configuration
           (kresd-config-file (plain-file "kresd.conf" "
net.listen('192.168.0.1', 5353)
user('knot-resolver', 'knot-resolver')
modules = @{ 'hints > iterate', 'stats', 'predict' @}
cache.size = 100 * MB
"))))
@end lisp

For more information, refer its
@url{https://knot-resolver.readthedocs.org/en/stable/daemon.html#configuration,
manual}.
@end deffn

@deftp {Data Type} knot-resolver-configuration
Data type representing the configuration of knot-resolver.

@table @asis
@item @code{package} (default: @var{knot-resolver})
Package object of the knot DNS resolver.

@item @code{kresd-config-file} (default: %kresd.conf)
File-like object of the kresd configuration file to use, by default it will
listen on @code{127.0.0.1} and @code{::1}.

@item @code{garbage-collection-interval} (default: 1000)
Number of milliseconds for @code{kres-cache-gc} to periodically trim the
cache.

@end table
@end deftp


@subsubheading Dnsmasq Service

@deffn {Scheme Variable} dnsmasq-service-type
This is the type of the dnsmasq service, whose value should be an
@code{dnsmasq-configuration} object as in this example:

@lisp
(service dnsmasq-service-type
         (dnsmasq-configuration
           (no-resolv? #t)
           (servers '("192.168.1.1"))))
@end lisp
@end deffn

@deftp {Data Type} dnsmasq-configuration
Data type representing the configuration of dnsmasq.

@table @asis
@item @code{package} (default: @var{dnsmasq})
Package object of the dnsmasq server.

@item @code{no-hosts?} (default: @code{#f})
When true, don't read the hostnames in /etc/hosts.

@item @code{port} (default: @code{53})
The port to listen on.  Setting this to zero completely disables DNS
responses, leaving only DHCP and/or TFTP functions.

@item @code{local-service?} (default: @code{#t})
Accept DNS queries only from hosts whose address is on a local subnet, ie a
subnet for which an interface exists on the server.

@item @code{listen-addresses} (default: @code{'()})
Listen on the given IP addresses.

@item @code{resolv-file} (default: @code{"/etc/resolv.conf"})
The file to read the IP address of the upstream nameservers from.

@item @code{no-resolv?} (default: @code{#f})
When true, don't read @var{resolv-file}.

@item @code{servers} (default: @code{'()})
Specify IP address of upstream servers directly.

@item @code{addresses} (default: @code{'()})
For each entry, specify an IP address to return for any host in the given
domains.  Queries in the domains are never forwarded and always replied to
with the specified IP address.

This is useful for redirecting hosts locally, for example:

@lisp
(service dnsmasq-service-type
         (dnsmasq-configuration
           (addresses
             '(; Redirect to a local web-server.
               "/example.org/127.0.0.1"
               ; Redirect subdomain to a specific IP.
               "/subdomain.example.org/192.168.1.42"))))
@end lisp

Note that rules in @file{/etc/hosts} take precedence over this.

@item @code{cache-size} (default: @code{150})
Set the size of dnsmasq's cache.  Setting the cache size to zero disables
caching.

@item @code{negative-cache?} (default: @code{#t})
When false, disable negative caching.

@item @code{tftp-enable?} (default: @code{#f})
Whether to enable the built-in TFTP server.

@item @code{tftp-no-fail?} (default: @code{#f})
If true, does not fail dnsmasq if the TFTP server could not start up.

@item @code{tftp-single-port?} (default: @code{#f})
Whether to use only one single port for TFTP.

@item @code{tftp-secure?} (default: @code{#f})
If true, only files owned by the user running the dnsmasq process are
accessible.

If dnsmasq is being run as root, different rules apply: @code{tftp-secure?}
has no effect, but only files which have the world-readable bit set are
accessible.

@item @code{tftp-max} (default: @code{#f})
If set, sets the maximal number of concurrent connections allowed.

@item @code{tftp-mtu} (default: @code{#f})
If set, sets the MTU for TFTP packets to that value.

@item @code{tftp-no-blocksize?} (default: @code{#f})
If true, stops the TFTP server from negotiating the blocksize with a client.

@item @code{tftp-lowercase?} (default: @code{#f})
Whether to convert all filenames in TFTP requests to lowercase.

@item @code{tftp-port-range} (default: @code{#f})
If set, fixes the dynamical ports (one per client) to the given range
(@code{"<start>,<end>"}).

@item @code{tftp-root} (default: @code{/var/empty,lo})
Look for files to transfer using TFTP relative to the given directory.  When
this is set, TFTP paths which include @samp{..} are rejected, to stop
clients getting outside the specified root.  Absolute paths (starting with
@samp{/}) are allowed, but they must be within the TFTP-root.  If the
optional interface argument is given, the directory is only used for TFTP
requests via that interface.

@item @code{tftp-unique-root} (default: @code{#f})
If set, add the IP or hardware address of the TFTP client as a path
component on the end of the TFTP-root.  Only valid if a TFTP root is set and
the directory exists.  Defaults to adding IP address (in standard
dotted-quad format).

For instance, if @option{--tftp-root} is @samp{/tftp} and client
@samp{1.2.3.4} requests file @file{myfile} then the effective path will be
@file{/tftp/1.2.3.4/myfile} if @file{/tftp/1.2.3.4} exists or
@file{/tftp/myfile} otherwise.  When @samp{=mac} is specified it will append
the MAC address instead, using lowercase zero padded digits separated by
dashes, e.g.: @samp{01-02-03-04-aa-bb}.  Note that resolving MAC addresses
is only possible if the client is in the local network or obtained a DHCP
lease from dnsmasq.

@end table
@end deftp

@subsubheading ddclient Service

@cindex ddclient
The ddclient service described below runs the ddclient daemon, which takes
care of automatically updating DNS entries for service providers such as
@uref{https://dyn.com/dns/, Dyn}.

The following example show instantiates the service with its default
configuration:

@lisp
(service ddclient-service-type)
@end lisp

Note that ddclient needs to access credentials that are stored in a
@dfn{secret file}, by default @file{/etc/ddclient/secrets} (see
@code{secret-file} below).  You are expected to create this file manually,
in an ``out-of-band'' fashion (you @emph{could} make this file part of the
service configuration, for instance by using @code{plain-file}, but it will
be world-readable @i{via} @file{/gnu/store}).  See the examples in the
@file{share/ddclient} directory of the @code{ddclient} package.

@c %start of fragment

Available @code{ddclient-configuration} fields are:

@deftypevr {@code{ddclient-configuration} parameter} package ddclient
The ddclient package.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} integer daemon
The period after which ddclient will retry to check IP and domain name.

Defaults to @samp{300}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} boolean syslog
Use syslog for the output.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string mail
Mail to user.

Defaults to @samp{"root"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string mail-failure
Mail failed update to user.

Defaults to @samp{"root"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string pid
The ddclient PID file.

Defaults to @samp{"/var/run/ddclient/ddclient.pid"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} boolean ssl
Enable SSL support.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string user
Specifies the user name or ID that is used when running ddclient program.

Defaults to @samp{"ddclient"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string group
Group of the user who will run the ddclient program.

Defaults to @samp{"ddclient"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} string secret-file
Secret file which will be appended to @file{ddclient.conf} file.  This file
contains credentials for use by ddclient.  You are expected to create it
manually.

Defaults to @samp{"/etc/ddclient/secrets.conf"}.

@end deftypevr

@deftypevr {@code{ddclient-configuration} parameter} list extra-options
Extra options will be appended to @file{ddclient.conf} file.

Defaults to @samp{()}.

@end deftypevr


@c %end of fragment


@node VPN服务
@subsection VPN服务
@cindex VPN (virtual private network)
@cindex virtual private network (VPN)

The @code{(gnu services vpn)} module provides services related to
@dfn{virtual private networks} (VPNs).

@subsubheading OpenVPN

It provides a @emph{client} service for your machine to connect to a VPN,
and a @emph{server} service for your machine to host a VPN@.

@deffn {Scheme Procedure} openvpn-client-service @
       [#:config (openvpn-client-configuration)]

Return a service that runs @command{openvpn}, a VPN daemon, as a client.
@end deffn

@deffn {Scheme Procedure} openvpn-server-service @
       [#:config (openvpn-server-configuration)]

Return a service that runs @command{openvpn}, a VPN daemon, as a server.

Both can be run simultaneously.
@end deffn

@c %automatically generated documentation

Available @code{openvpn-client-configuration} fields are:

@deftypevr {@code{openvpn-client-configuration} parameter} package openvpn
The OpenVPN package.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} string pid-file
The OpenVPN pid file.

Defaults to @samp{"/var/run/openvpn/openvpn.pid"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} proto proto
The protocol (UDP or TCP) used to open a channel between clients and
servers.

Defaults to @samp{udp}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} dev dev
The device type used to represent the VPN connection.

Defaults to @samp{tun}.

@end deftypevr

If you do not have some of these files (eg.@: you use a username and
password), you can disable any of the following three fields by setting it
to @code{'disabled}.

@deftypevr {@code{openvpn-client-configuration} parameter} maybe-string ca
The certificate authority to check connections against.

Defaults to @samp{"/etc/openvpn/ca.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} maybe-string cert
The certificate of the machine the daemon is running on.  It should be
signed by the authority given in @code{ca}.

Defaults to @samp{"/etc/openvpn/client.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} maybe-string key
The key of the machine the daemon is running on.  It must be the key whose
certificate is @code{cert}.

Defaults to @samp{"/etc/openvpn/client.key"}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} boolean comp-lzo?
Whether to use the lzo compression algorithm.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} boolean persist-key?
Don't re-read key files across SIGUSR1 or --ping-restart.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} boolean persist-tun?
Don't close and reopen TUN/TAP device or run up/down scripts across SIGUSR1
or --ping-restart restarts.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} boolean fast-io?
(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to
poll/epoll/select prior to the write operation.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} number verbosity
Verbosity level.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} tls-auth-client tls-auth
Add an additional layer of HMAC authentication on top of the TLS control
channel to protect against DoS attacks.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} maybe-string auth-user-pass
Authenticate with server using username/password.  The option is a file
containing username/password on 2 lines.  Do not use a file-like object as
it would be added to the store and readable by any user.

Defaults to @samp{'disabled}.
@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} key-usage verify-key-usage?
Whether to check the server certificate has server usage extension.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} bind bind?
Bind to a specific local port number.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} resolv-retry resolv-retry?
Retry resolving server address.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-client-configuration} parameter} openvpn-remote-list remote
A list of remote servers to connect to.

Defaults to @samp{()}.

Available @code{openvpn-remote-configuration} fields are:

@deftypevr {@code{openvpn-remote-configuration} parameter} string name
Server name.

Defaults to @samp{"my-server"}.

@end deftypevr

@deftypevr {@code{openvpn-remote-configuration} parameter} number port
Port number the server listens to.

Defaults to @samp{1194}.

@end deftypevr

@end deftypevr
@c %end of automatic openvpn-client documentation

@c %automatically generated documentation

Available @code{openvpn-server-configuration} fields are:

@deftypevr {@code{openvpn-server-configuration} parameter} package openvpn
The OpenVPN package.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string pid-file
The OpenVPN pid file.

Defaults to @samp{"/var/run/openvpn/openvpn.pid"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} proto proto
The protocol (UDP or TCP) used to open a channel between clients and
servers.

Defaults to @samp{udp}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} dev dev
The device type used to represent the VPN connection.

Defaults to @samp{tun}.

@end deftypevr

If you do not have some of these files (eg.@: you use a username and
password), you can disable any of the following three fields by setting it
to @code{'disabled}.

@deftypevr {@code{openvpn-server-configuration} parameter} maybe-string ca
The certificate authority to check connections against.

Defaults to @samp{"/etc/openvpn/ca.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} maybe-string cert
The certificate of the machine the daemon is running on.  It should be
signed by the authority given in @code{ca}.

Defaults to @samp{"/etc/openvpn/client.crt"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} maybe-string key
The key of the machine the daemon is running on.  It must be the key whose
certificate is @code{cert}.

Defaults to @samp{"/etc/openvpn/client.key"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean comp-lzo?
Whether to use the lzo compression algorithm.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean persist-key?
Don't re-read key files across SIGUSR1 or --ping-restart.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean persist-tun?
Don't close and reopen TUN/TAP device or run up/down scripts across SIGUSR1
or --ping-restart restarts.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean fast-io?
(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to
poll/epoll/select prior to the write operation.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} number verbosity
Verbosity level.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} tls-auth-server tls-auth
Add an additional layer of HMAC authentication on top of the TLS control
channel to protect against DoS attacks.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} number port
Specifies the port number on which the server listens.

Defaults to @samp{1194}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} ip-mask server
An ip and mask specifying the subnet inside the virtual network.

Defaults to @samp{"10.8.0.0 255.255.255.0"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} cidr6 server-ipv6
A CIDR notation specifying the IPv6 subnet inside the virtual network.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string dh
The Diffie-Hellman parameters file.

Defaults to @samp{"/etc/openvpn/dh2048.pem"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string ifconfig-pool-persist
The file that records client IPs.

Defaults to @samp{"/etc/openvpn/ipp.txt"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} gateway redirect-gateway?
When true, the server will act as a gateway for its clients.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} boolean client-to-client?
When true, clients are allowed to talk to each other inside the VPN.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} keepalive keepalive
Causes ping-like messages to be sent back and forth over the link so that
each side knows when the other side has gone down.  @code{keepalive}
requires a pair.  The first element is the period of the ping sending, and
the second element is the timeout before considering the other side down.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} number max-clients
The maximum number of clients.

Defaults to @samp{100}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} string status
The status file.  This file shows a small report on current connection.  It
is truncated and rewritten every minute.

Defaults to @samp{"/var/run/openvpn/status"}.

@end deftypevr

@deftypevr {@code{openvpn-server-configuration} parameter} openvpn-ccd-list client-config-dir
The list of configuration for some clients.

Defaults to @samp{()}.

Available @code{openvpn-ccd-configuration} fields are:

@deftypevr {@code{openvpn-ccd-configuration} parameter} string name
Client name.

Defaults to @samp{"client"}.

@end deftypevr

@deftypevr {@code{openvpn-ccd-configuration} parameter} ip-mask iroute
Client own network

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{openvpn-ccd-configuration} parameter} ip-mask ifconfig-push
Client VPN IP.

Defaults to @samp{#f}.

@end deftypevr

@end deftypevr


@c %end of automatic openvpn-server documentation

@subsubheading Wireguard

@defvr {Scheme Variable} wireguard-service-type
A service type for a Wireguard tunnel interface.  Its value must be a
@code{wireguard-configuration} record as in this example:

@lisp
(service wireguard-service-type
         (wireguard-configuration
          (peers
           (list
            (wireguard-peer
             (name "my-peer")
             (endpoint "my.wireguard.com:51820")
             (public-key "hzpKg9X1yqu1axN6iJp0mWf6BZGo8m1wteKwtTmDGF4=")
             (allowed-ips '("10.0.0.2/32")))))))
@end lisp

@end defvr

@deftp {Data Type} wireguard-configuration
Data type representing the configuration of the Wireguard service.

@table @asis
@item @code{wireguard}
The wireguard package to use for this service.

@item @code{interface} (default: @code{"wg0"})
The interface name for the VPN.

@item @code{addresses} (default: @code{'("10.0.0.1/32")})
The IP addresses to be assigned to the above interface.

@item @code{private-key} (default: @code{"/etc/wireguard/private.key"})
The private key file for the interface.  It is automatically generated if
the file does not exist.

@item @code{peers} (default: @code{'()})
The authorized peers on this interface.  This is a list of
@var{wireguard-peer} records.

@end table
@end deftp

@deftp {Data Type} wireguard-peer
Data type representing a Wireguard peer attached to a given interface.

@table @asis
@item @code{名字}
The peer name.

@item @code{endpoint} (default: @code{#f})
The optional endpoint for the peer, such as
@code{"demo.wireguard.com:51820"}.

@item @code{public-key}
The peer public-key represented as a base64 string.

@item @code{allowed-ips}
A list of IP addresses from which incoming traffic for this peer is allowed
and to which incoming traffic for this peer is directed.

@end table
@end deftp

@node 网络文件系统
@subsection 网络文件系统
@cindex NFS

The @code{(gnu services nfs)} module provides the following services, which
are most commonly used in relation to mounting or exporting directory trees
as @dfn{network file systems} (NFS).

While it is possible to use the individual components that together make up
a Network File System service, we recommended to configure an NFS server
with the @code{nfs-service-type}.

@subsubheading NFS Service
@cindex NFS, server

The NFS service takes care of setting up all NFS component services, kernel
configuration file systems, and installs configuration files in the
locations that NFS expects.

@defvr {Scheme Variable} nfs-service-type
A service type for a complete NFS server.
@end defvr

@deftp {Data Type} nfs-configuration
This data type represents the configuration of the NFS service and all of
its subsystems.

It has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The nfs-utils package to use.

@item @code{nfs-versions} (default: @code{'("4.2" "4.1" "4.0")})
If a list of string values is provided, the @command{rpc.nfsd} daemon will
be limited to supporting the given versions of the NFS protocol.

@item @code{exports} (default: @code{'()})
This is a list of directories the NFS server should export.  Each entry is a
list consisting of two elements: a directory name and a string containing
all options.  This is an example in which the directory @file{/export} is
served to all NFS clients as a read-only share:

@lisp
(nfs-configuration
 (exports
  '(("/export"
     "*(ro,insecure,no_subtree_check,crossmnt,fsid=0)"))))
@end lisp

@item @code{rpcmountd-port} (default: @code{#f})
The network port that the @command{rpc.mountd} daemon should use.

@item @code{rpcstatd-port} (default: @code{#f})
The network port that the @command{rpc.statd} daemon should use.

@item @code{rpcbind} (default: @code{rpcbind})
The rpcbind package to use.

@item @code{idmap-domain} (default: @code{"localdomain"})
The local NFSv4 domain name.

@item @code{nfsd-port} (default: @code{2049})
The network port that the @command{nfsd} daemon should use.

@item @code{nfsd-threads} (default: @code{8})
The number of threads used by the @command{nfsd} daemon.

@item @code{nfsd-tcp?} (default: @code{#t})
Whether the @command{nfsd} daemon should listen on a TCP socket.

@item @code{nfsd-udp?} (default: @code{#f})
Whether the @command{nfsd} daemon should listen on a UDP socket.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@item @code{debug} (default: @code{'()"})
A list of subsystems for which debugging output should be enabled.  This is
a list of symbols.  Any of these symbols are valid: @code{nfsd}, @code{nfs},
@code{rpc}, @code{idmap}, @code{statd}, or @code{mountd}.
@end table
@end deftp

If you don't need a complete NFS service or prefer to build it yourself you
can use the individual component services that are documented below.

@subsubheading RPC Bind Service
@cindex rpcbind

The RPC Bind service provides a facility to map program numbers into
universal addresses.  Many NFS related services use this facility.  Hence it
is automatically started when a dependent service starts.

@defvr {Scheme Variable} rpcbind-service-type
A service type for the RPC portmapper daemon.
@end defvr


@deftp {Data Type} rpcbind-configuration
Data type representing the configuration of the RPC Bind Service.  This type
has the following parameters:
@table @asis
@item @code{rpcbind} (default: @code{rpcbind})
The rpcbind package to use.

@item @code{warm-start?} (default: @code{#t})
If this parameter is @code{#t}, then the daemon will read a state file on
startup thus reloading state information saved by a previous instance.
@end table
@end deftp


@subsubheading Pipefs Pseudo File System
@cindex pipefs
@cindex rpc_pipefs

The pipefs file system is used to transfer NFS related data between the
kernel and user space programs.

@defvr {Scheme Variable} pipefs-service-type
A service type for the pipefs pseudo file system.
@end defvr

@deftp {Data Type} pipefs-configuration
Data type representing the configuration of the pipefs pseudo file system
service.  This type has the following parameters:
@table @asis
@item @code{mount-point} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory to which the file system is to be attached.
@end table
@end deftp


@subsubheading GSS Daemon Service
@cindex GSSD
@cindex GSS
@cindex global security system

The @dfn{global security system} (GSS) daemon provides strong security for
RPC based protocols.  Before exchanging RPC requests an RPC client must
establish a security context.  Typically this is done using the Kerberos
command @command{kinit} or automatically at login time using PAM services
(@pxref{Kerberos服务}).

@defvr {Scheme Variable} gss-service-type
A service type for the Global Security System (GSS) daemon.
@end defvr

@deftp {Data Type} gss-configuration
Data type representing the configuration of the GSS daemon service.  This
type has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The package in which the @command{rpc.gssd} command is to be found.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@end table
@end deftp


@subsubheading IDMAP Daemon Service
@cindex idmapd
@cindex name mapper

The idmap daemon service provides mapping between user IDs and user names.
Typically it is required in order to access file systems mounted via NFSv4.

@defvr {Scheme Variable} idmap-service-type
A service type for the Identity Mapper (IDMAP) daemon.
@end defvr

@deftp {Data Type} idmap-configuration
Data type representing the configuration of the IDMAP daemon service.  This
type has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The package in which the @command{rpc.idmapd} command is to be found.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@item @code{domain} (default: @code{#f})
The local NFSv4 domain name.  This must be a string or @code{#f}.  If it is
@code{#f} then the daemon will use the host's fully qualified domain name.

@item @code{verbosity} (default: @code{0})
The verbosity level of the daemon.

@end table
@end deftp

@node 持续集成
@subsection 持续集成

@cindex continuous integration
@uref{https://guix.gnu.org/cuirass/, Cuirass} is a continuous integration
tool for Guix.  It can be used both for development and for providing
substitutes to others (@pxref{substitutes}).

The @code{(gnu services cuirass)} module provides the following service.

@defvr {Scheme Procedure} cuirass-service-type
The type of the Cuirass service.  Its value must be a
@code{cuirass-configuration} object, as described below.
@end defvr

To add build jobs, you have to set the @code{specifications} field of the
configuration.  For instance, the following example will build all the
packages provided by the @code{my-channel} channel.

@lisp
(define %cuirass-specs
  #~(list (specification
           (name "my-channel")
           (build '(channels my-channel))
           (channels
            (cons (channel
                   (name 'my-channel)
                   (url "https://my-channel.git"))
                  %default-channels)))))

(service cuirass-service-type
         (cuirass-configuration
          (specifications %cuirass-specs)))
@end lisp

To build the @code{linux-libre} package defined by the default Guix channel,
one can use the following configuration.

@lisp
(define %cuirass-specs
  #~(list (specification
           (name "my-linux")
           (build '(packages "linux-libre")))))

(service cuirass-service-type
         (cuirass-configuration
          (specifications %cuirass-specs)))
@end lisp

The other configuration possibilities, as well as the specification record
itself are described in the Cuirass manual (@pxref{Specifications,,,
cuirass, Cuirass}).

While information related to build jobs is located directly in the
specifications, global settings for the @command{cuirass} process are
accessible in other @code{cuirass-configuration} fields.

@deftp {Data Type} cuirass-configuration
Data type representing the configuration of Cuirass.

@table @asis
@item @code{cuirass} (default: @code{cuirass})
The Cuirass package to use.

@item @code{log-file} (default: @code{"/var/log/cuirass.log"})
Location of the log file.

@item @code{web-log-file} (default: @code{"/var/log/cuirass-web.log"})
Location of the log file used by the web interface.

@item @code{cache-directory} (default: @code{"/var/cache/cuirass"})
Location of the repository cache.

@item @code{user} (default: @code{"cuirass"})
Owner of the @code{cuirass} process.

@item @code{group} (default: @code{"cuirass"})
Owner's group of the @code{cuirass} process.

@item @code{interval} (default: @code{60})
Number of seconds between the poll of the repositories followed by the
Cuirass jobs.

@item @code{parameters} (default: @code{#f})
Read parameters from the given @var{parameters} file.  The supported
parameters are described here (@pxref{Parameters,,, cuirass, Cuirass}).

@item @code{remote-server} (default: @code{#f})
A @code{cuirass-remote-server-configuration} record to use the build remote
mechanism or @code{#f} to use the default build mechanism.

@item @code{database} (default: @code{"dbname=cuirass host=/var/run/postgresql"})
Use @var{database} as the database containing the jobs and the past build
results. Since Cuirass uses PostgreSQL as a database engine, @var{database}
must be a string such as @code{"dbname=cuirass host=localhost"}.

@item @code{port} (default: @code{8081})
Port number used by the HTTP server.

@item @code{host} (default: @code{"localhost"})
Listen on the network interface for @var{host}.  The default is to accept
connections from localhost.

@item @code{specifications} (default: @code{#~'()})
A gexp (@pxref{G-表达式}) that evaluates to a list of specifications
records.  The specification record is described in the Cuirass manual
(@pxref{Specifications,,, cuirass, Cuirass}).

@item @code{use-substitutes?} (default: @code{#f})
This allows using substitutes to avoid building every dependencies of a job
from source.

@item @code{one-shot?} (default: @code{#f})
Only evaluate specifications and build derivations once.

@item @code{fallback?} (default: @code{#f})
When substituting a pre-built binary fails, fall back to building packages
locally.

@item @code{extra-options} (default: @code{'()})
Extra options to pass when running the Cuirass processes.

@end table
@end deftp

@cindex remote build
@subsubheading Cuirass remote building

Cuirass supports two mechanisms to build derivations.

@itemize
@item Using the local Guix daemon.
This is the default build mechanism.  Once the build jobs are evaluated,
they are sent to the local Guix daemon.  Cuirass then listens to the Guix
daemon output to detect the various build events.

@item Using the remote build mechanism.
The build jobs are not submitted to the local Guix daemon.  Instead, a
remote server dispatches build requests to the connect remote workers,
according to the build priorities.

@end itemize

To enable this build mode a @code{cuirass-remote-server-configuration}
record must be passed as @code{remote-server} argument of the
@code{cuirass-configuration} record.  The
@code{cuirass-remote-server-configuration} record is described below.

This build mode scales way better than the default build mode.  This is the
build mode that is used on the GNU Guix build farm at
@url{https://ci.guix.gnu.org}.  It should be preferred when using Cuirass to
build large amount of packages.

@deftp {Data Type} cuirass-remote-server-configuration
Data type representing the configuration of the Cuirass remote-server.

@table @asis
@item @code{backend-port} (default: @code{5555})
The TCP port for communicating with @code{remote-worker} processes using
ZMQ.  It defaults to @code{5555}.

@item @code{log-port} (default: @code{5556})
The TCP port of the log server.  It defaults to @code{5556}.

@item @code{publish-port} (default: @code{5557})
The TCP port of the publish server.  It defaults to @code{5557}.

@item @code{log-file} (default: @code{"/var/log/cuirass-remote-server.log"})
Location of the log file.

@item @code{cache} (default: @code{"/var/cache/cuirass/remote"})
Use @var{cache} directory to cache build log files.

@item @code{trigger-url} (default: @code{#f})
Once a substitute is successfully fetched, trigger substitute baking at
@var{trigger-url}.

@item @code{public-key}
@item @code{private-key}
Use the specific @var{file}s as the public/private key pair used to sign the
store items being published.

@end table
@end deftp

At least one remote worker must also be started on any machine of the local
network to actually perform the builds and report their status.

@deftp {Data Type} cuirass-remote-worker-configuration
Data type representing the configuration of the Cuirass remote-worker.

@table @asis
@item @code{cuirass} (default: @code{cuirass})
The Cuirass package to use.

@item @code{workers} (default: @code{1})
Start @var{workers} parallel workers.

@item @code{server} (default: @code{#f})
Do not use Avahi discovery and connect to the given @code{server} IP address
instead.

@item @code{systems} (default: @code{(list (%current-system))})
Only request builds for the given @var{systems}.

@item @code{log-file} (default: @code{"/var/log/cuirass-remote-worker.log"})
Location of the log file.

@item @code{publish-port} (default: @code{5558})
The TCP port of the publish server.  It defaults to @code{5558}.

@item @code{public-key}
@item @code{private-key}
Use the specific @var{file}s as the public/private key pair used to sign the
store items being published.

@end table
@end deftp

@subsubheading Laminar

@uref{https://laminar.ohwg.net/, Laminar} is a lightweight and modular
Continuous Integration service.  It doesn't have a configuration web UI
instead uses version-controllable configuration files and scripts.

Laminar encourages the use of existing tools such as bash and cron instead
of reinventing them.

@defvr {Scheme Procedure} laminar-service-type
The type of the Laminar service.  Its value must be a
@code{laminar-configuration} object, as described below.

All configuration values have defaults, a minimal configuration to get
Laminar running is shown below. By default, the web interface is available
on port 8080.

@lisp
(service laminar-service-type)
@end lisp
@end defvr

@deftp {Data Type} laminar-configuration
Data type representing the configuration of Laminar.

@table @asis
@item @code{laminar} (default: @code{laminar})
The Laminar package to use.

@item @code{home-directory} (default: @code{"/var/lib/laminar"})
The directory for job configurations and run directories.

@item @code{bind-http} (default: @code{"*:8080"})
The interface/port or unix socket on which laminard should listen for
incoming connections to the web frontend.

@item @code{bind-rpc} (default: @code{"unix-abstract:laminar"})
The interface/port or unix socket on which laminard should listen for
incoming commands such as build triggers.

@item @code{title} (default: @code{"Laminar"})
The page title to show in the web frontend.

@item @code{keep-rundirs} (default: @code{0})
Set to an integer defining how many rundirs to keep per job.  The
lowest-numbered ones will be deleted.  The default is 0, meaning all run
dirs will be immediately deleted.

@item @code{archive-url} (default: @code{#f})
The web frontend served by laminard will use this URL to form links to
artefacts archived jobs.

@item @code{base-url} (default: @code{#f})
Base URL to use for links to laminar itself.

@end table
@end deftp

@node 电源管理服务
@subsection 电源管理服务

@cindex tlp
@cindex power management with TLP
@subsubheading TLP daemon

The @code{(gnu services pm)} module provides a Guix service definition for
the Linux power management tool TLP.

