# Arch Build System

Related articles

- ABS FAQ
- Arch packaging standards
- Arch User Repository
- Creating packages
- Kernel Compilation with ABS
- makepkg
- Official repositories
- pacman
- PKGBUILD

This article provides an overview of the Arch Build System along with a walkthrough for beginners. It is not a complete reference guide! For a quick and simple introduction to the ABS, see the ABS FAQ. If you need more information, please reference the man pages.

Note: ABS syncs once a day so it may lag behind what is already available in the repositories.

## What is the Arch Build System?

The Arch Build System, ABS for short, 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 category 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 the ABS makepkg command, the software is first compiled and then packaged within the build directory before being installed. 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; an SVN hierarchy under `/var/abs/` on your (local) machine. It contains many subdirectories, named for all available official Arch Linux software from repositories specified in `/etc/abs.conf`, but not the packages themselves. The tree is created after installing the abs package with pacman and subsequently running the `abs` script.

PKGBUILDs
  A Bash script that contains the URL of the source code along with the compilation and packaging instructions.

makepkg
  ABS 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 the Creating packages wiki article.)

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.

## 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 first need to install abs from the official repositories.

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

As root, 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 file 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

As root, run:

    # abs

Your ABS tree is now created under `/var/abs`. Note the appropriate branches of the ABS tree now exist and correspond 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

`/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.conf.)

#### 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 available from the community repo:

##### 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 add or remove support for components, to patch or to change package versions, etc. (optional):

    $ nano PKGBUILD

Run makepkg as normal user (with `-s` switch to install with automatic 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 adds a level of convenience and automation, while still maintaining complete transparency and control of the build and installation functions by including them 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.

Categories:

- About Arch
- Package development
- Package management