\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename guix.info @documentencoding UTF-8 @settitle GNU Guix Reference Manual @c %**end of header @include version.texi @copying Copyright @copyright{} 2012, 2013, 2014 Ludovic Courtès@* Copyright @copyright{} 2013, 2014 Andreas Enge@* Copyright @copyright{} 2013 Nikita Karetnikov 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 Package management @direntry * guix: (guix). Guix, the functional package manager. * guix package: (guix)Invoking guix package Managing packages with Guix. * guix build: (guix)Invoking guix build Building packages with Guix. * guix system: (guix)Invoking guix system Managing the operating system configuration. @end direntry @dircategory Software development @direntry * guix environment: (guix)Invoking guix environment Building development environments with Guix. @end direntry @titlepage @title GNU Guix Reference Manual @subtitle Using the GNU Guix Functional Package Manager @author Ludovic Courtès @author Andreas Enge @author Nikita Karetnikov @page @vskip 0pt plus 1filll Edition @value{EDITION} @* @value{UPDATED} @* @insertcopying @end titlepage @contents @c ********************************************************************* @node Top @top GNU Guix This document describes GNU Guix version @value{VERSION}, a functional package management tool written for the GNU system. @menu * Introduction:: What is Guix about? * Installation:: Installing Guix. * Package Management:: Package installation, upgrade, etc. * Programming Interface:: Using Guix in Scheme. * Utilities:: Package management commands. * GNU Distribution:: Software for your friendly GNU system. * Contributing:: Your help needed! * Acknowledgments:: Thanks! * GNU Free Documentation License:: The license of this manual. * Concept Index:: Concepts. * Programming Index:: Data types, functions, and variables. @end menu @c ********************************************************************* @node Introduction @chapter Introduction GNU Guix@footnote{``Guix'' is pronounced like ``geeks'', or ``ɡiːks'' using the international phonetic alphabet (IPA).} is a functional package management tool for the GNU system. Package management consists of all activities that relate to building packages from sources, honoring their build-time and run-time dependencies, installing packages in user environments, upgrading installed packages to new versions or rolling back to a previous set, removing unused software packages, etc. @cindex functional package management The term @dfn{functional} refers to a specific package management discipline. In Guix, the package build and installation process is seen as a function, in the mathematical sense. That function takes inputs, such as build scripts, a compiler, and libraries, and returns an installed package. As a pure function, its result depends solely on its inputs---for instance, it cannot refer to software or scripts that were not explicitly passed as inputs. A build function always produces the same result when passed a given set of inputs. It cannot alter the system's environment in any way; for instance, it cannot create, modify, or delete files outside of its build and installation directories. This is achieved by running build processes in isolated environments (or @dfn{containers}), where only their explicit inputs are visible. @cindex store The result of package build functions is @dfn{cached} in the file system, in a special directory called @dfn{the store} (@pxref{The Store}). Each package is installed in a directory of its own, in the store---by default under @file{/gnu/store}. The directory name contains a hash of all the inputs used to build that package; thus, changing an input yields a different directory name. This approach is the foundation of Guix's salient features: support for transactional package upgrade and rollback, per-user installation, and garbage collection of packages (@pxref{Features}). Guix has a command-line interface, which allows users to build, install, upgrade, and remove packages, as well as a Scheme programming interface. Last but not least, Guix is used to build a distribution of the GNU system, with many GNU and non-GNU free software packages. @xref{GNU Distribution}. @c ********************************************************************* @node Installation @chapter Installation GNU Guix is available for download from its website at @url{http://www.gnu.org/software/guix/}. This section describes the software requirements of Guix, as well as how to install it and get ready to use it. Note that this section is concerned with the installation of the package manager, which can be done on top of a running GNU/Linux system. If, instead, you want to install the complete GNU operating system, @pxref{System Installation}. The build procedure for Guix is the same as for other GNU software, and is not covered here. Please see the files @file{README} and @file{INSTALL} in the Guix source tree for additional details. @menu * Requirements:: Software needed to build and run Guix. * Setting Up the Daemon:: Preparing the build daemon's environment. * Invoking guix-daemon:: Running the build daemon. @end menu @node Requirements @section Requirements GNU Guix depends on the following packages: @itemize @item @url{http://gnu.org/software/guile/, GNU Guile}, version 2.0.5 or later; @item @url{http://gnupg.org/, GNU libgcrypt}; @end itemize The following dependencies are optional: @itemize @item Installing @url{http://savannah.nongnu.org/projects/guile-json/, Guile-JSON} will allow you to use the @command{guix import pypi} command; it is of interest primarily for developers and not for casual users. @item Installing @uref{http://gnutls.org/, GnuTLS-Guile} will allow you to access @code{https} URLs with the @command{guix download} command (@pxref{Invoking guix download}) and the @command{guix import pypi} command. This is primarily of interest to developers. @xref{Guile Preparations, how to install the GnuTLS bindings for Guile,, gnutls-guile, GnuTLS-Guile}. @end itemize Unless @code{--disable-daemon} was passed to @command{configure}, the following packages are also needed: @itemize @item @url{http://sqlite.org, SQLite 3} @item @url{http://www.bzip.org, libbz2} @item @url{http://gcc.gnu.org, GCC's g++} @end itemize When a working installation of @url{http://nixos.org/nix/, the Nix package manager} is available, you can instead configure Guix with @code{--disable-daemon}. In that case, Nix replaces the three dependencies above. Guix is compatible with Nix, so it is possible to share the same store between both. To do so, you must pass @command{configure} not only the same @code{--with-store-dir} value, but also the same @code{--localstatedir} value. The latter is essential because it specifies where the database that stores metadata about the store is located, among other things. The default values for Nix are @code{--with-store-dir=/nix/store} and @code{--localstatedir=/nix/var}. Note that @code{--disable-daemon} is not required if your goal is to share the store with Nix. @node Setting Up the Daemon @section Setting Up the Daemon @cindex daemon Operations such as building a package or running the garbage collector are all performed by a specialized process, the @dfn{build daemon}, on behalf of clients. Only the daemon may access the store and its associated database. Thus, any operation that manipulates the store goes through the daemon. For instance, command-line tools such as @command{guix package} and @command{guix build} communicate with the daemon (@i{via} remote procedure calls) to instruct it what to do. The following sections explain how to prepare the build daemon's environment. @menu * Build Environment Setup:: Preparing the isolated build environment. * Daemon Offload Setup:: Offloading builds to remote machines. @end menu @node Build Environment Setup @subsection Build Environment Setup In a standard multi-user setup, Guix and its daemon---the @command{guix-daemon} program---are installed by the system administrator; @file{/gnu/store} is owned by @code{root} and @command{guix-daemon} runs as @code{root}. Unprivileged users may use Guix tools to build packages or otherwise access the store, and the daemon will do it on their behalf, ensuring that the store is kept in a consistent state, and allowing built packages to be shared among users. @cindex build users When @command{guix-daemon} runs as @code{root}, you may not want package build processes themselves to run as @code{root} too, for obvious security reasons. To avoid that, a special pool of @dfn{build users} should be created for use by build processes started by the daemon. These build users need not have a shell and a home directory: they will just be used when the daemon drops @code{root} privileges in build processes. Having several such users allows the daemon to launch distinct build processes under separate UIDs, which guarantees that they do not interfere with each other---an essential feature since builds are regarded as pure functions (@pxref{Introduction}). On a GNU/Linux system, a build user pool may be created like this (using Bash syntax and the @code{shadow} commands): @c See http://lists.gnu.org/archive/html/bug-guix/2013-01/msg00239.html @c for why `-G' is needed. @example # groupadd guix-builder # for i in `seq 1 10`; do useradd -g guix-builder -G guix-builder \ -d /var/empty -s `which nologin` \ -c "Guix build user $i" --system \ guix-builder$i; done @end example @noindent The @code{guix-daemon} program may then be run as @code{root} with: @example # guix-daemon --build-users-group=guix-builder @end example @cindex chroot @noindent This way, the daemon starts build processes in a chroot, under one of the @code{guix-builder} users. On GNU/Linux, by default, the chroot environment contains nothing but: @c Keep this list in sync with libstore/build.cc! ----------------------- @itemize @item a minimal @code{/dev} directory, created mostly independently from the host @code{/dev}@footnote{``Mostly'', because while the set of files that appear in the chroot's @code{/dev} is fixed, most of these files can only be created if the host has them.}; @item the @code{/proc} directory; it only shows the container's processes since a separate PID name space is used; @item @file{/etc/passwd} with an entry for the current user and an entry for user @file{nobody}; @item @file{/etc/group} with an entry for the user's group; @item @file{/etc/hosts} with an entry that maps @code{localhost} to @code{127.0.0.1}; @item a writable @file{/tmp} directory. @end itemize If you are installing Guix as an unprivileged user, it is still possible to run @command{guix-daemon}. 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 Daemon Offload Setup @subsection Using the Offload Facility @cindex offloading @cindex build hook When desired, the build daemon can @dfn{offload} derivation builds to other machines running Guix, using the @code{offload} @dfn{build hook}. When that feature is enabled, a list of user-specified build machines is read from @file{/etc/guix/machines.scm}; anytime a build is requested, for instance via @code{guix build}, the daemon attempts to offload it to one of the machines that satisfies the derivation's constraints, in particular its system type---e.g., @file{x86_64-linux}. 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 @file{/etc/guix/machines.scm} file typically looks like this: @example (list (build-machine (name "eightysix.example.org") (system "x86_64-linux") (user "bob") (speed 2.)) ; incredibly fast! (build-machine (name "meeps.example.org") (system "mips64el-linux") (user "alice") (private-key (string-append (getenv "HOME") "/.ssh/id-rsa-for-guix")))) @end example @noindent In the example above we specify a list of two build machines, one for the @code{x86_64} architecture and one for the @code{mips64el} architecture. In fact, this file is---not surprisingly!---a Scheme file that is evaluated when the @code{offload} hook is started. Its return value must be a list of @code{build-machine} objects. While this example shows a fixed list of build machines, one could imagine, say, using DNS-SD to return a list of potential build machines discovered in the local network (@pxref{Introduction, Guile-Avahi,, guile-avahi, Using Avahi in Guile Scheme Programs}). The @code{build-machine} data type is detailed below. @deftp {Data Type} build-machine This data type represents build machines the daemon may offload builds to. The important fields are: @table @code @item name The remote machine's host name. @item system The remote machine's system type---e.g., @code{"x86_64-linux"}. @item user The user account to use when connecting to the remote machine over SSH. Note that the SSH key pair must @emph{not} be passphrase-protected, to allow non-interactive logins. @end table A number of optional fields may be specified: @table @code @item port Port number of the machine's SSH server (default: 22). @item private-key The SSH private key file to use when connecting to the machine. @item parallel-builds The number of builds that may run in parallel on the machine (1 by default.) @item speed A ``relative speed factor''. The offload scheduler will tend to prefer machines with a higher speed factor. @item features A list of strings denoting specific features supported by the machine. An example is @code{"kvm"} for machines that have the KVM Linux modules and corresponding hardware support. Derivations can request features by name, and they will be scheduled on matching build machines. @end table @end deftp The @code{guix} command must be in the search path on the build machines, since offloading works by invoking the @code{guix archive} and @code{guix build} commands. There's one last thing to do once @file{machines.scm} is in place. As explained above, when offloading, files are transferred back and forth between the machine stores. For this to work, you need to generate a key pair to allow the daemon to export signed archives of files from the store (@pxref{Invoking guix archive}): @example # guix archive --generate-key @end example @noindent Thus, when receiving files, a machine's build daemon can make sure they are genuine, have not been tampered with, and that they are signed by an authorized key. @node Invoking guix-daemon @section Invoking @command{guix-daemon} The @command{guix-daemon} program implements all the