TLP enables various powersaving modes in userspace and kernel.  Contrary to
@code{upower-service}, it is not a passive, monitoring tool, as it will
apply custom settings each time a new power source is detected.  More
information can be found at @uref{https://linrunner.de/en/tlp/tlp.html, TLP
home page}.

@deffn {Scheme Variable} tlp-service-type
The service type for the TLP tool.  The default settings are optimised for
battery life on most systems, but you can tweak them to your heart's content
by adding a valid @code{tlp-configuration}:
@lisp
(service tlp-service-type
         (tlp-configuration
          (cpu-scaling-governor-on-ac (list "performance"))
          (sched-powersave-on-bat? #t)))
@end lisp
@end deffn

Each parameter definition is preceded by its type; for example,
@samp{boolean foo} indicates that the @code{foo} parameter should be
specified as a boolean.  Types starting with @code{maybe-} denote parameters
that won't show up in TLP config file when their value is @code{'disabled}.

@c The following documentation was initially generated by
@c (generate-tlp-documentation) in (gnu services pm).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as TLP updates.

Available @code{tlp-configuration} fields are:

@deftypevr {@code{tlp-configuration} parameter} package tlp
The TLP package.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean tlp-enable?
Set to true if you wish to enable TLP.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string tlp-default-mode
Default mode when no power supply can be detected.  Alternatives are AC and
BAT.

Defaults to @samp{"AC"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer disk-idle-secs-on-ac
Number of seconds Linux kernel has to wait after the disk goes idle, before
syncing on AC.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer disk-idle-secs-on-bat
Same as @code{disk-idle-ac} but on BAT mode.

Defaults to @samp{2}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer max-lost-work-secs-on-ac
Dirty pages flushing periodicity, expressed in seconds.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer max-lost-work-secs-on-bat
Same as @code{max-lost-work-secs-on-ac} but on BAT mode.

Defaults to @samp{60}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list cpu-scaling-governor-on-ac
CPU frequency scaling governor on AC mode.  With intel_pstate driver,
alternatives are powersave and performance.  With acpi-cpufreq driver,
alternatives are ondemand, powersave, performance and conservative.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list cpu-scaling-governor-on-bat
Same as @code{cpu-scaling-governor-on-ac} but on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-min-freq-on-ac
Set the min available frequency for the scaling governor on AC.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-max-freq-on-ac
Set the max available frequency for the scaling governor on AC.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-min-freq-on-bat
Set the min available frequency for the scaling governor on BAT.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-max-freq-on-bat
Set the max available frequency for the scaling governor on BAT.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-min-perf-on-ac
Limit the min P-state to control the power dissipation of the CPU, in AC
mode.  Values are stated as a percentage of the available performance.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-max-perf-on-ac
Limit the max P-state to control the power dissipation of the CPU, in AC
mode.  Values are stated as a percentage of the available performance.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-min-perf-on-bat
Same as @code{cpu-min-perf-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-max-perf-on-bat
Same as @code{cpu-max-perf-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean cpu-boost-on-ac?
Enable CPU turbo boost feature on AC mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean cpu-boost-on-bat?
Same as @code{cpu-boost-on-ac?} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean sched-powersave-on-ac?
Allow Linux kernel to minimize the number of CPU cores/hyper-threads used
under light load conditions.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean sched-powersave-on-bat?
Same as @code{sched-powersave-on-ac?} but on BAT mode.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean nmi-watchdog?
Enable Linux kernel NMI watchdog.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string phc-controls
For Linux kernels with PHC patch applied, change CPU voltages.  An example
value would be @samp{"F:V F:V F:V F:V"}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string energy-perf-policy-on-ac
Set CPU performance versus energy saving policy on AC@.  Alternatives are
performance, normal, powersave.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string energy-perf-policy-on-bat
Same as @code{energy-perf-policy-ac} but on BAT mode.

Defaults to @samp{"powersave"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disks-devices
Hard disk devices.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disk-apm-level-on-ac
Hard disk advanced power management level.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disk-apm-level-on-bat
Same as @code{disk-apm-bat} but on BAT mode.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-spindown-timeout-on-ac
Hard disk spin down timeout.  One value has to be specified for each
declared hard disk.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-spindown-timeout-on-bat
Same as @code{disk-spindown-timeout-on-ac} but on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-iosched
Select IO scheduler for disk devices.  One value has to be specified for
each declared hard disk.  Example alternatives are cfq, deadline and noop.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string sata-linkpwr-on-ac
SATA aggressive link power management (ALPM) level.  Alternatives are
min_power, medium_power, max_performance.

Defaults to @samp{"max_performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string sata-linkpwr-on-bat
Same as @code{sata-linkpwr-ac} but on BAT mode.

Defaults to @samp{"min_power"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string sata-linkpwr-blacklist
Exclude specified SATA host devices for link power management.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-on-off-boolean ahci-runtime-pm-on-ac?
Enable Runtime Power Management for AHCI controller and disks on AC mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-on-off-boolean ahci-runtime-pm-on-bat?
Same as @code{ahci-runtime-pm-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer ahci-runtime-pm-timeout
Seconds of inactivity before disk is suspended.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string pcie-aspm-on-ac
PCI Express Active State Power Management level.  Alternatives are default,
performance, powersave.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string pcie-aspm-on-bat
Same as @code{pcie-aspm-ac} but on BAT mode.

Defaults to @samp{"powersave"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-power-profile-on-ac
Radeon graphics clock speed level.  Alternatives are low, mid, high, auto,
default.

Defaults to @samp{"high"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-power-profile-on-bat
Same as @code{radeon-power-ac} but on BAT mode.

Defaults to @samp{"low"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-state-on-ac
Radeon dynamic power management method (DPM).  Alternatives are battery,
performance.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-state-on-bat
Same as @code{radeon-dpm-state-ac} but on BAT mode.

Defaults to @samp{"battery"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-perf-level-on-ac
Radeon DPM performance level.  Alternatives are auto, low, high.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-perf-level-on-bat
Same as @code{radeon-dpm-perf-ac} but on BAT mode.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} on-off-boolean wifi-pwr-on-ac?
Wifi power saving mode.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} on-off-boolean wifi-pwr-on-bat?
Same as @code{wifi-power-ac?} but on BAT mode.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} y-n-boolean wol-disable?
Disable wake on LAN.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer sound-power-save-on-ac
Timeout duration in seconds before activating audio power saving on Intel
HDA and AC97 devices.  A value of 0 disables power saving.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer sound-power-save-on-bat
Same as @code{sound-powersave-ac} but on BAT mode.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} y-n-boolean sound-power-save-controller?
Disable controller in powersaving mode on Intel HDA devices.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean bay-poweroff-on-bat?
Enable optical drive in UltraBay/MediaBay on BAT mode.  Drive can be powered
on again by releasing (and reinserting) the eject lever or by pressing the
disc eject button on newer models.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string bay-device
Name of the optical drive device to power off.

Defaults to @samp{"sr0"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string runtime-pm-on-ac
Runtime Power Management for PCI(e) bus devices.  Alternatives are on and
auto.

Defaults to @samp{"on"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string runtime-pm-on-bat
Same as @code{runtime-pm-ac} but on BAT mode.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean runtime-pm-all?
Runtime Power Management for all PCI(e) bus devices, except blacklisted
ones.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list runtime-pm-blacklist
Exclude specified PCI(e) device addresses from Runtime Power Management.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list runtime-pm-driver-blacklist
Exclude PCI(e) devices assigned to the specified drivers from Runtime Power
Management.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean usb-autosuspend?
Enable USB autosuspend feature.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string usb-blacklist
Exclude specified devices from USB autosuspend.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean usb-blacklist-wwan?
Exclude WWAN devices from USB autosuspend.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string usb-whitelist
Include specified devices into USB autosuspend, even if they are already
excluded by the driver or via @code{usb-blacklist-wwan?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean usb-autosuspend-disable-on-shutdown?
Enable USB autosuspend before shutdown.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean restore-device-state-on-startup?
Restore radio device state (bluetooth, wifi, wwan) from previous shutdown on
system startup.

Defaults to @samp{#f}.

@end deftypevr

@cindex thermald
@cindex CPU frequency scaling with thermald
@subsubheading Thermald daemon

The @code{(gnu services pm)} module provides an interface to thermald, a CPU
frequency scaling service which helps prevent overheating.

@defvr {Scheme Variable} thermald-service-type
This is the service type for @uref{https://01.org/linux-thermal-daemon/,
thermald}, the Linux Thermal Daemon, which is responsible for controlling
the thermal state of processors and preventing overheating.
@end defvr

@deftp {Data Type} thermald-configuration
Data type representing the configuration of @code{thermald-service-type}.

@table @asis
@item @code{ignore-cpuid-check?} (default: @code{#f})
Ignore cpuid check for supported CPU models.

@item @code{thermald} (default: @var{thermald})
Package object of thermald.

@end table
@end deftp

@node 音频服务
@subsection 音频服务

The @code{(gnu services audio)} module provides a service to start MPD (the
Music Player Daemon).

@cindex mpd
@subsubheading Music Player Daemon

The Music Player Daemon (MPD) is a service that can play music while being
controlled from the local machine or over the network by a variety of
clients.

The following example shows how one might run @code{mpd} as user
@code{"bob"} on port @code{6666}.  It uses pulseaudio for output.

@lisp
(service mpd-service-type
         (mpd-configuration
          (user "bob")
          (port "6666")))
@end lisp

@defvr {Scheme Variable} mpd-service-type
The service type for @command{mpd}
@end defvr

@deftp {Data Type} mpd-configuration
Data type representing the configuration of @command{mpd}.

@table @asis
@item @code{user} (default: @code{"mpd"})
The user to run mpd as.

@item @code{music-dir} (default: @code{"~/Music"})
The directory to scan for music files.

@item @code{playlist-dir} (default: @code{"~/.mpd/playlists"})
The directory to store playlists.

@item @code{db-file} (default: @code{"~/.mpd/tag_cache"})
The location of the music database.

@item @code{state-file} (default: @code{"~/.mpd/state"})
The location of the file that stores current MPD's state.

@item @code{sticker-file} (default: @code{"~/.mpd/sticker.sql"})
The location of the sticker database.

@item @code{port} (default: @code{"6600"})
The port to run mpd on.

@item @code{address} (default: @code{"any"})
The address that mpd will bind to.  To use a Unix domain socket, an absolute
path can be specified here.

@item @code{outputs} (default: @code{"(list (mpd-output))"})
The audio outputs that MPD can use.  By default this is a single output
using pulseaudio.

@end table
@end deftp

@deftp {Data Type} mpd-output
Data type representing an @command{mpd} audio output.

@table @asis
@item @code{name} (default: @code{"MPD"})
The name of the audio output.

@item @code{type} (default: @code{"pulse"})
The type of audio output.

@item @code{enabled?} (default: @code{#t})
Specifies whether this audio output is enabled when MPD is started.  By
default, all audio outputs are enabled.  This is just the default setting
when there is no state file; with a state file, the previous state is
restored.

@item @code{tags?} (default: @code{#t})
If set to @code{#f}, then MPD will not send tags to this output.  This is
only useful for output plugins that can receive tags, for example the
@code{httpd} output plugin.

@item @code{always-on?} (default: @code{#f})
If set to @code{#t}, then MPD attempts to keep this audio output always
open.  This may be useful for streaming servers, when you don’t want to
disconnect all listeners even when playback is accidentally stopped.

@item @code{mixer-type}
This field accepts a symbol that specifies which mixer should be used for
this audio output: the @code{hardware} mixer, the @code{software} mixer, the
@code{null} mixer (allows setting the volume, but with no effect; this can
be used as a trick to implement an external mixer External Mixer) or no
mixer (@code{none}).

@item @code{extra-options} (default: @code{'()})
An association list of option symbols to string values to be appended to the
audio output configuration.

@end table
@end deftp

The following example shows a configuration of @code{mpd} that provides an
HTTP audio streaming output.

@lisp
(service mpd-service-type
         (mpd-configuration
           (outputs
             (list (mpd-output
                     (name "streaming")
                     (type "httpd")
                     (mixer-type 'null)
                     (extra-options
                      `((encoder . "vorbis")
                        (port    . "8080"))))))))
@end lisp


@node 虚拟化服务
@subsection 虚拟化服务

The @code{(gnu services virtualization)} module provides services for the
libvirt and virtlog daemons, as well as other virtualization-related
services.

@subsubheading Libvirt daemon

@code{libvirtd} is the server side daemon component of the libvirt
virtualization management system.  This daemon runs on host servers and
performs required management tasks for virtualized guests.

@deffn {Scheme Variable} libvirt-service-type
This is the type of the @uref{https://libvirt.org, libvirt daemon}.  Its
value must be a @code{libvirt-configuration}.

@lisp
(service libvirt-service-type
         (libvirt-configuration
          (unix-sock-group "libvirt")
          (tls-port "16555")))
@end lisp
@end deffn

@c Auto-generated with (generate-libvirt-documentation)
Available @code{libvirt-configuration} fields are:

@deftypevr {@code{libvirt-configuration} parameter} package libvirt
Libvirt package.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean listen-tls?
Flag listening for secure TLS connections on the public TCP/IP port.  You
must set @code{listen} for this to have any effect.

It is necessary to setup a CA and issue server certificates before using
this capability.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean listen-tcp?
Listen for unencrypted TCP connections on the public TCP/IP port.  You must
set @code{listen} for this to have any effect.

Using the TCP socket requires SASL authentication by default.  Only SASL
mechanisms which support data encryption are allowed.  This is DIGEST_MD5
and GSSAPI (Kerberos5).

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tls-port
Port for accepting secure TLS connections.  This can be a port number, or
service name.

Defaults to @samp{"16514"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tcp-port
Port for accepting insecure TCP connections.  This can be a port number, or
service name.

Defaults to @samp{"16509"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string listen-addr
IP address or hostname used for client connections.

Defaults to @samp{"0.0.0.0"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean mdns-adv?
Flag toggling mDNS advertisement of the libvirt service.

Alternatively can disable for all services on a host by stopping the Avahi
daemon.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string mdns-name
Default mDNS advertisement name.  This must be unique on the immediate
broadcast network.

Defaults to @samp{"Virtualization Host <hostname>"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-group
UNIX domain socket group ownership.  This can be used to allow a 'trusted'
set of users access to management capabilities without becoming root.

Defaults to @samp{"root"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-ro-perms
UNIX socket permissions for the R/O socket.  This is used for monitoring VM
status only.

Defaults to @samp{"0777"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-rw-perms
UNIX socket permissions for the R/W socket.  Default allows only root.  If
PolicyKit is enabled on the socket, the default will change to allow
everyone (eg, 0777)

Defaults to @samp{"0770"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-admin-perms
UNIX socket permissions for the admin socket.  Default allows only owner
(root), do not change it unless you are sure to whom you are exposing the
access to.

Defaults to @samp{"0777"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-dir
The directory in which sockets will be found/created.

Defaults to @samp{"/var/run/libvirt"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-unix-ro
Authentication scheme for UNIX read-only sockets.  By default socket
permissions allow anyone to connect

Defaults to @samp{"polkit"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-unix-rw
Authentication scheme for UNIX read-write sockets.  By default socket
permissions only allow root.  If PolicyKit support was compiled into
libvirt, the default will be to use 'polkit' auth.

Defaults to @samp{"polkit"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-tcp
Authentication scheme for TCP sockets.  If you don't enable SASL, then all
TCP traffic is cleartext.  Don't do this outside of a dev/test scenario.

Defaults to @samp{"sasl"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-tls
Authentication scheme for TLS sockets.  TLS sockets already have encryption
provided by the TLS layer, and limited authentication is done by
certificates.

It is possible to make use of any SASL authentication mechanism as well, by
using 'sasl' for this option

Defaults to @samp{"none"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list access-drivers
API access control scheme.

By default an authenticated user is allowed access to all APIs.  Access
drivers can place restrictions on this.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string key-file
Server key file path.  If set to an empty string, then no private key is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string cert-file
Server key file path.  If set to an empty string, then no certificate is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string ca-file
Server key file path.  If set to an empty string, then no CA certificate is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string crl-file
Certificate revocation list path.  If set to an empty string, then no CRL is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean tls-no-sanity-cert
Disable verification of our own server certificates.

When libvirtd starts it performs some sanity checks against its own
certificates.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean tls-no-verify-cert
Disable verification of client certificates.

Client certificate verification is the primary authentication mechanism.
Any client which does not present a certificate signed by the CA will be
rejected.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list tls-allowed-dn-list
Whitelist of allowed x509 Distinguished Name.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list sasl-allowed-usernames
Whitelist of allowed SASL usernames.  The format for username depends on the
SASL authentication mechanism.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tls-priority
Override the compile time default TLS priority string.  The default is
usually @samp{"NORMAL"} unless overridden at build time.  Only set this is
it is desired for libvirt to deviate from the global default settings.

Defaults to @samp{"NORMAL"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-clients
Maximum number of concurrent client connections to allow over all sockets
combined.

Defaults to @samp{5000}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-queued-clients
Maximum length of queue of connections waiting to be accepted by the
daemon.  Note, that some protocols supporting retransmission may obey this
so that a later reattempt at connection succeeds.

Defaults to @samp{1000}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-anonymous-clients
Maximum length of queue of accepted but not yet authenticated clients.  Set
this to zero to turn this feature off

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer min-workers
Number of workers to start up initially.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-workers
Maximum number of worker threads.

If the number of active clients exceeds @code{min-workers}, then more
threads are spawned, up to max_workers limit.  Typically you'd want
max_workers to equal maximum number of clients allowed.

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer prio-workers
Number of priority workers.  If all workers from above pool are stuck, some
calls marked as high priority (notably domainDestroy) can be executed in
this pool.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-requests
Total global limit on concurrent RPC calls.

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-client-requests
Limit on concurrent requests from a single client connection.  To avoid one
client monopolizing the server this should be a small fraction of the global
max_requests and max_workers parameter.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-min-workers
Same as @code{min-workers} but for the admin interface.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-workers
Same as @code{max-workers} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-clients
Same as @code{max-clients} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-queued-clients
Same as @code{max-queued-clients} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-client-requests
Same as @code{max-client-requests} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer log-level
Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string log-filters
Logging filters.

A filter allows to select a different logging level for a given category of
logs.  The format for a filter is one of:

@itemize @bullet
@item
x:name

@item
x:+name

@end itemize

where @code{name} is a string which is matched against the category given in
the @code{VIR_LOG_INIT()} at the top of each libvirt source file, e.g.,
@samp{"remote"}, @samp{"qemu"}, or @samp{"util.json"} (the name in the
filter can be a substring of the full category name, in order to match
multiple similar categories), the optional @samp{"+"} prefix tells libvirt
to log stack trace for each message matching name, and @code{x} is the
minimal level where matching messages should be logged:

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple filters can be defined in a single filters statement, they just
need to be separated by spaces.

Defaults to @samp{"3:remote 4:event"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string log-outputs
Logging outputs.

An output is one of the places to save logging information.  The format for
an output can be:

@table @code
@item x:stderr
output goes to stderr

@item x:syslog:name
use syslog for the output and use the given name as the ident

@item x:file:file_path
output to a file, with the given filepath

@item x:journald
output to journald logging system

@end table

In all case the x prefix is the minimal level, acting as a filter

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple outputs can be defined, they just need to be separated by spaces.

Defaults to @samp{"3:stderr"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer audit-level
Allows usage of the auditing subsystem to be altered

@itemize @bullet
@item
0: disable all auditing

@item
1: enable auditing, only if enabled on host

@item
2: enable auditing, and exit if disabled on host.

@end itemize

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean audit-logging
Send audit messages via libvirt logging infrastructure.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-string host-uuid
Host UUID@.  UUID must not have all digits be the same.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string host-uuid-source
Source to read host UUID.

@itemize @bullet
@item
@code{smbios}: fetch the UUID from @code{dmidecode -s system-uuid}

@item
@code{machine-id}: fetch the UUID from @code{/etc/machine-id}

@end itemize

If @code{dmidecode} does not provide a valid UUID a temporary UUID will be
generated.

Defaults to @samp{"smbios"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer keepalive-interval
A keepalive message is sent to a client after @code{keepalive_interval}
seconds of inactivity to check if the client is still responding.  If set to
-1, libvirtd will never send keepalive requests; however clients can still
send them and the daemon will send responses.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer keepalive-count
Maximum number of keepalive messages that are allowed to be sent to the
client without getting any response before the connection is considered
broken.

In other words, the connection is automatically closed approximately after
@code{keepalive_interval * (keepalive_count + 1)} seconds since the last
message received from the client.  When @code{keepalive-count} is set to 0,
connections will be automatically closed after @code{keepalive-interval}
seconds of inactivity without sending any keepalive messages.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-keepalive-interval
Same as above but for admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-keepalive-count
Same as above but for admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer ovs-timeout
Timeout for Open vSwitch calls.

The @code{ovs-vsctl} utility is used for the configuration and its timeout
option is set by default to 5 seconds to avoid potential infinite waits
blocking libvirt.

Defaults to @samp{5}.

@end deftypevr

@c %end of autogenerated docs

@subsubheading Virtlog daemon
The virtlogd service is a server side daemon component of libvirt that is
used to manage logs from virtual machine consoles.

This daemon is not used directly by libvirt client applications, rather it
is called on their behalf by @code{libvirtd}.  By maintaining the logs in a
standalone daemon, the main @code{libvirtd} daemon can be restarted without
risk of losing logs.  The @code{virtlogd} daemon has the ability to
re-exec()  itself upon receiving @code{SIGUSR1}, to allow live upgrades
without downtime.

@deffn {Scheme Variable} virtlog-service-type
This is the type of the virtlog daemon.  Its value must be a
@code{virtlog-configuration}.

@lisp
(service virtlog-service-type
         (virtlog-configuration
          (max-clients 1000)))
@end lisp
@end deffn

@deftypevr {@code{virtlog-configuration} parameter} integer log-level
Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} string log-filters
Logging filters.

A filter allows to select a different logging level for a given category of
logs The format for a filter is one of:

@itemize @bullet
@item
x:name

@item
x:+name

@end itemize

where @code{name} is a string which is matched against the category given in
the @code{VIR_LOG_INIT()} at the top of each libvirt source file, e.g.,
"remote", "qemu", or "util.json" (the name in the filter can be a substring
of the full category name, in order to match multiple similar categories),
the optional "+" prefix tells libvirt to log stack trace for each message
matching name, and @code{x} is the minimal level where matching messages
should be logged:

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple filters can be defined in a single filters statement, they just
need to be separated by spaces.

Defaults to @samp{"3:remote 4:event"}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} string log-outputs
Logging outputs.

An output is one of the places to save logging information The format for an
output can be:

@table @code
@item x:stderr
output goes to stderr

@item x:syslog:name
use syslog for the output and use the given name as the ident

@item x:file:file_path
output to a file, with the given filepath

@item x:journald
output to journald logging system

@end table

In all case the x prefix is the minimal level, acting as a filter

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple outputs can be defined, they just need to be separated by spaces.

Defaults to @samp{"3:stderr"}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-clients
Maximum number of concurrent client connections to allow over all sockets
combined.

Defaults to @samp{1024}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-size
Maximum file size before rolling over.

Defaults to @samp{2MB}

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-backups
Maximum number of backup files to keep.

Defaults to @samp{3}

@end deftypevr

@anchor{transparent-emulation-qemu}
@subsubheading Transparent Emulation with QEMU

@cindex emulation
@cindex @code{binfmt_misc}
@code{qemu-binfmt-service-type} provides support for transparent emulation
of program binaries built for different architectures---e.g., it allows you
to transparently execute an ARMv7 program on an x86_64 machine.  It achieves
this by combining the @uref{https://www.qemu.org, QEMU} emulator and the
@code{binfmt_misc} feature of the kernel Linux.  This feature only allows
you to emulate GNU/Linux on a different architecture, but see below for
GNU/Hurd support.

@defvr {Scheme Variable} qemu-binfmt-service-type
This is the type of the QEMU/binfmt service for transparent emulation.  Its
value must be a @code{qemu-binfmt-configuration} object, which specifies the
QEMU package to use as well as the architecture we want to emulated:

@lisp
(service qemu-binfmt-service-type
         (qemu-binfmt-configuration
           (platforms (lookup-qemu-platforms "arm" "aarch64"))))
@end lisp

In this example, we enable transparent emulation for the ARM and aarch64
platforms.  Running @code{herd stop qemu-binfmt} turns it off, and running
@code{herd start qemu-binfmt} turns it back on (@pxref{Invoking herd, the
@command{herd} command,, shepherd, The GNU Shepherd Manual}).
@end defvr

@deftp {Data Type} qemu-binfmt-configuration
This is the configuration for the @code{qemu-binfmt} service.

@table @asis
@item @code{platforms} (default: @code{'()})
The list of emulated QEMU platforms.  Each item must be a @dfn{platform
object} as returned by @code{lookup-qemu-platforms} (see below).

For example, let's suppose you're on an x86_64 machine and you have this
service:

@lisp
(service qemu-binfmt-service-type
         (qemu-binfmt-configuration
           (platforms (lookup-qemu-platforms "arm"))))
@end lisp

You can run:

@example
guix build -s armhf-linux inkscape
@end example

@noindent
and it will build Inkscape for ARMv7 @emph{as if it were a native build},
transparently using QEMU to emulate the ARMv7 CPU@.  Pretty handy if you'd
like to test a package build for an architecture you don't have access to!

@item @code{qemu} (default: @code{qemu})
The QEMU package to use.
@end table
@end deftp

@deffn {Scheme Procedure} lookup-qemu-platforms @var{platforms}@dots{}
Return the list of QEMU platform objects corresponding to
@var{platforms}@dots{}.  @var{platforms} must be a list of strings
corresponding to platform names, such as @code{"arm"}, @code{"sparc"},
@code{"mips64el"}, and so on.
@end deffn

@deffn {Scheme Procedure} qemu-platform? @var{obj}
Return true if @var{obj} is a platform object.
@end deffn

@deffn {Scheme Procedure} qemu-platform-name @var{platform}
Return the name of @var{platform}---a string such as @code{"arm"}.
@end deffn


@subsubheading The Hurd in a Virtual Machine

@cindex @code{hurd}
@cindex the Hurd
@cindex childhurd

Service @code{hurd-vm} provides support for running GNU/Hurd in a virtual
machine (VM), a so-called @dfn{childhurd}.  This service is meant to be used
on GNU/Linux and the given GNU/Hurd operating system configuration is
cross-compiled.  The virtual machine is a Shepherd service that can be
referred to by the names @code{hurd-vm} and @code{childhurd} and be
controlled with commands such as:

@example
herd start hurd-vm
herd stop childhurd
@end example

When the service is running, you can view its console by connecting to it
with a VNC client, for example with:

@example
guix environment --ad-hoc tigervnc-client -- \
         vncviewer localhost:5900
@end example

The default configuration (see @code{hurd-vm-configuration} below)  spawns a
secure shell (SSH) server in your GNU/Hurd system, which QEMU (the virtual
machine emulator) redirects to port 10222 on the host.  Thus, you can
connect over SSH to the childhurd with:

@example
ssh root@@localhost -p 10022
@end example

The childhurd is volatile and stateless: it starts with a fresh root file
system every time you restart it.  By default though, all the files under
@file{/etc/childhurd} on the host are copied as is to the root file system
of the childhurd when it boots.  This allows you to initialize ``secrets''
inside the VM: SSH host keys, authorized substitute keys, and so on---see
the explanation of @code{secret-root} below.

@defvr {Scheme Variable} hurd-vm-service-type
This is the type of the Hurd in a Virtual Machine service.  Its value must
be a @code{hurd-vm-configuration} object, which specifies the operating
system (@pxref{操作系统参考}) and the disk size for the Hurd
Virtual Machine, the QEMU package to use as well as the options for running
it.

For example:

@lisp
(service hurd-vm-service-type
         (hurd-vm-configuration
          (disk-size (* 5000 (expt 2 20))) ;5G
          (memory-size 1024)))             ;1024MiB
@end lisp

would create a disk image big enough to build GNU@tie{}Hello, with some
extra memory.
@end defvr

@deftp {Data Type} hurd-vm-configuration
The data type representing the configuration for
@code{hurd-vm-service-type}.

@table @asis
@item @code{os} (default: @var{%hurd-vm-operating-system})
The operating system to instantiate.  This default is bare-bones with a
permissive OpenSSH secure shell daemon listening on port 2222
(@pxref{网络服务, @code{openssh-service-type}}).

@item @code{qemu} (default: @code{qemu-minimal})
The QEMU package to use.

@item @code{image} (default: @var{hurd-vm-disk-image})
The procedure used to build the disk-image built from this configuration.

@item @code{disk-size} (default: @code{'guess})
The size of the disk image.

@item @code{memory-size} (default: @code{512})
The memory size of the Virtual Machine in mebibytes.

@item @code{options} (default: @code{'("--snapshot")})
The extra options for running QEMU.

@item @code{id} (default: @code{#f})
If set, a non-zero positive integer used to parameterize Childhurd
instances.  It is appended to the service's name, e.g. @code{childhurd1}.

@item @code{net-options} (default: @var{hurd-vm-net-options})
The procedure used to produce the list of QEMU networking options.

By default, it produces

@lisp
'("--device" "rtl8139,netdev=net0"
  "--netdev" "user,id=net0\
              ,hostfwd=tcp:127.0.0.1:@var{secrets-port}-:1004\
              ,hostfwd=tcp:127.0.0.1:@var{ssh-port}-:2222\
              ,hostfwd=tcp:127.0.0.1:@var{vnc-port}-:5900")
@end lisp

with forwarded ports:

@example
@var{secrets-port}: @code{(+ 11004 (* 1000 @var{ID}))}
@var{ssh-port}: @code{(+ 10022 (* 1000 @var{ID}))}
@var{vnc-port}: @code{(+ 15900 (* 1000 @var{ID}))}
@end example

@item @code{secret-root} (default: @file{/etc/childhurd})
The root directory with out-of-band secrets to be installed into the
childhurd once it runs.  Childhurds are volatile which means that on every
startup, secrets such as the SSH host keys and Guix signing key are
recreated.

