     [file version.texi not included]

This manual documents GNU Guix version VERSION.

Copyright © 2012, 2013 Ludovic Courtès

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.''

GNU Guix
********

This document describes GNU Guix version VERSION, a functional package management tool written for the GNU system.

     Copyright © 2012, 2013 Ludovic Courtès

     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.''

Introduction
************

GNU Guix (``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 in all the activities that relate to building packages from source, honoring the build-time and run-time dependencies on packages, installing packages in user environments, upgrading installed packages to new versions or rolling back to a previous set, removing unused software packages, etc.

The term 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 depended on, and returns the 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.  Last but not least, a build function 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 dedicated ``chroots'', where only their explicit inputs are visible.

The result of package build functions is cached in the file system, in a special directory called the store (see The Store).  Each package is installed in a directory of its own, in the store---by default under /nix/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 upgrades and rollback, per-user installation, and garbage collection of packages (see Features).

Guix has a command-line interface allowing users to build, install, upgrade, and remove packages, as well as a Scheme programming interface. The remainder of this manual describes them.

Last but not least, Guix is used to build a distribution of the GNU system, with many GNU and non-GNU free software packages.  See GNU Distribution.

Installation
************

This section describes the software requirements of Guix, as well as how to install it and get ready to use it.

The build procedure for Guix is the same as for other GNU software, and is not covered here.  Please see the files README and INSTALL in the Guix source tree for additional details.

Requirements
============

GNU Guix depends on the following packages:

  * GNU Guile 2.0.x (http://gnu.org/software/guile/);

  * GNU libgcrypt (http://gnupg.org/)

Unless --disable-daemon was passed to configure, the following packages are also needed:

  * SQLite 3 (http://sqlite.org)

  * libbz2 (http://www.bzip.org)

  * GCC's g++ (http://gcc.gnu.org)

When a working installation of the Nix package manager is available, you can instead configure Guix with --disable-daemon.  In that case, Nix (http://nixos.org/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 configure not only the same --with-store-dir value, but also the same --localstatedir value (the latter is essential because it specifies where the database that store meta-data about the store is located, among other things.)  The default values are --with-store-dir=/nix/store and --localstatedir=/nix/var. Note that --disable-daemon is orthogonal and is not required if your goal is to share the same store as Nix.

Setting Up the Daemon
=====================

Operations such as building a package or running the garbage collector are all performed by a specialized process, the Guix 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 guix-package and guix-build communicate with the daemon (via remote procedure calls) to instruct it what to do.

In a standard multi-user setup, Guix and its daemon---the guix-daemon program---are installed by the system administrator; /nix/store is owned by root and guix-daemon runs as 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.

When guix-daemon runs as root, you may not want package build processes themselves to run as root too, for obvious security reasons.  To avoid that, a special pool of 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 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 (see Introduction).

On a GNU/Linux system, a build user pool may be created like this (using Bash syntax and the shadow commands):

     # 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 $i" guix-builder$i;
       done

The guix-daemon program may then be run as root with:

     # guix-daemon --build-users-group=guix-builder

Guix may also be used in a single-user setup, with guix-daemon running as an unprivileged user.  However, to maximize non-interference of build processes, the daemon still needs to perform certain operations that are restricted to root on GNU/Linux: it should be able to run build processes in a chroot, and to run them under different UIDs. To that end, the nix-setuid-helper program is provided; it is a small C program (less than 300 lines) that, if it is made setuid root, can be executed by the daemon to perform these operations on its behalf.  The root-owned /etc/nix-setuid.conf file is read by nix-setuid-helper; it should contain exactly two words: the user name under which the authorized guix-daemon runs, and the name of the build users group.

If you are installing Guix as an unprivileged user and do not have the ability to make nix-setuid-helper setuid-root, it is still possible to run 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 pure functions.

Invoking guix-daemon
====================

The 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 root like this:

     # guix-daemon --build-users-group=guix-builder

For details on how to set it up, Setting Up the Daemon.

By default, guix-daemon launches build processes under different UIDs, taken from the build group specified with --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 (see derivation), plus a set of specific system directories.  By default, the latter contains /dev and /dev/pts.

The following command-line options are supported:

--build-users-group=GROUP
     Take users from GROUP to run build processes (see build users).

--cache-failures
     Cache build failures.  By default, only successful builds are cached.

--cores=N
-c N
     Use N CPU cores to build each derivation; 0 means as many as available.