functionality to access the store. This includes launching build processes, running the garbage collector, querying the availability of a build result, etc. It is normally run as @code{root} like this: @example # guix-daemon --build-users-group=guix-builder @end example @noindent For details on how to set it up, @ref{Setting Up the Daemon}. @cindex chroot @cindex container, build environment @cindex build environment @cindex reproducible builds By default, @command{guix-daemon} launches build processes under different UIDs, taken from the build group specified with @code{--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{Programming Interface, 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{Features}). The following command-line options are supported: @table @code @item --build-users-group=@var{group} Take users from @var{group} to run build processes (@pxref{Setting Up the Daemon, build users}). @item --no-substitutes @cindex substitutes Do not use substitutes for build products. That is, always build things locally instead of allowing downloads of pre-built binaries (@pxref{Substitutes}). By default substitutes are used, unless the client---such as the @command{guix package} command---is explicitly invoked with @code{--no-substitutes}. When the daemon runs with @code{--no-substitutes}, clients can still explicitly enable substitution @i{via} the @code{set-build-options} remote procedure call (@pxref{The Store}). @item --substitute-urls=@var{urls} Consider @var{urls} the default whitespace-separated list of substitute source URLs. When this option is omitted, @code{http://hydra.gnu.org} is used. This means that substitutes may be downloaded from @var{urls}, as long as they are signed by a trusted signature (@pxref{Substitutes}). @cindex build hook @item --no-build-hook Do not use the @dfn{build hook}. The build hook is a helper program that the daemon can start and to which it submits build requests. This mechanism is used to offload builds to other machines (@pxref{Daemon Offload Setup}). @item --cache-failures Cache build failures. By default, only successful builds are cached. @item --cores=@var{n} @itemx -c @var{n} Use @var{n} CPU cores to build each derivation; @code{0} means as many as available. The default value is @code{1}, but it may be overridden by clients, such as the @code{--cores} option of @command{guix build} (@pxref{Invoking guix build}). The effect is to define the @code{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} Allow at most @var{n} build jobs in parallel. The default value is @code{1}. @item --debug Produce debugging output. This is useful to debug daemon start-up issues, but then it may be overridden by clients, for example the @code{--verbosity} option of @command{guix build} (@pxref{Invoking guix build}). @item --chroot-directory=@var{dir} Add @var{dir} to the build chroot. Doing this may change the result of build processes---for instance if they use optional dependencies found in @var{dir} when it is available, and not otherwise. For that reason, it is not recommended to do so. Instead, make sure that each derivation declares all the inputs that it needs. @item --disable-chroot Disable chroot builds. Using this option is not recommended since, again, it would allow build processes to gain access to undeclared dependencies. @item --disable-log-compression Disable compression of the build logs. Unless @code{--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. This option disables that. @item --disable-deduplication @cindex deduplication Disable automatic file ``deduplication'' in the store. By default, files added to the store are automatically ``deduplicated'': if a newly added file is identical to another one found in the store, the daemon makes the new file a hard link to the other file. This can noticeably reduce disk usage, at the expense of slightly increasde input/output load at the end of a build process. This option disables this optimization. @item --gc-keep-outputs[=yes|no] Tell whether the garbage collector (GC) must keep outputs of live derivations. When set to ``yes'', the GC will keep the outputs of any live derivation available in the store---the @code{.drv} files. The default is ``no'', meaning that derivation outputs are kept only if they are GC roots. @item --gc-keep-derivations[=yes|no] Tell whether the garbage collector (GC) must keep derivations corresponding to live outputs. When set to ``yes'', as is the case by default, the GC keeps derivations---i.e., @code{.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 ``no'' saves a bit of disk space. Note that when both @code{--gc-keep-derivations} and @code{--gc-keep-outputs} are used, 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 live. 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 @code{uname} system call will report 2.6 as the release number. This might be helpful to build programs that (usually wrongfully) depend on the kernel version number. @item --lose-logs Do not keep build logs. By default they are kept under @code{@var{localstatedir}/guix/log}. @item --system=@var{system} Assume @var{system} as the current system type. By default it is the architecture/kernel pair found at configure time, such as @code{x86_64-linux}. @item --listen=@var{socket} Listen for connections on @var{socket}, the file name of a Unix-domain socket. The default socket is @file{@var{localstatedir}/daemon-socket/socket}. This option is only useful in exceptional circumstances, such as if you need to run several daemons on the same machine. @end table @c ********************************************************************* @node Package Management @chapter Package Management The purpose of GNU Guix is to allow users to easily install, upgrade, and remove software packages, without having to know about their build procedure 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. Two user interfaces are provided for routine package management tasks: a command-line interface (@pxref{Invoking guix package, @code{guix package}}), and a visual user interface in Emacs (@pxref{Emacs Interface}). @menu * Features:: How Guix will make your life brighter. * Invoking guix package:: Package installation, removal, etc. * Emacs Interface:: Package management from Emacs. * Substitutes:: Downloading pre-built binaries. * Packages with Multiple Outputs:: Single source package, multiple outputs. * Invoking guix gc:: Running the garbage collector. * Invoking guix pull:: Fetching the latest Guix and distribution. * Invoking guix archive:: Exporting and importing store files. @end menu @node Features @section Features 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 (note that Guix comes with an Emacs extension to shorten those file names, @ref{Emacs Prettify}.) 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{Invoking guix package}). It operates on those per-user profiles, and can be used @emph{with normal user privileges}. 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 is subject to transactional upgrades and roll-back (@pxref{Using the Configuration System}). All those packages in the package store may be @emph{garbage-collected}. Guix can determine which packages are still referenced by the user profiles, and remove those that are provably no longer referenced (@pxref{Invoking 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 reproducible builds Finally, Guix takes a @dfn{purely functional} approach to package management, as described in the introduction (@pxref{Introduction}). 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{Invoking 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}). 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 package's dependencies in their profile (@pxref{Invoking guix environment}). @node Invoking guix package @section Invoking @command{guix package} 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. It operates only on the user's own profile, and works with normal user privileges (@pxref{Features}). Its syntax is: @example guix package @var{options} @end example Primarily, @var{options} specifies the operations to be performed during the transaction. Upon completion, a new profile is created, but previous 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 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 @code{PATH} environment variable, and so on. In a multi-user setup, user profiles must be stored in a place registered as a @dfn{garbage-collector root}, which @file{$HOME/.guix-profile} points to (@pxref{Invoking guix gc}). That directory is normally @code{@var{localstatedir}/profiles/per-user/@var{user}}, where @var{localstatedir} is the value passed to @code{configure} as @code{--localstatedir}, and @var{user} is the user name. It must be created by @code{root}, with @var{user} as the owner. When it does not exist, or is not owned by @var{user}, @command{guix package} emits an error about it. 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 a hyphen and version number, such as @code{guile-1.8.8}. 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{Packages with Multiple Outputs}). Packages with a corresponding name (and optionally version) are searched for among the GNU distribution modules (@pxref{Package Modules}). @cindex propagated inputs Sometimes packages have @dfn{propagated inputs}: these are dependencies that automatically get installed along with the required package. 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 independently. Besides, packages sometimes rely on the definition of environment variables for their search paths (see explanation of @code{--search-paths} below). Any missing or possibly incorrect environment variable definitions are reported here. @c XXX: keep me up-to-date Finally, when installing a GNU package, the tool reports the availability of a newer upstream version. In the future, it may provide the option of installing directly from the upstream version, even if that version is not yet in the distribution. @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{} 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 --remove=@var{package} @dots{} @itemx -r @var{package} @dots{} Remove the specified @var{package}s. As for @code{--install}, each @var{package} may specify a version number and/or output name in addition to the package name. For instance, @code{-r glibc:debug} would remove the @code{debug} output of @code{glibc}. @item --upgrade[=@var{regexp} @dots{}] @itemx -u [@var{regexp} @dots{}] Upgrade all the installed packages. If one or more @var{regexp}s are specified, upgrade only installed packages whose name matches a @var{regexp}. 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{Invoking guix pull}). @item --roll-back Roll back to the previous @dfn{generation} of the profile---i.e., undo the last transaction. When combined with options such as @code{--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 meta-data. Installing, removing, or upgrading packages from a generation that has been rolled back to overwrites previous future generations. Thus, the history of a profile's generations is always linear. @item --switch-generation=@var{pattern} @itemx -S @var{pattern} 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 @code{--roll-back}, use @code{--switch-generation=+1}. The difference between @code{--roll-back} and @code{--switch-generation=-1} is that @code{--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 @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 @code{CPATH} and @code{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 @code{--search-paths} will suggest setting these variables to @code{@var{profile}/include} and @code{@var{profile}/lib}, respectively. @item --profile=@var{profile} @itemx -p @var{profile} Use @var{profile} instead of the user's default profile. @item --verbose Produce verbose output. In particular, emit the environment's build log on the standard error port. @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} List the available packages whose synopsis or description matches @var{regexp}. Print all the meta-data 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 name: glibc version: 2.17 name: libgc version: 7.2alpha6 @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 @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: @example $ guix package --show=python-3.3.5 | recsel -p name,version name: python version: 3.3.5 @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 software distribution (@pxref{GNU Distribution}). When @var{regexp} is specified, list only installed 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{Packages with Multiple Outputs}), and the source location of its definition. @item --list-generations[=@var{pattern}] @itemx -l [@var{pattern}] 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{Packages with Multiple Outputs}), 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, @code{--list-generations=1} returns the first one. And @code{--list-generations=1,8,2} outputs three generations in the specified order. Neither spaces nor trailing commas are allowed. @item @emph{Ranges}. @code{--list-generations=2..9} prints the specified generations and everything in between. Note that the start of a range must be lesser than its end. It is also possible to omit the endpoint. For example, @code{--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, @code{--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, @code{--delete-generations=1m} deletes generations that are more than one month old. If the current generation matches, it is deleted atomically---i.e., by switching to the previous available generation. Note that the zeroth generation is never deleted. Note that deleting generations prevents roll-back to them. Consequently, this command must be used with care. @end table Finally, since @command{guix package} may actually start build processes, it supports all the common build options that @command{guix build} supports (@pxref{Invoking guix build, common build options}). @include emacs.texi @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. 