If the @file{/etc/childhurd} directory does not exist, the
@code{secret-service} running in the Childhurd will be sent an empty list of
secrets.

By default, the service automatically populates @file{/etc/childhurd} with
the following non-volatile secrets, unless they already exist:

@example
/etc/childhurd/etc/guix/acl
/etc/childhurd/etc/guix/signing-key.pub
/etc/childhurd/etc/guix/signing-key.sec
/etc/childhurd/etc/ssh/ssh_host_ed25519_key
/etc/childhurd/etc/ssh/ssh_host_ecdsa_key
/etc/childhurd/etc/ssh/ssh_host_ed25519_key.pub
/etc/childhurd/etc/ssh/ssh_host_ecdsa_key.pub
@end example

These files are automatically sent to the guest Hurd VM when it boots,
including permissions.

@cindex childhurd, offloading
@cindex Hurd, offloading
Having these files in place means that only a couple of things are missing
to allow the host to offload @code{i586-gnu} builds to the childhurd:

@enumerate
@item
Authorizing the childhurd's key on the host so that the host accepts build
results coming from the childhurd, which can be done like so:

@example
guix archive --authorize < \
  /etc/childhurd/etc/guix/signing-key.pub
@end example

@item
Adding the childhurd to @file{/etc/guix/machines.scm} (@pxref{下发工作给后台进程的设置}).
@end enumerate

We're working towards making that happen automatically---get in touch with
us at @email{guix-devel@@gnu.org} to discuss it!
@end table
@end deftp

Note that by default the VM image is volatile, i.e., once stopped the
contents are lost.  If you want a stateful image instead, override the
configuration's @code{image} and @code{options} without the
@code{--snapshot} flag using something along these lines:

@lisp
(service hurd-vm-service-type
         (hurd-vm-configuration
          (image   (const "/out/of/store/writable/hurd.img"))
          (options '())))
@end lisp

@subsubheading Ganeti

@cindex ganeti

@quotation 注
This service is considered experimental.  Configuration options may be
changed in a backwards-incompatible manner, and not all features have been
thorougly tested.  Users of this service are encouraged to share their
experience at @email{guix-devel@@gnu.org}.
@end quotation

Ganeti is a virtual machine management system.  It is designed to keep
virtual machines running on a cluster of servers even in the event of
hardware failures, and to make maintenance and recovery tasks easy.  It
consists of multiple services which are described later in this section.  In
addition to the Ganeti service, you will need the OpenSSH service
(@pxref{网络服务, @code{openssh-service-type}}), and update the
@file{/etc/hosts} file (@pxref{操作系统参考,
@code{hosts-file}}) with the cluster name and address (or use a DNS server).

All nodes participating in a Ganeti cluster should have the same Ganeti and
@file{/etc/hosts} configuration.  Here is an example configuration for a
Ganeti cluster node that supports multiple storage backends, and installs
the @code{debootstrap} and @code{guix} @dfn{OS providers}:

@lisp
(use-package-modules virtualization)
(use-service-modules base ganeti networking ssh)
(operating-system
  ;; @dots{}
  (host-name "node1")
  (hosts-file (plain-file "hosts" (format #f "
127.0.0.1       localhost
::1             localhost

192.168.1.200   ganeti.example.com
192.168.1.201   node1.example.com node1
192.168.1.202   node2.example.com node2
")))

  ;; Install QEMU so we can use KVM-based instances, and LVM, DRBD and Ceph
  ;; in order to use the "plain", "drbd" and "rbd" storage backends.
  (packages (append (map specification->package
                         '("qemu" "lvm2" "drbd-utils" "ceph"
                           ;; Add the debootstrap and guix OS providers.
                           "ganeti-instance-guix" "ganeti-instance-debootstrap"))
                    %base-packages))
  (services
   (append (list (static-networking-service "eth0" "192.168.1.201"
                                            #:netmask "255.255.255.0"
                                            #:gateway "192.168.1.254"
                                            #:name-servers '("192.168.1.252"
                                                             "192.168.1.253"))

                 ;; Ganeti uses SSH to communicate between nodes.
                 (service openssh-service-type
                          (openssh-configuration
                           (permit-root-login 'without-password)))

                 (service ganeti-service-type
                          (ganeti-configuration
                           ;; This list specifies allowed file system paths
                           ;; for storing virtual machine images.
                           (file-storage-paths '("/srv/ganeti/file-storage"))
                           ;; This variable configures a single "variant" for
                           ;; both Debootstrap and Guix that works with KVM.
                           (os %default-ganeti-os))))
           %base-services)))
@end lisp

Users are advised to read the
@url{http://docs.ganeti.org/ganeti/master/html/admin.html,Ganeti
administrators guide} to learn about the various cluster options and
day-to-day operations.  There is also a
@url{https://guix.gnu.org/blog/2020/running-a-ganeti-cluster-on-guix/,blog
post} describing how to configure and initialize a small cluster.

@defvr {Scheme Variable} ganeti-service-type
This is a service type that includes all the various services that Ganeti
nodes should run.

Its value is a @code{ganeti-configuration} object that defines the package
to use for CLI operations, as well as configuration for the various
daemons.  Allowed file storage paths and available guest operating systems
are also configured through this data type.
@end defvr

@deftp {Data Type} ganeti-configuration
The @code{ganeti} service takes the following configuration options:

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use.  It will be installed to the system
profile and make @command{gnt-cluster}, @command{gnt-instance}, etc
available.  Note that the value specified here does not affect the other
services as each refer to a specific @code{ganeti} package (see below).

@item @code{noded-configuration} (default: @code{(ganeti-noded-configuration)})
@itemx @code{confd-configuration} (default: @code{(ganeti-confd-configuration)})
@itemx @code{wconfd-configuration} (default: @code{(ganeti-wconfd-configuration)})
@itemx @code{luxid-configuration} (default: @code{(ganeti-luxid-configuration)})
@itemx @code{rapi-configuration} (default: @code{(ganeti-rapi-configuration)})
@itemx @code{kvmd-configuration} (default: @code{(ganeti-kvmd-configuration)})
@itemx @code{mond-configuration} (default: @code{(ganeti-mond-configuration)})
@itemx @code{metad-configuration} (default: @code{(ganeti-metad-configuration)})
@itemx @code{watcher-configuration} (default: @code{(ganeti-watcher-configuration)})
@itemx @code{cleaner-configuration} (default: @code{(ganeti-cleaner-configuration)})

These options control the various daemons and cron jobs that are distributed
with Ganeti.  The possible values for these are described in detail below.
To override a setting, you must use the configuration type for that service:

@lisp
(service ganeti-service-type
         (ganeti-configuration
          (rapi-configuration
           (ganeti-rapi-configuration
            (interface "eth1"))))
          (watcher-configuration
           (ganeti-watcher-configuration
            (rapi-ip "10.0.0.1"))))
@end lisp

@item @code{file-storage-paths} (default: @code{'()})
List of allowed directories for file storage backend.

@item @code{os} (default: @code{%default-ganeti-os})
List of @code{<ganeti-os>} records.
@end table

In essence @code{ganeti-service-type} is shorthand for declaring each
service individually:

@lisp
(service ganeti-noded-service-type)
(service ganeti-confd-service-type)
(service ganeti-wconfd-service-type)
(service ganeti-luxid-service-type)
(service ganeti-kvmd-service-type)
(service ganeti-mond-service-type)
(service ganeti-metad-service-type)
(service ganeti-watcher-service-type)
(service ganeti-cleaner-service-type)
@end lisp

Plus a service extension for @code{etc-service-type} that configures the
file storage backend and OS variants.

@end deftp

@deftp {Data Type} ganeti-os
This data type is suitable for passing to the @code{os} parameter of
@code{ganeti-configuration}.  It takes the following parameters:

@table @asis
@item @code{名字}
The name for this OS provider.  It is only used to specify where the
configuration ends up.  Setting it to ``debootstrap'' will create
@file{/etc/ganeti/instance-debootstrap}.

@item @code{extension}
The file extension for variants of this OS type.  For example @file{.conf}
or @file{.scm}.

@item @code{variants} (default: @code{'()})
List of @code{ganeti-os-variant} objects for this OS.

@end table
@end deftp

@deftp {Data Type} ganeti-os-variant
This is the data type for a Ganeti OS variant.  It takes the following
parameters:

@table @asis
@item @code{名字}
The name of this variant.

@item @code{configuration}
A configuration file for this variant.
@end table
@end deftp

@defvr {Scheme Variable} %default-debootstrap-hooks
This variable contains hooks to configure networking and the GRUB
bootloader.
@end defvr

@defvr {Scheme Variable} %default-debootstrap-extra-pkgs
This variable contains a list of packages suitable for a fully-virtualized
guest.
@end defvr

@deftp {Data Type} debootstrap-configuration

This data type creates configuration files suitable for the debootstrap OS
provider.

@table @asis
@item @code{hooks} (default: @code{%default-debootstrap-hooks})
When not @code{#f}, this must be a G-expression that specifies a directory
with scripts that will run when the OS is installed.  It can also be a list
of @code{(name . file-like)} pairs.  For example:

@lisp
`((99-hello-world . ,(plain-file "#!/bin/sh\necho Hello, World")))
@end lisp

That will create a directory with one executable named @code{99-hello-world}
and run it every time this variant is installed.  If set to @code{#f}, hooks
in @file{/etc/ganeti/instance-debootstrap/hooks} will be used, if any.
@item @code{proxy} (default: @code{#f})
Optional HTTP proxy to use.
@item @code{mirror} (default: @code{#f})
The Debian mirror.  Typically something like
@code{http://ftp.no.debian.org/debian}.  The default varies depending on the
distribution.
@item @code{arch} (default: @code{#f})
The dpkg architecture.  Set to @code{armhf} to debootstrap an ARMv7 instance
on an AArch64 host.  Default is to use the current system architecture.
@item @code{suite} (default: @code{"stable"})
When set, this must be a Debian distribution ``suite'' such as @code{buster}
or @code{focal}.  If set to @code{#f}, the default for the OS provider is
used.
@item @code{extra-pkgs} (default: @code{%default-debootstrap-extra-pkgs})
List of extra packages that will get installed by dpkg in addition to the
minimal system.
@item @code{components} (default: @code{#f})
When set, must be a list of Debian repository ``components''.  For example
@code{'("main" "contrib")}.
@item @code{generate-cache?} (default: @code{#t})
Whether to automatically cache the generated debootstrap archive.
@item @code{clean-cache} (default: @code{14})
Discard the cache after this amount of days.  Use @code{#f} to never clear
the cache.
@item @code{partition-style} (default: @code{'msdos})
The type of partition to create.  When set, it must be one of @code{'msdos},
@code{'none} or a string.
@item @code{partition-alignment} (default: @code{2048})
Alignment of the partition in sectors.
@end table
@end deftp

@deffn {Scheme Procedure} debootstrap-variant @var{name} @var{configuration}
This is a helper procedure that creates a @code{ganeti-os-variant} record.
It takes two parameters: a name and a @code{debootstrap-configuration}
object.
@end deffn

@deffn {Scheme Procedure} debootstrap-os @var{variants}@dots{}
This is a helper procedure that creates a @code{ganeti-os} record.  It takes
a list of variants created with @code{debootstrap-variant}.
@end deffn

@deffn {Scheme Procedure} guix-variant @var{name} @var{configuration}
This is a helper procedure that creates a @code{ganeti-os-variant} record
for use with the Guix OS provider.  It takes a name and a G-expression that
returns a ``file-like'' (@pxref{G-表达式, file-like objects}) object
containing a Guix System configuration.
@end deffn

@deffn {Scheme Procedure} guix-os @var{variants}@dots{}
This is a helper procedure that creates a @code{ganeti-os} record.  It takes
a list of variants produced by @code{guix-variant}.
@end deffn

@defvr {Scheme Variable} %default-debootstrap-variants
This is a convenience variable to make the debootstrap provider work ``out
of the box'' without users having to declare variants manually.  It contains
a single debootstrap variant with the default configuration:

@lisp
(list (debootstrap-variant
       "default"
       (debootstrap-configuration)))
@end lisp
@end defvr

@defvr {Scheme Variable} %default-guix-variants
This is a convenience variable to make the Guix OS provider work without
additional configuration.  It creates a virtual machine that has an SSH
server, a serial console, and authorizes the Ganeti hosts SSH keys.

@lisp
(list (guix-variant
       "default"
       (file-append ganeti-instance-guix
                    "/share/doc/ganeti-instance-guix/examples/dynamic.scm")))
@end lisp
@end defvr

Users can implement support for OS providers unbeknownst to Guix by
extending the @code{ganeti-os} and @code{ganeti-os-variant} records
appropriately.  For example:

@lisp
(ganeti-os
 (name "custom")
 (extension ".conf")
 (variants
  (list (ganeti-os-variant
         (name "foo")
         (configuration (plain-file "bar" "this is fine"))))))
@end lisp

That creates @file{/etc/ganeti/instance-custom/variants/foo.conf} which
points to a file in the store with contents @code{this is fine}.  It also
creates @file{/etc/ganeti/instance-custom/variants/variants.list} with
contents @code{foo}.

Obviously this may not work for all OS providers out there.  If you find the
interface limiting, please reach out to @email{guix-devel@@gnu.org}.

The rest of this section documents the various services that are included by
@code{ganeti-service-type}.

@defvr {Scheme Variable} ganeti-noded-service-type
@command{ganeti-noded} is the daemon responsible for node-specific functions
within the Ganeti system.  The value of this service must be a
@code{ganeti-noded-configuration} object.
@end defvr

@deftp {Data Type} ganeti-noded-configuration
This is the configuration for the @code{ganeti-noded} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{1811})
The TCP port on which the node daemon listens for network requests.

@item @code{address} (default: @code{"0.0.0.0"})
The network address that the daemon will bind to.  The default address means
bind to all available addresses.

@item @code{interface} (default: @code{#f})
When this is set, it must be a specific network interface (e.g.@:
@code{eth0})  that the daemon will bind to.

@item @code{max-clients} (default: @code{20})
This sets a limit on the maximum number of simultaneous client connections
that the daemon will handle.  Connections above this count are accepted, but
no responses will be sent until enough connections have closed.

@item @code{ssl?} (default: @code{#t})
Whether to use SSL/TLS to encrypt network communications.  The certificate
is automatically provisioned by the cluster and can be rotated with
@command{gnt-cluster renew-crypto}.

@item @code{ssl-key} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific encryption key for TLS
communications.

@item @code{ssl-cert} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific certificate for TLS communications.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.
Note that this will leak encryption details to the log files, use with
caution.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-confd-service-type
@command{ganeti-confd} answers queries related to the configuration of a
Ganeti cluster.  The purpose of this daemon is to have a highly available
and fast way to query cluster configuration values.  It is automatically
active on all @dfn{master candidates}.  The value of this service must be a
@code{ganeti-confd-configuration} object.

@end defvr

@deftp {Data Type} ganeti-confd-configuration
This is the configuration for the @code{ganeti-confd} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{1814})
The UDP port on which to listen for network requests.

@item @code{address} (default: @code{"0.0.0.0"})
Network address that the daemon will bind to.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-wconfd-service-type
@command{ganeti-wconfd} is the daemon that has authoritative knowledge about
the cluster configuration and is the only entity that can accept changes to
it.  All jobs that need to modify the configuration will do so by sending
appropriate requests to this daemon.  It only runs on the @dfn{master node}
and will automatically disable itself on other nodes.

The value of this service must be a @code{ganeti-wconfd-configuration}
object.
@end defvr

@deftp {Data Type} ganeti-wconfd-configuration
This is the configuration for the @code{ganeti-wconfd} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{no-voting?} (default: @code{#f})
The daemon will refuse to start if the majority of cluster nodes does not
agree that it is running on the master node.  Set to @code{#t} to start even
if a quorum can not be reached (dangerous, use with caution).

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-luxid-service-type
@command{ganeti-luxid} is a daemon used to answer queries related to the
configuration and the current live state of a Ganeti cluster.  Additionally,
it is the authoritative daemon for the Ganeti job queue.  Jobs can be
submitted via this daemon and it schedules and starts them.

It takes a @code{ganeti-luxid-configuration} object.
@end defvr

@deftp {Data Type} ganeti-luxid-configuration
This is the configuration for the @code{ganeti-wconfd} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{no-voting?} (default: @code{#f})
The daemon will refuse to start if it cannot verify that the majority of
cluster nodes believes that it is running on the master node.  Set to
@code{#t} to ignore such checks and start anyway (this can be dangerous).

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-rapi-service-type
@command{ganeti-rapi} provides a remote API for Ganeti clusters.  It runs on
the master node and can be used to perform cluster actions programmatically
via a JSON-based RPC protocol.

Most query operations are allowed without authentication (unless
@var{require-authentication?} is set), whereas write operations require
explicit authorization via the @file{/var/lib/ganeti/rapi/users} file.  See
the @url{http://docs.ganeti.org/ganeti/master/html/rapi.html, Ganeti Remote
API documentation} for more information.

The value of this service must be a @code{ganeti-rapi-configuration} object.
@end defvr

@deftp {Data Type} ganeti-rapi-configuration
This is the configuration for the @code{ganeti-rapi} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{require-authentication?} (default: @code{#f})
Whether to require authentication even for read-only operations.

@item @code{port} (default: @code{5080})
The TCP port on which to listen to API requests.

@item @code{address} (default: @code{"0.0.0.0"})
The network address that the service will bind to.  By default it listens on
all configured addresses.

@item @code{interface} (default: @code{#f})
When set, it must specify a specific network interface such as @code{eth0}
that the daemon will bind to.

@item @code{max-clients} (default: @code{20})
The maximum number of simultaneous client requests to handle.  Further
connections are allowed, but no responses are sent until enough connections
have closed.

@item @code{ssl?} (default: @code{#t})
Whether to use SSL/TLS encryption on the RAPI port.

@item @code{ssl-key} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific encryption key for TLS
communications.

@item @code{ssl-cert} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific certificate for TLS communications.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.
Note that this will leak encryption details to the log files, use with
caution.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-kvmd-service-type
@command{ganeti-kvmd} is responsible for determining whether a given KVM
instance was shut down by an administrator or a user.  Normally Ganeti will
restart an instance that was not stopped through Ganeti itself.  If the
cluster option @code{user_shutdown} is true, this daemon monitors the
@code{QMP} socket provided by QEMU and listens for shutdown events, and
marks the instance as @dfn{USER_down} instead of @dfn{ERROR_down} when it
shuts down gracefully by itself.

It takes a @code{ganeti-kvmd-configuration} object.
@end defvr

@deftp {Data Type} ganeti-kvmd-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-mond-service-type
@command{ganeti-mond} is an optional daemon that provides Ganeti monitoring
functionality.  It is responsible for running data collectors and publish
the collected information through a HTTP interface.

It takes a @code{ganeti-mond-configuration} object.
@end defvr

@deftp {Data Type} ganeti-mond-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{1815})
The port on which the daemon will listen.

@item @code{address} (default: @code{"0.0.0.0"})
The network address that the daemon will bind to.  By default it binds to
all available interfaces.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-metad-service-type
@command{ganeti-metad} is an optional daemon that can be used to provide
information about the cluster to instances or OS install scripts.

It takes a @code{ganeti-metad-configuration} object.
@end defvr

@deftp {Data Type} ganeti-metad-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{80})
The port on which the daemon will listen.

@item @code{address} (default: @code{#f})
If set, the daemon will bind to this address only.  If left unset, the
behavior depends on the cluster configuration.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-watcher-service-type
@command{ganeti-watcher} is a script designed to run periodically and ensure
the health of a cluster.  It will automatically restart instances that have
stopped without Ganeti's consent, and repairs DRBD links in case a node has
rebooted.  It also archives old cluster jobs and restarts Ganeti daemons
that are not running.  If the cluster parameter @code{ensure_node_health} is
set, the watcher will also shutdown instances and DRBD devices if the node
it is running on is declared offline by known master candidates.

It can be paused on all nodes with @command{gnt-cluster watcher pause}.

The service takes a @code{ganeti-watcher-configuration} object.
@end defvr

@deftp {Data Type} ganeti-watcher-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{schedule} (default: @code{'(next-second-from (next-minute (range 0 60 5)))})
How often to run the script.  The default is every five minutes.

@item @code{rapi-ip} (default: @code{#f})
This option needs to be specified only if the RAPI daemon is configured to
use a particular interface or address.  By default the cluster address is
used.

@item @code{job-age} (default: @code{(* 6 3600)})
Archive cluster jobs older than this age, specified in seconds.  The default
is 6 hours.  This keeps @command{gnt-job list} manageable.

@item @code{verify-disks?} (default: @code{#t})
If this is @code{#f}, the watcher will not try to repair broken DRBD links
automatically.  Administrators will need to use @command{gnt-cluster
verify-disks} manually instead.

@item @code{debug?} (default: @code{#f})
When @code{#t}, the script performs additional logging for debugging
purposes.

@end table
@end deftp

@defvr {Scheme Variable} ganeti-cleaner-service-type
@command{ganeti-cleaner} is a script designed to run periodically and remove
old files from the cluster.  This service type controls two @dfn{cron jobs}:
one intended for the master node that permanently purges old cluster jobs,
and one intended for every node that removes expired X509 certificates,
keys, and outdated @command{ganeti-watcher} information.  Like all Ganeti
services, it is safe to include even on non-master nodes as it will disable
itself as necessary.

It takes a @code{ganeti-cleaner-configuration} object.
@end defvr

@deftp {Data Type} ganeti-cleaner-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for the @command{gnt-cleaner} command.

@item @code{master-schedule} (default: @code{"45 1 * * *"})
How often to run the master cleaning job.  The default is once per day, at
01:45:00.

@item @code{node-schedule} (default: @code{"45 2 * * *"})
How often to run the node cleaning job.  The default is once per day, at
02:45:00.

@end table
@end deftp

@node 版本控制服务
@subsection 版本控制服务

The @code{(gnu services version-control)} module provides a service to allow
remote access to local Git repositories.  There are three options: the
@code{git-daemon-service}, which provides access to repositories via the
@code{git://} unsecured TCP-based protocol, extending the @code{nginx} web
server to proxy some requests to @code{git-http-backend}, or providing a web
interface with @code{cgit-service-type}.

@deffn {Scheme Procedure} git-daemon-service [#:config (git-daemon-configuration)]

Return a service that runs @command{git daemon}, a simple TCP server to
expose repositories over the Git protocol for anonymous access.

The optional @var{config} argument should be a
@code{<git-daemon-configuration>} object, by default it allows read-only
access to exported@footnote{By creating the magic file
@file{git-daemon-export-ok} in the repository directory.} repositories under
@file{/srv/git}.

@end deffn

@deftp {Data Type} git-daemon-configuration
Data type representing the configuration for @code{git-daemon-service}.

@table @asis
@item @code{package} (default: @code{git})
Package object of the Git distributed version control system.

@item @code{export-all?} (default: @code{#f})
Whether to allow access for all Git repositories, even if they do not have
the @file{git-daemon-export-ok} file.

@item @code{base-path} (default: @file{/srv/git})
Whether to remap all the path requests as relative to the given path.  If
you run @command{git daemon} with @code{(base-path "/srv/git")} on
@samp{example.com}, then if you later try to pull
@indicateurl{git://example.com/hello.git}, git daemon will interpret the
path as @file{/srv/git/hello.git}.

@item @code{user-path} (default: @code{#f})
Whether to allow @code{~user} notation to be used in requests.  When
specified with empty string, requests to @indicateurl{git://host/~alice/foo}
is taken as a request to access @code{foo} repository in the home directory
of user @code{alice}.  If @code{(user-path "@var{path}")} is specified, the
same request is taken as a request to access @file{@var{path}/foo}
repository in the home directory of user @code{alice}.

@item @code{listen} (default: @code{'()})
Whether to listen on specific IP addresses or hostnames, defaults to all.

@item @code{port} (default: @code{#f})
Whether to listen on an alternative port, which defaults to 9418.

@item @code{whitelist} (default: @code{'()})
If not empty, only allow access to this list of directories.

@item @code{extra-options} (default: @code{'()})
Extra options will be passed to @command{git daemon}, please run
@command{man git-daemon} for more information.

@end table
@end deftp

The @code{git://} protocol lacks authentication.  When you pull from a
repository fetched via @code{git://}, you don't know whether the data you
receive was modified or is even coming from the specified host, and your
connection is subject to eavesdropping.  It's better to use an authenticated
and encrypted transport, such as @code{https}.  Although Git allows you to
serve repositories using unsophisticated file-based web servers, there is a
faster protocol implemented by the @code{git-http-backend} program.  This
program is the back-end of a proper Git web service.  It is designed to sit
behind a FastCGI proxy.  @xref{Web服务}, for more on running the
necessary @code{fcgiwrap} daemon.

Guix has a separate configuration data type for serving Git repositories
over HTTP.

@deftp {Data Type} git-http-configuration
Data type representing the configuration for a future
@code{git-http-service-type}; can currently be used to configure Nginx
through @code{git-http-nginx-location-configuration}.

@table @asis
@item @code{package} (default: @var{git})
Package object of the Git distributed version control system.

@item @code{git-root} (default: @file{/srv/git})
Directory containing the Git repositories to expose to the world.

@item @code{export-all?} (default: @code{#f})
Whether to expose access for all Git repositories in @var{git-root}, even if
they do not have the @file{git-daemon-export-ok} file.

@item @code{uri-path} (default: @samp{/git/})
Path prefix for Git access.  With the default @samp{/git/} prefix, this will
map @indicateurl{http://@var{server}/git/@var{repo}.git} to
@file{/srv/git/@var{repo}.git}.  Requests whose URI paths do not begin with
this prefix are not passed on to this Git instance.

@item @code{fcgiwrap-socket} (default: @code{127.0.0.1:9000})
The socket on which the @code{fcgiwrap} daemon is listening.  @xref{Web服务}.
@end table
@end deftp

There is no @code{git-http-service-type}, currently; instead you can create
an @code{nginx-location-configuration} from a @code{git-http-configuration}
and then add that location to a web server.

@deffn {Scheme Procedure} git-http-nginx-location-configuration @
       [config=(git-http-configuration)] Compute an
@code{nginx-location-configuration} that corresponds to the given Git http
configuration.  An example nginx service definition to serve the default
@file{/srv/git} over HTTPS might be:

@lisp
(service nginx-service-type
         (nginx-configuration
          (server-blocks
           (list
            (nginx-server-configuration
             (listen '("443 ssl"))
             (server-name "git.my-host.org")
             (ssl-certificate
              "/etc/letsencrypt/live/git.my-host.org/fullchain.pem")
             (ssl-certificate-key
              "/etc/letsencrypt/live/git.my-host.org/privkey.pem")
             (locations
              (list
               (git-http-nginx-location-configuration
                (git-http-configuration (uri-path "/"))))))))))
@end lisp

This example assumes that you are using Let's Encrypt to get your TLS
certificate.  @xref{证书服务}.  The default @code{certbot}
service will redirect all HTTP traffic on @code{git.my-host.org} to HTTPS@.
You will also need to add an @code{fcgiwrap} proxy to your system services.
@xref{Web服务}.
@end deffn

@subsubheading Cgit Service

@cindex Cgit service
@cindex Git, web interface
@uref{https://git.zx2c4.com/cgit/, Cgit} is a web frontend for Git
repositories written in C.

The following example will configure the service with default values.  By
default, Cgit can be accessed on port 80 (@code{http://localhost:80}).

@lisp
(service cgit-service-type)
@end lisp

The @code{file-object} type designates either a file-like object
(@pxref{G-表达式, file-like objects}) or a string.

@c %start of fragment

Available @code{cgit-configuration} fields are:

@deftypevr {@code{cgit-configuration} parameter} package package
The CGIT package.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} nginx-server-configuration-list nginx
NGINX configuration.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object about-filter
Specifies a command which will be invoked to format the content of about
pages (both top-level and for each repository).

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string agefile
Specifies a path, relative to each repository path, which can be used to
specify the date and time of the youngest commit in the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object auth-filter
Specifies a command that will be invoked for authenticating repository
access.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string branch-sort
Flag which, when set to @samp{age}, enables date ordering in the branch ref
list, and when set @samp{name} enables ordering by branch name.

Defaults to @samp{"name"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string cache-root
Path used to store the cgit cache entries.

Defaults to @samp{"/var/cache/cgit"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-static-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of repository pages accessed with a fixed SHA1.

Defaults to @samp{-1}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-dynamic-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of repository pages accessed without a fixed SHA1.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-repo-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of the repository summary page.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-root-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of the repository index page.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-scanrc-ttl
Number which specifies the time-to-live, in minutes, for the result of
scanning a path for Git repositories.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-about-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of the repository about page.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-snapshot-ttl
Number which specifies the time-to-live, in minutes, for the cached version
of snapshots.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-size
The maximum number of entries in the cgit cache.  When set to @samp{0},
caching is disabled.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean case-sensitive-sort?
Sort items in the repo list case sensitively.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list clone-prefix
List of common prefixes which, when combined with a repository URL,
generates valid clone URLs for the repository.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list clone-url
List of @code{clone-url} templates.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object commit-filter
Command which will be invoked to format commit messages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string commit-sort
Flag which, when set to @samp{date}, enables strict date ordering in the
commit log, and when set to @samp{topo} enables strict topological ordering.

Defaults to @samp{"git log"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object css
URL which specifies the css document to include in all cgit pages.

