Arch Build System

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This article provides an overview of the Arch Build System (ABS) along with a walkthrough for beginners. It is not intended to be a complete reference guide.

What is the Arch Build System?

The Arch Build System is a ports-like system for building and packaging software from source code. While pacman is the specialized Arch tool for binary package management (including packages built with the ABS), ABS is a collection of tools for compiling source into installable .pkg.tar.xz packages.

What is a ports-like system?

Ports is a system used by *BSD to automate the process of building software from source code. The system uses a port to download, unpack, patch, compile, and install the given software. A port is merely a small directory on the user's computer, named after the corresponding software to be installed, that contains a few files with the instructions for building and installing the software from source. This makes installing software as simple as typing make or make install clean within the port's directory.

ABS is a similar concept

ABS is made up of a directory tree that can be checked out using SVN. This tree represents, but does not contain, all official Arch software. Subdirectories do not contain the software package nor the source but rather a PKGBUILD file and sometimes other files. By issuing makepkg inside a directory containing a PKGBUILD, the software is first compiled and then packaged within the build directory. Then you can use pacman to install or upgrade your new package.

ABS overview

'ABS' may be used as an umbrella term since it includes and relies on several other components; therefore, though not technically accurate, 'ABS' can refer to the following tools as a complete toolkit:

SVN tree
The directory structure containing files needed to build all official packages but not the packages themselves nor the source files of the software. It is available in svn and git repositories.
PKGBUILD
A Bash script that contains the URL of the source code along with the compilation and packaging instructions.
makepkg
shell command tool which reads the PKGBUILDs, automatically downloads and compiles the sources and creates a .pkg.tar* according to the PKGEXT array in makepkg.conf. You may also use makepkg to make your own custom packages from the AUR or third-party sources. See Creating packages for more information.
pacman
pacman is completely separate, but is necessarily invoked either by makepkg or manually, to install and remove the built packages and for fetching dependencies.
AUR
The Arch User Repository is separate from ABS but AUR (unsupported) PKGBUILDs are built using makepkg to compile and package up software. In contrast to the ABS tree on your local machine, the AUR exists as a website interface. It contains many thousands of user-contributed PKGBUILDs for software which is unavailable as an official Arch package. If you need to build a package outside the official Arch tree, chances are it is in the AUR.
Warning: Official PKGBUILDs assume that packages are built in a clean chroot. Building software on a dirty build system may fail or cause unexpected behaviour at runtime, because if the build system detects dependencies dynamically, the result depends on what packages are available on the build system.

SVN tree

The core, extra, and testing repositories are in the packages SVN respository for checkout. The community and multilib repositories are in the community SVN repository.

Each package has its own subdirectory. Within it there are repos and trunk directories. repos is further broken down by repository name (e.g., core) and architecture. PKGBUILD's and files found in repos are used in official builds. Files found in trunk are used by developers in preparation before being copied to repos.

For example, the tree for acl looks like this:

acl
acl/repos
acl/repos/core-i686
acl/repos/core-i686/PKGBUILD
acl/repos/core-x86_64
acl/repos/core-x86_64/PKGBUILD
acl/trunk
acl/trunk/PKGBUILD

The source code for the package is not present in the ABS directory. Instead, the PKGBUILD contains a URL that will download the source code when the package is built.

Why would I want to use ABS?

The Arch Build System is used to:

  • Compile or recompile a package, for any reason
  • Make and install new packages from source of software for which no packages are yet available (see Creating packages)
  • Customize existing packages to fit your needs (enabling or disabling options, patching)
  • Rebuild your entire system using your compiler flags, "à la FreeBSD" (e.g. with pacbuilder-svnAUR)
  • Cleanly build and install your own custom kernel (see Kernel compilation)
  • Get kernel modules working with your custom kernel
  • Easily compile and install a newer, older, beta, or development version of an Arch package by editing the version number in the PKGBUILD

ABS is not necessary to use Arch Linux, but it is useful for automating certain tasks of source compilation.

How to use ABS

Retrieve PKGBUILD source

Tip: An alternative method is to install and use the asp package which is a thin wrapper around the svntogit repositories.

Prerequisites

Install the subversion package.

Non-recursive checkout

Warning: Do not download the whole repository; only follow the instructions below. The entire SVN repository is huge. Not only will it take an obscene amount of disk space, but it will also tax the archlinux.org server for you to download it. If you abuse this service, your address may be blocked. Never use the public SVN for any sort of scripting.

To checkout the core, extra, and testing repositories:

$ svn checkout --depth=empty svn://svn.archlinux.org/packages

To checkout the community and multilib repositories:

$ svn checkout --depth=empty svn://svn.archlinux.org/community

In both cases, it simply creates an empty directory, but it does know that it is an svn checkout.

Checkout a package

In the directory containing the svn repository you checked out (i.e., packages or community), do:

$ svn update package-name

This will pull the package you requested into your checkout. From now on, any time you svn update at the top level, this will be updated as well.

If you specify a package that does not exist, svn will not warn you. It will just print something like "At revision 115847", without creating any files. If that happens, check your spelling of the package name and that the package has not been moved to another repository (i.e. from community to the main repository).

Tip: To checkout an older version of a package, see #Checkout an older version of a package.

You should periodically update all of your checked out packages if you wish to perform rebuilds on more recent revisions of the repositories. To do so, do:

$ svn update

Configure makepkg

See makepkg#Configuration on how to configure makepkg for building packages from the PKGBUILD's you have checked out.

Build package

Copy the directory containing the PKGBUILD you wish to modify to a new location. Then make the desired modifications. From there, use makepkg as described in makepkg#Usage to create and install the new package.

Tips and tricks

Preserve modified packages

Updating the system with pacman will replace a modified package from ABS with the package of the same name from the official repositories. See the following instructions for how to avoid this.

Insert a group array into the PKGBUILD, and add the package to a group called modified.

PKGBUILD
groups=('modified')

Add this group to the section IgnoreGroup in /etc/pacman.conf.

/etc/pacman.conf
IgnoreGroup = modified

If new versions are available in the official repositories during a system update, pacman prints a note that it is skipping this update because it is in the IgnoreGroup section. At this point the modified package should be rebuilt from ABS to avoid partial upgrades.

Checkout an older version of a package

Within the svn repository you checked out as described in #Non-recursive checkout (i.e. "packages" or "community"), first examine the log:

$ svn log package-name

Find out the revision you want by examining the history, then specify the revision you wish to checkout. For example, to checkout revision r1729 you would do:

$ svn update -r1729 package-name

This will update an existing working copy of package-name to the chosen revision.

You can also specify a date. If no revision on that day exists, svn will grab the most recent package before that time. The following example checks out the revision from 2009-03-03:

$ svn update -r{20090303} package-name

It is possible to checkout packages at versions before they were moved to another repository as well; check the logs thoroughly for the date they were moved or the last revision number.

Other tools

  • pbget - retrieve PKGBUILDs for individual packages directly from the web interface. Includes AUR support.
  • asp - a tool to manage the build source files used to create Arch Linux packages. Uses the git interface which offers more up to date sources.