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. The @code{hydra.gnu.org} server is a front-end to a build farm that builds packages from the GNU distribution continuously for some architectures, and makes them available as substitutes. This is the default source of substitutes; it can be overridden by passing @command{guix-daemon} the @code{--substitute-urls} option (@pxref{Invoking guix-daemon}). @cindex security @cindex digital signatures To allow Guix to download substitutes from @code{hydra.gnu.org}, you must add its public key to the access control list (ACL) of archive imports, using the @command{guix archive} command (@pxref{Invoking guix archive}). Doing so implies that you trust @code{hydra.gnu.org} to not be compromised and to serve genuine substitutes. This public key is installed along with Guix, in @code{@var{prefix}/share/guix/hydra.gnu.org.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 < hydra.gnu.org.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 The following files 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 This indicates that substitutes from @code{hydra.gnu.org} are usable and will be downloaded, when possible, for future builds. Guix ignores substitutes that are not signed, or that are not signed by one of the keys listed in the ACL. It also detects and raises an error when attempting to use a substitute that has been tampered with. The substitute mechanism can be disabled globally by running @code{guix-daemon} with @code{--no-substitutes} (@pxref{Invoking guix-daemon}). It can also be disabled temporarily by passing the @code{--no-substitutes} option to @command{guix package}, @command{guix build}, and other command-line tools. 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{hydra.gnu.org} substitutes can be convenient, we encourage users to also build on their own, or even run their own build farm, such that @code{hydra.gnu.org} is less of an interesting target. Guix has the foundations to maximize build reproducibility (@pxref{Features}). 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. 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 Packages with Multiple Outputs @section Packages with Multiple Outputs @cindex multiple-output packages @cindex package outputs Often, packages defined in Guix have a single @dfn{output}---i.e., the source package leads exactly one directory in the store. When running @command{guix package -i 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 package -i glib @end example The command to install its documentation is: @example guix package -i glib:doc @end example Some packages install programs with different ``dependency footprints''. For instance, the WordNet package install 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. 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{Installing Debugging Files}). The outputs of a packages are listed in the third column of the output of @command{guix package --list-available} (@pxref{Invoking guix package}). @node Invoking guix gc @section Invoking @command{guix gc} @cindex garbage collector 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. 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 includes default user profiles, and may be augmented with @command{guix build --root}, for example (@pxref{Invoking guix build}). 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{Invoking guix package}). 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 @code{--delete} option), or to print garbage-collector information. The available options are listed below: @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 --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-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 List the references (respectively, the referrers) of store files given as arguments. @item --requisites @itemx -R 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. @end table @node Invoking guix pull @section Invoking @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. 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. The @command{guix pull} command is usually invoked with no arguments, but it supports the following options: @table @code @item --verbose Produce verbose output, writing build logs to the standard error output. @item --url=@var{url} Download the source tarball of Guix from @var{url}. By default, the tarball is taken from its canonical address at @code{gnu.org}, for the stable branch of Guix. @item --bootstrap Use the bootstrap Guile to build the latest Guix. This option is only useful to Guix developers. @end table @node Invoking guix archive @section Invoking @command{guix archive} The @command{guix archive} command allows users to @dfn{export} files from the store into a single archive, and to later @dfn{import} them. In particular, it allows store files to be transferred from one machine to another machine's store. For example, to transfer the @code{emacs} package to a machine connected over SSH, one would run: @example guix archive --export emacs | ssh the-machine guix archive --import @end example @noindent However, note that, in this example, all of @code{emacs} and its dependencies are transferred, regardless of what is already available in the target machine's store. The @code{--missing} option can help figure out which items are missing from the target's store. Archives are stored in the ``Nix archive'' or ``Nar'' format, which is comparable in spirit to `tar', but with a few noteworthy differences that make it more appropriate for our purposes. First, rather than recording all Unix meta-data 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. 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. @c FIXME: Add xref to daemon doc about signatures. 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. @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 @code{--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 daemons. This is a prerequisite before archives can be exported with @code{--export}. Note that this operation usually takes time, because it needs to gather enough entropy to generate the key pair. 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, it is a 4096-bit RSA key. Alternately, @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{http://people.csail.mit.edu/rivest/Sexp.txt, ``advanced-format s-expressions''} and is structured as an access-control list in the @url{http://theworld.com/~cme/spki.txt, Simple Public-Key Infrastructure (SPKI)}. @end table To export store files as an archive to the 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{Invoking 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 same options that can be passed to the @command{guix build} command (@pxref{Invoking guix build, common build options}). @c ********************************************************************* @node Programming Interface @chapter Programming Interface 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 a 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 * Defining Packages:: Defining new packages. * Build Systems:: Specifying how packages are built. * The Store:: Manipulating the package store. * Derivations:: Low-level interface to package derivations. * The Store Monad:: Purely functional interface to the store. * G-Expressions:: Manipulating build expressions. @end menu @node Defining Packages @section Defining Packages 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: @example (define-module (gnu packages hello) #:use-module (guix packages) #:use-module (guix download) #:use-module (guix build-system gnu) #:use-module (guix licenses)) (define-public hello (package (name "hello") (version "2.8") (source (origin (method url-fetch) (uri (string-append "mirror://gnu/hello/hello-" version ".tar.gz")) (sha256 (base32 "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6")))) (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 "http://www.gnu.org/software/hello/") (license gpl3+))) @end example @noindent Without being a Scheme expert, the reader may have guessed the meaning of the various fields here. This expression binds variable @code{hello} to a @code{} 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"}. In the example above, @var{hello} is defined into 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{Package Modules}). There are a few points worth noting in the above package definition: @itemize @item The @code{source} field of the package is an @code{} object. 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{Invoking guix download}) and @code{guix hash} (@pxref{Invoking 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{Build Systems}). Here, @var{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. @item The @code{arguments} field specifies options for the build system (@pxref{Build Systems}). Here it is interpreted by @var{gnu-build-system} as a request run @file{configure} with the @code{--enable-silent-rules} flag. @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 @var{gawk} variable; @var{gawk} is itself bound to a @code{} object. Note that GCC, Coreutils, Bash, and other essential tools do not need to be specified as inputs here. Instead, @var{gnu-build-system} takes care of ensuring that they are present (@pxref{Build Systems}). 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 Once a package definition is in place@footnote{Simple package definitions like the one above may be automatically converted from the Nixpkgs distribution using the @command{guix import} command.}, the package may actually be built using the @code{guix build} command-line tool (@pxref{Invoking guix build}). @xref{Packaging Guidelines}, for more information on how to test package definitions, and @ref{Invoking guix lint}, for information on how to check a definition for style conformance. Eventually, updating the package definition to a new upstream version can be partly automated by the @command{guix refresh} command (@pxref{Invoking guix refresh}). Behind the scenes, a derivation corresponding to the @code{} object is first computed by the @code{package-derivation} procedure. That derivation is stored in a @code{.drv} file under @file{/gnu/store}. The build actions it prescribes may then be realized by using the @code{build-derivations} procedure (@pxref{The Store}). @deffn {Scheme Procedure} package-derivation @var{store} @var{package} [@var{system}] Return the @code{} object of @var{package} for @var{system} (@pxref{Derivations}). @var{package} must be a valid @code{} 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{The Store}). @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{} 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{"mips64el-linux-gnu"} (@pxref{Configuration Names, GNU configuration triplets,, configure, GNU Configure and Build System}). @end deffn @node Build Systems @section Build Systems @cindex build system Each package definition specifies a @dfn{build system} and arguments for that build system (@pxref{Defining Packages}). This @code{build-system} field represents the build procedure of the package, as well implicit dependencies of that build procedure. Build systems are @code{} 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}). Build systems accept an optional list of @dfn{arguments}. In package definitions, these are passed @i{via} the @code{arguments} field (@pxref{Defining Packages}). 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 @var{gnu-build-system}, which implements the standard build procedure for GNU packages and many other packages. It is provided by the @code{(guix build-system gnu)} module. @defvr {Scheme Variable} gnu-build-system @var{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 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}, notably@footnote{Please see the @code{(guix build gnu-build-system)} modules for more details about the build phases.}: @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 @code{--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-builds?} 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{Installing Debugging Files}). @end table @vindex %standard-phases The build-side module @code{(guix build gnu-build-system)} defines @var{%standard-phases} as the default list of build phases. @var{%standard-phases} is a list of symbol/procedure pairs, where the procedure implements the actual phase. The list of phases used for a particular package can be changed with the @code{#:phases} parameter. For instance, passing: @example #:phases (alist-delete 'configure %standard-phases) @end example means that all the phases described above will be used, except the @code{configure} phase. 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 don't have to mention them. @end defvr Other @code{} objects are defined to support other conventions and tools used by free software packages. They inherit most of @var{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} cmake-build-system This variable is exported by @code{(guix build-system cmake)}. It implements the build procedure for packages using the @url{http://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} 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 @var{gnu-build-system}: @table @code @item glib-or-gtk-wrap The phase @code{glib-or-gtk-wrap} ensures that programs found under @file{bin/} are able to find GLib's ``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 @code{XDG_DATA_DIRS} and @code{GTK_PATH} environment variables. @item glib-or-gtk-compile-schemas The phase @code{glib-or-gtk-compile-schemas} makes sure that all GLib's @uref{https://developer.gnome.org/gio/stable/glib-compile-schemas.html, GSettings schemas} 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} 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 their @code{PYTHONPATH} environment variable points to all the Python libraries they depend on. Which Python package is used can be specified with the @code{#:python} parameter. @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 consists in running @code{perl Makefile.PL PREFIX=/gnu/store/@dots{}}, followed by @code{make} and @code{make install}. The initial @code{perl Makefile.PL} invocation passes flags specified by the @code{#:make-maker-flags} parameter. Which Perl package is used can be specified with @code{#:perl}. @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}. Which Ruby package is used can be specified with the @code{#:ruby} parameter. @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's output(s)---as with @code{build-expression->derivation} (@pxref{Derivations, @code{build-expression->derivation}}). @end defvr @node The Store @section The Store @cindex store @cindex store paths Conceptually, the @dfn{store} is where derivations that have been successfully built are stored---by default, under @file{/gnu/store}. Sub-directories in the store are referred to as @dfn{store paths}. The store has an associated database that contains information such has the store paths referred to by each store path, and the list of @emph{valid} store paths---paths that result from a successful build. The store is always accessed by the daemon on behalf of its clients (@pxref{Invoking guix-daemon}). To manipulate the store, clients connect to the daemon over a Unix-domain socket, send it requests, and read the result---these are remote procedure calls, or RPCs. The @code{(guix store)} module provides procedures to connect to the daemon, and to perform RPCs. These are described below. @deffn {Scheme Procedure} open-connection [@var{file}] [#:reserve-space? #t] Connect to the daemon over the Unix-domain socket at @var{file}. 