Defaults to @samp{"/share/cgit/cgit.css"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object email-filter
Specifies a command which will be invoked to format names and email address
of committers, authors, and taggers, as represented in various places
throughout the cgit interface.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean embedded?
Flag which, when set to @samp{#t}, will make cgit generate a HTML fragment
suitable for embedding in other HTML pages.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-commit-graph?
Flag which, when set to @samp{#t}, will make cgit print an ASCII-art commit
history graph to the left of the commit messages in the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-filter-overrides?
Flag which, when set to @samp{#t}, allows all filter settings to be
overridden in repository-specific cgitrc files.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-follow-links?
Flag which, when set to @samp{#t}, allows users to follow a file in the log
view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-http-clone?
If set to @samp{#t}, cgit will act as an dumb HTTP endpoint for Git clones.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-index-links?
Flag which, when set to @samp{#t}, will make cgit generate extra links
"summary", "commit", "tree" for each repo in the repository index.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-index-owner?
Flag which, when set to @samp{#t}, will make cgit display the owner of each
repo in the repository index.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-log-filecount?
Flag which, when set to @samp{#t}, will make cgit print the number of
modified files for each commit on the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-log-linecount?
Flag which, when set to @samp{#t}, will make cgit print the number of added
and removed lines for each commit on the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-remote-branches?
Flag which, when set to @code{#t}, will make cgit display remote branches in
the summary and refs views.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-subject-links?
Flag which, when set to @code{1}, will make cgit use the subject of the
parent commit as link text when generating links to parent commits in commit
view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-html-serving?
Flag which, when set to @samp{#t}, will make cgit use the subject of the
parent commit as link text when generating links to parent commits in commit
view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-tree-linenumbers?
Flag which, when set to @samp{#t}, will make cgit generate linenumber links
for plaintext blobs printed in the tree view.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-git-config?
Flag which, when set to @samp{#f}, will allow cgit to use Git config to set
any repo specific settings.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object favicon
URL used as link to a shortcut icon for cgit.

Defaults to @samp{"/favicon.ico"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string footer
The content of the file specified with this option will be included verbatim
at the bottom of all pages (i.e.@: it replaces the standard "generated
by..."@: message).

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string head-include
The content of the file specified with this option will be included verbatim
in the HTML HEAD section on all pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string header
The content of the file specified with this option will be included verbatim
at the top of all pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object include
Name of a configfile to include before the rest of the current config- file
is parsed.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string index-header
The content of the file specified with this option will be included verbatim
above the repository index.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string index-info
The content of the file specified with this option will be included verbatim
below the heading on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean local-time?
Flag which, if set to @samp{#t}, makes cgit print commit and tag times in
the servers timezone.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object logo
URL which specifies the source of an image which will be used as a logo on
all cgit pages.

Defaults to @samp{"/share/cgit/cgit.png"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string logo-link
URL loaded when clicking on the cgit logo image.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object owner-filter
Command which will be invoked to format the Owner column of the main page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-atom-items
Number of items to display in atom feeds view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-commit-count
Number of entries to list per page in "log" view.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-message-length
Number of commit message characters to display in "log" view.

Defaults to @samp{80}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-repo-count
Specifies the number of entries to list per page on the repository index
page.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-repodesc-length
Specifies the maximum number of repo description characters to display on
the repository index page.

Defaults to @samp{80}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-blob-size
Specifies the maximum size of a blob to display HTML for in KBytes.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string max-stats
Maximum statistics period.  Valid values are @samp{week},@samp{month},
@samp{quarter} and @samp{year}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} mimetype-alist mimetype
Mimetype for the specified filename extension.

Defaults to @samp{((gif "image/gif") (html "text/html") (jpg "image/jpeg")
(jpeg "image/jpeg") (pdf "application/pdf") (png "image/png") (svg
"image/svg+xml"))}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object mimetype-file
Specifies the file to use for automatic mimetype lookup.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string module-link
Text which will be used as the formatstring for a hyperlink when a submodule
is printed in a directory listing.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean nocache?
If set to the value @samp{#t} caching will be disabled.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean noplainemail?
If set to @samp{#t} showing full author email addresses will be disabled.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean noheader?
Flag which, when set to @samp{#t}, will make cgit omit the standard header
on all pages.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} project-list project-list
A list of subdirectories inside of @code{repository-directory}, relative to
it, that should loaded as Git repositories.  An empty list means that all
subdirectories will be loaded.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object readme
Text which will be used as default value for @code{cgit-repo-readme}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean remove-suffix?
If set to @code{#t} and @code{repository-directory} is enabled, if any
repositories are found with a suffix of @code{.git}, this suffix will be
removed for the URL and name.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer renamelimit
Maximum number of files to consider when detecting renames.

Defaults to @samp{-1}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string repository-sort
The way in which repositories in each section are sorted.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} robots-list robots
Text used as content for the @code{robots} meta-tag.

Defaults to @samp{("noindex" "nofollow")}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-desc
Text printed below the heading on the repository index page.

Defaults to @samp{"a fast webinterface for the git dscm"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-readme
The content of the file specified with this option will be included verbatim
below the ``about'' link on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-title
Text printed as heading on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean scan-hidden-path
If set to @samp{#t} and repository-directory is enabled,
repository-directory will recurse into directories whose name starts with a
period.  Otherwise, repository-directory will stay away from such
directories, considered as ``hidden''.  Note that this does not apply to the
@file{.git} directory in non-bare repos.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list snapshots
Text which specifies the default set of snapshot formats that cgit generates
links for.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} repository-directory repository-directory
Name of the directory to scan for repositories (represents
@code{scan-path}).

Defaults to @samp{"/srv/git"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string section
The name of the current repository section - all repositories defined after
this option will inherit the current section name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string section-sort
Flag which, when set to @samp{1}, will sort the sections on the repository
listing by name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer section-from-path
A number which, if defined prior to repository-directory, specifies how many
path elements from each repo path to use as a default section name.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean side-by-side-diffs?
If set to @samp{#t} shows side-by-side diffs instead of unidiffs per
default.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object source-filter
Specifies a command which will be invoked to format plaintext blobs in the
tree view.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-branches
Specifies the number of branches to display in the repository ``summary''
view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-log
Specifies the number of log entries to display in the repository ``summary''
view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-tags
Specifies the number of tags to display in the repository ``summary'' view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string strict-export
Filename which, if specified, needs to be present within the repository for
cgit to allow access to that repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string virtual-root
URL which, if specified, will be used as root for all cgit links.

Defaults to @samp{"/"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} repository-cgit-configuration-list repositories
A list of @dfn{cgit-repo} records to use with config.

Defaults to @samp{()}.

Available @code{repository-cgit-configuration} fields are:

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list snapshots
A mask of snapshot formats for this repo that cgit generates links for,
restricted by the global @code{snapshots} setting.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object source-filter
Override the default @code{source-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string url
The relative URL used to access the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object about-filter
Override the default @code{about-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string branch-sort
Flag which, when set to @samp{age}, enables date ordering in the branch ref
list, and when set to @samp{name} enables ordering by branch name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list clone-url
A list of URLs which can be used to clone repo.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object commit-filter
Override the default @code{commit-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string commit-sort
Flag which, when set to @samp{date}, enables strict date ordering in the
commit log, and when set to @samp{topo} enables strict topological ordering.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string defbranch
The name of the default branch for this repository.  If no such branch
exists in the repository, the first branch name (when sorted) is used as
default instead.  By default branch pointed to by HEAD, or ``master'' if
there is no suitable HEAD.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string desc
The value to show as repository description.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string homepage
The value to show as repository homepage.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object email-filter
Override the default @code{email-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-commit-graph?
A flag which can be used to disable the global setting
@code{enable-commit-graph?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-log-filecount?
A flag which can be used to disable the global setting
@code{enable-log-filecount?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-log-linecount?
A flag which can be used to disable the global setting
@code{enable-log-linecount?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-remote-branches?
Flag which, when set to @code{#t}, will make cgit display remote branches in
the summary and refs views.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-subject-links?
A flag which can be used to override the global setting
@code{enable-subject-links?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-html-serving?
A flag which can be used to override the global setting
@code{enable-html-serving?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-boolean hide?
Flag which, when set to @code{#t}, hides the repository from the repository
index.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-boolean ignore?
Flag which, when set to @samp{#t}, ignores the repository.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object logo
URL which specifies the source of an image which will be used as a logo on
this repo’s pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string logo-link
URL loaded when clicking on the cgit logo image.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object owner-filter
Override the default @code{owner-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string module-link
Text which will be used as the formatstring for a hyperlink when a submodule
is printed in a directory listing.  The arguments for the formatstring are
the path and SHA1 of the submodule commit.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} module-link-path module-link-path
Text which will be used as the formatstring for a hyperlink when a submodule
with the specified subdirectory path is printed in a directory listing.

Defaults to @samp{()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string max-stats
Override the default maximum statistics period.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string name
The value to show as repository name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string owner
A value used to identify the owner of the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string path
An absolute path to the repository directory.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string readme
A path (relative to repo) which specifies a file to include verbatim as the
``About'' page for this repo.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string section
The name of the current repository section - all repositories defined after
this option will inherit the current section name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list extra-options
Extra options will be appended to cgitrc file.

Defaults to @samp{()}.

@end deftypevr

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list extra-options
Extra options will be appended to cgitrc file.

Defaults to @samp{()}.

@end deftypevr


@c %end of fragment

However, it could be that you just want to get a @code{cgitrc} up and
running.  In that case, you can pass an @code{opaque-cgit-configuration} as
a record to @code{cgit-service-type}.  As its name indicates, an opaque
configuration does not have easy reflective capabilities.

Available @code{opaque-cgit-configuration} fields are:

@deftypevr {@code{opaque-cgit-configuration} parameter} package cgit
The cgit package.
@end deftypevr

@deftypevr {@code{opaque-cgit-configuration} parameter} string string
The contents of the @code{cgitrc}, as a string.
@end deftypevr

For example, if your @code{cgitrc} is just the empty string, you could
instantiate a cgit service like this:

@lisp
(service cgit-service-type
         (opaque-cgit-configuration
          (cgitrc "")))
@end lisp

@subsubheading Gitolite Service

@cindex Gitolite service
@cindex Git, hosting
@uref{https://gitolite.com/gitolite/, Gitolite} is a tool for hosting Git
repositories on a central server.

Gitolite can handle multiple repositories and users, and supports flexible
configuration of the permissions for the users on the repositories.

The following example will configure Gitolite using the default @code{git}
user, and the provided SSH public key.

@lisp
(service gitolite-service-type
         (gitolite-configuration
           (admin-pubkey (plain-file
                           "yourname.pub"
                           "ssh-rsa AAAA... guix@@example.com"))))
@end lisp

Gitolite is configured through a special admin repository which you can
clone, for example, if you setup Gitolite on @code{example.com}, you would
run the following command to clone the admin repository.

@example
git clone git@@example.com:gitolite-admin
@end example

When the Gitolite service is activated, the provided @code{admin-pubkey}
will be inserted in to the @file{keydir} directory in the gitolite-admin
repository.  If this results in a change in the repository, it will be
committed using the message ``gitolite setup by GNU Guix''.

@deftp {Data Type} gitolite-configuration
Data type representing the configuration for @code{gitolite-service-type}.

@table @asis
@item @code{package} (default: @var{gitolite})
Gitolite package to use.

@item @code{user} (default: @var{git})
User to use for Gitolite.  This will be user that you use when accessing
Gitolite over SSH.

@item @code{group} (default: @var{git})
Group to use for Gitolite.

@item @code{home-directory} (default: @var{"/var/lib/gitolite"})
Directory in which to store the Gitolite configuration and repositories.

@item @code{rc-file} (default: @var{(gitolite-rc-file)})
A ``file-like'' object (@pxref{G-表达式, file-like objects}),
representing the configuration for Gitolite.

@item @code{admin-pubkey} (default: @var{#f})
A ``file-like'' object (@pxref{G-表达式, file-like objects}) used to
setup Gitolite.  This will be inserted in to the @file{keydir} directory
within the gitolite-admin repository.

To specify the SSH key as a string, use the @code{plain-file} function.

@lisp
(plain-file "yourname.pub" "ssh-rsa AAAA... guix@@example.com")
@end lisp

@end table
@end deftp

@deftp {Data Type} gitolite-rc-file
Data type representing the Gitolite RC file.

@table @asis
@item @code{umask} (default: @code{#o0077})
This controls the permissions Gitolite sets on the repositories and their
contents.

A value like @code{#o0027} will give read access to the group used by
Gitolite (by default: @code{git}).  This is necessary when using Gitolite
with software like cgit or gitweb.

@item @code{git-config-keys} (default: @code{""})
Gitolite allows you to set git config values using the @samp{config}
keyword.  This setting allows control over the config keys to accept.

@item @code{roles} (default: @code{'(("READERS" . 1) ("WRITERS" . ))})
Set the role names allowed to be used by users running the perms command.

@item @code{enable} (default: @code{'("help" "desc" "info" "perms" "writable" "ssh-authkeys" "git-config" "daemon" "gitweb")})
This setting controls the commands and features to enable within Gitolite.

@end table
@end deftp


@node 游戏服务
@subsection 游戏服务

@subsubheading The Battle for Wesnoth Service
@cindex wesnothd
@uref{https://wesnoth.org, The Battle for Wesnoth} is a fantasy, turn based
tactical strategy game, with several single player campaigns, and
multiplayer games (both networked and local).

@defvar {Scheme Variable} wesnothd-service-type
Service type for the wesnothd service.  Its value must be a
@code{wesnothd-configuration} object.  To run wesnothd in the default
configuration, instantiate it as:

@lisp
(service wesnothd-service-type)
@end lisp
@end defvar

@deftp {Data Type} wesnothd-configuration
Data type representing the configuration of @command{wesnothd}.

@table @asis
@item @code{package} (default: @code{wesnoth-server})
The wesnoth server package to use.

@item @code{port} (default: @code{15000})
The port to bind the server to.
@end table
@end deftp


@node PAM Mount Service
@subsection PAM Mount Service
@cindex pam-mount

The @code{(gnu services pam-mount)} module provides a service allowing users
to mount volumes when they log in.  It should be able to mount any volume
format supported by the system.

@defvar {Scheme Variable} pam-mount-service-type
Service type for PAM Mount support.
@end defvar

@deftp {Data Type} pam-mount-configuration
Data type representing the configuration of PAM Mount.

It takes the following parameters:

@table @asis
@item @code{rules}
The configuration rules that will be used to generate
@file{/etc/security/pam_mount.conf.xml}.

The configuration rules are SXML elements (@pxref{SXML,,, guile, GNU Guile
Reference Manual}), and the default ones don't mount anything for anyone at
login:

@lisp
`((debug (@@ (enable "0")))
  (mntoptions (@@ (allow ,(string-join
                          '("nosuid" "nodev" "loop"
                            "encryption" "fsck" "nonempty"
                            "allow_root" "allow_other")
                          ","))))
  (mntoptions (@@ (require "nosuid,nodev")))
  (logout (@@ (wait "0")
             (hup "0")
             (term "no")
             (kill "no")))
  (mkmountpoint (@@ (enable "1")
                   (remove "true"))))
@end lisp

Some @code{volume} elements must be added to automatically mount volumes at
login.  Here's an example allowing the user @code{alice} to mount her
encrypted @env{HOME} directory and allowing the user @code{bob} to mount the
partition where he stores his data:

@lisp
(define pam-mount-rules
`((debug (@@ (enable "0")))
            (volume (@@ (user "alice")
                       (fstype "crypt")
                       (path "/dev/sda2")
                       (mountpoint "/home/alice")))
            (volume (@@ (user "bob")
                       (fstype "auto")
                       (path "/dev/sdb3")
                       (mountpoint "/home/bob/data")
                       (options "defaults,autodefrag,compress")))
            (mntoptions (@@ (allow ,(string-join
                                    '("nosuid" "nodev" "loop"
                                      "encryption" "fsck" "nonempty"
                                      "allow_root" "allow_other")
                                    ","))))
            (mntoptions (@@ (require "nosuid,nodev")))
            (logout (@@ (wait "0")
                       (hup "0")
                       (term "no")
                       (kill "no")))
            (mkmountpoint (@@ (enable "1")
                             (remove "true")))))

(service pam-mount-service-type
         (pam-mount-configuration
           (rules pam-mount-rules)))
@end lisp

The complete list of possible options can be found in the man page for
@uref{http://pam-mount.sourceforge.net/pam_mount.conf.5.html,
pam_mount.conf}.
@end table
@end deftp


@node Guix Services
@subsection Guix Services

@subsubheading Guix Build Coordinator
The @uref{https://git.cbaines.net/guix/build-coordinator/,Guix Build
Coordinator} aids in distributing derivation builds among machines running
an @dfn{agent}.  The build daemon is still used to build the derivations,
but the Guix Build Coordinator manages allocating builds and working with
the results.

@quotation 注
This service is considered experimental.  Configuration options may be
changed in a backwards-incompatible manner, and not all features have been
thorougly tested.
@end quotation

The Guix Build Coordinator consists of one @dfn{coordinator}, and one or
more connected @dfn{agent} processes.  The coordinator process handles
clients submitting builds, and allocating builds to agents.  The agent
processes talk to a build daemon to actually perform the builds, then send
the results back to the coordinator.

There is a script to run the coordinator component of the Guix Build
Coordinator, but the Guix service uses a custom Guile script instead, to
provide better integration with G-expressions used in the configuration.

@defvar {Scheme Variable} guix-build-coordinator-service-type
Service type for the Guix Build Coordinator.  Its value must be a
@code{guix-build-coordinator-configuration} object.
@end defvar

@deftp {Data Type} guix-build-coordinator-configuration
Data type representing the configuration of the Guix Build Coordinator.

@table @asis
@item @code{package} (default: @code{guix-build-coordinator})
The Guix Build Coordinator package to use.

@item @code{user} (default: @code{"guix-build-coordinator"})
The system user to run the service as.

@item @code{group} (default: @code{"guix-build-coordinator"})
The system group to run the service as.

@item @code{database-uri-string} (default: @code{"sqlite:///var/lib/guix-build-coordinator/guix_build_coordinator.db"})
The URI to use for the database.

@item @code{agent-communication-uri} (default: @code{"http://0.0.0.0:8745"})
The URI describing how to listen to requests from agent processes.

@item @code{client-communication-uri} (default: @code{"http://127.0.0.1:8746"})
The URI describing how to listen to requests from clients.  The client API
allows submitting builds and currently isn't authenticated, so take care
when configuring this value.

@item @code{allocation-strategy} (default: @code{#~basic-build-allocation-strategy})
A G-expression for the allocation strategy to be used.  This is a procedure
that takes the datastore as an argument and populates the allocation plan in
the database.

@item @code{hooks} (default: @var{'()})
An association list of hooks.  These provide a way to execute arbitrary code
upon certain events, like a build result being processed.

@item @code{guile} (default: @code{guile-3.0-latest})
The Guile package with which to run the Guix Build Coordinator.

@end table
@end deftp

@defvar {Scheme Variable} guix-build-coordinator-agent-service-type
Service type for a Guix Build Coordinator agent.  Its value must be a
@code{guix-build-coordinator-agent-configuration} object.
@end defvar

@deftp {Data Type} guix-build-coordinator-agent-configuration
Data type representing the configuration a Guix Build Coordinator agent.

@table @asis
@item @code{package} (default: @code{guix-build-coordinator})
The Guix Build Coordinator package to use.

@item @code{user} (default: @code{"guix-build-coordinator-agent"})
The system user to run the service as.

@item @code{coordinator} (default: @code{"http://localhost:8745"})
The URI to use when connecting to the coordinator.

@item @code{authentication}
Record describing how this agent should authenticate with the coordinator.
Possible record types are described below.

@item @code{systems} (default: @code{#f})
The systems for which this agent should fetch builds.  The agent process
will use the current system it's running on as the default.

@item @code{max-parallel-builds} (default: @code{1})
The number of builds to perform in parallel.

@item @code{derivation-substitute-urls} (default: @code{#f})
URLs from which to attempt to fetch substitutes for derivations, if the
derivations aren't already available.

@item @code{non-derivation-substitute-urls} (default: @code{#f})
URLs from which to attempt to fetch substitutes for build inputs, if the
input store items aren't already available.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-password-auth
Data type representing an agent authenticating with a coordinator via a UUID
and password.

@table @asis
@item @code{uuid}
The UUID of the agent.  This should be generated by the coordinator process,
stored in the coordinator database, and used by the intended agent.

@item @code{password}
The password to use when connecting to the coordinator.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-password-file-auth
Data type representing an agent authenticating with a coordinator via a UUID
and password read from a file.

@table @asis
@item @code{uuid}
The UUID of the agent.  This should be generated by the coordinator process,
stored in the coordinator database, and used by the intended agent.

@item @code{password-file}
A file containing the password to use when connecting to the coordinator.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-dynamic-auth
Data type representing an agent authenticating with a coordinator via a
dynamic auth token and agent name.

@table @asis
@item @code{agent-name}
Name of an agent, this is used to match up to an existing entry in the
database if there is one.  When no existing entry is found, a new entry is
automatically added.

@item @code{token}
Dynamic auth token, this is created and stored in the coordinator database,
and is used by the agent to authenticate.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-dynamic-auth-with-file
Data type representing an agent authenticating with a coordinator via a
dynamic auth token read from a file and agent name.

@table @asis
@item @code{agent-name}
Name of an agent, this is used to match up to an existing entry in the
database if there is one.  When no existing entry is found, a new entry is
automatically added.

@item @code{token-file}
File containing the dynamic auth token, this is created and stored in the
coordinator database, and is used by the agent to authenticate.

@end table
@end deftp

The Guix Build Coordinator package contains a script to query an instance of
the Guix Data Service for derivations to build, and then submit builds for
those derivations to the coordinator.  The service type below assists in
running this script.  This is an additional tool that may be useful when
building derivations contained within an instance of the Guix Data Service.

@defvar {Scheme Variable} guix-build-coordinator-queue-builds-service-type
Service type for the
guix-build-coordinator-queue-builds-from-guix-data-service script.  Its
value must be a @code{guix-build-coordinator-queue-builds-configuration}
object.
@end defvar

@deftp {Data Type} guix-build-coordinator-queue-builds-configuration
Data type representing the options to the queue builds from guix data
service script.

@table @asis
@item @code{package} (default: @code{guix-build-coordinator})
The Guix Build Coordinator package to use.

@item @code{user} (default: @code{"guix-build-coordinator-queue-builds"})
The system user to run the service as.

@item @code{coordinator} (default: @code{"http://localhost:8745"})
The URI to use when connecting to the coordinator.

@item @code{systems} (default: @code{#f})
The systems for which to fetch derivations to build.

@item @code{systems-and-targets} (default: @code{#f})
An association list of system and target pairs for which to fetch
derivations to build.

@item @code{guix-data-service} (default: @code{"https://data.guix.gnu.org"})
The Guix Data Service instance from which to query to find out about
derivations to build.

@item @code{processed-commits-file} (default: @code{"/var/cache/guix-build-coordinator-queue-builds/processed-commits"})
A file to record which commits have been processed, to avoid needlessly
processing them again if the service is restarted.

@end table
@end deftp

@subsubheading Guix Data Service
The @uref{http://data.guix.gnu.org,Guix Data Service} processes, stores and
provides data about GNU Guix.  This includes information about packages,
derivations and lint warnings.

The data is stored in a PostgreSQL database, and available through a web
interface.

@defvar {Scheme Variable} guix-data-service-type
Service type for the Guix Data Service.  Its value must be a
@code{guix-data-service-configuration} object.  The service optionally
extends the getmail service, as the guix-commits mailing list is used to
find out about changes in the Guix git repository.
@end defvar

@deftp {Data Type} guix-data-service-configuration
Data type representing the configuration of the Guix Data Service.

@table @asis
@item @code{package} (default: @code{guix-data-service})
The Guix Data Service package to use.

@item @code{user} (default: @code{"guix-data-service"})
The system user to run the service as.

@item @code{group} (default: @code{"guix-data-service"})
The system group to run the service as.

@item @code{port} (default: @code{8765})
The port to bind the web service to.

@item @code{host} (default: @code{"127.0.0.1"})
The host to bind the web service to.

@item @code{getmail-idle-mailboxes} (default: @code{#f})
If set, this is the list of mailboxes that the getmail service will be
configured to listen to.

@item @code{commits-getmail-retriever-configuration} (default: @code{#f})
If set, this is the @code{getmail-retriever-configuration} object with which
to configure getmail to fetch mail from the guix-commits mailing list.

@item @code{extra-options} (default: @var{'()})
Extra command line options for @code{guix-data-service}.

@item @code{extra-process-jobs-options} (default: @var{'()})
Extra command line options for @code{guix-data-service-process-jobs}.

@end table
@end deftp

@node Linux Services
@subsection Linux Services

@cindex oom
@cindex out of memory killer
@cindex earlyoom
@cindex early out of memory daemon
@subsubheading Early OOM Service

@uref{https://github.com/rfjakob/earlyoom,Early OOM}, also known as
Earlyoom, is a minimalist out of memory (OOM) daemon that runs in user space
and provides a more responsive and configurable alternative to the in-kernel
OOM killer.  It is useful to prevent the system from becoming unresponsive
when it runs out of memory.

@deffn {Scheme Variable} earlyoom-service-type
The service type for running @command{earlyoom}, the Early OOM daemon.  Its
value must be a @code{earlyoom-configuration} object, described below.  The
service can be instantiated in its default configuration with:

@lisp
(service earlyoom-service-type)
@end lisp
@end deffn

@deftp {Data Type} earlyoom-configuration
This is the configuration record for the @code{earlyoom-service-type}.

@table @asis
@item @code{earlyoom} (default: @var{earlyoom})
The Earlyoom package to use.

@item @code{minimum-available-memory} (default: @code{10})
The threshold for the minimum @emph{available} memory, in percentages.

@item @code{minimum-free-swap} (default: @code{10})
The threshold for the minimum free swap memory, in percentages.

@item @code{prefer-regexp} (default: @code{#f})
A regular expression (as a string) to match the names of the processes that
should be preferably killed.

@item @code{avoid-regexp} (default: @code{#f})
A regular expression (as a string) to match the names of the processes that
should @emph{not} be killed.

@item @code{memory-report-interval} (default: @code{0})
The interval in seconds at which a memory report is printed.  It is disabled
by default.

@item @code{ignore-positive-oom-score-adj?} (default: @code{#f})
A boolean indicating whether the positive adjustments set in
@file{/proc/*/oom_score_adj} should be ignored.

@item @code{show-debug-messages?} (default: @code{#f})
A boolean indicating whether debug messages should be printed.  The logs are
saved at @file{/var/log/earlyoom.log}.

@item @code{send-notification-command} (default: @code{#f})
This can be used to provide a custom command used for sending notifications.
@end table
@end deftp

@cindex modprobe
@cindex kernel module loader
@subsubheading Kernel Module Loader Service

The kernel module loader service allows one to load loadable kernel modules
at boot.  This is especially useful for modules that don't autoload and need
to be manually loaded, as it's the case with @code{ddcci}.

@deffn {Scheme Variable} kernel-module-loader-service-type
The service type for loading loadable kernel modules at boot with
@command{modprobe}.  Its value must be a list of strings representing module
names.  For example loading the drivers provided by
@code{ddcci-driver-linux}, in debugging mode by passing some module
parameters, can be done as follow:

@lisp
(use-modules (gnu) (gnu services))
(use-package-modules linux)
(use-service-modules linux)

(define ddcci-config
  (plain-file "ddcci.conf"
              "options ddcci dyndbg delay=120"))

(operating-system
  ...
  (services (cons* (service kernel-module-loader-service-type
                            '("ddcci" "ddcci_backlight"))
                   (simple-service 'ddcci-config etc-service-type
                                   (list `("modprobe.d/ddcci.conf"
                                           ,ddcci-config)))
                   %base-services))
  (kernel-loadable-modules (list ddcci-driver-linux)))
@end lisp
@end deffn

@cindex zram
@cindex compressed swap
@cindex Compressed RAM-based block devices
@subsubheading Zram Device Service

The Zram device service provides a compressed swap device in system memory.
The Linux Kernel documentation has more information about
@uref{https://www.kernel.org/doc/html/latest/admin-guide/blockdev/zram.html,zram}
devices.

@deffn {Scheme Variable} zram-device-service-type
This service creates the zram block device, formats it as swap and enables
it as a swap device.  The service's value is a
@code{zram-device-configuration} record.

@deftp {Data Type} zram-device-configuration
This is the data type representing the configuration for the zram-device
service.

@table @asis
@item @code{size} (default @code{"1G"})
This is the amount of space you wish to provide for the zram device.  It
accepts a string and can be a number of bytes or use a suffix, eg.:
@code{"512M"} or @code{1024000}.
@item @code{compression-algorithm} (default @code{'lzo})
This is the compression algorithm you wish to use.  It is difficult to list
all the possible compression options, but common ones supported by Guix's
Linux Libre Kernel include @code{'lzo}, @code{'lz4} and @code{'zstd}.
@item @code{memory-limit} (default @code{0})
This is the maximum amount of memory which the zram device can use.  Setting
it to '0' disables the limit.  While it is generally expected that
compression will be 2:1, it is possible that uncompressable data can be
written to swap and this is a method to limit how much memory can be used.
It accepts a string and can be a number of bytes or use a suffix, eg.:
@code{"2G"}.
@item @code{priority} (default @code{-1})
This is the priority of the swap device created from the zram device.
@code{swapon} accepts values between -1 and 32767, with higher values
indicating higher priority.  Higher priority swap will generally be used
first.
@end table

@end deftp
@end deffn

@node Hurd Services
@subsection Hurd Services

@defvr {Scheme Variable} hurd-console-service-type
This service starts the fancy @code{VGA} console client on the Hurd.

The service's value is a @code{hurd-console-configuration} record.
@end defvr

@deftp {Data Type} hurd-console-configuration
This is the data type representing the configuration for the
hurd-console-service.

@table @asis
@item @code{hurd} (default: @var{hurd})
The Hurd package to use.
@end table
@end deftp

@defvr {Scheme Variable} hurd-getty-service-type
This service starts a tty using the Hurd @code{getty} program.

The service's value is a @code{hurd-getty-configuration} record.
@end defvr

@deftp {Data Type} hurd-getty-configuration
This is the data type representing the configuration for the
hurd-getty-service.

@table @asis
@item @code{hurd} (default: @var{hurd})
The Hurd package to use.

@item @code{tty}
The name of the console this Getty runs on---e.g., @code{"tty1"}.

