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 (the ABS tree) residing under /var/abs. This tree contains many subdirectories, each within a repo name and each named by their respective package. This tree represents (but does not contain) all official Arch software, retrievable through the SVN system. You may refer to each package-named subdirectory as an 'ABS', much the way one would refer to a 'port'. These ABS (or subdirectories) do not contain the software package nor the source but rather a PKGBUILD file (and sometimes other files). A PKGBUILD is a simple Bash build script — a text file containing the compilation and packaging instructions as well as the URL of the appropriate source tarball to be downloaded. (The most important component of ABS are PKGBUILDs.) By issuing inside the ABS makepkg command, the software is first compiled and then packaged within the build directory. Now you may use pacman (the Arch Linux package manager) to install, upgrade, and remove 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:

ABS tree
The ABS 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 and the abs script (from the abs package) downloads them using rsync into /var/abs/ on your (local) machine. On the local system, the tree contains subdirectories for each repository specified in /etc/abs.conf, which in turn contain a subdirectory for each package.
Note: ABS tree syncs once a day so it may lag behind what is already available in the 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.

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)
  • 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

Building packages using abs consists of these steps:

  1. Install the abs package with pacman.
  2. Run abs as root to create the ABS tree by synchronizing it with the Arch Linux server.
  3. Copy the build files (usually residing under /var/abs/<repo>/<pkgname>) to a build directory.
  4. Navigate to that directory, edit the PKGBUILD (if desired/necessary) and do makepkg.
  5. According to instructions in the PKGBUILD, makepkg will download the appropriate source tarball, unpack it, patch (if desired), compile according to CFLAGS specified in makepkg.conf, and finally compress the built files into a package with the extension .pkg.tar.gz or .pkg.tar.xz.
  6. Installing is as easy as doing pacman -U <.pkg.tar.xz file>. Package removal is also handled by pacman.

Install tools

To use the ABS, you need to install abs.

This will grab the abs-sync scripts, various build scripts, and rsync (as a dependency, if you do not already have it).

Before you can actually build anything, however, you will also need basic compiling tools. These are handily collected in the package group base-devel. This group can be installed with pacman.

/etc/abs.conf

Edit /etc/abs.conf to include your desired repositories.

Remove the ! in front of the appropriate repositories. For example:

REPOS=(core extra community !testing)

ABS tree

The ABS tree is an SVN directory hierarchy located under /var/abs and looks like this:

| -- core/
|     || -- acl/
|     ||     || -- PKGBUILD
|     || -- attr/
|     ||     || -- PKGBUILD
|     || -- abs/
|     ||     || -- PKGBUILD
|     || -- autoconf/
|     ||     || -- PKGBUILD
|     || -- ...
| -- extra/
|     || -- acpid/
|     ||     || -- PKGBUILD
|     || -- apache/
|     ||     || -- PKGBUILD
|     || -- ...
| -- community/
|     || -- ...

The ABS tree has exactly the same structure as the package database:

  • First-level: Repository name
  • Second-level: Package name directories
  • Third level: PKGBUILD (contains information needed to build a package) and other related files (patches, other files needed for building the package)

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. So the size of abs tree is quite small.

Download ABS tree

Run:

# abs

Your ABS tree is now created under /var/abs. Note that tree branches were created corresponding to the ones you specified in /etc/abs.conf.

The abs command should be run periodically to keep in sync with the official repositories. Individual ABS package files can also be downloaded with:

# abs <repository>/<package>

This way you do not have to check out the entire abs tree just to build one package.

/etc/makepkg.conf

Merge-arrows-2.pngThis article or section is a candidate for merging with makepkg.Merge-arrows-2.png

Notes: please use the second argument of the template to provide more detailed indications. (Discuss in Talk:Arch Build System#)
makepkg's /etc/makepkg.conf specifies global environment variables and compiler flags which you may wish to edit if you are using an SMP system, or to specify other desired optimizations. The default settings are for i686 and x86_64 optimizations which will work fine for those architectures on single-CPU systems. (The defaults will work on SMP machines, but will only use one core/CPU when compiling — see makepkg for details.)

Set the PACKAGER variable in /etc/makepkg.conf

Setting the PACKAGER variable in /etc/makepkg.conf is an optional but highly recommended step. It allows a "flag" to quickly identify which packages have been built and/or installed by YOU, not the official maintainer! This is easily accomplished using expac:

Showing all packages (including those from AUR)
$ grep myname /etc/makepkg.conf
PACKAGER="myname <myemail@myserver.com>"
$ expac "%n %p" | grep "myname" | column -t
archey3 myname
binutils myname
gcc myname
gcc-libs myname
glibc myname
tar myname
Showing only packages contained in repos

This example only shows packages contained in the repos defined in /etc/pacman.conf:

$ . /etc/makepkg.conf; grep -xvFf <(pacman -Qqm) <(expac "%n\t%p" | grep "$PACKAGER$" | cut -f1)
binutils
gcc
gcc-libs
glibc
tar

Create a build directory

It is recommended to create a build directory where the actual compiling will take place; you should never modify the ABS tree by building within it, as data will be lost (overwritten) on each ABS update. It is good practice to use your home directory, though some Arch users prefer to create a 'local' directory under /var/abs/, owned by a normal user.

Create your build directory. e.g.:

$ mkdir -p $HOME/abs

Copy the ABS from the tree (/var/abs/<repository>/<pkgname>) to the build directory.

Build package

In our example, we will build the slim display manager package.

Copy the slim ABS from the ABS tree to a build directory:

$ cp -r /var/abs/extra/slim/ ~/abs

Navigate to the build directory:

$ cd ~/abs/slim

Modify the PKGBUILD to your liking, then run makepkg (with the -s flag to enable automatic build-time dependency handling):

$ makepkg -s
Note: Before complaining about missing (make) dependencies, remember that the group base-devel is assumed to be installed when building with makepkg. See #Install tools.

Install as root:

# pacman -U slim-1.3.0-2-i686.pkg.tar.xz

That's it. You have just built slim from source and cleanly installed it to your system with pacman. Package removal is also handled by pacman with pacman -R slim.

The ABS method of installing software provides comfortability, while still maintaining complete transparency and control of the build and install functions included in the PKGBUILD.

fakeroot

Essentially, the same steps are being executed in the traditional method (generally including the ./configure, make, make install steps) but the software is installed into a fake root environment. (A fake root is simply a subdirectory within the build directory that functions and behaves as the system's root directory. In conjunction with the fakeroot program, makepkg creates a fake root directory, and installs the compiled binaries and associated files into it, with root as owner.) The fake root, or subdirectory tree containing the compiled software, is then compressed into an archive with the extension .pkg.tar.xz, or a package. When invoked, pacman then extracts the package (installs it) into the system's real root directory (/).

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.

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.