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 @var{%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} Return @code{#t} when @var{path} is a valid store path. @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{server} @var{derivations} Build @var{derivations} (a list of @code{} objects or derivation paths), and return when the worker is done building them. Return @code{#t} on success. @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{The Store 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 contain 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 The inputs of the derivations, 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 @code{.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{The Store}). 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] [#:local-build? #f] Build a derivation with the given arguments, and return the resulting @code{} 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. When @var{local-build?} is true, declare that the derivation is not a good candidate for offloading and should rather be built locally (@pxref{Daemon Offload Setup}). This is the case for small derivations where the costs of data transfers would outweigh the benefits. @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{} # /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-Expressions}. 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] @ [#:local-build? #f] [#: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}, and @var{local-build?}. @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{} # @dots{}> @end lisp @node The Store Monad @section The Store 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 includes 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: @example (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 example Using @code{(guix monads)}, it may be rewritten as a monadic function: @c FIXME: Find a better example, one that uses 'mlet'. @example (define (sh-symlink) ;; Same, but return a monadic value. (gexp->derivation "sh" #~(symlink (string-append #$bash "/bin/bash") #$output))) @end example There are two things to note in the second version: the @code{store} parameter is now implicit, and the monadic value returned by @code{package-file}---a wrapper around @code{package-derivation} and @code{derivation->output-path}---is @dfn{bound} using @code{mlet} instead of plain @code{let}. Calling the monadic @code{profile.sh} has no effect. To get the desired effect, one must use @code{run-with-store}: @example (run-with-store (open-connection) (profile.sh)) @result{} /gnu/store/...-profile.sh @end example Note that the @code{(guix monad-repl)} module extends Guile's 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 = # @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 = # @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 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 procedure @var{mproc}@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.}. @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}. The form (@var{var} -> @var{val}) binds @var{var} to the ``normal'' value @var{val}, as per @code{let}. @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. 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 The interface to the store monad provided by @code{(guix monads)} is as follows. @defvr {Scheme Variable} %store-monad The store 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} Return as a monadic value the absolute file name in the store of the file containing @var{text}, a string. @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, packages, derivations, and store file names; 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: @example (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 example In this example, the resulting @file{/gnu/store/@dots{}-profile.sh} file will references @var{coreutils}, @var{grep}, and @var{sed}, thereby preventing them from being garbage-collected during its lifetime. @end deffn @deffn {Monadic Procedure} interned-file @var{file} [@var{name}] @ [#:recursive? #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. The example below adds a file to the store, under two different names: @example (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 example @end deffn @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. @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{Defining Packages}). @end deffn @node G-Expressions @section G-Expressions @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}). Those build actions are performed when asking the daemon to actually build the derivations; they are run by the daemon in a container (@pxref{Invoking guix-daemon}). @cindex strata of code It should come as no surprise that we like to write those 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}, etc. 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 Scheme's homoiconicity---code has a direct representation as data---comes in handy for that. But we need more than Scheme's normal @code{quasiquote} mechanism 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 in three syntactic forms: @code{gexp}, @code{ungexp}, and @code{ungexp-splicing} (or simply: @code{#~}, @code{#$}, and @code{#$@@}), which are comparable respectively to @code{quasiquote}, @code{unquote}, and @code{unquote-splicing} (@pxref{Expression Syntax, @code{quasiquote},, guile, GNU Guile Reference Manual}). However, there are major differences: @itemize @item Gexps are meant to be written to a file and run or manipulated by other processes. @item When a package or derivation is unquoted inside a gexp, the result is as if its output file name had been introduced. @item Gexps carry information about the packages or derivations they refer to, and these dependencies are automatically added as inputs to the build processes that use them. @end itemize To illustrate the idea, here is an example of a gexp: @example (define build-exp #~(begin (mkdir #$output) (chdir #$output) (symlink (string-append #$coreutils "/bin/ls") "list-files"))) @end example 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}: @example (gexp->derivation "the-thing" build-exp) @end example 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{#$output} (equivalent to @code{(ungexp output)}) is replaced by a string containing the derivation's output directory name. @cindex cross compilation In a cross-compilation context, it is useful to distinguish between references to the @emph{native} build of a package---that can run on the host---versus references to cross builds of a package. To that end, the @code{#+} plays the same role as @code{#$}, but is a reference to a native package build: @example (gexp->derivation "vi" #~(begin (mkdir #$output) (system* (string-append #+coreutils "/bin/ln") "-s" (string-append #$emacs "/bin/emacs") (string-append #$output "/bin/vi"))) #:target "mips64el-linux") @end example @noindent In the example above, the native build of @var{coreutils} is used, so that @command{ln} can actually run on the host; but then the cross-compiled build of @var{emacs} is referenced. The syntactic form to construct gexps is summarized below. @deffn {Scheme Syntax} #~@var{exp} @deffnx {Scheme Syntax} (gexp @var{exp}) Return a G-expression containing @var{exp}. @var{exp} may contain one or more of the following forms: @table @code @item #$@var{obj} @itemx (ungexp @var{obj}) Introduce a reference to @var{obj}. @var{obj} may be 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 any package or derivation references 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 #$@var{package-or-derivation}:@var{output} @itemx (ungexp @var{package-or-derivation} @var{output}) This is like the form above, but referring explicitly to the @var{output} of @var{package-or-derivation}---this is useful when @var{package-or-derivation} produces multiple outputs (@pxref{Packages with Multiple Outputs}). @item #+@var{obj} @itemx #+@var{obj}:output @itemx (ungexp-native @var{obj}) @itemx (ungexp-native @var{obj} @var{output}) Same as @code{ungexp}, but produces a reference to the @emph{native} build of @var{obj} when used in a cross compilation context. @item #$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 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{The Store Monad}, for more information about monads.) @deffn {Monadic Procedure} gexp->derivation @var{name} @var{exp} @ [#:system (%current-system)] [#:target #f] [#:inputs '()] @ [#:hash #f] [#:hash-algo #f] @ [#:recursive? #f] [#:env-vars '()] [#:modules '()] @ [#:module-path @var{%load-path}] @ [#:references-graphs #f] [#:local-build? #f] @ [#: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}. When @var{target} is true, it is used as the cross-compilation target triplet for packages referred to by @var{exp}. 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))}. 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. The other arguments are as for @code{derivation} (@pxref{Derivations}). @end deffn @deffn {Monadic Procedure} gexp->script @var{name} @var{exp} Return an executable script @var{name} that runs @var{exp} using @var{guile} with @var{modules} in its search path. The example below builds a script that simply invokes the @command{ls} command: @example (use-modules (guix gexp) (gnu packages base)) (gexp->script "list-files" #~(execl (string-append #$coreutils "/bin/ls") "ls")) @end example When ``running'' it through the store (@pxref{The Store 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 (string-append "/gnu/store/@dots{}-coreutils-8.22"/bin/ls") "ls") @end example @end deffn @deffn {Monadic Procedure} gexp->file @var{name} @var{exp} Return a derivation that builds a file @var{name} containing @var{exp}. The resulting file holds references to all the dependencies of @var{exp} or a subset thereof. @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. @c ********************************************************************* @node Utilities @chapter Utilities This section describes tools primarily targeted at developers and users who write new package definitions. They complement the Scheme programming interface of Guix in a convenient way. @menu * Invoking guix build:: Building packages from the command line. * Invoking guix download:: Downloading a file and printing its hash. * Invoking guix hash:: Computing the cryptographic hash of a file. * Invoking guix refresh:: Updating package definitions. * Invoking guix lint:: Finding errors in package definitions. * Invoking guix environment:: Setting up development environments. @end menu @node Invoking guix build @section Invoking @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{Invoking 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 @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{Package Modules}). Alternatively, the @code{--expression} option may be used to specify a Scheme expression that evaluates to a package; this is useful when disambiguation among several same-named packages or package variants is needed. The @var{options} may be zero or more of the following: @table @code @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. Alternately, @var{expr} may be a G-expression, in which case it is used as a build program passed to @code{gexp->derivation} (@pxref{G-Expressions}). Lastly, @var{expr} may refer to a zero-argument monadic procedure (@pxref{The Store 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 packages' source derivations, 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 GCC's source tarball. The returned source tarball is the result of applying any patches and code snippets specified in the package's @code{origin} (@pxref{Defining Packages}). @item --system=@var{system} @itemx -s @var{system} Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of the host's system type. An example use of this is on Linux-based systems, which can emulate different personalities. For instance, passing @code{--system=i686-linux} on an @code{x86_64-linux} system allows users to build packages in a complete 32-bit environment. @item --target=@var{triplet} @cindex cross-compilation Cross-build for @var{triplet}, which must be a valid GNU triplet, such as @code{"mips64el-linux-gnu"} (@pxref{Configuration Names, GNU configuration triplets,, configure, GNU Configure and Build System}). @item --with-source=@var{source} Use @var{source} as the source of the corresponding package. @var{source} must be a file name or a URL, as for @command{guix download} (@pxref{Invoking guix download}). The ``corresponding package'' is taken to be one specified on the command line whose name 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, the version string is inferred from @var{source}; in the previous example, it's @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, @code{--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 @item --no-grafts Do not ``graft'' packages. In practice, this means that package updates available as grafts are not applied. @xref{Security Updates}, for more information on grafts. @item --derivations @itemx -d Return the derivation paths, not the output paths, of the given packages. @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 --log-file Return the build log file names for the given @var{package-or-derivation}s, 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 @end table @cindex common build options In addition, 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{Package Modules}). 