@item @code{baud-rate} (default: @code{38400})
An integer specifying the baud rate of the tty.

@end table
@end deftp

@node 其它各种服务
@subsection 其它各种服务

@cindex fingerprint
@subsubheading Fingerprint Service

The @code{(gnu services authentication)} module provides a DBus service to
read and identify fingerprints via a fingerprint sensor.

@defvr {Scheme Variable} fprintd-service-type
The service type for @command{fprintd}, which provides the fingerprint
reading capability.

@lisp
(service fprintd-service-type)
@end lisp
@end defvr

@cindex sysctl
@subsubheading System Control Service

The @code{(gnu services sysctl)} provides a service to configure kernel
parameters at boot.

@defvr {Scheme Variable} sysctl-service-type
The service type for @command{sysctl}, which modifies kernel parameters
under @file{/proc/sys/}.  To enable IPv4 forwarding, it can be instantiated
as:

@lisp
(service sysctl-service-type
         (sysctl-configuration
           (settings '(("net.ipv4.ip_forward" . "1")))))
@end lisp

Since @code{sysctl-service-type} is used in the default lists of services,
@code{%base-services} and @code{%desktop-services}, you can use
@code{modify-services} to change its configuration and add the kernel
parameters that you want (@pxref{服务参考,
@code{modify-services}}).

@lisp
(modify-services %base-services
  (sysctl-service-type config =>
                       (sysctl-configuration
                         (settings (append '(("net.ipv4.ip_forward" . "1"))
                                           %default-sysctl-settings)))))
@end lisp

@end defvr

@deftp {Data Type} sysctl-configuration
The data type representing the configuration of @command{sysctl}.

@table @asis
@item @code{sysctl} (default: @code{(file-append procps "/sbin/sysctl"})
The @command{sysctl} executable to use.

@item @code{settings} (default: @code{%default-sysctl-settings})
An association list specifies kernel parameters and their values.
@end table
@end deftp

@defvr {Scheme Variable} %default-sysctl-settings
An association list specifying the default @command{sysctl} parameters on
Guix System.
@end defvr

@cindex pcscd
@subsubheading PC/SC Smart Card Daemon Service

The @code{(gnu services security-token)} module provides the following
service to run @command{pcscd}, the PC/SC Smart Card Daemon.
@command{pcscd} is the daemon program for pcsc-lite and the MuscleCard
framework.  It is a resource manager that coordinates communications with
smart card readers, smart cards and cryptographic tokens that are connected
to the system.

@defvr {Scheme Variable} pcscd-service-type
Service type for the @command{pcscd} service.  Its value must be a
@code{pcscd-configuration} object.  To run pcscd in the default
configuration, instantiate it as:

@lisp
(service pcscd-service-type)
@end lisp
@end defvr

@deftp {Data Type} pcscd-configuration
The data type representing the configuration of @command{pcscd}.

@table @asis
@item @code{pcsc-lite} (default: @code{pcsc-lite})
The pcsc-lite package that provides pcscd.
@item @code{usb-drivers} (default: @code{(list ccid)})
List of packages that provide USB drivers to pcscd.  Drivers are expected to
be under @file{pcsc/drivers} in the store directory of the package.
@end table
@end deftp

@cindex lirc
@subsubheading Lirc Service

The @code{(gnu services lirc)} module provides the following service.

@deffn {Scheme Procedure} lirc-service [#:lirc lirc] @
       [#:device #f] [#:driver #f] [#:config-file #f] @ [#:extra-options '()]
Return a service that runs @url{http://www.lirc.org,LIRC}, a daemon that
decodes infrared signals from remote controls.

Optionally, @var{device}, @var{driver} and @var{config-file} (configuration
file name) may be specified.  See @command{lircd} manual for details.

Finally, @var{extra-options} is a list of additional command-line options
passed to @command{lircd}.
@end deffn

@cindex spice
@subsubheading Spice Service

The @code{(gnu services spice)} module provides the following service.

@deffn {Scheme Procedure} spice-vdagent-service [#:spice-vdagent]
Returns a service that runs @url{https://www.spice-space.org,VDAGENT}, a
daemon that enables sharing the clipboard with a vm and setting the guest
display resolution when the graphical console window resizes.
@end deffn

@cindex inputattach
@subsubheading inputattach Service

@cindex tablet input, for Xorg
@cindex touchscreen input, for Xorg
The @uref{https://linuxwacom.github.io/, inputattach} service allows you to
use input devices such as Wacom tablets, touchscreens, or joysticks with the
Xorg display server.

@deffn {Scheme Variable} inputattach-service-type
Type of a service that runs @command{inputattach} on a device and dispatches
events from it.
@end deffn

@deftp {Data Type} inputattach-configuration
@table @asis
@item @code{device-type} (default: @code{"wacom"})
The type of device to connect to.  Run @command{inputattach --help}, from
the @code{inputattach} package, to see the list of supported device types.

@item @code{device} (default: @code{"/dev/ttyS0"})
The device file to connect to the device.

@item @code{baud-rate} (default: @code{#f})
Baud rate to use for the serial connection.  Should be a number or
@code{#f}.

@item @code{log-file} (default: @code{#f})
If true, this must be the name of a file to log messages to.
@end table
@end deftp

@subsubheading Dictionary Service
@cindex dictionary
The @code{(gnu services dict)} module provides the following service:

@defvr {Scheme Variable} dicod-service-type
This is the type of the service that runs the @command{dicod} daemon, an
implementation of DICT server (@pxref{Dicod,,, dico, GNU Dico Manual}).
@end defvr

@deffn {Scheme Procedure} dicod-service [#:config (dicod-configuration)]
Return a service that runs the @command{dicod} daemon, an implementation of
DICT server (@pxref{Dicod,,, dico, GNU Dico Manual}).

The optional @var{config} argument specifies the configuration for
@command{dicod}, which should be a @code{<dicod-configuration>} object, by
default it serves the GNU Collaborative International Dictionary of English.

You can add @command{open localhost} to your @file{~/.dico} file to make
@code{localhost} the default server for @command{dico} client
(@pxref{Initialization File,,, dico, GNU Dico Manual}).
@end deffn

@deftp {Data Type} dicod-configuration
Data type representing the configuration of dicod.

@table @asis
@item @code{dico} (default: @var{dico})
Package object of the GNU Dico dictionary server.

@item @code{interfaces} (default: @var{'("localhost")})
This is the list of IP addresses and ports and possibly socket file names to
listen to (@pxref{Server Settings, @code{listen} directive,, dico, GNU Dico
Manual}).

@item @code{handlers} (default: @var{'()})
List of @code{<dicod-handler>} objects denoting handlers (module instances).

@item @code{databases} (default: @var{(list %dicod-database:gcide)})
List of @code{<dicod-database>} objects denoting dictionaries to be served.
@end table
@end deftp

@deftp {Data Type} dicod-handler
Data type representing a dictionary handler (module instance).

@table @asis
@item @code{名字}
Name of the handler (module instance).

@item @code{module} (default: @var{#f})
Name of the dicod module of the handler (instance).  If it is @code{#f}, the
module has the same name as the handler.  (@pxref{模块,,, dico, GNU Dico
Manual}).

@item @code{options}
List of strings or gexps representing the arguments for the module handler
@end table
@end deftp

@deftp {Data Type} dicod-database
Data type representing a dictionary database.

@table @asis
@item @code{名字}
Name of the database, will be used in DICT commands.

@item @code{handler}
Name of the dicod handler (module instance) used by this database
(@pxref{Handlers,,, dico, GNU Dico Manual}).

@item @code{complex?} (default: @var{#f})
Whether the database configuration complex.  The complex configuration will
need a corresponding @code{<dicod-handler>} object, otherwise not.

@item @code{options}
List of strings or gexps representing the arguments for the database
(@pxref{Databases,,, dico, GNU Dico Manual}).
@end table
@end deftp

@defvr {Scheme Variable} %dicod-database:gcide
A @code{<dicod-database>} object serving the GNU Collaborative International
Dictionary of English using the @code{gcide} package.
@end defvr

The following is an example @code{dicod-service} configuration.

@lisp
(dicod-service #:config
  (dicod-configuration
   (handlers (list (dicod-handler
                    (name "wordnet")
                    (module "dictorg")
                    (options
                     (list #~(string-append "dbdir=" #$wordnet))))))
   (databases (list (dicod-database
                     (name "wordnet")
                     (complex? #t)
                     (handler "wordnet")
                     (options '("database=wn")))
                    %dicod-database:gcide))))
@end lisp

@cindex Docker
@subsubheading Docker Service

The @code{(gnu services docker)} module provides the following services.

@defvr {Scheme Variable} docker-service-type

This is the type of the service that runs
@url{https://www.docker.com,Docker}, a daemon that can execute application
bundles (sometimes referred to as ``containers'') in isolated environments.

@end defvr

@deftp {Data Type} docker-configuration
This is the data type representing the configuration of Docker and
Containerd.

@table @asis

@item @code{package} (default: @code{docker})
The Docker daemon package to use.

@item @code{package} (default: @code{docker-cli})
The Docker client package to use.

@item @code{containerd} (default: @var{containerd})
The Containerd package to use.

@item @code{proxy} (default @var{docker-libnetwork-cmd-proxy})
The Docker user-land networking proxy package to use.

@item @code{enable-proxy?} (default @code{#t})
Enable or disable the use of the Docker user-land networking proxy.

@item @code{debug?} (default @code{#f})
Enable or disable debug output.

@item @code{enable-iptables?} (default @code{#t})
Enable or disable the addition of iptables rules.

@end table
@end deftp

@cindex Singularity, container service
@defvr {Scheme Variable} singularity-service-type
This is the type of the service that allows you to run
@url{https://www.sylabs.io/singularity/, Singularity}, a Docker-style tool
to create and run application bundles (aka. ``containers'').  The value for
this service is the Singularity package to use.

The service does not install a daemon; instead, it installs helper programs
as setuid-root (@pxref{setuid程序}) such that unprivileged users can
invoke @command{singularity run} and similar commands.
@end defvr

@cindex Audit
@subsubheading Auditd Service

The @code{(gnu services auditd)} module provides the following service.

@defvr {Scheme Variable} auditd-service-type

This is the type of the service that runs
@url{https://people.redhat.com/sgrubb/audit/,auditd}, a daemon that tracks
security-relevant information on your system.

Examples of things that can be tracked:

@enumerate
@item
File accesses
@item
System calls
@item
Invoked commands
@item
Failed login attempts
@item
Firewall filtering
@item
Network access
@end enumerate

@command{auditctl} from the @code{audit} package can be used in order to add
or remove events to be tracked (until the next reboot).  In order to
permanently track events, put the command line arguments of auditctl into a
file called @code{audit.rules} in the configuration directory (see below).
@command{aureport} from the @code{audit} package can be used in order to
view a report of all recorded events.  The audit daemon by default logs into
the file @file{/var/log/audit.log}.

@end defvr

@deftp {Data Type} auditd-configuration
This is the data type representing the configuration of auditd.

@table @asis

@item @code{audit} (default: @code{audit})
The audit package to use.

@item @code{configuration-directory} (default: @code{%default-auditd-configuration-directory})
The directory containing the configuration file for the audit package, which
must be named @code{auditd.conf}, and optionally some audit rules to
instantiate on startup.

@end table
@end deftp

@cindex rshiny
@subsubheading R-Shiny service

The @code{(gnu services science)} module provides the following service.

@defvr {Scheme Variable} rshiny-service-type

This is a type of service which is used to run a webapp created with
@code{r-shiny}.  This service sets the @env{R_LIBS_USER} environment
variable and runs the provided script to call @code{runApp}.

@deftp {Data Type} rshiny-configuration
This is the data type representing the configuration of rshiny.

@table @asis

@item @code{package} (default: @code{r-shiny})
The package to use.

@item @code{binary} (defaunlt @code{"rshiny"})
The name of the binary or shell script located at @code{package/bin/} to run
when the service is run.

The common way to create this file is as follows:

@lisp
@dots{}
(let* ((out       (assoc-ref %outputs "out"))
       (targetdir (string-append out "/share/" ,name))
       (app       (string-append out "/bin/" ,name))
       (Rbin      (string-append (assoc-ref %build-inputs "r-min")
                                 "/bin/Rscript")))
  ;; @dots{}
  (mkdir-p (string-append out "/bin"))
  (call-with-output-file app
    (lambda (port)
      (format port
"#!~a
library(shiny)
setwd(\"~a\")
runApp(launch.browser=0, port=4202)~%\n"
      Rbin targetdir))))
@end lisp

@end table
@end deftp
@end defvr

@cindex Nix
@subsubheading Nix service

The @code{(gnu services nix)} module provides the following service.

@defvr {Scheme Variable} nix-service-type

This is the type of the service that runs build daemon of the
@url{https://nixos.org/nix/, Nix} package manager.  Here is an example
showing how to use it:

@lisp
(use-modules (gnu))
(use-service-modules nix)
(use-package-modules package-management)

(operating-system
  ;; @dots{}
  (packages (append (list nix)
                    %base-packages))

  (services (append (list (service nix-service-type))
                    %base-services)))
@end lisp

After @command{guix system reconfigure} configure Nix for your user:

@itemize
@item Add a Nix channel and update it.  See
@url{https://nixos.org/nix/manual/, Nix Package Manager Guide}.

@item Create a symlink to your profile and activate Nix profile:
@end itemize

@example
$ ln -s "/nix/var/nix/profiles/per-user/$USER/profile" ~/.nix-profile
$ source /run/current-system/profile/etc/profile.d/nix.sh
@end example

@end defvr

@deftp {Data Type} nix-configuration
This data type represents the configuration of the Nix daemon.

@table @asis
@item @code{nix} (default: @code{nix})
The Nix package to use.

@item @code{sandbox} (default: @code{#t})
Specifies whether builds are sandboxed by default.

@item @code{build-sandbox-items} (default: @code{'()})
This is a list of strings or objects appended to the
@code{build-sandbox-items} field of the configuration file.

@item @code{extra-config} (default: @code{'()})
This is a list of strings or objects appended to the configuration file.  It
is used to pass extra text to be added verbatim to the configuration file.

@item @code{extra-options} (default: @code{'()})
Extra command line options for @code{nix-service-type}.
@end table
@end deftp

@node setuid程序
@section setuid程序

@cindex setuid programs
Some programs need to run with ``root'' privileges, even when they are
launched by unprivileged users.  A notorious example is the @command{passwd}
program, which users can run to change their password, and which needs to
access the @file{/etc/passwd} and @file{/etc/shadow} files---something
normally restricted to root, for obvious security reasons.  To address that,
these executables are @dfn{setuid-root}, meaning that they always run with
root privileges (@pxref{How Change Persona,,, libc, The GNU C Library
Reference Manual}, for more info about the setuid mechanism).

The store itself @emph{cannot} contain setuid programs: that would be a
security issue since any user on the system can write derivations that
populate the store (@pxref{仓库}).  Thus, a different mechanism is
used: instead of changing the setuid bit directly on files that are in the
store, we let the system administrator @emph{declare} which programs should
be setuid root.

The @code{setuid-programs} field of an @code{operating-system} declaration
contains a list of G-expressions denoting the names of programs to be
setuid-root (@pxref{使用配置系统}).  For instance, the
@command{passwd} program, which is part of the Shadow package, can be
designated by this G-expression (@pxref{G-表达式}):

@example
#~(string-append #$shadow "/bin/passwd")
@end example

A default set of setuid programs is defined by the @code{%setuid-programs}
variable of the @code{(gnu system)} module.

@defvr {Scheme Variable} %setuid-programs
A list of G-expressions denoting common programs that are setuid-root.

The list includes commands such as @command{passwd}, @command{ping},
@command{su}, and @command{sudo}.
@end defvr

Under the hood, the actual setuid programs are created in the
@file{/run/setuid-programs} directory at system activation time.  The files
in this directory refer to the ``real'' binaries, which are in the store.

@node X.509证书
@section X.509证书

@cindex HTTPS, certificates
@cindex X.509 certificates
@cindex TLS
Web servers available over HTTPS (that is, HTTP over the transport-layer
security mechanism, TLS) send client programs an @dfn{X.509 certificate}
that the client can then use to @emph{authenticate} the server.  To do that,
clients verify that the server's certificate is signed by a so-called
@dfn{certificate authority} (CA).  But to verify the CA's signature, clients
must have first acquired the CA's certificate.

Web browsers such as GNU@tie{}IceCat include their own set of CA
certificates, such that they are able to verify CA signatures
out-of-the-box.

However, most other programs that can talk HTTPS---@command{wget},
@command{git}, @command{w3m}, etc.---need to be told where CA certificates
can be found.

@cindex @code{nss-certs}
In Guix, this is done by adding a package that provides certificates to the
@code{packages} field of the @code{operating-system} declaration
(@pxref{操作系统参考}).  Guix includes one such package,
@code{nss-certs}, which is a set of CA certificates provided as part of
Mozilla's Network Security Services.

Note that it is @emph{not} part of @code{%base-packages}, so you need to
explicitly add it.  The @file{/etc/ssl/certs} directory, which is where most
applications and libraries look for certificates by default, points to the
certificates installed globally.

Unprivileged users, including users of Guix on a foreign distro, can also
install their own certificate package in their profile.  A number of
environment variables need to be defined so that applications and libraries
know where to find them.  Namely, the OpenSSL library honors the
@env{SSL_CERT_DIR} and @env{SSL_CERT_FILE} variables.  Some applications add
their own environment variables; for instance, the Git version control
system honors the certificate bundle pointed to by the @env{GIT_SSL_CAINFO}
environment variable.  Thus, you would typically run something like:

@example
guix install nss-certs
export SSL_CERT_DIR="$HOME/.guix-profile/etc/ssl/certs"
export SSL_CERT_FILE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
export GIT_SSL_CAINFO="$SSL_CERT_FILE"
@end example

As another example, R requires the @env{CURL_CA_BUNDLE} environment variable
to point to a certificate bundle, so you would have to run something like
this:

@example
guix install nss-certs
export CURL_CA_BUNDLE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
@end example

For other applications you may want to look up the required environment
variable in the relevant documentation.


@node Name Service Switch
@section Name Service Switch

@cindex name service switch
@cindex NSS
The @code{(gnu system nss)} module provides bindings to the configuration
file of the libc @dfn{name service switch} or @dfn{NSS} (@pxref{NSS
Configuration File,,, libc, The GNU C Library Reference Manual}).  In a
nutshell, the NSS is a mechanism that allows libc to be extended with new
``name'' lookup methods for system databases, which includes host names,
service names, user accounts, and more (@pxref{Name Service Switch, System
Databases and Name Service Switch,, libc, The GNU C Library Reference
Manual}).

The NSS configuration specifies, for each system database, which lookup
method is to be used, and how the various methods are chained together---for
instance, under which circumstances NSS should try the next method in the
list.  The NSS configuration is given in the @code{name-service-switch}
field of @code{operating-system} declarations (@pxref{操作系统参考, @code{name-service-switch}}).

@cindex nss-mdns
@cindex .local, host name lookup
As an example, the declaration below configures the NSS to use the
@uref{https://0pointer.de/lennart/projects/nss-mdns/, @code{nss-mdns}
back-end}, which supports host name lookups over multicast DNS (mDNS)  for
host names ending in @code{.local}:

@lisp
(name-service-switch
   (hosts (list %files    ;first, check /etc/hosts

                ;; If the above did not succeed, try
                ;; with 'mdns_minimal'.
                (name-service
                  (name "mdns_minimal")

                  ;; 'mdns_minimal' is authoritative for
                  ;; '.local'.  When it returns "not found",
                  ;; no need to try the next methods.
                  (reaction (lookup-specification
                             (not-found => return))))

                ;; Then fall back to DNS.
                (name-service
                  (name "dns"))

                ;; Finally, try with the "full" 'mdns'.
                (name-service
                  (name "mdns")))))
@end lisp

Do not worry: the @code{%mdns-host-lookup-nss} variable (see below)
contains this configuration, so you will not have to type it if all you want
is to have @code{.local} host lookup working.

Note that, in this case, in addition to setting the
@code{name-service-switch} of the @code{operating-system} declaration, you
also need to use @code{avahi-service-type} (@pxref{网络服务,
@code{avahi-service-type}}), or @code{%desktop-services}, which includes it
(@pxref{桌面服务}).  Doing this makes @code{nss-mdns} accessible to
the name service cache daemon (@pxref{基础服务, @code{nscd-service}}).

For convenience, the following variables provide typical NSS configurations.

@defvr {Scheme Variable} %default-nss
This is the default name service switch configuration, a
@code{name-service-switch} object.
@end defvr

@defvr {Scheme Variable} %mdns-host-lookup-nss
This is the name service switch configuration with support for host name
lookup over multicast DNS (mDNS) for host names ending in @code{.local}.
@end defvr

The reference for name service switch configuration is given below.  It is a
direct mapping of the configuration file format of the C library , so please
refer to the C library manual for more information (@pxref{NSS Configuration
File,,, libc, The GNU C Library Reference Manual}).  Compared to the
configuration file format of libc NSS, it has the advantage not only of
adding this warm parenthetic feel that we like, but also static checks: you
will know about syntax errors and typos as soon as you run @command{guix
system}.

@deftp {Data Type} name-service-switch

This is the data type representation the configuration of libc's name
service switch (NSS).  Each field below represents one of the supported
system databases.

@table @code
@item aliases
@itemx ethers
@itemx group
@itemx gshadow
@itemx hosts
@itemx initgroups
@itemx netgroup
@itemx networks
@itemx password
@itemx public-key
@itemx rpc
@itemx services
@itemx shadow
The system databases handled by the NSS@.  Each of these fields must be a
list of @code{<name-service>} objects (see below).
@end table
@end deftp

@deftp {Data Type} name-service

This is the data type representing an actual name service and the associated
lookup action.

@table @code
@item 名字
A string denoting the name service (@pxref{Services in the NSS
configuration,,, libc, The GNU C Library Reference Manual}).

Note that name services listed here must be visible to nscd.  This is
achieved by passing the @code{#:name-services} argument to
@code{nscd-service} the list of packages providing the needed name services
(@pxref{基础服务, @code{nscd-service}}).

@item reaction
An action specified using the @code{lookup-specification} macro
(@pxref{Actions in the NSS configuration,,, libc, The GNU C Library
Reference Manual}).  For example:

@lisp
(lookup-specification (unavailable => continue)
                      (success => return))
@end lisp
@end table
@end deftp

@node 初始的内存虚拟硬盘
@section 初始的内存虚拟硬盘

@cindex initrd
@cindex initial RAM disk
For bootstrapping purposes, the Linux-Libre kernel is passed an @dfn{initial
RAM disk}, or @dfn{initrd}.  An initrd contains a temporary root file system
as well as an initialization script.  The latter is responsible for mounting
the real root file system, and for loading any kernel modules that may be
needed to achieve that.

The @code{initrd-modules} field of an @code{operating-system} declaration
allows you to specify Linux-libre kernel modules that must be available in
the initrd.  In particular, this is where you would list modules needed to
actually drive the hard disk where your root partition is---although the
default value of @code{initrd-modules} should cover most use cases.  For
example, assuming you need the @code{megaraid_sas} module in addition to the
default modules to be able to access your root file system, you would write:

@lisp
(operating-system
  ;; @dots{}
  (initrd-modules (cons "megaraid_sas" %base-initrd-modules)))
@end lisp

@defvr {Scheme Variable} %base-initrd-modules
This is the list of kernel modules included in the initrd by default.
@end defvr

Furthermore, if you need lower-level customization, the @code{initrd} field
of an @code{operating-system} declaration allows you to specify which initrd
you would like to use.  The @code{(gnu system linux-initrd)} module provides
three ways to build an initrd: the high-level @code{base-initrd} procedure
and the low-level @code{raw-initrd} and @code{expression->initrd}
procedures.

The @code{base-initrd} procedure is intended to cover most common uses.  For
example, if you want to add a bunch of kernel modules to be loaded at boot
time, you can define the @code{initrd} field of the operating system
declaration like this:

@lisp
(initrd (lambda (file-systems . rest)
          ;; Create a standard initrd but set up networking
          ;; with the parameters QEMU expects by default.
          (apply base-initrd file-systems
                 #:qemu-networking? #t
                 rest)))
@end lisp

The @code{base-initrd} procedure also handles common use cases that involves
using the system as a QEMU guest, or as a ``live'' system with volatile root
file system.

The @code{base-initrd} procedure is built from @code{raw-initrd} procedure.
Unlike @code{base-initrd}, @code{raw-initrd} doesn't do anything high-level,
such as trying to guess which kernel modules and packages should be included
to the initrd.  An example use of @code{raw-initrd} is when a user has a
custom Linux kernel configuration and default kernel modules included by
@code{base-initrd} are not available.

The initial RAM disk produced by @code{base-initrd} or @code{raw-initrd}
honors several options passed on the Linux kernel command line (that is,
arguments passed @i{via} the @code{linux} command of GRUB, or the
@code{-append} option of QEMU), notably:

@table @code
@item --load=@var{boot}
Tell the initial RAM disk to load @var{boot}, a file containing a Scheme
program, once it has mounted the root file system.

Guix uses this option to yield control to a boot program that runs the
service activation programs and then spawns the GNU@tie{}Shepherd, the
initialization system.

@item --root=@var{root}
Mount @var{root} as the root file system.  @var{root} can be a device name
like @code{/dev/sda1}, a file system label, or a file system UUID.  When
unspecified, the device name from the root file system of the operating
system declaration is used.

@item --system=@var{system}
Have @file{/run/booted-system} and @file{/run/current-system} point to
@var{system}.

@item modprobe.blacklist=@var{modules}@dots{}
@cindex module, black-listing
@cindex black list, of kernel modules
Instruct the initial RAM disk as well as the @command{modprobe} command
(from the kmod package) to refuse to load @var{modules}.  @var{modules} must
be a comma-separated list of module names---e.g., @code{usbkbd,9pnet}.

@item --repl
Start a read-eval-print loop (REPL) from the initial RAM disk before it
tries to load kernel modules and to mount the root file system.  Our
marketing team calls it @dfn{boot-to-Guile}.  The Schemer in you will love
it.  @xref{Using Guile Interactively,,, guile, GNU Guile Reference Manual},
for more information on Guile's REPL.

@end table

Now that you know all the features that initial RAM disks produced by
@code{base-initrd} and @code{raw-initrd} provide, here is how to use it and
customize it further.

@cindex initrd
@cindex initial RAM disk
@deffn {Scheme Procedure} raw-initrd @var{file-systems} @
       [#:linux-modules '()] [#:mapped-devices '()] @ [#:keyboard-layout #f] @
[#:helper-packages '()] [#:qemu-networking? #f] [#:volatile-root? #f] Return
a derivation that builds a raw initrd.  @var{file-systems} is a list of file
systems to be mounted by the initrd, possibly in addition to the root file
system specified on the kernel command line via @option{--root}.
@var{linux-modules} is a list of kernel modules to be loaded at boot time.
@var{mapped-devices} is a list of device mappings to realize before
@var{file-systems} are mounted (@pxref{映射的设备}).
@var{helper-packages} is a list of packages to be copied in the initrd.  It
may include @code{e2fsck/static} or other packages needed by the initrd to
check the root file system.

When true, @var{keyboard-layout} is a @code{<keyboard-layout>} record
denoting the desired console keyboard layout.  This is done before
@var{mapped-devices} are set up and before @var{file-systems} are mounted
such that, should the user need to enter a passphrase or use the REPL, this
happens using the intended keyboard layout.

When @var{qemu-networking?} is true, set up networking with the standard
QEMU parameters.  When @var{virtio?} is true, load additional modules so
that the initrd can be used as a QEMU guest with para-virtualized I/O
drivers.

When @var{volatile-root?} is true, the root file system is writable but any
changes to it are lost.
@end deffn

@deffn {Scheme Procedure} base-initrd @var{file-systems} @
       [#:mapped-devices '()] [#:keyboard-layout #f] @ [#:qemu-networking? #f]
[#:volatile-root? #f] @ [#:linux-modules '()] Return as a file-like object a
generic initrd, with kernel modules taken from @var{linux}.
@var{file-systems} is a list of file-systems to be mounted by the initrd,
possibly in addition to the root file system specified on the kernel command
line via @option{--root}.  @var{mapped-devices} is a list of device mappings
to realize before @var{file-systems} are mounted.

When true, @var{keyboard-layout} is a @code{<keyboard-layout>} record
denoting the desired console keyboard layout.  This is done before
@var{mapped-devices} are set up and before @var{file-systems} are mounted
such that, should the user need to enter a passphrase or use the REPL, this
happens using the intended keyboard layout.

@var{qemu-networking?} and @var{volatile-root?} behaves as in
@code{raw-initrd}.

The initrd is automatically populated with all the kernel modules necessary
for @var{file-systems} and for the given options.  Additional kernel modules
can be listed in @var{linux-modules}.  They will be added to the initrd, and
loaded at boot time in the order in which they appear.
@end deffn

Needless to say, the initrds we produce and use embed a statically-linked
Guile, and the initialization program is a Guile program.  That gives a lot
of flexibility.  The @code{expression->initrd} procedure builds such an
initrd, given the program to run in that initrd.

@deffn {Scheme Procedure} expression->initrd @var{exp} @
       [#:guile %guile-3.0-static-stripped] [#:name "guile-initrd"] Return as a
file-like object a Linux initrd (a gzipped cpio archive)  containing
@var{guile} and that evaluates @var{exp}, a G-expression, upon booting.  All
the derivations referenced by @var{exp} are automatically copied to the
initrd.
@end deffn

@node 引导设置
@section 引导设置

@cindex bootloader
@cindex boot loader

The operating system supports multiple bootloaders.  The bootloader is
configured using @code{bootloader-configuration} declaration.  All the
fields of this structure are bootloader agnostic except for one field,
@code{bootloader} that indicates the bootloader to be configured and
installed.

Some of the bootloaders do not honor every field of
@code{bootloader-configuration}.  For instance, the extlinux bootloader does
not support themes and thus ignores the @code{theme} field.