     The default value is 1, but it may be overridden by clients, such as the --cores option of guix-build (see Invoking guix-build).

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

--max-jobs=N
-M N
     Allow at most N build jobs in parallel.  The default value is 1.

--debug
     Produce debugging output.

     This is useful to debug daemon start-up issues, but then it may be overridden by clients, for example the --verbosity option of guix-build (see Invoking guix-build).

--chroot-directory=DIR
     Add DIR to the build chroot.

     Doing this may change the result of build processes---for instance if they use optional dependencies found in 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.

--disable-chroot
     Disable chroot builds.

     Using this option is not recommended since, again, it would allow build processes to gain access to undeclared dependencies.

--disable-log-compression
     Disable compression of the build logs.

     Unless --lose-logs is used, all the build logs are kept in the LOCALSTATEDIR.  To save space, the daemon automatically compresses them with bzip2 by default.  This option disables that.

--disable-store-optimization
     Disable automatic file ``deduplication'' in the store.

     By default, files added to the store are automatically ``deduplicated'': if a newly added file is identical as another one found in the store, the daemon makes the new file a hard link to the other file.  This slightly increases the input/output load at the end of a build process. This option disables this.

--impersonate-linux-2.6
     On Linux-based systems, impersonate Linux 2.6.  This means that the kernel's 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.

--lose-logs
     Do not keep build logs.  By default they are kept under LOCALSTATEDIR/nix/log.

--system=SYSTEM
     Assume SYSTEM as the current system type.  By default it is the architecture/kernel pair found at configure time, such as x86_64-linux.

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.

Features
========

When using Guix, each package ends up in the package store, in its own directory---something that resembles /nix/store/xxx-package-1.2, where xxx is a base32 string.

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

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

The guix-package command is the central tool to manage packages (see Invoking guix-package).  It operates on those per-user profiles, and can be used with normal user privileges.

The command provides the obvious install, remove, and upgrade operations.  Each invocation is actually a transaction: either the specified operation succeeds, or nothing happens.  Thus, if the 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 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.

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

Finally, Guix takes a purely functional approach to package management, as described in the introduction (see Introduction). Each /nix/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, and helps maximize reproducibility.

This foundation allows Guix to support transparent binary/source
deployment (This feature is not implemented as of version
VERSION.  Please contact bug-guix@gnu.org for more
details.).  When a pre-built binary for a /nix/store path is available from an external source, Guix just downloads it; otherwise, it builds the package from source, locally.

Invoking guix-package
=====================

The 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 (see Features).  Its syntax is:

     guix-package OPTIONS

Primarily, 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 each user, a symlink to the user's default profile is automatically created in $HOME/.guix-profile.  This symlink always points to the current generation of the user's default profile.  Thus, users can add $HOME/.guix-profile/bin to their PATH environment variable, and so on.

In a multi-user setup, user profiles must be stored in a place registered as a garbage-collector root, which $HOME/.guix-profile points to (see Invoking guix-gc).  That directory is normally LOCALSTATEDIR/profiles/per-user/USER, where LOCALSTATEDIR is the value passed to configure as --localstatedir, and USER is the user name.  It must be created by root, with USER as the owner.  When it does not exist, guix-package emits an error about it.

The OPTIONS can be among the following:

--install=PACKAGE
-i PACKAGE
     Install PACKAGE.

     PACKAGE may specify either a simple package name, such as guile, or a package name followed by a hyphen and version number, such as guile-1.8.8.  In addition, PACKAGE may contain a colon, followed by the name of one of the outputs of the package, as in gcc:doc or binutils-2.22:lib.

--remove=PACKAGE
-r PACKAGE
     Remove PACKAGE.

--upgrade=REGEXP
-u REGEXP
     Upgrade all the installed packages matching REGEXP.

--roll-back
     Roll back to the previous generation of the profile---i.e., undo the last transaction.

     When combined with options such as --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 empty profile, also known as profile zero---i.e., it contains no files apart from its own meta-data.

--profile=PROFILE
-p PROFILE
     Use PROFILE instead of the user's default profile.

--dry-run
-n
     Show what would be done without actually doing it.

--verbose
     Produce verbose output.  In particular, emit the environment's build log on the standard error port.

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

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

--list-installed[=REGEXP]
-I [REGEXP]
     List currently installed packages in the specified profile.  When REGEXP is specified, list only installed packages whose name matches 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, out for the default output, include for its headers, etc.), and the path of this package in the store.