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 fail, 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. @item --dry-run @itemx -n Do not build the derivations. @item --fallback When substituting a pre-built binary fails, fall back to building packages locally. @item --no-substitutes Do not use substitutes for build products. That is, always build things locally instead of allowing downloads of pre-built binaries (@pxref{Substitutes}). @item --no-build-hook Do not attempt to offload builds @i{via} the daemon's ``build hook'' (@pxref{Daemon Offload Setup}). That is, always build things locally instead of offloading builds to remote machines. @item --max-silent-time=@var{seconds} When the build or substitution process remains silent for more than @var{seconds}, terminate it and report a build failure. @item --timeout=@var{seconds} Likewise, when the build or substitution process lasts for more than @var{seconds}, terminate it and report a build failure. By default there is no timeout. This behavior can be restored with @code{--timeout=0}. @item --verbosity=@var{level} Use the given verbosity level. @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. @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. @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 store)} module. @node Invoking guix download @section Invoking @command{guix download} When writing a package definition, developers typically need to download the package's source tarball, compute its SHA256 hash, and write that hash in the package definition (@pxref{Defining Packages}). 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{Invoking 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. The following option is available: @table @code @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}, @ref{Invoking guix hash}. @end table @node Invoking guix hash @section Invoking @command{guix hash} The @command{guix hash} command computes the SHA256 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{Defining Packages}). The general syntax is: @example guix hash @var{option} @var{file} @end example @command{guix hash} has the following option: @table @code @item --format=@var{fmt} @itemx -f @var{fmt} Write the hash in the format specified by @var{fmt}. Supported formats: @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. In this case, the hash is computed on an archive containing @var{file}, including its children if it is a directory. Some of @var{file}'s meta-data 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. Meta-data such as time stamps has no impact on the hash (@pxref{Invoking guix archive}). @c FIXME: Replace xref above with xref to an ``Archive'' section when @c it exists. @end table @node Invoking guix refresh @section Invoking @command{guix refresh} The primary audience of the @command{guix refresh} command is developers of the GNU software distribution. By default, it 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 It does so by browsing each package's FTP directory and determining the highest version number of the source tarballs therein@footnote{Currently, this only works for GNU packages.}. When passed @code{--update}, it modifies distribution source files to update the version numbers and source tarball hashes of those packages' recipes (@pxref{Defining Packages}). 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{gpg}, and finally computing its hash. 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 it's 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 --update @itemx -u Update distribution source files (package recipes) in place. @ref{Defining Packages}, 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. @end table In addition, @command{guix refresh} can be passed one or more package names, as in this example: @example guix refresh -u emacs idutils @end example @noindent The command above specifically updates the @code{emacs} and @code{idutils} packages. The @code{--select} option would have no effect in this case. 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. @end table Be aware that the @code{--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. The following options can be used to customize GnuPG operation: @table @code @item --key-server=@var{host} Use @var{host} as the OpenPGP key server when importing a public key. @item --gpg=@var{command} Use @var{command} as the GnuPG 2.x command. @var{command} is searched for in @code{$PATH}. @end table @node Invoking guix lint @section Invoking @command{guix lint} The @command{guix lint} is meant to help package developers avoid common errors and use a consistent style. It runs a few checks on a given set of packages in order to find common mistakes in their definitions. 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 --checkers @itemx -c Only enable the checkers specified in a comma-separated list using the names returned by @code{--list-checkers}. @item --list-checkers @itemx -l List and describe all the available checkers that will be run on packages and exit. @end table @node Invoking guix environment @section Invoking @command{guix environment} @cindex reproducible build environments 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 the necessary 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 examples spawns a new shell that is capable of building the GNU Guile source code: @example guix environment guile @end example If the specified packages are not built yet, @command{guix environment} automatically builds them. The new shell's environment 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 @code{--pure} option. 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. The @code{--exec} option can be used to specify the command to run instead. @example guix environment guile --exec=make @end example The following options are available: @table @code @item --expression=@var{expr} @itemx -e @var{expr} Create an environment for the package that @var{expr} evaluates to. @item --load=@var{file} @itemx -l @var{file} Create an environment for the package that the code within @var{file} evaluates to. @item --exec=@var{command} @item -E @var{command} Execute @var{command} in the new environment. @item --pure Unset existing environment variables when building the new environment. This has the effect of creating an environment in which search paths only contain package inputs. @item --search-paths Display the environment variable definitions that make up the environment. @end table It also supports all of the common build options that @command{guix build} supports (@pxref{Invoking guix build, common build options}). @c ********************************************************************* @node GNU Distribution @chapter GNU Distribution Guix comes with a distribution of free software@footnote{The term ``free'' here refers to the @url{http://www.gnu.org/philosophy/free-sw.html,freedom provided to users of that software}.} that forms the basis of the GNU system. This includes core GNU packages such as GNU libc, GCC, and Binutils, as well as many GNU and non-GNU applications. The complete list of available packages can be browsed @url{http://www.gnu.org/software/guix/package-list.html,on-line} or by running @command{guix package} (@pxref{Invoking guix package}): @example guix package --list-available @end example Our goal is to build a practical 100% free software distribution of Linux-based and other variants of GNU, with a focus on the promotion and tight integration of GNU components, and an emphasis on programs and tools that help users exert that freedom. The GNU distribution is currently available on the following platforms: @table @code @item x86_64-linux Intel/AMD @code{x86_64} architecture, Linux-Libre kernel; @item i686-linux Intel 32-bit architecture (IA32), Linux-Libre kernel; @item mips64el-linux little-endian 64-bit MIPS processors, specifically the Loongson series, n32 application binary interface (ABI), and Linux-Libre kernel. @end table @noindent For information on porting to other architectures or kernels, @xref{Porting}. @menu * System Installation:: Installing the whole operating system. * System Configuration:: Configuring a GNU system. * Installing Debugging Files:: Feeding the debugger. * Security Updates:: Deploying security fixes quickly. * Package Modules:: Packages from the programmer's viewpoint. * Packaging Guidelines:: Growing the distribution. * Bootstrapping:: GNU/Linux built from scratch. * Porting:: Targeting another platform or kernel. @end menu Building this distribution is a cooperative effort, and you are invited to join! @ref{Contributing}, for information about how you can help. @node System Installation @section System Installation This section explains how to install the complete GNU operating system on a machine. The Guix package manager can also be installed on top of a running GNU/Linux system, @pxref{Installation}. @ifinfo @c This paragraph is for people reading this from tty2 of the @c installation image. You're 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{Help,,, info, Info: An Introduction}. Hit @kbd{l} afterwards to come back here. @end ifinfo @subsection Limitations As of version @value{VERSION}, GNU@tie{}Guix and the GNU system distribution are alpha software. It may contain bugs and lack important features. Thus, if you are looking for a stable production system that respects your freedom as a computer user, a good solution at this point is to consider @url{http://www.gnu.org/distros/free-distros.html, one of more established GNU/Linux distributions}. We hope you can soon switch to the GNU system without fear, of course. In the meantime, you can also keep using your distribution and try out the package manager on top of it (@pxref{Installation}). Before you proceed with the installation, be aware of the following noteworthy limitations applicable to version @value{VERSION}: @itemize @item The installation process does not include a graphical user interface and requires familiarity with GNU/Linux (see the following subsections to get a feel of what that means.) @item The system does not yet provide graphical desktop environments such as GNOME and KDE. @item Support for the Logical Volume Manager (LVM) is missing. @item Few system services are currently supported out-of-the-box (@pxref{Services}). @item On the order of 1,000 packages are available, which means that you may occasionally find that a useful package is missing. @end itemize You've been warned. But more than a disclaimer, this is an invitation to report issues (and success stories!), and join us in improving it. @xref{Contributing}, for more info. @subsection USB Stick Installation An installation image for USB sticks can be downloaded from @url{ftp://alpha.gnu.org/gnu/guix/gnu-usb-install-@value{VERSION}.@var{system}.xz}, where @var{system} is 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 This image contains a single partition with the tools necessary for an installation. It is meant to be copied @emph{as is} to a large-enough USB stick. To copy the image to a USB stick, follow these steps: @enumerate @item Decompress the image using the @command{xz} command: @example xz -d gnu-usb-install-@value{VERSION}.@var{system}.xz @end example @item Insert a USB stick of 1@tie{}GiB or more in your machine, and determine its device name. Assuming that USB stick is known as @file{/dev/sdX}, copy the image with: @example dd if=gnu-usb-install-@value{VERSION}.x86_64 of=/dev/sdX @end example Access to @file{/dev/sdX} usually requires root privileges. @end enumerate Once this is done, you should be able to reboot the system and boot from the USB stick. The latter usually requires you to get in the BIOS' boot menu, where you can choose to boot from the USB stick. @subsection Preparing for Installation Once you have successfully booted the image on the USB stick, you should end up with a root prompt. Several console TTYs are configured and can be used to run commands as root. TTY2 shows this documentation, browsable using the Info reader commands (@pxref{Help,,, info, Info: An Introduction}). To install the system, you would: @enumerate @item Configure the network, by running @command{dhclient eth0} (to get an automatically assigned IP address from the wired network interface controller), or using the @command{ifconfig} command. The system automatically loads drivers for your network interface controllers. Setting up network access is almost always a requirement because the image does not contain all the software and tools that may be needed. @item Unless this has already been done, you must partition and format the target partitions. Preferably, assign partitions a label so that you can easily and reliably refer to them in @code{file-system} declarations (@pxref{File Systems}). This is typically done using the @code{-L} option of @command{mkfs.ext4} and related commands. The installation image includes Parted (@pxref{Overview,,, parted, GNU Parted User Manual}), @command{fdisk}, and e2fsprogs, the suite of tools to manipulate ext2/ext3/ext4 file systems. @item Once that is done, mount the target root partition under @file{/mnt}. @item Lastly, run @code{deco start cow-store /mnt}. This will make @file{/gnu/store} copy-on-write, such that packages added to it during the installation phase will be written to the target disk rather than kept in memory. @end enumerate @subsection Proceeding with the Installation With the target partitions ready, you now have to edit a file and provide the declaration of the operating system to be installed. To that end, the installation system comes with two text editors: GNU nano (@pxref{Top,,, nano, GNU nano Manual}), and GNU Zile, an Emacs clone. It is better to store that file on the target root file system, say, as @file{/mnt/etc/config.scm}. A minimal operating system configuration, with just the bare minimum and only a root account would look like this (on the installation system, this example is available as @file{/etc/configuration-template.scm}): @example @include os-config.texi @end example @noindent For more information on @code{operating-system} declarations, @pxref{Using the Configuration System}. Once that is done, 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 will copy all the necessary files, and install GRUB on @file{/dev/sdX}, unless you pass the @option{--no-grub} option. For more information, @pxref{Invoking 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. Cross fingers, and join us on @code{#guix} on the Freenode IRC network or on @file{guix-devel@@gnu.org} to share your experience---good or not so good. @subsection Building the Installation Image The installation image described above was built using the @command{guix system} command, specifically: @example guix system disk-image --image-size=800MiB gnu/system/install.scm @end example @xref{Invoking guix system}, for more information. See @file{gnu/system/install.scm} in the source tree for more information about the installation image. @node System Configuration @section System Configuration @cindex system configuration The GNU 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. 