@deftp {Data Type} bootloader-configuration
The type of a bootloader configuration declaration.

@table @asis

@item @code{bootloader}
@cindex EFI, bootloader
@cindex UEFI, bootloader
@cindex BIOS, bootloader
The bootloader to use, as a @code{bootloader} object.  For now
@code{grub-bootloader}, @code{grub-efi-bootloader},
@code{grub-efi-netboot-bootloader}, @code{extlinux-bootloader} and
@code{u-boot-bootloader} are supported.

@cindex ARM, bootloaders
@cindex AArch64, bootloaders
Available bootloaders are described in @code{(gnu bootloader @dots{})}
modules.  In particular, @code{(gnu bootloader u-boot)} contains definitions
of bootloaders for a wide range of ARM and AArch64 systems, using the
@uref{https://www.denx.de/wiki/U-Boot/, U-Boot bootloader}.

@vindex grub-efi-bootloader
@code{grub-efi-bootloader} allows to boot on modern systems using the
@dfn{Unified Extensible Firmware Interface} (UEFI).  This is what you should
use if the installation image contains a @file{/sys/firmware/efi} directory
when you boot it on your system.

@vindex grub-bootloader
@code{grub-bootloader} allows you to boot in particular Intel-based machines
in ``legacy'' BIOS mode.

@vindex grub-efi-netboot-bootloader
@code{grub-efi-netboot-bootloader} allows you to boot your system over
network through TFTP@.  In combination with an NFS root file system this
allows you to build a diskless Guix system.

The installation of the @code{grub-efi-netboot-bootloader} generates the
content of the TFTP root directory at @code{target} (@pxref{引导设置, @code{target}}), to be served by a TFTP server.  You may want
to mount your TFTP server directory onto @code{target} to move the required
files to the TFTP server automatically.

If you plan to use an NFS root file system as well (actually if you mount
the store from an NFS share), then the TFTP server needs to serve the file
@file{/boot/grub/grub.cfg} and other files from the store (like GRUBs
background image, the kernel (@pxref{操作系统参考,
@code{kernel}}) and the initrd (@pxref{操作系统参考,
@code{initrd}})), too.  All these files from the store will be accessed by
GRUB through TFTP with their normal store path, for example as
@file{tftp://tftp-server/gnu/store/…-initrd/initrd.cpio.gz}.

Two symlinks are created to make this possible.  The first symlink is
@code{target}@file{/efi/Guix/boot/grub/grub.cfg} pointing to
@file{../../../boot/grub/grub.cfg}, where @code{target} may be
@file{/boot}.  In this case the link is not leaving the served TFTP root
directory, but otherwise it does.  The second link is
@code{target}@file{/gnu/store} and points to @file{../gnu/store}.  This link
is leaving the served TFTP root directory.

The assumption behind all this is that you have an NFS server exporting the
root file system for your Guix system, and additionally a TFTP server
exporting your @code{target} directory—usually @file{/boot}—from that same
root file system for your Guix system.  In this constellation the symlinks
will work.

For other constellations you will have to program your own bootloader
installer, which then takes care to make necessary files from the store
accessible through TFTP, for example by copying them into the TFTP root
directory at @code{target}.

It is important to note that symlinks pointing outside the TFTP root
directory may need to be allowed in the configuration of your TFTP server.
Further the store link exposes the whole store through TFTP@.  Both points
need to be considered carefully for security aspects.

Beside the @code{grub-efi-netboot-bootloader}, the already mentioned TFTP
and NFS servers, you also need a properly configured DHCP server to make the
booting over netboot possible.  For all this we can currently only recommend
you to look for instructions about @acronym{PXE, Preboot eXecution
Environment}.

@item @code{target}
This is a string denoting the target onto which to install the bootloader.

The interpretation depends on the bootloader in question.  For
@code{grub-bootloader}, for example, it should be a device name understood
by the bootloader @command{installer} command, such as @code{/dev/sda} or
@code{(hd0)} (@pxref{Invoking grub-install,,, grub, GNU GRUB Manual}).  For
@code{grub-efi-bootloader}, it should be the mount point of the EFI file
system, usually @file{/boot/efi}.  For @code{grub-efi-netboot-bootloader},
@code{target} should be the mount point corresponding to the TFTP root
directory of your TFTP server.

@item @code{menu-entries} (default: @code{()})
A possibly empty list of @code{menu-entry} objects (see below), denoting
entries to appear in the bootloader menu, in addition to the current system
entry and the entry pointing to previous system generations.

@item @code{default-entry} (default: @code{0})
The index of the default boot menu entry.  Index 0 is for the entry of the
current system.

@item @code{timeout} (default: @code{5})
The number of seconds to wait for keyboard input before booting.  Set to 0
to boot immediately, and to -1 to wait indefinitely.

@cindex keyboard layout, for the bootloader
@item @code{keyboard-layout} (default: @code{#f})
If this is @code{#f}, the bootloader's menu (if any) uses the default
keyboard layout, usually US@tie{}English (``qwerty'').

Otherwise, this must be a @code{keyboard-layout} object (@pxref{键盘布局}).

@quotation 注
This option is currently ignored by bootloaders other than @code{grub} and
@code{grub-efi}.
@end quotation

@item @code{theme} (default: @var{#f})
The bootloader theme object describing the theme to use.  If no theme is
provided, some bootloaders might use a default theme, that's true for GRUB.

@item @code{terminal-outputs} (default: @code{'(gfxterm)})
The output terminals used for the bootloader boot menu, as a list of
symbols.  GRUB accepts the values: @code{console}, @code{serial},
@code{serial_@{0-3@}}, @code{gfxterm}, @code{vga_text}, @code{mda_text},
@code{morse}, and @code{pkmodem}.  This field corresponds to the GRUB
variable @code{GRUB_TERMINAL_OUTPUT} (@pxref{Simple configuration,,,
grub,GNU GRUB manual}).

@item @code{terminal-inputs} (default: @code{'()})
The input terminals used for the bootloader boot menu, as a list of
symbols.  For GRUB, the default is the native platform terminal as
determined at run-time.  GRUB accepts the values: @code{console},
@code{serial}, @code{serial_@{0-3@}}, @code{at_keyboard}, and
@code{usb_keyboard}.  This field corresponds to the GRUB variable
@code{GRUB_TERMINAL_INPUT} (@pxref{Simple configuration,,, grub,GNU GRUB
manual}).

@item @code{serial-unit} (default: @code{#f})
The serial unit used by the bootloader, as an integer from 0 to 3.  For
GRUB, it is chosen at run-time; currently GRUB chooses 0, which corresponds
to COM1 (@pxref{Serial terminal,,, grub,GNU GRUB manual}).

@item @code{serial-speed} (default: @code{#f})
The speed of the serial interface, as an integer.  For GRUB, the default
value is chosen at run-time; currently GRUB chooses 9600@tie{}bps
(@pxref{Serial terminal,,, grub,GNU GRUB manual}).
@end table

@end deftp

@cindex dual boot
@cindex boot menu
Should you want to list additional boot menu entries @i{via} the
@code{menu-entries} field above, you will need to create them with the
@code{menu-entry} form.  For example, imagine you want to be able to boot
another distro (hard to imagine!), you can define a menu entry along these
lines:

@lisp
(menu-entry
  (label "The Other Distro")
  (linux "/boot/old/vmlinux-2.6.32")
  (linux-arguments '("root=/dev/sda2"))
  (initrd "/boot/old/initrd"))
@end lisp

Details below.

@deftp {Data Type} menu-entry
The type of an entry in the bootloader menu.

@table @asis

@item @code{label}
The label to show in the menu---e.g., @code{"GNU"}.

@item @code{linux} (default: @code{#f})
The Linux kernel image to boot, for example:

@lisp
(file-append linux-libre "/bzImage")
@end lisp

For GRUB, it is also possible to specify a device explicitly in the file
path using GRUB's device naming convention (@pxref{Naming convention,,,
grub, GNU GRUB manual}), for example:

@example
"(hd0,msdos1)/boot/vmlinuz"
@end example

If the device is specified explicitly as above, then the @code{device} field
is ignored entirely.

@item @code{linux-arguments} (default: @code{()})
The list of extra Linux kernel command-line arguments---e.g.,
@code{("console=ttyS0")}.

@item @code{initrd} (default: @code{#f})
A G-Expression or string denoting the file name of the initial RAM disk to
use (@pxref{G-表达式}).

@item @code{device} (default: @code{#f})
The device where the kernel and initrd are to be found---i.e., for GRUB,
@dfn{root} for this menu entry (@pxref{root,,, grub, GNU GRUB manual}).

This may be a file system label (a string), a file system UUID (a
bytevector, @pxref{文件系统}), or @code{#f}, in which case the
bootloader will search the device containing the file specified by the
@code{linux} field (@pxref{search,,, grub, GNU GRUB manual}).  It must
@emph{not} be an OS device name such as @file{/dev/sda1}.

@item @code{multiboot-kernel} (default: @code{#f})
The kernel to boot in Multiboot-mode (@pxref{multiboot,,, grub, GNU GRUB
manual}).  When this field is set, a Multiboot menu-entry is generated.  For
example:

@lisp
(file-append mach "/boot/gnumach")
@end lisp

@item @code{multiboot-arguments} (default: @code{()})
The list of extra command-line arguments for the multiboot-kernel.

@item @code{multiboot-modules} (default: @code{()})
The list of commands for loading Multiboot modules.  For example:

@lisp
(list (list (file-append hurd "/hurd/ext2fs.static") "ext2fs"
             @dots{})
      (list (file-append libc "/lib/ld.so.1") "exec"
             @dots{}))
@end lisp

@end table
@end deftp

@cindex HDPI
@cindex HiDPI
@cindex resolution
@c FIXME: Write documentation once it's stable.
For now only GRUB has theme support.  GRUB themes are created using the
@code{grub-theme} form, which is not fully documented yet.

@deftp {Data Type} grub-theme
Data type representing the configuration of the GRUB theme.

@table @asis
@item @code{gfxmode} (default: @code{'("auto")})
The GRUB @code{gfxmode} to set (a list of screen resolution strings,
@pxref{gfxmode,,, grub, GNU GRUB manual}).
@end table
@end deftp

@deffn {Scheme Procedure} grub-theme
Return the default GRUB theme used by the operating system if no
@code{theme} field is specified in @code{bootloader-configuration} record.

It comes with a fancy background image displaying the GNU and Guix logos.
@end deffn

For example, to override the default resolution, you may use something like

@lisp
(bootloader
 (bootloader-configuration
 ;; @dots{}
 (theme (grub-theme
         (inherit (grub-theme))
         (gfxmode '("1024x786x32" "auto"))))))
@end lisp

@node 调用guix system
@section Invoking @code{guix system}

Once you have written an operating system declaration as seen in the
previous section, it can be @dfn{instantiated} using the @command{guix
system} command.  The synopsis is:

@example
guix system @var{options}@dots{} @var{action} @var{file}
@end example

@var{file} must be the name of a file containing an @code{operating-system}
declaration.  @var{action} specifies how the operating system is
instantiated.  Currently the following values are supported:

@table @code
@item search
Display available service type definitions that match the given regular
expressions, sorted by relevance:

@cindex HDPI
@cindex HiDPI
@cindex resolution
@example
$ guix system search console
name: console-fonts
location: gnu/services/base.scm:806:2
extends: shepherd-root
description: Install the given fonts on the specified ttys (fonts are per
+ virtual console on GNU/Linux).  The value of this service is a list of
+ tty/font pairs.  The font can be the name of a font provided by the `kbd'
+ package or any valid argument to `setfont', as in this example:
+
+      '(("tty1" . "LatGrkCyr-8x16")
+        ("tty2" . (file-append
+                      font-tamzen
+                      "/share/kbd/consolefonts/TamzenForPowerline10x20.psf"))
+        ("tty3" . (file-append
+                      font-terminus
+                      "/share/consolefonts/ter-132n"))) ; for HDPI
relevance: 9

name: mingetty
location: gnu/services/base.scm:1190:2
extends: shepherd-root
description: Provide console login using the `mingetty' program.
relevance: 2

name: login
location: gnu/services/base.scm:860:2
extends: pam
description: Provide a console log-in service as specified by its
+ configuration value, a `login-configuration' object.
relevance: 2

@dots{}
@end example

As for @command{guix package --search}, the result is written in
@code{recutils} format, which makes it easy to filter the output
(@pxref{Top, GNU recutils databases,, recutils, GNU recutils manual}).

@item reconfigure
Build the operating system described in @var{file}, activate it, and switch
to it@footnote{This action (and the related actions @code{switch-generation}
and @code{roll-back}) are usable only on systems already running Guix
System.}.

@quotation 注
@c The paragraph below refers to the problem discussed at
@c <https://lists.gnu.org/archive/html/guix-devel/2014-08/msg00057.html>.
It is highly recommended to run @command{guix pull} once before you run
@command{guix system reconfigure} for the first time (@pxref{调用guix pull}).  Failing to do that you would see an older version of Guix once
@command{reconfigure} has completed.
@end quotation

This effects all the configuration specified in @var{file}: user accounts,
system services, global package list, setuid programs, etc.  The command
starts system services specified in @var{file} that are not currently
running; if a service is currently running this command will arrange for it
to be upgraded the next time it is stopped (e.g.@: by @code{herd stop X} or
@code{herd restart X}).

This command creates a new generation whose number is one greater than the
current generation (as reported by @command{guix system list-generations}).
If that generation already exists, it will be overwritten.  This behavior
mirrors that of @command{guix package} (@pxref{调用guix package}).

It also adds a bootloader menu entry for the new OS configuration, ---unless
@option{--no-bootloader} is passed.  For GRUB, it moves entries for older
configurations to a submenu, allowing you to choose an older system
generation at boot time should you need it.

@cindex provenance tracking, of the operating system
Upon completion, the new system is deployed under
@file{/run/current-system}.  This directory contains @dfn{provenance
meta-data}: the list of channels in use (@pxref{通道}) and @var{file}
itself, when available.  You can view it by running:

@example
guix system describe
@end example

This information is useful should you later want to inspect how this
particular generation was built.  In fact, assuming @var{file} is
self-contained, you can later rebuild generation @var{n} of your operating
system with:

@example
guix time-machine \
  -C /var/guix/profiles/system-@var{n}-link/channels.scm -- \
  system reconfigure \
  /var/guix/profiles/system-@var{n}-link/configuration.scm
@end example

You can think of it as some sort of built-in version control! Your system is
not just a binary artifact: @emph{it carries its own source}.  @xref{服务参考, @code{provenance-service-type}}, for more information on
provenance tracking.

By default, @command{reconfigure} @emph{prevents you from downgrading your
system}, which could (re)introduce security vulnerabilities and also cause
problems with ``stateful'' services such as database management systems.
You can override that behavior by passing @option{--allow-downgrades}.

@item switch-generation
@cindex generations
Switch to an existing system generation.  This action atomically switches
the system profile to the specified system generation.  It also rearranges
the system's existing bootloader menu entries.  It makes the menu entry for
the specified system generation the default, and it moves the entries for
the other generations to a submenu, if supported by the bootloader being
used.  The next time the system boots, it will use the specified system
generation.

The bootloader itself is not being reinstalled when using this command.
Thus, the installed bootloader is used with an updated configuration file.

The target generation can be specified explicitly by its generation number.
For example, the following invocation would switch to system generation 7:

@example
guix system switch-generation 7
@end example

The target generation can also be specified relative to the current
generation with the form @code{+N} or @code{-N}, where @code{+3} means ``3
generations ahead of the current generation,'' and @code{-1} means ``1
generation prior to the current generation.'' When specifying a negative
value such as @code{-1}, you must precede it with @code{--} to prevent it
from being parsed as an option.  For example:

@example
guix system switch-generation -- -1
@end example

Currently, the effect of invoking this action is @emph{only} to switch the
system profile to an existing generation and rearrange the bootloader menu
entries.  To actually start using the target system generation, you must
reboot after running this action.  In the future, it will be updated to do
the same things as @command{reconfigure}, like activating and deactivating
services.

This action will fail if the specified generation does not exist.

@item roll-back
@cindex rolling back
Switch to the preceding system generation.  The next time the system boots,
it will use the preceding system generation.  This is the inverse of
@command{reconfigure}, and it is exactly the same as invoking
@command{switch-generation} with an argument of @code{-1}.

Currently, as with @command{switch-generation}, you must reboot after
running this action to actually start using the preceding system generation.

@item delete-generations
@cindex deleting system generations
@cindex saving space
Delete system generations, making them candidates for garbage collection
(@pxref{调用guix gc}, for information on how to run the ``garbage
collector'').

This works in the same way as @samp{guix package --delete-generations}
(@pxref{调用guix package, @option{--delete-generations}}).  With no
arguments, all system generations but the current one are deleted:

@example
guix system delete-generations
@end example

You can also select the generations you want to delete.  The example below
deletes all the system generations that are more than two month old:

@example
guix system delete-generations 2m
@end example

Running this command automatically reinstalls the bootloader with an updated
list of menu entries---e.g., the ``old generations'' sub-menu in GRUB no
longer lists the generations that have been deleted.

@item build
Build the derivation of the operating system, which includes all the
configuration files and programs needed to boot and run the system.  This
action does not actually install anything.

@item init
Populate the given directory with all the files necessary to run the
operating system specified in @var{file}.  This is useful for first-time
installations of Guix System.  For instance:

@example
guix system init my-os-config.scm /mnt
@end example

copies to @file{/mnt} all the store items required by the configuration
specified in @file{my-os-config.scm}.  This includes configuration files,
packages, and so on.  It also creates other essential files needed for the
system to operate correctly---e.g., the @file{/etc}, @file{/var}, and
@file{/run} directories, and the @file{/bin/sh} file.

This command also installs bootloader on the target specified in
@file{my-os-config}, unless the @option{--no-bootloader} option was passed.

@item vm
@cindex virtual machine
@cindex VM
@anchor{guix system vm}
Build a virtual machine that contains the operating system declared in
@var{file}, and return a script to run that virtual machine (VM).

@quotation 注
The @code{vm} action and others below can use KVM support in the Linux-libre
kernel.  Specifically, if the machine has hardware virtualization support,
the corresponding KVM kernel module should be loaded, and the
@file{/dev/kvm} device node must exist and be readable and writable by the
user and by the build users of the daemon (@pxref{设置构建环境}).
@end quotation

Arguments given to the script are passed to QEMU as in the example below,
which enables networking and requests 1@tie{}GiB of RAM for the emulated
machine:

@example
$ /gnu/store/@dots{}-run-vm.sh -m 1024 -smp 2 -net user,model=virtio-net-pci
@end example

The VM shares its store with the host system.

Additional file systems can be shared between the host and the VM using the
@option{--share} and @option{--expose} command-line options: the former
specifies a directory to be shared with write access, while the latter
provides read-only access to the shared directory.

The example below creates a VM in which the user's home directory is
accessible read-only, and where the @file{/exchange} directory is a
read-write mapping of @file{$HOME/tmp} on the host:

@example
guix system vm my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange
@end example

On GNU/Linux, the default is to boot directly to the kernel; this has the
advantage of requiring only a very tiny root disk image since the store of
the host can then be mounted.

The @option{--full-boot} option forces a complete boot sequence, starting
with the bootloader.  This requires more disk space since a root image
containing at least the kernel, initrd, and bootloader data files must be
created.  The @option{--image-size} option can be used to specify the size
of the image.

@cindex System images, creation in various formats
@cindex Creating system images in various formats
@item image
@itemx docker-image
Return a virtual machine, disk image, or Docker image of the operating
system declared in @var{file} that stands alone.  By default, @command{guix
system} estimates the size of the image needed to store the system, but you
can use the @option{--image-size} option to specify a value.  Docker images
are built to contain exactly what they need, so the @option{--image-size}
option is ignored in the case of @code{docker-image}.

@cindex image, creating disk images
The @code{image} command can produce various image types.  The image type
can be selected using the @option{--image-type} option.  It defaults to
@code{efi-raw}.  When its value is @code{iso9660}, the @option{--label}
option can be used to specify a volume ID with @code{image}.  By default,
the root file system of a disk image is mounted non-volatile; the
@option{--volatile} option can be provided to make it volatile instead.
When using @code{image}, the bootloader installed on the generated image is
taken from the provided @code{operating-system} definition.  The following
example demonstrates how to generate an image that uses the
@code{grub-efi-bootloader} bootloader and boot it with QEMU:

@example
image=$(guix system image --image-type=qcow2 \
        gnu/system/examples/lightweight-desktop.tmpl)
cp $image /tmp/my-image.qcow2
chmod +w /tmp/my-image.qcow2
qemu-system-x86_64 -enable-kvm -hda /tmp/my-image.qcow2 -m 1000 \
                   -bios $(guix build ovmf)/share/firmware/ovmf_x64.bin
@end example

When using the @code{efi-raw} image type, a raw disk image is produced; it
can be copied as is to a USB stick, for instance.  Assuming @code{/dev/sdc}
is the device corresponding to a USB stick, one can copy the image to it
using the following command:

@example
# dd if=$(guix system image my-os.scm) of=/dev/sdc status=progress
@end example

The @code{--list-image-types} command lists all the available image types.

@cindex creating virtual machine images
When using the @code{qcow2} image type, the returned image is in qcow2
format, which the QEMU emulator can efficiently use. @xref{在虚拟机里运行Guix}, for more information on how to run the image in a virtual machine.  The
@code{grub-bootloader} bootloader is always used independently of what is
declared in the @code{operating-system} file passed as argument.  This is to
make it easier to work with QEMU, which uses the SeaBIOS BIOS by default,
expecting a bootloader to be installed in the Master Boot Record (MBR).

@cindex docker-image, creating docker images
When using @code{docker-image}, a Docker image is produced.  Guix builds the
image from scratch, not from a pre-existing Docker base image.  As a result,
it contains @emph{exactly} what you define in the operating system
configuration file.  You can then load the image and launch a Docker
container using commands like the following:

@example
image_id="$(docker load < guix-system-docker-image.tar.gz)"
container_id="$(docker create $image_id)"
docker start $container_id
@end example

This command starts a new Docker container from the specified image.  It
will boot the Guix system in the usual manner, which means it will start any
services you have defined in the operating system configuration.  You can
get an interactive shell running in the container using @command{docker
exec}:

@example
docker exec -ti $container_id /run/current-system/profile/bin/bash --login
@end example

Depending on what you run in the Docker container, it may be necessary to
give the container additional permissions.  For example, if you intend to
build software using Guix inside of the Docker container, you may need to
pass the @option{--privileged} option to @code{docker create}.

Last, the @option{--network} option applies to @command{guix system
docker-image}: it produces an image where network is supposedly shared with
the host, and thus without services like nscd or NetworkManager.

@item container
Return a script to run the operating system declared in @var{file} within a
container.  Containers are a set of lightweight isolation mechanisms
provided by the kernel Linux-libre.  Containers are substantially less
resource-demanding than full virtual machines since the kernel, shared
objects, and other resources can be shared with the host system; this also
means they provide thinner isolation.

Currently, the script must be run as root in order to support more than a
single user and group.  The container shares its store with the host system.

As with the @code{vm} action (@pxref{guix system vm}), additional file
systems to be shared between the host and container can be specified using
the @option{--share} and @option{--expose} options:

@example
guix system container my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange
@end example

@quotation 注
This option requires Linux-libre 3.19 or newer.
@end quotation

@end table

@var{options} can contain any of the common build options (@pxref{普通的构建选项}).  In addition, @var{options} can contain one of the
following:

@table @option
@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the operating-system @var{expr} evaluates to.  This is an
alternative to specifying a file which evaluates to an operating system.
This is used to generate the Guix system installer @pxref{构建安装镜像}).

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system} instead of the host system type.  This
works as per @command{guix build} (@pxref{调用guix build}).

@item --derivation
@itemx -d
Return the derivation file name of the given operating system without
building anything.

@cindex provenance tracking, of the operating system
@item --save-provenance
As discussed above, @command{guix system init} and @command{guix system
reconfigure} always save provenance information @i{via} a dedicated service
(@pxref{服务参考, @code{provenance-service-type}}).  However, other
commands don't do that by default.  If you wish to, say, create a virtual
machine image that contains provenance information, you can run:

@example
guix system image -t qcow2 --save-provenance config.scm
@end example

That way, the resulting image will effectively ``embed its own source'' in
the form of meta-data in @file{/run/current-system}.  With that information,
one can rebuild the image to make sure it really contains what it pretends
to contain; or they could use that to derive a variant of the image.

@item --image-type=@var{type}
@itemx -t @var{type}
For the @code{image} action, create an image with given @var{type}.

When this option is omitted, @command{guix system} uses the @code{efi-raw}
image type.

@cindex ISO-9660 format
@cindex CD image format
@cindex DVD image format
@option{--image-type=iso9660} produces an ISO-9660 image, suitable for
burning on CDs and DVDs.

@item --image-size=@var{size}
For the @code{image} action, create an image of the given @var{size}.
@var{size} may be a number of bytes, or it may include a unit as a suffix
(@pxref{Block size, size specifications,, coreutils, GNU Coreutils}).

When this option is omitted, @command{guix system} computes an estimate of
the image size as a function of the size of the system declared in
@var{file}.

@item --network
@itemx -N
For the @code{container} action, allow containers to access the host
network, that is, do not create a network namespace.

@item --root=@var{file}
@itemx -r @var{file}
Make @var{file} a symlink to the result, and register it as a garbage
collector root.

@item --skip-checks
Skip pre-installation safety checks.

By default, @command{guix system init} and @command{guix system reconfigure}
perform safety checks: they make sure the file systems that appear in the
@code{operating-system} declaration actually exist (@pxref{文件系统}),
and that any Linux kernel modules that may be needed at boot time are listed
in @code{initrd-modules} (@pxref{初始的内存虚拟硬盘}).  Passing this option
skips these tests altogether.

@item --allow-downgrades
Instruct @command{guix system reconfigure} to allow system downgrades.

By default, @command{reconfigure} prevents you from downgrading your
system.  It achieves that by comparing the provenance info of your system
(shown by @command{guix system describe}) with that of your @command{guix}
command (shown by @command{guix describe}).  If the commits for
@command{guix} are not descendants of those used for your system,
@command{guix system reconfigure} errors out.  Passing
@option{--allow-downgrades} allows you to bypass these checks.

@quotation 注
Make sure you understand its security implications before using
@option{--allow-downgrades}.
@end quotation

@cindex on-error
@cindex on-error strategy
@cindex error strategy
@item --on-error=@var{strategy}
Apply @var{strategy} when an error occurs when reading @var{file}.
@var{strategy} may be one of the following:

@table @code
@item nothing-special
Report the error concisely and exit.  This is the default strategy.

@item backtrace
Likewise, but also display a backtrace.

@item debug
Report the error and enter Guile's debugger.  From there, you can run
commands such as @code{,bt} to get a backtrace, @code{,locals} to display
local variable values, and more generally inspect the state of the program.
@xref{Debug Commands,,, guile, GNU Guile Reference Manual}, for a list of
available debugging commands.
@end table
@end table

Once you have built, configured, re-configured, and re-re-configured your
Guix installation, you may find it useful to list the operating system
generations available on disk---and that you can choose from the bootloader
boot menu:

@table @code

@item describe
Describe the current system generation: its file name, the kernel and
bootloader used, etc., as well as provenance information when available.

@item list-generations
List a summary of each generation of the operating system available on disk,
in a human-readable way.  This is similar to the @option{--list-generations}
option of @command{guix package} (@pxref{调用guix package}).

Optionally, one can specify a pattern, with the same syntax that is used in
@command{guix package --list-generations}, to restrict the list of
generations displayed.  For instance, the following command displays
generations that are up to 10 days old:

@example
$ guix system list-generations 10d
@end example

@end table

The @command{guix system} command has even more to offer! The following
sub-commands allow you to visualize how your system services relate to each
other:

@anchor{system-extension-graph}
@table @code

@item extension-graph
Emit to standard output the @dfn{service extension graph} of the operating
system defined in @var{file} (@pxref{合成服务}, for more
information on service extensions).  By default the output is in
Dot/Graphviz format, but you can choose a different format with
@option{--graph-backend}, as with @command{guix graph} (@pxref{调用guix graph, @option{--backend}}):

The command:

@example
$ guix system extension-graph @var{file} | xdot -
@end example

shows the extension relations among services.

@anchor{system-shepherd-graph}
@item shepherd-graph
Emit to standard output the @dfn{dependency graph} of shepherd services of
the operating system defined in @var{file}.  @xref{Shepherd服务}, for
more information and for an example graph.

Again, the default output format is Dot/Graphviz, but you can pass
@option{--graph-backend} to select a different one.

@end table

@node 调用 guix deploy
@section Invoking @code{guix deploy}

We've already seen @code{operating-system} declarations used to manage a
machine's configuration locally.  Suppose you need to configure multiple
machines, though---perhaps you're managing a service on the web that's
comprised of several servers.  @command{guix deploy} enables you to use
those same @code{operating-system} declarations to manage multiple remote
hosts at once as a logical ``deployment''.

@quotation 注
The functionality described in this section is still under development and
is subject to change.  Get in touch with us on @email{guix-devel@@gnu.org}!
@end quotation

@example
guix deploy @var{file}
@end example

Such an invocation will deploy the machines that the code within @var{file}
evaluates to.  As an example, @var{file} might contain a definition like
this:

@lisp
;; This is a Guix deployment of a "bare bones" setup, with
;; no X11 display server, to a machine with an SSH daemon
;; listening on localhost:2222. A configuration such as this
;; may be appropriate for virtual machine with ports
;; forwarded to the host's loopback interface.

