Arch build system
The Arch build system (ABS) is a ports-like system for building and packaging software from source code. While pacman is the specialized Arch tool for binary package management, the Arch build system is a collection of tools for compiling source into installable .pkg.tar.zst packages.
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.
The Arch build system is based on a similar concept. It comprises a collection of git repositories for every package available in Arch Linux. Each repository contains a PKGBUILD file (and sometimes other files), and does not contain the software source nor binary. By running makepkg inside a directory, the software sources are downloaded, the software is compiled, and then packaged within the build directory. Then you can use pacman to install the package.
Toolchain
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The Arch build system includes and relies on several components and tools that are used in the process of building packages from source:
Repository 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 the form of Git repositories hosted on gitlab.archlinux.org. See the section #Repository structure for more information. PKGBUILD A Bash script that contains the URL of the source code along with the compilation and packaging instructions. makepkg A 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 the official repository of PKGBUILDs, but packages from the AUR can be built using the same tools. 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.
Repository structure
The core, extra, core-testing, and extra-testing official repositories are hosted on the Arch Linux GitLab instance.
Each package has its own repository in the archlinux/packaging/packages namespace. Each repository contains the PKGBUILD and files used in official builds. Also some files which are used by the developers for the build process can be found there.
For example, the tree for acl looks like this:
acl ├── keys │ └── pgp │ ├── 259B3792B3D6D319212CC4DCD5BF9FEB0313653A.asc │ ├── 600CD204FBCEA418BD2CA74F154343260542DF34.asc │ └── B902B5271325F892AC251AD441633B9FE837F581.asc └── PKGBUILD
The source code for the package is not present in the directory. Instead, the PKGBUILD contains a URL that will download the source code when the package is built.
Use cases
The Arch build system automates certain tasks related to compilation from source. Its use cases are:
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Reason: The main use case is obviously building official binary packages for Arch Linux by developers and packagers. User customizations and unofficial builds are secondary. (Discuss in Talk:Arch build system)
- Any use case that requires you to compile or recompile a package.
- 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 (e.g. enabling or disabling options, patching).
- Rebuild your entire system using your compiler flags, «à la FreeBSD».
- Cleanly build and install your own custom kernel (see Kernel compilation).
- Get kernel modules working with a 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.
Usage
Retrieve PKGBUILD source
To retrieve the PKGBUILD file required to build a certain package from source, you can either use the pkgctl tool or directly use Git.
Using the pkgctl tool
As a precondition, install the devtools package. pkgctl is a tool work with build source files for Arch Linux packages using Git.
To clone the git repository with the latest build files using pkgctl, the following command is used:
$ pkgctl repo clone pkgname
Tip: This clones over SSH by default so if you have not set an SSH key in your Arch GitLab account, you need to clone over HTTPS: pkgctl repo clone —protocol=https pkgname .
Note that here, build source files refers to PKGBUILD, possibly with some few other required files, such as keys. That is, the essential files the are required for Arch Linux build system. It does not refer to the source files of the package that were written by the team that authored the package, such as C or Python files.
This will give you not only the current source build files, but also their previous versions. Furthermore, you can use all other git commands to checkout an older version of the package or to track custom changes.
If you want to get a specific version of a package you can use something like the following:
$ pkgctl repo clone --switch="2:1.19.5-1" go
Do read pkgctl-repo-clone(1) for more insight, and for the other commands available.
Using git directly
Use the following git command to clone a package:
$ git clone https://gitlab.archlinux.org/archlinux/packaging/packages/pkgname.git
For example, to copy the Apache build files:
$ git clone https://gitlab.archlinux.org/archlinux/packaging/packages/apache.git
Build package
Configure makepkg for building packages from the PKGBUILDs you have checked out, as explained in makepkg#Configuration.
Then, copy the directory containing the PKGBUILD you wish to modify to a new location. Make the desired modifications there and use makepkg there 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 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 .
Add this group to the section IgnoreGroup in /etc/pacman.conf .
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 to avoid partial upgrades.
Other tools
- pbget — retrieve PKGBUILDs for individual packages directly from the web interface. Includes AUR support.
SYNOPSIS
makepkg [options] [ENVVAR=value] [ENVVAR+=value] .
DESCRIPTION
makepkg is a script to automate the building of packages. The requirements for using the script are a build-capable *nix platform and a custom build script for each package you wish to build (known as a PKGBUILD). See PKGBUILD(5) for details on creating your own build scripts.
The advantage to a script-based build is that the work is only done once. Once you have the build script for a package, makepkg will do the rest: download and validate source files, check dependencies, configure the build-time settings, build the package, install the package into a temporary root, make customizations, generate meta-info, and package the whole thing up for pacman to use.
makepkg uses your current locale by default and does not unset it when building packages. If you wish to share your build output with others when seeking help or for other purposes, you may wish to run «LC_ALL=C makepkg» so your logs and output are not localized.
OPTIONS
Ignore a missing or incomplete arch field in the build script. This is for rebuilding packages from source when the PKGBUILD may be slightly outdated and not updated with an arch=(‘yourarch’) field.
Do not perform any dependency checks. This will let you override and ignore any dependencies required. There is a good chance this option will break the build process if all of the dependencies are not installed.
Do not extract source files or run the prepare() function (if present); use whatever source already exists in the $srcdir/ directory. This is handy if you want to go into $srcdir/ and manually patch or tweak code, then make a package out of the result. Keep in mind that creating a patch may be a better solution to allow others to use your PKGBUILD.
For each source file in the source array of PKGBUILD, download the file if required and perform the integrity checks. No extraction or build is performed. Dependencies specified in the PKGBUILD will not be handled unless —syncdeps is used. Useful for performing subsequent offline builds.
makepkg will not build a package if a built package already exists in the PKGDEST (set in makepkg.conf(5)) directory, which may default to the current directory. This allows the built package to be overwritten.
For each source file in the source array of PKGBUILD, download the file if required and generate integrity checks. The integrity checks generated are determined by the checks present in the PKGBUILD, falling back to the value of the INTEGRITY_CHECK array in makepkg.conf(5) if these are absent This output can be redirected into your PKGBUILD for source validation using «makepkg -g >> PKGBUILD».