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{Features}). Another one 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 system's own tools. @c Yes, we're talking of Puppet, Chef, & co. here. ↑ 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 * Using the Configuration System:: Customizing your GNU system. * operating-system Reference:: Detail of operating-system declarations. * File Systems:: Configuring file system mounts. * Mapped Devices:: Block device extra processing. * User Accounts:: Specifying user accounts. * Services:: Specifying system services. * Setuid Programs:: Programs running with root privileges. * Initial RAM Disk:: Linux-Libre bootstrapping. * GRUB Configuration:: Configuring the boot loader. * Invoking guix system:: Instantiating a system configuration. * Defining Services:: Adding new service definitions. @end menu @node Using the Configuration System @subsection Using the Configuration System 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{Invoking 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 (use-modules (gnu) ; for 'user-account', '%base-services', etc. (gnu packages emacs) ; for 'emacs' (gnu services ssh)) ; for 'lsh-service' (operating-system (host-name "komputilo") (timezone "Europe/Paris") (locale "fr_FR.UTF-8") (bootloader (grub-configuration (device "/dev/sda"))) (file-systems (cons (file-system (device "/dev/sda1") ; or partition label (mount-point "/") (type "ext3")) %base-file-systems)) (users (list (user-account (name "alice") (password "") (uid 1000) (group 100) (comment "Bob's sister") (home-directory "/home/alice")))) (packages (cons emacs %base-packages)) (services (cons (lsh-service #:port 2222 #:allow-root-login? #t) %base-services))) @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. @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 @code{PATH} environment variable---in addition to the per-user profiles (@pxref{Invoking guix package}). The @var{%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 Emacs to those, taken from the @code{(gnu packages emacs)} module (@pxref{Package Modules}). @vindex %base-services The @code{services} field lists @dfn{system services} to be made available when the system starts (@pxref{Services}). The @code{operating-system} declaration above specifies that, in addition to the basic services, we want the @command{lshd} secure shell daemon listening on port 2222, and allowing remote @code{root} logins (@pxref{Invoking lshd,,, lsh, GNU lsh Manual}). Under the hood, @code{lsh-service} arranges so that @code{lshd} is started with the right command-line options, possibly with supporting configuration files generated as needed (@pxref{Defining Services}). @xref{operating-system Reference}, for details about the available @code{operating-system} fields. Assuming the above snippet 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{Invoking guix system}). The normal way to change the system's configuration is by updating this file and re-running the @command{guix system} command. At the Scheme level, the bulk of an @code{operating-system} declaration is instantiated with the following monadic procedure (@pxref{The Store 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 @node operating-system Reference @subsection @code{operating-system} Reference This section summarizes all the options available in @code{operating-system} declarations (@pxref{Using the Configuration System}). @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{Using the Configuration System}). @table @asis @item @code{kernel} (default: @var{linux-libre}) The package object of the operating system to use@footnote{Currently only the Linux-libre kernel is supported. In the future, it will be possible to use the GNU@tie{}Hurd.}. @item @code{bootloader} The system bootloader configuration object. @xref{GRUB Configuration}. @item @code{initrd} (default: @code{base-initrd}) A two-argument monadic procedure that returns an initial RAM disk for the Linux kernel. @xref{Initial RAM Disk}. @item @code{firmware} (default: @var{%base-firmware}) @cindex firmware List of firmware packages loadable by the operating system kernel. The default includes firmware needed for Atheros-based WiFi devices (Linux-libre module @code{ath9k}.) @item @code{host-name} The host name. @item @code{hosts-file} @cindex hosts file A zero-argument monadic procedure that returns a text file for use as @file{/etc/hosts} (@pxref{Host Names,,, libc, The GNU C Library Reference Manual}). The default is to produce a file with entries for @code{localhost} and @var{host-name}. @item @code{mapped-devices} (default: @code{'()}) A list of mapped devices. @xref{Mapped Devices}. @item @code{file-systems} A list of file systems. @xref{File Systems}. @item @code{swap-devices} (default: @code{'()}) @cindex swap devices A list of strings identifying devices to be used for ``swap space'' (@pxref{Memory Concepts,,, libc, The GNU C Library Reference Manual}). For example, @code{'("/dev/sda3")}. @item @code{users} (default: @code{'()}) @itemx @code{groups} (default: @var{%base-groups}) List of user accounts and groups. @xref{User Accounts}. @item @code{skeletons} (default: @code{(default-skeletons)}) A monadic list of pairs of target file name and files. These are the files that will be used as skeletons as new accounts are created. For instance, a valid value may look like this: @example (mlet %store-monad ((bashrc (text-file "bashrc" "\ export PATH=$HOME/.guix-profile/bin"))) (return `((".bashrc" ,bashrc)))) @end example @item @code{issue} (default: @var{%default-issue}) A string denoting the contents of the @file{/etc/issue} file, which is what displayed when users log in on a text console. @item @code{packages} (default: @var{%base-packages}) The set of packages installed in the global profile, which is accessible at @file{/run/current-system/profile}. The default set includes core utilities, but it is good practice to install non-core utilities in user profiles (@pxref{Invoking guix package}). @item @code{timezone} A timezone identifying string---e.g., @code{"Europe/Paris"}. @item @code{locale} (default: @code{"en_US.UTF-8"}) The name of the default locale (@pxref{Locales,,, libc, The GNU C Library Reference Manual}). @item @code{services} (default: @var{%base-services}) A list of monadic values denoting system services. @xref{Services}. @item @code{pam-services} (default: @code{(base-pam-services)}) @cindex PAM @cindex pluggable authentication modules Linux @dfn{pluggable authentication module} (PAM) services. @c FIXME: Add xref to PAM services section. @item @code{setuid-programs} (default: @var{%setuid-programs}) List of string-valued G-expressions denoting setuid programs. @xref{Setuid Programs}. @item @code{sudoers} (default: @var{%sudoers-specification}) @cindex sudoers The contents of the @file{/etc/sudoers} file as a string. 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 @end deftp @node File Systems @subsection File Systems The list of file systems to be mounted is specified in the @code{file-systems} field of the operating system's declaration (@pxref{Using the Configuration System}). Each file system is declared using the @code{file-system} form, like this: @example (file-system (mount-point "/home") (device "/dev/sda3") (type "ext4")) @end example 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. By default it is the name of a node under @file{/dev}, but its meaning depends on the @code{title} field described below. @item @code{title} (default: @code{'device}) This is a symbol that specifies how the @code{device} field is to be interpreted. When it is the symbol @code{device}, then the @code{device} field is interpreted as a file name; when it is @code{label}, then @code{device} is interpreted as a partition label name; when it is @code{uuid}, @code{device} is interpreted as a partition unique identifier (UUID). The @code{label} and @code{uuid} options offer a way to refer to disk partitions without having to hard-code their actual device name. @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), and @code{no-exec} (disallow program execution.) @item @code{options} (default: @code{#f}) This is either @code{#f}, or a string denoting mount options. @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. @end table @end deftp 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 @var{%devtmpfs-file-system} (see below.) Operating system declarations should always contain at least these. @end defvr @defvr {Scheme Variable} %devtmpfs-file-system The @code{devtmpfs} file system to be mounted on @file{/dev}. This is a requirement for udev (@pxref{Base Services, @code{udev-service}}). @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} %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 @node Mapped Devices @subsection Mapped Devices @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, 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. Mapped devices are declared using the @code{mapped-device} form: @example (mapped-device (source "/dev/sda3") (target "home") (type luks-device-mapping)) @end example @noindent @cindex disk encryption @cindex LUKS This example specifies a mapping from @file{/dev/sda3} to @file{/dev/mapper/home} using LUKS---the @url{http://code.google.com/p/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{File Systems}). The @code{mapped-device} form is detailed 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 string specifies the name of the block device to be mapped, such as @code{"/dev/sda3"}. @item target This string specifies the name of the mapping to be established. For example, specifying @code{"my-partition"} will lead to the creation of the @code{"/dev/mapper/my-partition"} device. @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 same-named package. This relies on the @code{dm-crypt} Linux kernel module. @end defvr @node User Accounts @subsection User Accounts User accounts are specified with the @code{user-account} form: @example (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") (home-directory "/home/alice")) @end example @deftp {Data Type} user-account Objects of this type represent user accounts. The following members may be specified: @table @asis @item @code{name} The name of the user account. @item @code{group} 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's owner full name. @item @code{home-directory} This is the name of the home directory for the account. @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-Expressions}). @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. @item @code{password} (default: @code{#f}) Unless @code{#f}, this is the password to be used for the account. @end table @end deftp User group declarations are even simpler: @example (user-group (name "students")) @end example @deftp {Data Type} user-group This type is for, well, user groups. There are just a few fields: @table @asis @item @code{name} The group's name. @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 group's password. @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 @node Services @subsection Services @cindex system services An important part of preparing an @code{operating-system} declaration is listing @dfn{system services} and their configuration (@pxref{Using the Configuration System}). System services are typically daemons launched when the system boots, or other actions needed at that time---e.g., configuring network access. They are managed by GNU@tie{}dmd (@pxref{Introduction,,, dmd, GNU dmd Manual}). The following sections document the available services, starting with the core services. @menu * Base Services:: Essential system services. * Networking Services:: Network setup, SSH daemon, etc. * X Window:: Graphical display. @end menu @node Base Services @subsubsection Base Services 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@footnote{Technically, this is a list of monadic services. @xref{The Store Monad}.} one would expect from the system: a login service (mingetty) on each tty, syslogd, libc's 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 @var{%base-services}, like this: @example (cons* (avahi-service) (lshd-service) %base-services) @end example @end defvr @deffn {Monadic Procedure} host-name-service @var{name} Return a service that sets the host name to @var{name}. @end deffn @deffn {Monadic Procedure} mingetty-service @var{tty} [#:motd] @ [#:auto-login #f] [#:login-program] [#:login-pause? #f] @ [#:allow-empty-passwords? #f] Return a service to run mingetty on @var{tty}. When @var{allow-empty-passwords?} is true, allow empty log-in password. When @var{auto-login} is true, it must be a user name under which to log-in automatically. @var{login-pause?} can be set to @code{#t} in conjunction with @var{auto-login}, in which case the user will have to press a key before the login shell is launched. When true, @var{login-program} is a gexp or a monadic gexp denoting the name of the log-in program (the default is the @code{login} program from the Shadow tool suite.) @var{motd} is a monadic value containing a text file to use as the ``message of the day''. @end deffn @deffn {Monadic Procedure} nscd-service [#:glibc glibc] Return a service that runs libc's name service cache daemon (nscd). @end deffn @deffn {Monadic Procedure} syslog-service Return a service that runs @code{syslogd} with reasonable default settings. @end deffn @deffn {Monadic Procedure} guix-service [#:guix guix] @ [#:builder-group "guixbuild"] [#:build-accounts 10] @ [#:authorize-hydra-key? #f] [#:use-substitutes? #t] @ [#:extra-options '()] Return a service that runs the build daemon from @var{guix}, and has @var{build-accounts} user accounts available under @var{builder-group}. When @var{authorize-hydra-key?