(use-service-modules networking ssh)
(use-package-modules bootloaders)

(define %system
  (operating-system
   (host-name "gnu-deployed")
   (timezone "Etc/UTC")
   (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
                (target "/dev/vda")
                (terminal-outputs '(console))))
   (file-systems (cons (file-system
                        (mount-point "/")
                        (device "/dev/vda1")
                        (type "ext4"))
                       %base-file-systems))
   (services
    (append (list (service dhcp-client-service-type)
                  (service openssh-service-type
                           (openssh-configuration
                            (permit-root-login #t)
                            (allow-empty-passwords? #t))))
            %base-services))))

(list (machine
       (operating-system %system)
       (environment managed-host-environment-type)
       (configuration (machine-ssh-configuration
                       (host-name "localhost")
                       (system "x86_64-linux")
                       (user "alice")
                       (identity "./id_rsa")
                       (port 2222)))))
@end lisp

The file should evaluate to a list of @var{machine} objects.  This example,
upon being deployed, will create a new generation on the remote system
realizing the @code{operating-system} declaration @code{%system}.
@code{environment} and @code{configuration} specify how the machine should
be provisioned---that is, how the computing resources should be created and
managed.  The above example does not create any resources, as a
@code{'managed-host} is a machine that is already running the Guix system
and available over the network.  This is a particularly simple case; a more
complex deployment may involve, for example, starting virtual machines
through a Virtual Private Server (VPS) provider.  In such a case, a
different @var{environment} type would be used.

Do note that you first need to generate a key pair on the coordinator
machine to allow the daemon to export signed archives of files from the
store (@pxref{调用guix archive}), though this step is automatic on Guix
System:

@example
# guix archive --generate-key
@end example

@noindent
Each target machine must authorize the key of the master machine so that it
accepts store items it receives from the coordinator:

@example
# guix archive --authorize < coordinator-public-key.txt
@end example

@code{user}, in this example, specifies the name of the user account to log
in as to perform the deployment.  Its default value is @code{root}, but root
login over SSH may be forbidden in some cases.  To work around this,
@command{guix deploy} can log in as an unprivileged user and employ
@code{sudo} to escalate privileges.  This will only work if @code{sudo} is
currently installed on the remote and can be invoked non-interactively as
@code{user}.  That is, the line in @code{sudoers} granting @code{user} the
ability to use @code{sudo} must contain the @code{NOPASSWD} tag.  This can
be accomplished with the following operating system configuration snippet:

@lisp
(use-modules ...
             (gnu system))               ;for %sudoers-specification

(define %user "username")

(operating-system
  ...
  (sudoers-file
     (plain-file "sudoers"
                 (string-append (plain-file-content %sudoers-specification)
                                (format #f "~a ALL = NOPASSWD: ALL~%"
                                        %user)))))

@end lisp

For more information regarding the format of the @file{sudoers} file,
consult @command{man sudoers}.

@deftp {Data Type} machine
This is the data type representing a single machine in a heterogeneous Guix
deployment.

@table @asis
@item @code{operating-system}
The object of the operating system configuration to deploy.

@item @code{environment}
An @code{environment-type} describing how the machine should be provisioned.

@item @code{configuration} (default: @code{#f})
An object describing the configuration for the machine's
@code{environment}.  If the @code{environment} has a default configuration,
@code{#f} may be used.  If @code{#f} is used for an environment with no
default configuration, however, an error will be thrown.
@end table
@end deftp

@deftp {Data Type} machine-ssh-configuration
This is the data type representing the SSH client parameters for a machine
with an @code{environment} of @code{managed-host-environment-type}.

@table @asis
@item @code{host-name}
@item @code{build-locally?} (default: @code{#t})
If false, system derivations will be built on the machine being deployed to.
@item @code{系统}
The system type describing the architecture of the machine being deployed
to---e.g., @code{"x86_64-linux"}.
@item @code{authorize?} (default: @code{#t})
If true, the coordinator's signing key will be added to the remote's ACL
keyring.
@item @code{port}（默认值：@code{22}）
@item @code{user} (default: @code{"root"})
@item @code{identity} (default: @code{#f})
If specified, the path to the SSH private key to use to authenticate with
the remote host.

@item @code{host-key} (default: @code{#f})
This should be the SSH host key of the machine, which looks like this:

@example
ssh-ed25519 AAAAC3Nz@dots{} root@@example.org
@end example

When @code{host-key} is @code{#f}, the server is authenticated against the
@file{~/.ssh/known_hosts} file, just like the OpenSSH @command{ssh} client
does.

@item @code{allow-downgrades?} (default: @code{#f})
Whether to allow potential downgrades.

Like @command{guix system reconfigure}, @command{guix deploy} compares the
channel commits currently deployed on the remote host (as returned by
@command{guix system describe}) to those currently in use (as returned by
@command{guix describe}) to determine whether commits currently in use are
descendants of those deployed.  When this is not the case and
@code{allow-downgrades?} is false, it raises an error.  This ensures you do
not accidentally downgrade remote machines.
@end table
@end deftp

@deftp {Data Type} digital-ocean-configuration
This is the data type describing the Droplet that should be created for a
machine with an @code{environment} of @code{digital-ocean-environment-type}.

@table @asis
@item @code{ssh-key}
The path to the SSH private key to use to authenticate with the remote
host.  In the future, this field may not exist.
@item @code{tags}
A list of string ``tags'' that uniquely identify the machine.  Must be given
such that no two machines in the deployment have the same set of tags.
@item @code{region}
A Digital Ocean region slug, such as @code{"nyc3"}.
@item @code{size}
A Digital Ocean size slug, such as @code{"s-1vcpu-1gb"}
@item @code{enable-ipv6?}
Whether or not the droplet should be created with IPv6 networking.
@end table
@end deftp

@node 在虚拟机里运行Guix
@section Running Guix in a Virtual Machine

@cindex virtual machine
To run Guix in a virtual machine (VM), one can use the pre-built Guix VM
image distributed at
@url{@value{BASE-URL}/guix-system-vm-image-@value{VERSION}.x86_64-linux.qcow2}.
This image is a compressed image in QCOW format.  You will first need to
decompress with @command{xz -d}, and then you can pass it to an emulator
such as QEMU (see below for details).

This image boots the Xfce graphical environment and it contains some
commonly used tools.  You can install more software in the image by running
@command{guix package} in a terminal (@pxref{调用guix package}).  You
can also reconfigure the system based on its initial configuration file
available as @file{/run/current-system/configuration.scm} (@pxref{使用配置系统}).

Instead of using this pre-built image, one can also build their own virtual
machine image using @command{guix system vm-image} (@pxref{调用guix system}).  The returned image is in qcow2 format, which the
@uref{https://qemu.org/, QEMU emulator} can efficiently use.

@cindex QEMU
If you built your own image, you must copy it out of the store (@pxref{仓库}) and give yourself permission to write to the copy before you can use
it.  When invoking QEMU, you must choose a system emulator that is suitable
for your hardware platform.  Here is a minimal QEMU invocation that will
boot the result of @command{guix system image -t qcow2} on x86_64 hardware:

@example
$ qemu-system-x86_64 \
   -nic user,model=virtio-net-pci \
   -enable-kvm -m 1024 \
   -device virtio-blk,drive=myhd \
   -drive if=none,file=/tmp/qemu-image,id=myhd
@end example

Here is what each of these options means:

@table @code
@item qemu-system-x86_64
This specifies the hardware platform to emulate.  This should match the
host.

@item -nic user,model=virtio-net-pci
Enable the unprivileged user-mode network stack.  The guest OS can access
the host but not vice versa.  This is the simplest way to get the guest OS
online.  @code{model} specifies which network device to emulate:
@code{virtio-net-pci} is a special device made for virtualized operating
systems and recommended for most uses.  Assuming your hardware platform is
x86_64, you can get a list of available NIC models by running
@command{qemu-system-x86_64 -nic model=help}.

@item -enable-kvm
If your system has hardware virtualization extensions, enabling the virtual
machine support (KVM) of the Linux kernel will make things run faster.

@c To run Xfce + 'guix pull', we need at least 1G of RAM.
@item -m 1024
RAM available to the guest OS, in mebibytes.  Defaults to 128@tie{}MiB,
which may be insufficient for some operations.

@item -device virtio-blk,drive=myhd
Create a @code{virtio-blk} drive called ``myhd''.  @code{virtio-blk} is a
``paravirtualization'' mechanism for block devices that allows QEMU to
achieve better performance than if it were emulating a complete disk drive.
See the QEMU and KVM documentation for more info.

@item -drive if=none,file=/tmp/qemu-image,id=myhd
Use our QCOW image, the @file{/tmp/qemu-image} file, as the backing store of
the ``myhd'' drive.
@end table

The default @command{run-vm.sh} script that is returned by an invocation of
@command{guix system vm} does not add a @command{-nic user} flag by
default.  To get network access from within the vm add the
@code{(dhcp-client-service)} to your system definition and start the VM
using @command{$(guix system vm config.scm) -nic user}.  An important caveat
of using @command{-nic user} for networking is that @command{ping} will not
work, because it uses the ICMP protocol.  You'll have to use a different
command to check for network connectivity, for example @command{guix
download}.

@subsection Connecting Through SSH

@cindex SSH
@cindex SSH server
To enable SSH inside a VM you need to add an SSH server like
@code{openssh-service-type} to your VM (@pxref{网络服务,
@code{openssh-service-type}}).  In addition you need to forward the SSH
port, 22 by default, to the host.  You can do this with

@example
$(guix system vm config.scm) -nic user,model=virtio-net-pci,hostfwd=tcp::10022-:22
@end example

To connect to the VM you can run

@example
ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -p 10022 localhost
@end example

The @command{-p} tells @command{ssh} the port you want to connect to.
@command{-o UserKnownHostsFile=/dev/null} prevents @command{ssh} from
complaining every time you modify your @command{config.scm} file and the
@command{-o StrictHostKeyChecking=no} prevents you from having to allow a
connection to an unknown host every time you connect.

@subsection Using @command{virt-viewer} with Spice

As an alternative to the default @command{qemu} graphical client you can use
the @command{remote-viewer} from the @command{virt-viewer} package.  To
connect pass the @command{-spice port=5930,disable-ticketing} flag to
@command{qemu}.  See previous section for further information on how to do
this.

Spice also allows you to do some nice stuff like share your clipboard with
your VM@.  To enable that you'll also have to pass the following flags to
@command{qemu}:

@example
-device virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x5
-chardev spicevmc,name=vdagent,id=vdagent
-device virtserialport,nr=1,bus=virtio-serial0.0,chardev=vdagent,
name=com.redhat.spice.0
@end example

You'll also need to add the @code{(spice-vdagent-service)} to your system
definition (@pxref{其它各种服务, Spice service}).

@node 定义服务
@section 定义服务

The previous sections show the available services and how one can combine
them in an @code{operating-system} declaration.  But how do we define them
in the first place? And what is a service anyway?

@menu
* 合成服务::             服务合成的模型。
* 服务类型和服务::    类型和服务。
* 服务参考::             API参考。
* Shepherd服务::           一种特别的服务。
@end menu

@node 合成服务
@subsection 合成服务

@cindex services
@cindex daemons
Here we define a @dfn{service} as, broadly, something that extends the
functionality of the operating system.  Often a service is a process---a
@dfn{daemon}---started when the system boots: a secure shell server, a Web
server, the Guix build daemon, etc.  Sometimes a service is a daemon whose
execution can be triggered by another daemon---e.g., an FTP server started
by @command{inetd} or a D-Bus service activated by @command{dbus-daemon}.
Occasionally, a service does not map to a daemon.  For instance, the
``account'' service collects user accounts and makes sure they exist when
the system runs; the ``udev'' service collects device management rules and
makes them available to the eudev daemon; the @file{/etc} service populates
the @file{/etc} directory of the system.

@cindex service extensions
Guix system services are connected by @dfn{extensions}.  For instance, the
secure shell service @emph{extends} the Shepherd---the initialization
system, running as PID@tie{}1---by giving it the command lines to start and
stop the secure shell daemon (@pxref{网络服务,
@code{openssh-service-type}}); the UPower service extends the D-Bus service
by passing it its @file{.service} specification, and extends the udev
service by passing it device management rules (@pxref{桌面服务,
@code{upower-service}}); the Guix daemon service extends the Shepherd by
passing it the command lines to start and stop the daemon, and extends the
account service by passing it a list of required build user accounts
(@pxref{基础服务}).

All in all, services and their ``extends'' relations form a directed acyclic
graph (DAG).  If we represent services as boxes and extensions as arrows, a
typical system might provide something like this:

@image{images/service-graph,,5in,Typical service extension graph.}

@cindex system service
At the bottom, we see the @dfn{system service}, which produces the directory
containing everything to run and boot the system, as returned by the
@command{guix system build} command.  @xref{服务参考}, to learn
about the other service types shown here.  @xref{system-extension-graph, the
@command{guix system extension-graph} command}, for information on how to
generate this representation for a particular operating system definition.

@cindex service types
Technically, developers can define @dfn{service types} to express these
relations.  There can be any number of services of a given type on the
system---for instance, a system running two instances of the GNU secure
shell server (lsh) has two instances of @code{lsh-service-type}, with
different parameters.

The following section describes the programming interface for service types
and services.

@node 服务类型和服务
@subsection 服务类型和服务

A @dfn{service type} is a node in the DAG described above.  Let us start
with a simple example, the service type for the Guix build daemon
(@pxref{调用guix-daemon}):

@lisp
(define guix-service-type
  (service-type
   (name 'guix)
   (extensions
    (list (service-extension shepherd-root-service-type guix-shepherd-service)
          (service-extension account-service-type guix-accounts)
          (service-extension activation-service-type guix-activation)))
   (default-value (guix-configuration))))
@end lisp

@noindent
It defines three things:

@enumerate
@item
A name, whose sole purpose is to make inspection and debugging easier.

@item
A list of @dfn{service extensions}, where each extension designates the
target service type and a procedure that, given the parameters of the
service, returns a list of objects to extend the service of that type.

Every service type has at least one service extension.  The only exception
is the @dfn{boot service type}, which is the ultimate service.

@item
Optionally, a default value for instances of this type.
@end enumerate

In this example, @code{guix-service-type} extends three services:

@table @code
@item shepherd-root-service-type
The @code{guix-shepherd-service} procedure defines how the Shepherd service
is extended.  Namely, it returns a @code{<shepherd-service>} object that
defines how @command{guix-daemon} is started and stopped (@pxref{Shepherd服务}).

@item account-service-type
This extension for this service is computed by @code{guix-accounts}, which
returns a list of @code{user-group} and @code{user-account} objects
representing the build user accounts (@pxref{调用guix-daemon}).

@item activation-service-type
Here @code{guix-activation} is a procedure that returns a gexp, which is a
code snippet to run at ``activation time''---e.g., when the service is
booted.
@end table

A service of this type is instantiated like this:

@lisp
(service guix-service-type
         (guix-configuration
           (build-accounts 5)
           (extra-options '("--gc-keep-derivations"))))
@end lisp

The second argument to the @code{service} form is a value representing the
parameters of this specific service instance.
@xref{guix-configuration-type, @code{guix-configuration}}, for information
about the @code{guix-configuration} data type.  When the value is omitted,
the default value specified by @code{guix-service-type} is used:

@lisp
(service guix-service-type)
@end lisp

@code{guix-service-type} is quite simple because it extends other services
but is not extensible itself.

@c @subsubsubsection Extensible Service Types

The service type for an @emph{extensible} service looks like this:

@lisp
(define udev-service-type
  (service-type (name 'udev)
                (extensions
                 (list (service-extension shepherd-root-service-type
                                          udev-shepherd-service)))

                (compose concatenate)       ;concatenate the list of rules
                (extend (lambda (config rules)
                          (match config
                            (($ <udev-configuration> udev initial-rules)
                             (udev-configuration
                              (udev udev)   ;the udev package to use
                              (rules (append initial-rules rules)))))))))
@end lisp

This is the service type for the
@uref{https://wiki.gentoo.org/wiki/Project:Eudev, eudev device management
daemon}.  Compared to the previous example, in addition to an extension of
@code{shepherd-root-service-type}, we see two new fields:

@table @code
@item compose
This is the procedure to @dfn{compose} the list of extensions to services of
this type.

Services can extend the udev service by passing it lists of rules; we
compose those extensions simply by concatenating them.

@item extend
This procedure defines how the value of the service is @dfn{extended} with
the composition of the extensions.

Udev extensions are composed into a list of rules, but the udev service
value is itself a @code{<udev-configuration>} record.  So here, we extend
that record by appending the list of rules it contains to the list of
contributed rules.

@item description
This is a string giving an overview of the service type.  The string can
contain Texinfo markup (@pxref{Overview,,, texinfo, GNU Texinfo}).  The
@command{guix system search} command searches these strings and displays
them (@pxref{调用guix system}).
@end table

There can be only one instance of an extensible service type such as
@code{udev-service-type}.  If there were more, the @code{service-extension}
specifications would be ambiguous.

Still here? The next section provides a reference of the programming
interface for services.

@node 服务参考
@subsection 服务参考

We have seen an overview of service types (@pxref{服务类型和服务}).  This section provides a reference on how to manipulate services
and service types.  This interface is provided by the @code{(gnu services)}
module.

@deffn {Scheme Procedure} service @var{type} [@var{value}]
Return a new service of @var{type}, a @code{<service-type>} object (see
below).  @var{value} can be any object; it represents the parameters of this
particular service instance.

When @var{value} is omitted, the default value specified by @var{type} is
used; if @var{type} does not specify a default value, an error is raised.

For instance, this:

@lisp
(service openssh-service-type)
@end lisp

@noindent
is equivalent to this:

@lisp
(service openssh-service-type
         (openssh-configuration))
@end lisp

In both cases the result is an instance of @code{openssh-service-type} with
the default configuration.
@end deffn

@deffn {Scheme Procedure} service? @var{obj}
Return true if @var{obj} is a service.
@end deffn

@deffn {Scheme Procedure} service-kind @var{service}
Return the type of @var{service}---i.e., a @code{<service-type>} object.
@end deffn

@deffn {Scheme Procedure} service-value @var{service}
Return the value associated with @var{service}.  It represents its
parameters.
@end deffn

Here is an example of how a service is created and manipulated:

@lisp
(define s
  (service nginx-service-type
           (nginx-configuration
            (nginx nginx)
            (log-directory log-directory)
            (run-directory run-directory)
            (file config-file))))

(service? s)
@result{} #t

(eq? (service-kind s) nginx-service-type)
@result{} #t
@end lisp

The @code{modify-services} form provides a handy way to change the
parameters of some of the services of a list such as @code{%base-services}
(@pxref{基础服务, @code{%base-services}}).  It evaluates to a list of
services.  Of course, you could always use standard list combinators such as
@code{map} and @code{fold} to do that (@pxref{SRFI-1, List Library,, guile,
GNU Guile Reference Manual}); @code{modify-services} simply provides a more
concise form for this common pattern.

@deffn {Scheme Syntax} modify-services @var{services} @
  (@var{type} @var{variable} => @var{body}) @dots{}

Modify the services listed in @var{services} according to the given
clauses.  Each clause has the form:

@example
(@var{type} @var{variable} => @var{body})
@end example

where @var{type} is a service type---e.g., @code{guix-service-type}---and
@var{variable} is an identifier that is bound within the @var{body} to the
service parameters---e.g., a @code{guix-configuration} instance---of the
original service of that @var{type}.

The @var{body} should evaluate to the new service parameters, which will be
used to configure the new service.  This new service will replace the
original in the resulting list.  Because a service's service parameters are
created using @code{define-record-type*}, you can write a succinct
@var{body} that evaluates to the new service parameters by using the
@code{inherit} feature that @code{define-record-type*} provides.

@xref{使用配置系统}, for example usage.

@end deffn

Next comes the programming interface for service types.  This is something
you want to know when writing new service definitions, but not necessarily
when simply looking for ways to customize your @code{operating-system}
declaration.

@deftp {Data Type} service-type
@cindex service type
This is the representation of a @dfn{service type} (@pxref{服务类型和服务}).

@table @asis
@item @code{名字}
This is a symbol, used only to simplify inspection and debugging.

@item @code{extensions}
A non-empty list of @code{<service-extension>} objects (see below).

@item @code{compose} (default: @code{#f})
If this is @code{#f}, then the service type denotes services that cannot be
extended---i.e., services that do not receive ``values'' from other
services.

Otherwise, it must be a one-argument procedure.  The procedure is called by
@code{fold-services} and is passed a list of values collected from
extensions.  It may return any single value.

@item @code{extend} (default: @code{#f})
If this is @code{#f}, services of this type cannot be extended.

Otherwise, it must be a two-argument procedure: @code{fold-services} calls
it, passing it the initial value of the service as the first argument and
the result of applying @code{compose} to the extension values as the second
argument.  It must return a value that is a valid parameter value for the
service instance.

@item @code{description}
This is a string, possibly using Texinfo markup, describing in a couple of
sentences what the service is about.  This string allows users to find about
the service through @command{guix system search} (@pxref{调用guix system}).

@item @code{default-value} (default: @code{&no-default-value})
The default value associated for instances of this service type.  This
allows users to use the @code{service} form without its second argument:

@lisp
(service @var{type})
@end lisp

The returned service in this case has the default value specified by
@var{type}.
@end table

@xref{服务类型和服务}, for examples.
@end deftp

@deffn {Scheme Procedure} service-extension @var{target-type} @
                              @var{compute} Return a new extension for services of type
@var{target-type}.  @var{compute} must be a one-argument procedure:
@code{fold-services} calls it, passing it the value associated with the
service that provides the extension; it must return a valid value for the
target service.
@end deffn

@deffn {Scheme Procedure} service-extension? @var{obj}
Return true if @var{obj} is a service extension.
@end deffn

Occasionally, you might want to simply extend an existing service.  This
involves creating a new service type and specifying the extension of
interest, which can be verbose; the @code{simple-service} procedure provides
a shorthand for this.

@deffn {Scheme Procedure} simple-service @var{name} @var{target} @var{value}
Return a service that extends @var{target} with @var{value}.  This works by
creating a singleton service type @var{name}, of which the returned service
is an instance.

For example, this extends mcron (@pxref{执行计划任务}) with an
additional job:

@lisp
(simple-service 'my-mcron-job mcron-service-type
                #~(job '(next-hour (3)) "guix gc -F 2G"))
@end lisp
@end deffn

At the core of the service abstraction lies the @code{fold-services}
procedure, which is responsible for ``compiling'' a list of services down to
a single directory that contains everything needed to boot and run the
system---the directory shown by the @command{guix system build} command
(@pxref{调用guix system}).  In essence, it propagates service
extensions down the service graph, updating each node parameters on the way,
until it reaches the root node.

@deffn {Scheme Procedure} fold-services @var{services} @
                            [#:target-type @var{system-service-type}] Fold @var{services} by propagating
their extensions down to the root of type @var{target-type}; return the root
service adjusted accordingly.
@end deffn

Lastly, the @code{(gnu services)} module also defines several essential
service types, some of which are listed below.

@defvr {Scheme Variable} system-service-type
This is the root of the service graph.  It produces the system directory as
returned by the @command{guix system build} command.
@end defvr

@defvr {Scheme Variable} boot-service-type
The type of the ``boot service'', which produces the @dfn{boot script}.  The
boot script is what the initial RAM disk runs when booting.
@end defvr

@defvr {Scheme Variable} etc-service-type
The type of the @file{/etc} service.  This service is used to create files
under @file{/etc} and can be extended by passing it name/file tuples such
as:

@lisp
(list `("issue" ,(plain-file "issue" "Welcome!\n")))
@end lisp

In this example, the effect would be to add an @file{/etc/issue} file
pointing to the given file.
@end defvr

@defvr {Scheme Variable} setuid-program-service-type
Type for the ``setuid-program service''.  This service collects lists of
executable file names, passed as gexps, and adds them to the set of
setuid-root programs on the system (@pxref{setuid程序}).
@end defvr

@defvr {Scheme Variable} profile-service-type
Type of the service that populates the @dfn{system profile}---i.e., the
programs under @file{/run/current-system/profile}.  Other services can
extend it by passing it lists of packages to add to the system profile.
@end defvr

@cindex provenance tracking, of the operating system
@anchor{provenance-service-type}
@defvr {Scheme Variable} provenance-service-type
This is the type of the service that records @dfn{provenance meta-data} in
the system itself.  It creates several files under
@file{/run/current-system}:

@table @file
@item channels.scm
This is a ``channel file'' that can be passed to @command{guix pull -C} or
@command{guix time-machine -C}, and which describes the channels used to
build the system, if that information was available (@pxref{通道}).

@item configuration.scm
This is the file that was passed as the value for this
@code{provenance-service-type} service.  By default, @command{guix system
reconfigure} automatically passes the OS configuration file it received on
the command line.

@item provenance
This contains the same information as the two other files but in a format
that is more readily processable.
@end table

In general, these two pieces of information (channels and configuration
file) are enough to reproduce the operating system ``from source''.

@quotation Caveats
This information is necessary to rebuild your operating system, but it is
not always sufficient.  In particular, @file{configuration.scm} itself is
insufficient if it is not self-contained---if it refers to external Guile
modules or to extra files.  If you want @file{configuration.scm} to be
self-contained, we recommend that modules or files it refers to be part of a
channel.

Besides, provenance meta-data is ``silent'' in the sense that it does not
change the bits contained in your system, @emph{except for the meta-data
bits themselves}.  Two different OS configurations or sets of channels can
lead to the same system, bit-for-bit; when @code{provenance-service-type} is
used, these two systems will have different meta-data and thus different
store file names, which makes comparison less trivial.
@end quotation

This service is automatically added to your operating system configuration
when you use @command{guix system reconfigure}, @command{guix system init},
or @command{guix deploy}.
@end defvr

@node Shepherd服务
@subsection Shepherd服务

@cindex shepherd services
@cindex PID 1
@cindex init system
The @code{(gnu services shepherd)} module provides a way to define services
managed by the GNU@tie{}Shepherd, which is the initialization system---the
first process that is started when the system boots, also known as
PID@tie{}1 (@pxref{介绍,,, shepherd, The GNU Shepherd Manual}).

Services in the Shepherd can depend on each other.  For instance, the SSH
daemon may need to be started after the syslog daemon has been started,
which in turn can only happen once all the file systems have been mounted.
The simple operating system defined earlier (@pxref{使用配置系统}) results in a service graph like this:

@image{images/shepherd-graph,,5in,Typical shepherd service graph.}

You can actually generate such a graph for any operating system definition
using the @command{guix system shepherd-graph} command
(@pxref{system-shepherd-graph, @command{guix system shepherd-graph}}).

The @code{%shepherd-root-service} is a service object representing
PID@tie{}1, of type @code{shepherd-root-service-type}; it can be extended by
passing it lists of @code{<shepherd-service>} objects.

@deftp {Data Type} shepherd-service
The data type representing a service managed by the Shepherd.

@table @asis
@item @code{provision}
This is a list of symbols denoting what the service provides.

These are the names that may be passed to @command{herd start},
@command{herd status}, and similar commands (@pxref{Invoking herd,,,
shepherd, The GNU Shepherd Manual}).  @xref{Slots of services, the
@code{provides} slot,, shepherd, The GNU Shepherd Manual}, for details.

@item @code{requirement} (default: @code{'()})
List of symbols denoting the Shepherd services this one depends on.

@cindex one-shot services, for the Shepherd
@item @code{one-shot?} (default: @code{#f})
Whether this service is @dfn{one-shot}.  One-shot services stop immediately
after their @code{start} action has completed.  @xref{Slots of services,,,
shepherd, The GNU Shepherd Manual}, for more info.

@item @code{respawn?} (default: @code{#t})
Whether to restart the service when it stops, for instance when the
underlying process dies.

@item @code{start}
@itemx @code{stop} (default: @code{#~(const #f)})
The @code{start} and @code{stop} fields refer to the Shepherd's facilities
to start and stop processes (@pxref{Service De- and Constructors,,,
shepherd, The GNU Shepherd Manual}).  They are given as G-expressions that
get expanded in the Shepherd configuration file (@pxref{G-表达式}).

@item @code{actions} (default: @code{'()})
@cindex actions, of Shepherd services
This is a list of @code{shepherd-action} objects (see below) defining
@dfn{actions} supported by the service, in addition to the standard
@code{start} and @code{stop} actions.  Actions listed here become available
as @command{herd} sub-commands:

@example
herd @var{action} @var{service} [@var{arguments}@dots{}]
@end example

@item @code{auto-start?} (default: @code{#t})
Whether this service should be started automatically by the Shepherd.  If it
is @code{#f} the service has to be started manually with @code{herd start}.

@item @code{documentation}
A documentation string, as shown when running:

@example
herd doc @var{service-name}
@end example

where @var{service-name} is one of the symbols in @code{provision}
(@pxref{Invoking herd,,, shepherd, The GNU Shepherd Manual}).

@item @code{modules} (default: @code{%default-modules})
This is the list of modules that must be in scope when @code{start} and
@code{stop} are evaluated.

@end table
@end deftp

The example below defines a Shepherd service that spawns @command{syslogd},
the system logger from the GNU Networking Utilities (@pxref{syslogd
invocation, @command{syslogd},, inetutils, GNU Inetutils}):

@example
(let ((config (plain-file "syslogd.conf" "@dots{}")))
  (shepherd-service
    (documentation "Run the syslog daemon (syslogd).")
    (provision '(syslogd))
    (requirement '(user-processes))
    (start #~(make-forkexec-constructor
               (list #$(file-append inetutils "/libexec/syslogd")
                     "--rcfile" #$config)
               #:pid-file "/var/run/syslog.pid"))
    (stop #~(make-kill-destructor))))
@end example

Key elements in this example are the @code{start} and @code{stop} fields:
they are @dfn{staged} code snippets that use the
@code{make-forkexec-constructor} procedure provided by the Shepherd and its
dual, @code{make-kill-destructor} (@pxref{Service De- and Constructors,,,
shepherd, The GNU Shepherd Manual}).  The @code{start} field will have
@command{shepherd} spawn @command{syslogd} with the given option; note that
we pass @code{config} after @option{--rcfile}, which is a configuration file
declared above (contents of this file are omitted).  Likewise, the
@code{stop} field tells how this service is to be stopped; in this case, it
is stopped by making the @code{kill} system call on its PID@.  Code staging
is achieved using G-expressions: @code{#~} stages code, while @code{#$}
``escapes'' back to host code (@pxref{G-表达式}).