--list-available[=REGEXP]
-A [REGEXP]
     List packages currently available in the software distribution (see GNU Distribution).  When REGEXP is specified, list only installed packages whose name matches REGEXP.

     For each package, print the following items separated by tabs: its name, its version string, the parts of the package (out for the main files, lib for libraries and possibly headers, etc.), and the source location of its definition.

Invoking guix-gc
================

Packages that are installed but not used may be garbage-collected. The guix-gc command allows users to explicitly run the garbage collector to reclaim space from the /nix/store directory.

The garbage collector has a set of known roots: any file under /nix/store reachable from a root is considered live and cannot be deleted; any other file is considered dead and may be deleted.  The set of garbage collector roots includes default user profiles, and may be augmented with guix-build --root, for example (see Invoking guix-build).

The 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 --delete option), or to print garbage-collector information.  The available options are listed below:

--collect-garbage[=MIN]
-C [MIN]
     Collect garbage---i.e., unreachable /nix/store files and sub-directories.  This is the default operation when no option is specified.

     When MIN is given, stop once MIN bytes have been collected. MIN may be a number of bytes, or it may include a unit as a suffix, such as MiB for mebibytes and GB for gigabytes.

     When MIN is omitted, collect all the garbage.

--delete
-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.

--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.

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

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 /nix/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.

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 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.

This chapter describes all these APIs in turn, starting from high-level package definitions.

Defining Packages
=================

The high-level interface to package definitions is implemented in the (guix packages) and (guix build-system) modules.  As an example, the package definition, or recipe, for the GNU Hello package looks like this:

     (use-modules (guix packages)
                  (guix download)
                  (guix build-system gnu)
                  (guix licenses))

     (define 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)
         (inputs `(("gawk" ,gawk)))
         (synopsis "GNU Hello")
         (description "Yeah...")
         (home-page "http://www.gnu.org/software/hello/")
         (license gpl3+)))

Without being a Scheme expert, the reader may have guessed the meaning of the various fields here.  This expression binds variable HELLO to a <package> object, which is essentially a record (see Scheme records (GNU Guile Reference Manual)). This package object can be inspected using procedures found in the (guix packages) module; for instance, (package-name hello) returns---surprise!---"hello".

There are a few points worth noting in the above package definition:

  * The source field of the package is an <origin> object. Here, the url-fetch method from (guix download) is used, meaning that the source is a file to be downloaded over FTP or HTTP.

     The mirror://gnu prefix instructs url-fetch to use one of the GNU mirrors defined in (guix download).

     The 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 (base32 ...) form introduces the base32 representation of the hash.  A convenient way to obtain this information is with the guix-download tool.

  * The build-system field is set to GNU-BUILD-SYSTEM.  The GNU-BUILD-SYSTEM variable is defined in the (guix build-system gnu) module, and is bound to a <build-system> object.

     Naturally, GNU-BUILD-SYSTEM represents the familiar GNU Build System, and variants thereof (see configuration and makefile conventions (GNU Coding Standards)).  In a nutshell, packages using the GNU Build System may be configured, built, and installed with the usual ./configure && make && make check && make install command sequence.  This is what GNU-BUILD-SYSTEM does.

     In addition, GNU-BUILD-SYSTEM ensures that the ``standard'' environment for GNU packages is available.  This includes tools such as GCC, Coreutils, Bash, Make, Diffutils, and Patch.

  * The 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 "gawk" whose value is that of the GAWK variable; GAWK is itself bound to a <package> object.

     Note that GCC, Coreutils, Bash, and other essential tools do not need to be specified as inputs here.  Instead, GNU-BUILD-SYSTEM takes care of ensuring that they are present.

     However, any other dependencies need to be specified in the inputs field.  Any dependency not specified here will simply be unavailable to the build process, possibly leading to a build failure.

There are other fields that package definitions may provide.  Of particular interest is the arguments field.  When specified, it must be bound to a list of additional arguments to be passed to the build system.  For instance, the above definition could be augmented with the following field initializer:

         (arguments `(#:tests? #f
                      #:configure-flags '("--enable-silent-rules")))

These are keyword arguments (see keyword arguments in Guile (GNU Guile Reference Manual)).  They are passed to GNU-BUILD-SYSTEM, which interprets them as meaning ``do not run make check'', and ``run configure with the --enable-silent-rules flag''.  The value of these keyword parameters is actually evaluated in the build stratum---i.e., by a Guile process launched by the daemon (see Derivations).

Once a package definition is in place (Simple package definitions like the one above may be automatically converted from the Nixpkgs distribution using the guix-import command.), the package may actually be built using the guix-build command-line tool (see Invoking guix-build).

Behind the scenes, a derivation corresponding to the <package> object is first computed by the package-derivation procedure. That derivation is stored in a .drv file under /nix/store. The build actions it prescribes may then be realized by using the build-derivations procedure (see The Store).

 -- Scheme Procedure: package-derivation STORE PACKAGE [SYSTEM]
     Return the derivation path and corresponding <derivation> object of PACKAGE for SYSTEM (see Derivations).

     PACKAGE must be a valid <package> object, and SYSTEM must be a string denoting the target system type---e.g., "x86_64-linux" for an x86_64 Linux-based GNU system.  STORE must be a connection to the daemon, which operates on the store (see The Store).

The Store
=========

Conceptually, the store is where derivations that have been successfully built are stored---by default, under /nix/store. Sub-directories in the store are referred to as 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 valid store paths---paths that result from a successful build.

The store is always accessed by the daemon on behalf of its clients (see 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 (guix store) module provides procedures to connect to the daemon, and to perform RPCs.  These are described below.

 -- Scheme Procedure: open-connection [FILE] [#:reserve-space? #t]
     Connect to the daemon over the Unix-domain socket at FILE.  When 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.

     FILE defaults to %DEFAULT-SOCKET-PATH, which is the normal location given the options that were passed to configure.

 -- Scheme Procedure: close-connection SERVER
     Close the connection to SERVER.

 -- 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.

Procedures that make RPCs all take a server object as their first argument.

 -- Scheme Procedure: valid-path? SERVER PATH
     Return #t when PATH is a valid store path.

 -- Scheme Procedure: add-text-to-store SERVER NAME TEXT REFERENCES
     Add TEXT under file NAME in the store, and return its store path.  REFERENCES is the list of store paths referred to by the resulting store path.

 -- Scheme Procedure: build-derivations SERVER DERIVATIONS
     Build DERIVATIONS (a list of derivation paths), and return when the worker is done building them.  Return #t on success.

This section is currently incomplete.

Derivations
===========

Low-level build actions and the environment in which they are performed are represented by derivations.  A derivation contain the following pieces of information:

  * The outputs of the derivation---derivations produce at least one file or directory in the store, but may produce more.

  * The inputs of the derivations, which may be other derivations or plain files in the store (patches, build scripts, etc.)

  * The system type targeted by the derivation---e.g., x86_64-linux.

  * The file name of a build script in the store, along with the arguments to be passed.

  * A list of environment variables to be defined.

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 .drv---these files are referred to as derivation paths.  Derivations paths can be passed to the build-derivations procedure to perform the build actions they prescribe (see The Store).

The (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 derivation procedure:

 -- Scheme Procedure: derivation STORE NAME SYSTEM BUILDER ARGS ENV-VARS INPUTS [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] [#:hash-mode #f]
     Build a derivation with the given arguments.  Return the resulting store path and <derivation> object.

     When HASH, HASH-ALGO, and HASH-MODE are given, a fixed-output derivation is created---i.e., one whose result is known in advance, such as a file download.

Here's an example with a shell script as its builder, assuming STORE is an open connection to the daemon, and BASH points to a Bash executable in the store:

     (use-modules (guix utils)
                  (guix store)
                  (guix derivations))

     (call-with-values
       (lambda ()
         (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" (%current-system)
                       bash `("-e" ,builder)
                       '(("HOME" . "/homeless")) '())))
       list)
     => ("/nix/store/...-foo.drv" #<<derivation> ...>)

As can be guessed, this primitive is cumbersome to use directly.  An improved variant is build-expression->derivation, which allows the caller to directly pass a Guile expression as the build script:

 -- Scheme Procedure: build-expression->derivation STORE NAME SYSTEM EXP INPUTS [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] [#:env-vars '()] [#:modules '()] [#:guile-for-build #f]
     Return a derivation that executes Scheme expression EXP as a builder for derivation NAME.  INPUTS must be a list of (name drv-path sub-drv) tuples; when SUB-DRV is omitted, "out" is assumed.  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 EXP---e.g., ((guix build utils) (guix build gnu-build-system)).

     EXP is evaluated in an environment where %outputs is bound to a list of output/path pairs, and where %build-inputs is bound to a list of string/output-path pairs made from INPUTS. Optionally, 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 EXP to exit; thus, when EXP returns #f, the build is considered to have failed.

     EXP is built using GUILE-FOR-BUILD (a derivation).  When GUILE-FOR-BUILD is omitted or is #f, the value of the %guile-for-build fluid is used instead.

Here's an example of a single-output derivation that creates a directory containing one file:

     (let ((builder '(let ((out (assoc-ref %outputs "out")))
                       (mkdir out)    ; create /nix/store/...-goo
                       (call-with-output-file (string-append out "/test")
                         (lambda (p)
                           (display '(hello guix) p))))))
       (build-expression->derivation store "goo" (%current-system)
                                     builder '()))

     => "/nix/store/...-goo.drv"
     => #<<derivation> ...>

Remember that the build expression passed to build-expression->derivation is run by a separate Guile process than the one that calls build-expression->derivation: it is run by a Guile process launched by the daemon, typically in a chroot.  So, while there is a single language for both the host and the build side, there are really two strata of code: the host-side, and the build-side code (The term stratum in this context was coined by Manuel Serrano et al. in the context of their work on Hop.). This distinction is important to keep in mind, notably when using higher-level constructs such as GNU-BUILD-SYSTEM (see Defining Packages).  For this reason, Guix modules that are meant to be used in the build stratum are kept in the (guix build ...) name space.

Utilities
*********

Invoking guix-build
===================

The 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 guix-package command (see Invoking guix-package).  Thus, it is mainly useful for distribution developers.

The general syntax is:

     guix-build OPTIONS PACKAGE-OR-DERIVATION...

PACKAGE-OR-DERIVATION may be either the name of a package found in the software distribution such as coreutils or coreutils-8.20, or a derivation such as /nix/store/...-coreutils-8.19.drv.  Alternatively, the --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 OPTIONS may be zero or more of the following:

--expression=EXPR
-e EXPR
     Build the package EXPR evaluates to.

     For example, EXPR may be (@ (gnu packages guile) guile-1.8), which unambiguously designates this specific variant of version 1.8 of Guile.

--source
-S
     Build the packages' source derivations, rather than the packages themselves.

     For instance, guix-build -S gcc returns something like /nix/store/...-gcc-4.7.2.tar.bz2, which is GCC's source tarball.

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., 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 --system=i686-linux on an x86_64-linux system allows users to build packages in a complete 32-bit environment.

--derivations
-d
     Return the derivation paths, not the output paths, of the given packages.

--keep-failed
-K
     Keep the build tree of failed builds.  Thus, if a build fail, its build tree is kept under /tmp, in a directory whose name is shown at the end of the build log.  This is useful when debugging build issues.

--dry-run
-n
     Do not build the derivations.

--no-substitutes
     Build instead of resorting to pre-built substitutes.

--cores=N
-c N
     Allow the use of up to N CPU cores for the build.  The special value 0 means to use as many CPU cores as available.

--root=FILE
-r FILE
     Make FILE a symlink to the result, and register it as a garbage collector root.

--verbosity=LEVEL
     Use the given verbosity level.  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.

Behind the scenes, guix-build is essentially an interface to the package-derivation procedure of the (guix packages) module, and to the build-derivations procedure of the (guix store) module.

GNU Distribution
****************

Guix comes with a distribution of free software (The term ``free'' here refers to the freedom provided to users of that software (http://www.gnu.org/philosophy/free-sw.html).)  that form 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 seen by running guix-package (see Invoking guix-package):

     guix-package --list-available

The package definitions of the distribution may are provided by Guile modules in the (gnu packages ...) name space---for instance, the (gnu packages emacs) module exports a variable named emacs, which is bound to a <package> object (see Defining Packages).  The (gnu packages) module provides facilities for searching for packages.

The distribution is fully bootstrapped and 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 bootstrap binaries, provided by the (gnu packages bootstrap) module.  These are statically-linked binaries of the core tools without which building anything at all would be impossible.

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.

Building this distribution is a cooperative effort, and you are invited to join!  Please get in touch with us on bug-guix@gnu.org.  We welcome ideas, bug reports, patches, and anything that may be helpful to the project.

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.

GNU Free Documentation License
******************************

     [file fdl-1.3.texi not included]