} is true, the @code{hydra.gnu.org} public key provided by @var{guix} is authorized upon activation, meaning that substitutes from @code{hydra.gnu.org} are used by default. If @var{use-substitutes?} is false, the daemon is run with @option{--no-substitutes} (@pxref{Invoking guix-daemon, @option{--no-substitutes}}). Finally, @var{extra-options} is a list of additional command-line options passed to @command{guix-daemon}. @end deffn @deffn {Monadic Procedure} udev-service [#:udev udev] Run @var{udev}, which populates the @file{/dev} directory dynamically. @end deffn @node Networking Services @subsubsection Networking Services The @code{(gnu system networking)} module provides services to configure the network interface. @cindex DHCP, networking service @deffn {Monadic Procedure} dhcp-client-service [#:dhcp @var{isc-dhcp}] Return a service that runs @var{dhcp}, a Dynamic Host Configuration Protocol (DHCP) client, on all the non-loopback network interfaces. @end deffn @deffn {Monadic Procedure} static-networking-service @var{interface} @var{ip} @ [#:gateway #f] [#:name-services @code{'()}] Return a service that starts @var{interface} with address @var{ip}. If @var{gateway} is true, it must be a string specifying the default network gateway. @end deffn @deffn {Monadic Procedure} ntp-service [#:ntp @var{ntp}] @ [#:name-service @var{%ntp-servers}] Return a service that runs the daemon from @var{ntp}, the @uref{http://www.ntp.org, Network Time Protocol package}. The daemon will keep the system clock synchronized with that of @var{servers}. @end deffn @defvr {Scheme Variable} %ntp-servers List of host names used as the default NTP servers. @end defvr @deffn {Monadic Procedure} tor-service [#:tor tor] Return a service to run the @uref{https://torproject.org,Tor} daemon. The daemon runs with the default settings (in particular the default exit policy) as the @code{tor} unprivileged user. @end deffn @deffn {Monadic Procedure} bitlbee-service [#:bitlbee bitlbee] @ [#:interface "127.0.0.1"] [#:port 6667] @ [#:extra-settings ""] Return a service that runs @url{http://bitlbee.org,BitlBee}, a daemon that acts as a gateway between IRC and chat networks. The daemon will listen to the interface corresponding to the IP address specified in @var{interface}, on @var{port}. @code{127.0.0.1} means that only local clients can connect, whereas @code{0.0.0.0} means that connections can come from any networking interface. In addition, @var{extra-settings} specifies a string to append to the configuration file. @end deffn Furthermore, @code{(gnu system ssh)} provides the following service. @deffn {Monadic Procedure} lsh-service [#:host-key "/etc/lsh/host-key"] @ [#: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? #f] 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{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{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 accepts log-ins with empty passwords, and @var{root-login?} specifies whether to accepts log-ins as root. The other options should be self-descriptive. @end deffn @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{operating-system Reference, @file{/etc/hosts}}): @example (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. (text-file "hosts" (string-append (local-host-aliases host-name) %facebook-host-aliases)))) @end example This mechanism can prevent programs running locally, such as Web browsers, from accessing Facebook. @end defvr @node X Window @subsubsection X Window 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}, currently SLiM. @deffn {Monadic Procedure} slim-service [#:allow-empty-passwords? #f] @ [#:auto-login? #f] [#:default-user ""] [#:startx] Return a service that spawns the SLiM graphical login manager, which in turn starts the X display server with @var{startx}, a command as returned by @code{xorg-start-command}. When @var{allow-empty-passwords?} is true, allow logins with an empty password. When @var{auto-login?} is true, log in automatically as @var{default-user}. @end deffn @deffn {Monadic Procedure} xorg-start-command [#:guile] @ [#:drivers '()] [#:resolutions '()] [#:xorg-server @var{xorg-server}] Return a derivation that builds a @var{guile} script to start the X server from @var{xorg-server}. Usually the X server is started by a login manager. @var{drivers} 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")}. Likewise, when @var{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))}. @end deffn @node Setuid Programs @subsection Setuid Programs @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} programs, which can users can run to change their password, and which requires write access to 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 mechanisms.) 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{The Store}). 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{Using the Configuration System}). For instance, the @command{passwd} program, which is part of the Shadow package, can be designated by this G-expression (@pxref{G-Expressions}): @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 Initial RAM Disk @subsection Initial RAM Disk @cindex initial RAM disk (initrd) @cindex initrd (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} 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 two ways to build an initrd: the high-level @code{base-initrd} procedure, and the low-level @code{expression->initrd} procedure. 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: @example (initrd (lambda (file-systems . rest) (apply base-initrd file-systems #:extra-modules '("my.ko" "modules.ko") rest))) @end example The @code{base-initrd} procedure also handles common use cases that involves using the system as a QEMU guest, or as a ``live'' system whose root file system is volatile. @deffn {Monadic Procedure} base-initrd @var{file-systems} @ [#:qemu-networking? #f] [#:virtio? #f] [#:volatile-root? #f] @ [#:extra-modules '()] [#:mapped-devices '()] Return a monadic derivation that builds a generic 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 @code{--root}. @var{mapped-devices} is a list of device mappings to realize before @var{file-systems} are mounted (@pxref{Mapped Devices}). When @var{qemu-networking?} is true, set up networking with the standard QEMU parameters. When @var{virtio?} is true, load additional modules so 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. The initrd is automatically populated with all the kernel modules necessary for @var{file-systems} and for the given options. However, additional kernel modules can be listed in @var{extra-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 {Monadic Procedure} expression->initrd @var{exp} @ [#:guile %guile-static-stripped] [#:name "guile-initrd"] @ [#:modules '()] Return a derivation that builds 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. @var{modules} is a list of Guile module names to be embedded in the initrd. @end deffn @node GRUB Configuration @subsection GRUB Configuration @cindex GRUB @cindex boot loader The operating system uses GNU@tie{}GRUB as its boot loader (@pxref{Overview, overview of GRUB,, grub, GNU GRUB Manual}). It is configured using @code{grub-configuration} declarations. This data type is exported by the @code{(gnu system grub)} module, and described below. @deftp {Data Type} grub-configuration The type of a GRUB configuration declaration. @table @asis @item @code{device} This is a string denoting the boot device. It must be a device name understood by the @command{grub-install} command, such as @code{/dev/sda} or @code{(hd0)} (@pxref{Invoking grub-install,,, grub, GNU GRUB Manual}). @item @code{menu-entries} (default: @code{()}) A possibly empty list of @code{menu-entry} objects (see below), denoting entries to appear in the GRUB boot 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 current system's entry. @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. @item @code{theme} (default: @var{%default-theme}) The @code{grub-theme} object describing the theme to use. @end table @end deftp 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: @deftp {Data Type} menu-entry The type of an entry in the GRUB boot menu. @table @asis @item @code{label} The label to show in the menu---e.g., @code{"GNU System"}. @item @code{linux} The Linux kernel to boot. @item @code{linux-arguments} (default: @code{()}) The list of extra Linux kernel command-line arguments---e.g., @code{("console=ttyS0")}. @item @code{initrd} A G-Expression or string denoting the file name of the initial RAM disk to use (@pxref{G-Expressions}). @end table @end deftp @c FIXME: Write documentation once it's stable. Themes are created using the @code{grub-theme} form, which is not documented yet. @defvr {Scheme Variable} %default-theme This is the default GRUB theme used by the operating system, with a fancy background image displaying the GNU and Guix logos. @end defvr @node Invoking guix system @subsection 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 instantiate. Currently the following values are supported: @table @code @item reconfigure Build the operating system described in @var{file}, activate it, and switch to it@footnote{This action is usable only on systems already running GNU.}. This effects all the configuration specified in @var{file}: user accounts, system services, global package list, setuid programs, etc. It also adds a GRUB menu entry for the new OS configuration, and moves entries for older configurations to a submenu---unless @option{--no-grub} is passed. @item build Build the operating system's derivation, 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 the GNU 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 GRUB on the device specified in @file{my-os-config}, unless the @option{--no-grub} option was passed. @item vm @cindex virtual machine Build a virtual machine that contain the operating system declared in @var{file}, and return a script to run that virtual machine (VM). Arguments given to the script are passed as is to QEMU. The VM shares its store with the host system. 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 host's store can then be mounted. The @code{--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 @code{--image-size} option can be used to specify the image's size. @item vm-image @itemx disk-image Return a virtual machine or disk image of the operating system declared in @var{file} that stands alone. Use the @option{--image-size} option to specify the size of the image. When using @code{vm-image}, the returned image is in qcow2 format, which the QEMU emulator can efficiently use. When using @code{disk-image}, 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 on it using the following command: @example # dd if=$(guix system disk-image my-os.scm) of=/dev/sdc @end example @end table @var{options} can contain any of the common build options provided by @command{guix build} (@pxref{Invoking guix build}). In addition, @var{options} can contain one of the following: @table @option @item --system=@var{system} @itemx -s @var{system} Attempt to build for @var{system} instead of the host's system type. This works as per @command{guix build} (@pxref{Invoking guix build}). @item --image-size=@var{size} For the @code{vm-image} and @code{disk-image} actions, 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}). @end table Note that all the actions above, except @code{build} and @code{init}, rely on KVM support in the Linux-Libre kernel. Specifically, the machine should have 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 daemon's build users. @node Defining Services @subsection Defining Services The @code{(gnu services @dots{})} modules define several procedures that allow users to declare the operating system's services (@pxref{Using the Configuration System}). These procedures are @emph{monadic procedures}---i.e., procedures that return a monadic value in the store monad (@pxref{The Store Monad}). For examples of such procedures, @xref{Services}. @cindex service definition The monadic value returned by those procedures is a @dfn{service definition}---a structure as returned by the @code{service} form. Service definitions specifies the inputs the service depends on, and an expression to start and stop the service. Behind the scenes, service definitions are ``translated'' into the form suitable for the configuration file of dmd, the init system (@pxref{Services,,, dmd, GNU dmd Manual}). As an example, here is what the @code{nscd-service} procedure looks like: @lisp (define (nscd-service) (with-monad %store-monad (return (service (documentation "Run libc's name service cache daemon.") (provision '(nscd)) (activate #~(begin (use-modules (guix build utils)) (mkdir-p "/var/run/nscd"))) (start #~(make-forkexec-constructor (string-append #$glibc "/sbin/nscd") "-f" "/dev/null" "--foreground")) (stop #~(make-kill-destructor)) (respawn? #f))))) @end lisp @noindent The @code{activate}, @code{start}, and @code{stop} fields are G-expressions (@pxref{G-Expressions}). The @code{activate} field contains a script to run at ``activation'' time; it makes sure that the @file{/var/run/nscd} directory exists before @command{nscd} is started. The @code{start} and @code{stop} fields refer to dmd's facilities to start and stop processes (@pxref{Service De- and Constructors,,, dmd, GNU dmd Manual}). The @code{provision} field specifies the name under which this service is known to dmd, and @code{documentation} specifies on-line documentation. Thus, the commands @command{deco start ncsd}, @command{deco stop nscd}, and @command{deco doc nscd} will do what you would expect (@pxref{Invoking deco,,, dmd, GNU dmd Manual}). @node Installing Debugging Files @section Installing Debugging Files @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. 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 Distribution}). 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{Packages with Multiple Outputs}). 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 package -i 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 @code{.