@deftp {Data Type} shepherd-action
This is the data type that defines additional actions implemented by a
Shepherd service (see above).

@table @code
@item 名字
Symbol naming the action.

@item documentation
This is a documentation string for the action.  It can be viewed by running:

@example
herd doc @var{service} action @var{action}
@end example

@item procedure
This should be a gexp that evaluates to a procedure of at least one
argument, which is the ``running value'' of the service (@pxref{Slots of
services,,, shepherd, The GNU Shepherd Manual}).
@end table

The following example defines an action called @code{say-hello} that kindly
greets the user:

@lisp
(shepherd-action
  (name 'say-hello)
  (documentation "Say hi!")
  (procedure #~(lambda (running . args)
                 (format #t "Hello, friend! arguments: ~s\n"
                         args)
                 #t)))
@end lisp

Assuming this action is added to the @code{example} service, then you can
do:

@example
# herd say-hello example
Hello, friend! arguments: ()
# herd say-hello example a b c
Hello, friend! arguments: ("a" "b" "c")
@end example

This, as you can see, is a fairly sophisticated way to say hello.
@xref{Service Convenience,,, shepherd, The GNU Shepherd Manual}, for more
info on actions.
@end deftp

@defvr {Scheme Variable} shepherd-root-service-type
The service type for the Shepherd ``root service''---i.e., PID@tie{}1.

This is the service type that extensions target when they want to create
shepherd services (@pxref{服务类型和服务}, for an example).
Each extension must pass a list of @code{<shepherd-service>}.  Its value
must be a @code{shepherd-configuration}, as described below.
@end defvr

@deftp {Data Type} shepherd-configuration
This data type represents the Shepherd's configuration.

@table @code
@item shepherd (default: @code{shepherd})
The Shepherd package to use.

@item services (default: @code{'()})
A list of @code{<shepherd-service>} to start.  You should probably use the
service extension mechanism instead (@pxref{Shepherd服务}).
@end table
@end deftp

The following example specifies the Shepherd package for the operating
system:

@lisp
(operating-system
  ;; ...
  (services (append (list openssh-service-type))
            ;; ...
            %desktop-services)
  ;; ...
  ;; Use own Shepherd package.
  (essential-services
   (modify-services (operating-system-default-essential-services
                     this-operating-system)
     (shepherd-root-service-type config => (shepherd-configuration
                                            (inherit config)
                                            (shepherd my-shepherd))))))
@end lisp

@defvr {Scheme Variable} %shepherd-root-service
This service represents PID@tie{}1.
@end defvr


@node 文档
@chapter 文档

@cindex documentation, searching for
@cindex searching for documentation
@cindex Info, documentation format
@cindex man pages
@cindex manual pages
In most cases packages installed with Guix come with documentation.  There
are two main documentation formats: ``Info'', a browsable hypertext format
used for GNU software, and ``manual pages'' (or ``man pages''), the linear
documentation format traditionally found on Unix.  Info manuals are accessed
with the @command{info} command or with Emacs, and man pages are accessed
using @command{man}.

You can look for documentation of software installed on your system by
keyword.  For example, the following command searches for information about
``TLS'' in Info manuals:

@example
$ info -k TLS
"(emacs)Network Security" -- STARTTLS
"(emacs)Network Security" -- TLS
"(gnutls)Core TLS API" -- gnutls_certificate_set_verify_flags
"(gnutls)Core TLS API" -- gnutls_certificate_set_verify_function
@dots{}
@end example

@noindent
The command below searches for the same keyword in man pages:

@example
$ man -k TLS
SSL (7)              - OpenSSL SSL/TLS library
certtool (1)         - GnuTLS certificate tool
@dots {}
@end example

These searches are purely local to your computer so you have the guarantee
that documentation you find corresponds to what you have actually installed,
you can access it off-line, and your privacy is respected.

Once you have these results, you can view the relevant documentation by
running, say:

@example
$ info "(gnutls)Core TLS API"
@end example

@noindent
or:

@example
$ man certtool
@end example

Info manuals contain sections and indices as well as hyperlinks like those
found in Web pages.  The @command{info} reader (@pxref{Top, Info reader,,
info-stnd, Stand-alone GNU Info}) and its Emacs counterpart (@pxref{Misc
Help,,, emacs, The GNU Emacs Manual}) provide intuitive key bindings to
navigate manuals.  @xref{入门,,, info, Info: An Introduction},
for an introduction to Info navigation.

@node 安装调试文件
@chapter 安装调试文件

@cindex debugging files
Program binaries, as produced by the GCC compilers for instance, are
typically written in the ELF format, with a section containing
@dfn{debugging information}.  Debugging information is what allows the
debugger, GDB, to map binary code to source code; it is required to debug a
compiled program in good conditions.

This chapter explains how to use separate debug info when packages provide
it, and how to rebuild packages with debug info when it's missing.

@menu
* Separate Debug Info::      Installing 'debug' outputs.
* Rebuilding Debug Info::    Building missing debug info.
@end menu

@node Separate Debug Info
@section Separate Debug Info

The problem with debugging information is that is takes up a fair amount of
disk space.  For example, debugging information for the GNU C Library weighs
in at more than 60 MiB@.  Thus, as a user, keeping all the debugging info of
all the installed programs is usually not an option.  Yet, space savings
should not come at the cost of an impediment to debugging---especially in
the GNU system, which should make it easier for users to exert their
computing freedom (@pxref{GNU发行版}).

Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a mechanism
that allows users to get the best of both worlds: debugging information can
be stripped from the binaries and stored in separate files.  GDB is then
able to load debugging information from those files, when they are available
(@pxref{Separate Debug Files,,, gdb, Debugging with GDB}).

The GNU distribution takes advantage of this by storing debugging
information in the @code{lib/debug} sub-directory of a separate package
output unimaginatively called @code{debug} (@pxref{有多个输出的软件包}).  Users can choose to install the @code{debug} output of a package
when they need it.  For instance, the following command installs the
debugging information for the GNU C Library and for GNU Guile:

@example
guix install glibc:debug guile:debug
@end example

GDB must then be told to look for debug files in the user's profile, by
setting the @code{debug-file-directory} variable (consider setting it from
the @file{~/.gdbinit} file, @pxref{Startup,,, gdb, Debugging with GDB}):

@example
(gdb) set debug-file-directory ~/.guix-profile/lib/debug
@end example

From there on, GDB will pick up debugging information from the @file{.debug}
files under @file{~/.guix-profile/lib/debug}.

In addition, you will most likely want GDB to be able to show the source
code being debugged.  To do that, you will have to unpack the source code of
the package of interest (obtained with @code{guix build --source},
@pxref{调用guix build}), and to point GDB to that source directory
using the @code{directory} command (@pxref{Source Path, @code{directory},,
gdb, Debugging with GDB}).

@c XXX: keep me up-to-date
The @code{debug} output mechanism in Guix is implemented by the
@code{gnu-build-system} (@pxref{构建系统}).  Currently, it is
opt-in---debugging information is available only for the packages with
definitions explicitly declaring a @code{debug} output.  To check whether a
package has a @code{debug} output, use @command{guix package
--list-available} (@pxref{调用guix package}).

Read on for how to deal with packages lacking a @code{debug} output.

@node Rebuilding Debug Info
@section Rebuilding Debug Info

@cindex debugging info, rebuilding
As we saw above, some packages, but not all, provide debugging info in a
@code{debug} output.  What can you do when debugging info is missing? The
@option{--with-debug-info} option provides a solution to that: it allows you
to rebuild the package(s) for which debugging info is missing---and only
those---and to graft those onto the application you're debugging.  Thus,
while it's not as fast as installing a @code{debug} output, it is relatively
inexpensive.

Let's illustrate that.  Suppose you're experiencing a bug in Inkscape and
would like to see what's going on in GLib, a library that's deep down in its
dependency graph.  As it turns out, GLib does not have a @code{debug} output
and the backtrace GDB shows is all sadness:

@example
(gdb) bt
#0  0x00007ffff5f92190 in g_getenv ()
   from /gnu/store/@dots{}-glib-2.62.6/lib/libglib-2.0.so.0
#1  0x00007ffff608a7d6 in gobject_init_ctor ()
   from /gnu/store/@dots{}-glib-2.62.6/lib/libgobject-2.0.so.0
#2  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@@entry=1, argv=argv@@entry=0x7fffffffcfd8, 
    env=env@@entry=0x7fffffffcfe8) at dl-init.c:72
#3  0x00007ffff7fe2866 in call_init (env=0x7fffffffcfe8, argv=0x7fffffffcfd8, argc=1, l=<optimized out>)
    at dl-init.c:118
@end example

To address that, you install Inkscape linked against a variant GLib that
contains debug info:

@example
guix install inkscape --with-debug-info=glib
@end example

This time, debugging will be a whole lot nicer:

@example
$ gdb --args sh -c 'exec inkscape'
@dots{}
(gdb) b g_getenv
Function "g_getenv" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (g_getenv) pending.
(gdb) r
Starting program: /gnu/store/@dots{}-profile/bin/sh -c exec\ inkscape
@dots{}
(gdb) bt
#0  g_getenv (variable=variable@@entry=0x7ffff60c7a2e "GOBJECT_DEBUG") at ../glib-2.62.6/glib/genviron.c:252
#1  0x00007ffff608a7d6 in gobject_init () at ../glib-2.62.6/gobject/gtype.c:4380
#2  gobject_init_ctor () at ../glib-2.62.6/gobject/gtype.c:4493
#3  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@@entry=3, argv=argv@@entry=0x7fffffffd088, 
    env=env@@entry=0x7fffffffd0a8) at dl-init.c:72
@dots{}
@end example

Much better!

Note that there can be packages for which @option{--with-debug-info} will
not have the desired effect.  @xref{软件包变换选项。,
@option{--with-debug-info}}, for more information.

@node 安全更新
@chapter 安全更新

@cindex security updates
@cindex security vulnerabilities
Occasionally, important security vulnerabilities are discovered in software
packages and must be patched.  Guix developers try hard to keep track of
known vulnerabilities and to apply fixes as soon as possible in the
@code{master} branch of Guix (we do not yet provide a ``stable'' branch
containing only security updates).  The @command{guix lint} tool helps
developers find out about vulnerable versions of software packages in the
distribution:

@smallexample
$ guix lint -c cve
gnu/packages/base.scm:652:2: glibc@@2.21: probably vulnerable to CVE-2015-1781, CVE-2015-7547
gnu/packages/gcc.scm:334:2: gcc@@4.9.3: probably vulnerable to CVE-2015-5276
gnu/packages/image.scm:312:2: openjpeg@@2.1.0: probably vulnerable to CVE-2016-1923, CVE-2016-1924
@dots{}
@end smallexample

@xref{调用guix lint}, for more information.

Guix follows a functional package management discipline
(@pxref{介绍}), which implies that, when a package is changed,
@emph{every package that depends on it} must be rebuilt.  This can
significantly slow down the deployment of fixes in core packages such as
libc or Bash, since basically the whole distribution would need to be
rebuilt.  Using pre-built binaries helps (@pxref{substitutes}), but
deployment may still take more time than desired.

@cindex grafts
To address this, Guix implements @dfn{grafts}, a mechanism that allows for
fast deployment of critical updates without the costs associated with a
whole-distribution rebuild.  The idea is to rebuild only the package that
needs to be patched, and then to ``graft'' it onto packages explicitly
installed by the user and that were previously referring to the original
package.  The cost of grafting is typically very low, and order of
magnitudes lower than a full rebuild of the dependency chain.

@cindex replacements of packages, for grafts
For instance, suppose a security update needs to be applied to Bash.  Guix
developers will provide a package definition for the ``fixed'' Bash, say
@code{bash-fixed}, in the usual way (@pxref{定义软件包}).  Then, the
original package definition is augmented with a @code{replacement} field
pointing to the package containing the bug fix:

@lisp
(define bash
  (package
    (name "bash")
    ;; @dots{}
    (replacement bash-fixed)))
@end lisp

From there on, any package depending directly or indirectly on Bash---as
reported by @command{guix gc --requisites} (@pxref{调用guix gc})---that
is installed is automatically ``rewritten'' to refer to @code{bash-fixed}
instead of @code{bash}.  This grafting process takes time proportional to
the size of the package, usually less than a minute for an ``average''
package on a recent machine.  Grafting is recursive: when an indirect
dependency requires grafting, then grafting ``propagates'' up to the package
that the user is installing.

Currently, the length of the name and version of the graft and that of the
package it replaces (@code{bash-fixed} and @code{bash} in the example above)
must be equal.  This restriction mostly comes from the fact that grafting
works by patching files, including binary files, directly.  Other
restrictions may apply: for instance, when adding a graft to a package
providing a shared library, the original shared library and its replacement
must have the same @code{SONAME} and be binary-compatible.

The @option{--no-grafts} command-line option allows you to forcefully avoid
grafting (@pxref{普通的构建选项, @option{--no-grafts}}).  Thus, the
command:

@example
guix build bash --no-grafts
@end example

@noindent
returns the store file name of the original Bash, whereas:

@example
guix build bash
@end example

@noindent
returns the store file name of the ``fixed'', replacement Bash.  This allows
you to distinguish between the two variants of Bash.

To verify which Bash your whole profile refers to, you can run
(@pxref{调用guix gc}):

@example
guix gc -R $(readlink -f ~/.guix-profile) | grep bash
@end example

@noindent
@dots{} and compare the store file names that you get with those above.
Likewise for a complete Guix system generation:

@example
guix gc -R $(guix system build my-config.scm) | grep bash
@end example

Lastly, to check which Bash running processes are using, you can use the
@command{lsof} command:

@example
lsof | grep /gnu/store/.*bash
@end example


@node 引导
@chapter 引导

@c Adapted from the ELS 2013 paper.

@cindex bootstrapping

Bootstrapping in our context refers to how the distribution gets built
``from nothing''.  Remember that the build environment of a derivation
contains nothing but its declared inputs (@pxref{介绍}).  So there's
an obvious chicken-and-egg problem: how does the first package get built?
How does the first compiler get compiled?

It is tempting to think of this question as one that only die-hard hackers
may care about.  However, while the answer to that question is technical in
nature, its implications are wide-ranging.  How the distribution is
bootstrapped defines the extent to which we, as individuals and as a
collective of users and hackers, can trust the software we run.  It is a
central concern from the standpoint of @emph{security} and from a @emph{user
freedom} viewpoint.

@cindex bootstrap binaries
The GNU system is primarily made of C code, with libc at its core.  The GNU
build system itself assumes the availability of a Bourne shell and
command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and
`grep'.  Furthermore, build programs---programs that run @code{./configure},
@code{make}, etc.---are written in Guile Scheme (@pxref{Derivations}).
Consequently, to be able to build anything at all, from scratch, Guix relies
on pre-built binaries of Guile, GCC, Binutils, libc, and the other packages
mentioned above---the @dfn{bootstrap binaries}.

These bootstrap binaries are ``taken for granted'', though we can also
re-create them if needed (@pxref{Preparing to Use the Bootstrap Binaries}).

@menu
* Reduced Binary Seed Bootstrap::  A Bootstrap worthy of GNU.
* Preparing to Use the Bootstrap Binaries::  Building that what matters 
                                               most.
@end menu

@node Reduced Binary Seed Bootstrap
@section The Reduced Binary Seed Bootstrap

Guix---like other GNU/Linux distributions---is traditionally bootstrapped
from a set of bootstrap binaries: Bourne shell, command-line tools provided
by GNU Coreutils, Awk, Findutils, `sed', and `grep' and Guile, GCC,
Binutils, and the GNU C Library (@pxref{引导}).  Usually, these
bootstrap binaries are ``taken for granted.''

Taking the bootstrap binaries for granted means that we consider them to be
a correct and trustworthy ``seed'' for building the complete system.
Therein lies a problem: the combined size of these bootstrap binaries is
about 250MB (@pxref{Bootstrappable Builds,,, mes, GNU Mes}).  Auditing or
even inspecting these is next to impossible.

For @code{i686-linux} and @code{x86_64-linux}, Guix now features a ``Reduced
Binary Seed'' bootstrap @footnote{We would like to say: ``Full Source
Bootstrap'' and while we are working towards that goal it would be hyperbole
to use that term for what we do now.}.

The Reduced Binary Seed bootstrap removes the most critical tools---from a
trust perspective---from the bootstrap binaries: GCC, Binutils and the GNU C
Library are replaced by: @code{bootstrap-mescc-tools} (a tiny assembler and
linker) and @code{bootstrap-mes} (a small Scheme Interpreter and a C
compiler written in Scheme and the Mes C Library, built for TinyCC and for
GCC).

Using these new binary seeds the ``missing'' Binutils, GCC, and the GNU C
Library are built from source.  From here on the more traditional bootstrap
process resumes.  This approach has reduced the bootstrap binaries in size
to about 145MB in Guix v1.1.

The next step that Guix has taken is to replace the shell and all its
utilities with implementations in Guile Scheme, the @emph{Scheme-only
bootstrap}.  Gash (@pxref{Gash,,, gash, The Gash manual}) is a
POSIX-compatible shell that replaces Bash, and it comes with Gash Utils
which has minimalist replacements for Awk, the GNU Core Utilities, Grep,
Gzip, Sed, and Tar.  The rest of the bootstrap binary seeds that were
removed are now built from source.

Building the GNU System from source is currently only possible by adding
some historical GNU packages as intermediate steps@footnote{Packages such as
@code{gcc-2.95.3}, @code{binutils-2.14}, @code{glibc-2.2.5},
@code{gzip-1.2.4}, @code{tar-1.22}, and some others.  For details, see
@file{gnu/packages/commencement.scm}.}.  As Gash and Gash Utils mature, and
GNU packages become more bootstrappable again (e.g., new releases of GNU Sed
will also ship as gzipped tarballs again, as alternative to the hard to
bootstrap @code{xz}-compression), this set of added packages can hopefully
be reduced again.

The graph below shows the resulting dependency graph for
@code{gcc-core-mesboot0}, the bootstrap compiler used for the traditional
bootstrap of the rest of the Guix System.

@c ./pre-inst-env guix graph -e '(@@ (gnu packages commencement) gcc-core-mesboot0)' | sed -re 's,((bootstrap-mescc-tools|bootstrap-mes|guile-bootstrap).*shape =) box,\1 ellipse,' > doc/images/gcc-core-mesboot0-graph.dot
@image{images/gcc-core-mesboot0-graph,6in,,Dependency graph of
gcc-core-mesboot0}

The only significant binary bootstrap seeds that remain@footnote{ Ignoring
the 68KB @code{mescc-tools}; that will be removed later, together with
@code{mes}.} are a Scheme interpreter and a Scheme compiler: GNU Mes and GNU
Guile@footnote{Not shown in this graph are the static binaries for
@file{bash}, @code{tar}, and @code{xz} that are used to get Guile running.}.

This further reduction has brought down the size of the binary seed to about
60MB for @code{i686-linux} and @code{x86_64-linux}.

Work is ongoing to remove all binary blobs from our free software bootstrap
stack, working towards a Full Source Bootstrap.  Also ongoing is work to
bring these bootstraps to the @code{arm-linux} and @code{aarch64-linux}
architectures and to the Hurd.

If you are interested, join us on @samp{#bootstrappable} on the Freenode IRC
network or discuss on @email{bug-mes@@gnu.org} or
@email{gash-devel@@nongnu.org}.

@node Preparing to Use the Bootstrap Binaries
@section Preparing to Use the Bootstrap Binaries

@c As of Emacs 24.3, Info-mode displays the image, but since it's a
@c large image, it's hard to scroll.  Oh well.
@image{images/bootstrap-graph,6in,,Dependency graph of the early bootstrap
derivations}

The figure above shows the very beginning of the dependency graph of the
distribution, corresponding to the package definitions of the @code{(gnu
packages bootstrap)} module.  A similar figure can be generated with
@command{guix graph} (@pxref{调用guix graph}), along the lines of:

@example
guix graph -t derivation \
  -e '(@@@@ (gnu packages bootstrap) %bootstrap-gcc)' \
  | dot -Tps > gcc.ps
@end example

or, for the further Reduced Binary Seed bootstrap

@example
guix graph -t derivation \
  -e '(@@@@ (gnu packages bootstrap) %bootstrap-mes)' \
  | dot -Tps > mes.ps
@end example

At this level of detail, things are slightly complex.  First, Guile itself
consists of an ELF executable, along with many source and compiled Scheme
files that are dynamically loaded when it runs.  This gets stored in the
@file{guile-2.0.7.tar.xz} tarball shown in this graph.  This tarball is part
of Guix's ``source'' distribution, and gets inserted into the store with
@code{add-to-store} (@pxref{仓库}).

But how do we write a derivation that unpacks this tarball and adds it to
the store? To solve this problem, the @code{guile-bootstrap-2.0.drv}
derivation---the first one that gets built---uses @code{bash} as its
builder, which runs @code{build-bootstrap-guile.sh}, which in turn calls
@code{tar} to unpack the tarball.  Thus, @file{bash}, @file{tar}, @file{xz},
and @file{mkdir} are statically-linked binaries, also part of the Guix
source distribution, whose sole purpose is to allow the Guile tarball to be
unpacked.

Once @code{guile-bootstrap-2.0.drv} is built, we have a functioning Guile
that can be used to run subsequent build programs.  Its first task is to
download tarballs containing the other pre-built binaries---this is what the
@file{.tar.xz.drv} derivations do.  Guix modules such as
@code{ftp-client.scm} are used for this purpose.  The
@code{module-import.drv} derivations import those modules in a directory in
the store, using the original layout.  The @code{module-import-compiled.drv}
derivations compile those modules, and write them in an output directory
with the right layout.  This corresponds to the @code{#:modules} argument of
@code{build-expression->derivation} (@pxref{Derivations}).

Finally, the various tarballs are unpacked by the derivations
@code{gcc-bootstrap-0.drv}, @code{glibc-bootstrap-0.drv}, or
@code{bootstrap-mes-0.drv} and @code{bootstrap-mescc-tools-0.drv}, at which
point we have a working C tool chain.

@unnumberedsec Building the Build Tools

Bootstrapping is complete when we have a full tool chain that does not
depend on the pre-built bootstrap tools discussed above.  This no-dependency
requirement is verified by checking whether the files of the final tool
chain contain references to the @file{/gnu/store} directories of the
bootstrap inputs.  The process that leads to this ``final'' tool chain is
described by the package definitions found in the @code{(gnu packages
commencement)} module.

The @command{guix graph} command allows us to ``zoom out'' compared to the
graph above, by looking at the level of package objects instead of
individual derivations---remember that a package may translate to several
derivations, typically one derivation to download its source, one to build
the Guile modules it needs, and one to actually build the package from
source.  The command:

@example
guix graph -t bag \
  -e '(@@@@ (gnu packages commencement)
          glibc-final-with-bootstrap-bash)' | xdot -
@end example

@noindent
displays the dependency graph leading to the ``final'' C
library@footnote{You may notice the @code{glibc-intermediate} label,
suggesting that it is not @emph{quite} final, but as a good approximation,
we will consider it final.}, depicted below.

@image{images/bootstrap-packages,6in,,Dependency graph of the early
packages}

@c See <https://lists.gnu.org/archive/html/gnu-system-discuss/2012-10/msg00000.html>.
The first tool that gets built with the bootstrap binaries is
GNU@tie{}Make---noted @code{make-boot0} above---which is a prerequisite for
all the following packages.  From there Findutils and Diffutils get built.

Then come the first-stage Binutils and GCC, built as pseudo cross
tools---i.e., with @option{--target} equal to @option{--host}.  They are
used to build libc.  Thanks to this cross-build trick, this libc is
guaranteed not to hold any reference to the initial tool chain.

From there the final Binutils and GCC (not shown above) are built.  GCC uses
@command{ld} from the final Binutils, and links programs against the
just-built libc.  This tool chain is used to build the other packages used
by Guix and by the GNU Build System: Guile, Bash, Coreutils, etc.

And voilà! At this point we have the complete set of build tools that the
GNU Build System expects.  These are in the @code{%final-inputs} variable of
the @code{(gnu packages commencement)} module, and are implicitly used by
any package that uses @code{gnu-build-system} (@pxref{构建系统,
@code{gnu-build-system}}).


@unnumberedsec Building the Bootstrap Binaries

@cindex bootstrap binaries
Because the final tool chain does not depend on the bootstrap binaries,
those rarely need to be updated.  Nevertheless, it is useful to have an
automated way to produce them, should an update occur, and this is what the
@code{(gnu packages make-bootstrap)} module provides.

The following command builds the tarballs containing the bootstrap binaries
(Binutils, GCC, glibc, for the traditional bootstrap and
linux-libre-headers, bootstrap-mescc-tools, bootstrap-mes for the Reduced
Binary Seed bootstrap, and Guile, and a tarball containing a mixture of
Coreutils and other basic command-line tools):

@example
guix build bootstrap-tarballs
@end example

The generated tarballs are those that should be referred to in the
@code{(gnu packages bootstrap)} module mentioned at the beginning of this
section.

Still here? Then perhaps by now you've started to wonder: when do we reach a
fixed point? That is an interesting question! The answer is unknown, but if
you would like to investigate further (and have significant computational
and storage resources to do so), then let us know.

@unnumberedsec Reducing the Set of Bootstrap Binaries

Our traditional bootstrap includes GCC, GNU Libc, Guile, etc.  That's a lot
of binary code! Why is that a problem? It's a problem because these big
chunks of binary code are practically non-auditable, which makes it hard to
establish what source code produced them.  Every unauditable binary also
leaves us vulnerable to compiler backdoors as described by Ken Thompson in
the 1984 paper @emph{Reflections on Trusting Trust}.

This is mitigated by the fact that our bootstrap binaries were generated
from an earlier Guix revision.  Nevertheless it lacks the level of
transparency that we get in the rest of the package dependency graph, where
Guix always gives us a source-to-binary mapping.  Thus, our goal is to
reduce the set of bootstrap binaries to the bare minimum.

The @uref{https://bootstrappable.org, Bootstrappable.org web site} lists
on-going projects to do that.  One of these is about replacing the bootstrap
GCC with a sequence of assemblers, interpreters, and compilers of increasing
complexity, which could be built from source starting from a simple and
auditable assembler.

Our first major achievement is the replacement of of GCC, the GNU C Library
and Binutils by MesCC-Tools (a simple hex linker and macro assembler) and
Mes (@pxref{Top, GNU Mes Reference Manual,, mes, GNU Mes}, a Scheme
interpreter and C compiler in Scheme).  Neither MesCC-Tools nor Mes can be
fully bootstrapped yet and thus we inject them as binary seeds.  We call
this the Reduced Binary Seed bootstrap, as it has halved the size of our
bootstrap binaries! Also, it has eliminated the C compiler binary;
i686-linux and x86_64-linux Guix packages are now bootstrapped without any
binary C compiler.

Work is ongoing to make MesCC-Tools and Mes fully bootstrappable and we are
also looking at any other bootstrap binaries.  Your help is welcome!

@node 移植
@chapter Porting to a New Platform

As discussed above, the GNU distribution is self-contained, and
self-containment is achieved by relying on pre-built ``bootstrap binaries''
(@pxref{引导}).  These binaries are specific to an operating system
kernel, CPU architecture, and application binary interface (ABI).  Thus, to
port the distribution to a platform that is not yet supported, one must
build those bootstrap binaries, and update the @code{(gnu packages
bootstrap)} module to use them on that platform.

Fortunately, Guix can @emph{cross compile} those bootstrap binaries.  When
everything goes well, and assuming the GNU tool chain supports the target
platform, this can be as simple as running a command like this one:

@example
guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs
@end example

For this to work, the @code{glibc-dynamic-linker} procedure in @code{(gnu
packages bootstrap)} must be augmented to return the right file name for
libc's dynamic linker on that platform; likewise,
@code{system->linux-architecture} in @code{(gnu packages linux)} must be
taught about the new platform.

Once these are built, the @code{(gnu packages bootstrap)} module needs to be
updated to refer to these binaries on the target platform.  That is, the
hashes and URLs of the bootstrap tarballs for the new platform must be added
alongside those of the currently supported platforms.  The bootstrap Guile
tarball is treated specially: it is expected to be available locally, and
@file{gnu/local.mk} has rules to download it for the supported
architectures; a rule for the new platform must be added as well.

In practice, there may be some complications.  First, it may be that the
extended GNU triplet that specifies an ABI (like the @code{eabi} suffix
above) is not recognized by all the GNU tools.  Typically, glibc recognizes
some of these, whereas GCC uses an extra @option{--with-abi} configure flag
(see @code{gcc.scm} for examples of how to handle this).  Second, some of
the required packages could fail to build for that platform.  Lastly, the
generated binaries could be broken for some reason.

@c *********************************************************************
@include contributing.zh_CN.texi

@c *********************************************************************
@node 致谢
@chapter 致谢

Guix is based on the @uref{https://nixos.org/nix/, Nix package manager},
which was designed and implemented by Eelco Dolstra, with contributions from
other people (see the @file{nix/AUTHORS} file in Guix).  Nix pioneered
functional package management, and promoted unprecedented features, such as
transactional package upgrades and rollbacks, per-user profiles, and
referentially transparent build processes.  Without this work, Guix would
not exist.

基于 Nix 的软件发行版 Nixpkgs 和 NixOS 也给 Guix 带来了灵感。

GNU@tie{}Guix itself is a collective work with contributions from a number
of people.  See the @file{AUTHORS} file in Guix for more information on
these fine people.  The @file{THANKS} file lists people who have helped by
reporting bugs, taking care of the infrastructure, providing artwork and
themes, making suggestions, and more---thank you!


@c *********************************************************************
@node GNU自由文档许可证
@appendix GNU自由文档许可证
@cindex license, GNU Free Documentation License
@include fdl-1.3.texi

@c *********************************************************************
@node 概念索引
@unnumbered 概念索引
@printindex cp

@node 编程索引
@unnumbered 编程索引
@syncodeindex tp fn
@syncodeindex vr fn
@printindex fn

@bye

@c Local Variables:
@c ispell-local-dictionary: "american";
@c End:
