DeveloperWiki:Building in a clean chroot

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Why

Building in a clean chroot prevents missing dependencies in packages, whether due to unwanted linking or packages missing in the depends array in the PKGBUILD. It also allows users to build a package for the stable repositories (core, extra) while having packages from core-testing or extra-testing installed.

Convenience way

To quickly build a package in a clean chroot without any further tinkering, one can use the helper scripts from the devtools package.

These helper scripts should be called in the same directory where the PKGBUILD is, just like with makepkg. For instance, extra-x86_64-build automatically sets up a chroot from a clean chroot matrix in /var/lib/archbuild, updates it, and builds a package for the extra repository. For multilib builds there is just multilib-build without an architecture. Consult the table below for information on which script to use when building for a specific repository and architecture.

The -c parameter resets the chroot matrix, which can be useful in case of breakage. It is not needed for building in a clean chroot.

Note:
  • core is omitted because those packages are required to go through core-testing first before landing in core.
  • If the objective is to build a core package for your own local usage, it may be desirable to use the stable repositories instead of the testing ones. In this case you may simply use the extra build scripts.
Target repository Architecture Build script to use Pacman configuration file used
extra x86_64 extra-x86_64-build /usr/share/devtools/pacman.conf.d/extra.conf
core-testing / extra-testing x86_64 extra-testing-x86_64-build /usr/share/devtools/pacman.conf.d/extra-testing.conf
core-staging / extra-staging x86_64 extra-staging-x86_64-build /usr/share/devtools/pacman.conf.d/extra-staging.conf
multilib x86_64 multilib-build /usr/share/devtools/pacman.conf.d/multilib.conf
multilib-testing x86_64 multilib-testing-build /usr/share/devtools/pacman.conf.d/multilib-testing.conf
multilib-staging x86_64 multilib-staging-build /usr/share/devtools/pacman.conf.d/multilib-staging.conf
Tip: pkgctl-build(1) automatically chooses the right build script to build in a clean chroot.

Classic way

Setting up a chroot

The devtools package provides tools for creating and building within clean chroots. Install it if not done already.

To make a clean chroot, create a directory in which the chroot will reside. For example, $HOME/chroot. 

$ mkdir ~/chroot

Define the CHROOT variable: 

$ CHROOT=$HOME/chroot

Now create the chroot (the sub directory root is required because the $CHROOT directory will get other sub directories for clean working copies): 

$ mkarchroot $CHROOT/root base-devel
Note:
  • One can also define the CHROOT variable in $HOME/.bashrc using the export command if the location is to be repeatedly used.
  • On btrfs, the chroot is created as a subvolume, so you have to remove it by removing the subvolume by running btrfs subvolume delete $CHROOT/root as root.

Edit ~/.makepkg.conf to set the packager name and any makeflags. Also adjust the mirrorlist in $CHROOT/root/etc/pacman.d/mirrorlist and enable the testing repositories in $CHROOT/root/etc/pacman.conf, if desired.

Note: The ~ and $HOME variable are resolved to /root/ by the makechrootpkg script (described below).

Custom pacman.conf

Alternatively, provide a custom pacman.conf and makepkg.conf with the following: 

$ mkarchroot -C <pacman.conf> -M <makepkg.conf> $CHROOT/root base-devel
Warning: Using a custom pacman.conf or makepkg.conf during the initial creation of clean chroot can result in unintended custom adjustments to the chroot environment. Use with caution.

Building in the chroot

Firstly, make sure the base chroot ($CHROOT/root) is up to date: 

$ arch-nspawn $CHROOT/root pacman -Syu

Then, build a package by calling makechrootpkg in the directory containing its PKGBUILD: 

$ makechrootpkg -c -r $CHROOT
Note: Passing the -c flag to makechrootpkg ensures that the working chroot ($CHROOT/$USER) is cleaned before building.

Pre-install required packages

To build a package with dependencies unavailable from the repositories enabled in $CHROOT/root/pacman.conf, pre-install them to the working chroot with -I package: 

$ makechrootpkg -c -r $CHROOT -I build-dependency-1.0-1-x86_64.pkg.tar.xz -I required-package-2.0-2-x86_64.pkg.tar.xz

Passing arguments to makepkg

To pass arguments to makepkg, list them after an end-of-options marker; e.g., to force a check(): 

$ makechrootpkg -c -r $CHROOT -- --check

Handling major rebuilds

The cleanest way to handle a major rebuild is to use the staging repositories. Build the first package against extra and push it to staging. Then rebuild all following packages against staging and push them there.

If you cannot use staging, you can build against custom packages using a command like this: 

# extra-x86_64-build -- -I ~/packages/foobar/foobar-2-1-any.pkg.tar.xz

You can specify more than one package to be installed using multiple -I arguments.

A simpler, but dirtier way to handle a major rebuild is to install all built packages in the chroot, never cleaning it. Build the first package using: 

# extra-x86_64-build

And build all following packages using: 

# makechrootpkg -n -r /var/lib/archbuild/extra-x86_64

Running namcap (the -n argument) implies installing the package in the chroot. *-build also does this by default.

Tips and tricks

Build in tmpfs

If the system has enough RAM, it is possible to specify a tmpfs for the devtools build scripts. 

# mount --mkdir -t tmpfs -o defaults,size=20G tmpfs /mnt/chroots/arch
# extra-x86_64-build -c -r /mnt/chroots/arch
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