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{Invoking 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{Build Systems}). Currently, it is opt-in---debugging information is available only for those packages whose definition explicitly declares a @code{debug} output. This may be changed to opt-out in the future, if our build farm servers can handle the load. To check whether a package has a @code{debug} output, use @command{guix package --list-available} (@pxref{Invoking guix package}). @node Security Updates @section Security Updates @quotation Note As of version @value{VERSION}, the feature described in this section is experimental. @end quotation @cindex security updates Occasionally, important security vulnerabilities are discovered in core software packages and must be patched. Guix follows a functional package management discipline (@pxref{Introduction}), 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 that, 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 @var{bash-fixed}, in the usual way (@pxref{Defining Packages}). Then, the original package definition is augmented with a @code{replacement} field pointing to the package containing the bug fix: @example (define bash (package (name "bash") ;; @dots{} (replacement bash-fixed))) @end example From there on, any package depending directly or indirectly on Bash that is installed will automatically be ``rewritten'' to refer to @var{bash-fixed} instead of @var{bash}. This grafting process takes time proportional to the size of the package, but expect less than a minute for an ``average'' package on a recent machine. Currently, the graft and the package it replaces (@var{bash-fixed} and @var{bash} in the example above) must have the exact same @code{name} and @code{version} fields. 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. @node Package Modules @section Package Modules 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{Modules, 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{} object (@pxref{Defining Packages}). The @code{(gnu packages @dots{})} module name space is automatically scanned for packages by the command-line tools. For instance, when running @code{guix package -i 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 customization, of packages @cindex package module search path Users can store package definitions in modules with different names---e.g., @code{(my-packages emacs)}. These package definitions will not be visible by default. Thus, users can invoke commands such as @command{guix package} and @command{guix build} have to be used with the @code{-e} option so that they know where to find the package, or use the @code{-L} option of these commands to make those modules visible (@pxref{Invoking guix build, @code{--load-path}}), or define the @code{GUIX_PACKAGE_PATH} environment variable. This environment variable makes it easy to extend or customize the distribution and is honored by all the user interfaces. @defvr {Environment Variable} GUIX_PACKAGE_PATH This is a colon-separated list of directories to search for package modules. Directories listed in this variable take precedence over the distribution's own modules. @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, @ref{Bootstrapping}. @node Packaging Guidelines @section Packaging Guidelines The GNU distribution is nascent and may well lack some of your favorite packages. This section describes how you can help make the distribution grow. @xref{Contributing}, for additional information on how you can help. Free software packages are usually distributed in the form of @dfn{source code tarballs}---typically @file{tar.gz} files that contain all the source files. Adding a package to the distribution means essentially two things: adding a @dfn{recipe} that describes how to build the package, including a list of other packages required to build it, and adding @dfn{package meta-data} along with that recipe, such as a description and licensing information. In Guix all this information is embodied in @dfn{package definitions}. Package definitions provide a high-level view of the package. They are written using the syntax of the Scheme programming language; in fact, for each package we define a variable bound to the package definition, and export that variable from a module (@pxref{Package Modules}). However, in-depth Scheme knowledge is @emph{not} a prerequisite for creating packages. For more information on package definitions, @ref{Defining Packages}. Once a package definition is in place, stored in a file in the Guix source tree, it can be tested using the @command{guix build} command (@pxref{Invoking guix build}). For example, assuming the new package is called @code{gnew}, you may run this command from the Guix build tree: @example ./pre-inst-env guix build gnew --keep-failed @end example Using @code{--keep-failed} makes it easier to debug build failures since it provides access to the failed build tree. Another useful command-line option when debugging is @code{--log-file}, to access the build log. If the package is unknown to the @command{guix} command, it may be that the source file contains a syntax error, or lacks a @code{define-public} clause to export the package variable. To figure it out, you may load the module from Guile to get more information about the actual error: @example ./pre-inst-env guile -c '(use-modules (gnu packages gnew))' @end example Once your package builds correctly, please send us a patch (@pxref{Contributing}). Well, if you need help, we will be happy to help you too. Once the patch is committed in the Guix repository, the new package automatically gets built on the supported platforms by @url{http://hydra.gnu.org/gnu/master, our continuous integration system}. @cindex substituter Users can obtain the new package definition simply by running @command{guix pull} (@pxref{Invoking guix pull}). When @code{hydra.gnu.org} is done building the package, installing the package automatically downloads binaries from there (@pxref{Substitutes}). The only place where human intervention is needed is to review and apply the patch. @menu * Software Freedom:: What may go into the distribution. * Package Naming:: What's in a name? * Version Numbers:: When the name is not enough. * Python Modules:: Taming the snake. * Perl Modules:: Little pearls. @end menu @node Software Freedom @subsection Software Freedom @c Adapted from http://www.gnu.org/philosophy/philosophy.html. The GNU operating system has been developed so that users can have freedom in their computing. GNU is @dfn{free software}, meaning that users have the @url{http://www.gnu.org/philosophy/free-sw.html,four essential freedoms}: to run the program, to study and change the program in source code form, to redistribute exact copies, and to distribute modified versions. Packages found in the GNU distribution provide only software that conveys these four freedoms. In addition, the GNU distribution follow the @url{http://www.gnu.org/distros/free-system-distribution-guidelines.html,free software distribution guidelines}. Among other things, these guidelines reject non-free firmware, recommendations of non-free software, and discuss ways to deal with trademarks and patents. Some packages contain a small and optional subset that violates the above guidelines, for instance because this subset is itself non-free code. When that happens, the offending items are removed with appropriate patches or code snippets in the package definition's @code{origin} form (@pxref{Defining Packages}). That way, @code{guix build --source} returns the ``freed'' source rather than the unmodified upstream source. @node Package Naming @subsection Package Naming A package has actually two names associated with it: First, there is the name of the @emph{Scheme variable}, the one following @code{define-public}. By this name, the package can be made known in the Scheme code, for instance as input to another package. Second, there is the string in the @code{name} field of a package definition. This name is used by package management commands such as @command{guix package} and @command{guix build}. Both are usually the same and correspond to the lowercase conversion of the project name chosen upstream, with underscores replaced with hyphens. For instance, GNUnet is available as @code{gnunet}, and SDL_net as @code{sdl-net}. We do not add @code{lib} prefixes for library packages, unless these are already part of the official project name. But see @pxref{Python Modules} and @ref{Perl Modules} for special rules concerning modules for the Python and Perl languages. @node Version Numbers @subsection Version Numbers We usually package only the latest version of a given free software project. But sometimes, for instance for incompatible library versions, two (or more) versions of the same package are needed. These require different Scheme variable names. We use the name as defined in @ref{Package Naming} for the most recent version; previous versions use the same name, suffixed by @code{-} and the smallest prefix of the version number that may distinguish the two versions. The name inside the package definition is the same for all versions of a package and does not contain any version number. For instance, the versions 2.24.20 and 3.9.12 of GTK+ may be packaged as follows: @example (define-public gtk+ (package (name "gtk+") (version "3.9.12") ...)) (define-public gtk+-2 (package (name "gtk+") (version "2.24.20") ...)) @end example If we also wanted GTK+ 3.8.2, this would be packaged as @example (define-public gtk+-3.8 (package (name "gtk+") (version "3.8.2") ...)) @end example @node Python Modules @subsection Python Modules We currently package Python 2 and Python 3, under the Scheme variable names @code{python-2} and @code{python} as explained in @ref{Version Numbers}. To avoid confusion and naming clashes with other programming languages, it seems desirable that the name of a package for a Python module contains the word @code{python}. Some modules are compatible with only one version of Python, others with both. If the package Foo compiles only with Python 3, we name it @code{python-foo}; if it compiles only with Python 2, we name it @code{python2-foo}. If it is compatible with both versions, we create two packages with the corresponding names. If a project already contains the word @code{python}, we drop this; for instance, the module python-dateutil is packaged under the names @code{python-dateutil} and @code{python2-dateutil}. @node Perl Modules @subsection Perl Modules Perl programs standing for themselves are named as any other package, using the lowercase upstream name. For Perl packages containing a single class, we use the lowercase class name, replace all occurrences of @code{::} by dashes and prepend the prefix @code{perl-}. So the class @code{XML::Parser} becomes @code{perl-xml-parser}. Modules containing several classes keep their lowercase upstream name and are also prepended by @code{perl-}. Such modules tend to have the word @code{perl} somewhere in their name, which gets dropped in favor of the prefix. For instance, @code{libwww-perl} becomes @code{perl-libwww}. @node Bootstrapping @section Bootstrapping @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{Introduction}). So there's an obvious chicken-and-egg problem: how does the first package get built? How does the first compiler get compiled? Note that this is a question of interest only to the curious hacker, not to the regular user, so you can shamelessly skip this section if you consider yourself a ``regular user''. @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 (more on that later). @unnumberedsubsec 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. 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{The Store}). 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 @code{.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}, etc., at which point we have a working C tool chain. @unnumberedsubsec Building the Build Tools @c TODO: Add a package-level dependency graph generated from (gnu @c packages base). 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 base)} module. @c See . The first tool that gets built with the bootstrap binaries is GNU Make, 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 @code{--target} equal to @code{--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 are built. GCC uses @code{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{Defining Packages}). @unnumberedsubsec Building the 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 (Guile, Binutils, GCC, libc, 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. @node Porting @section 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{Bootstrapping}). 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 Once these are built, the @code{(gnu packages bootstrap)} module needs to be updated to refer to these binaries on the target platform. In addition, the @code{glibc-dynamic-linker} procedure in that module 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. 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 @code{--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 ********************************************************************* @node Contributing @chapter Contributing This project is a cooperative effort, and we need your help to make it grow! Please get in touch with us on @email{guix-devel@@gnu.org} and @code{#guix} on the Freenode IRC network. We welcome ideas, bug reports, patches, and anything that may be helpful to the project. We particularly welcome help on packaging (@pxref{Packaging Guidelines}). Please see the @url{http://git.savannah.gnu.org/cgit/guix.git/tree/HACKING, @file{HACKING} file} that comes with the Guix source code for practical details about contributions. @c ********************************************************************* @node Acknowledgments @chapter Acknowledgments Guix is based on the Nix package manager, which was designed and implemented by Eelco Dolstra. 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. The Nix-based software distributions, Nixpkgs and NixOS, have also been an inspiration for Guix. @c ********************************************************************* @node GNU Free Documentation License @appendix GNU Free Documentation License @include fdl-1.3.texi @c ********************************************************************* @node Concept Index @unnumbered Concept Index @printindex cp @node Programming Index @unnumbered Programming Index @syncodeindex tp fn @syncodeindex vr fn @printindex fn @bye @c Local Variables: @c ispell-local-dictionary: "american"; @c End: