# DeveloperWiki:Building in a Clean Chroot

## Introduction

This article is part of the DeveloperWiki.

## 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, community) while having packages from [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-i686-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 [testing] first before landing in [core].
Note: 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. In this case you may simply use the extra build scripts.

Target repository | Architecture | Build script to use | Pacman configuration file used
--- | --- | --- | ---
extra / community | i686 | extra-i686-build | /usr/share/devtools/pacman-extra.conf
extra / community | x86_64 | extra-x86_64-build | /usr/share/devtools/pacman-extra.conf
testing / community-testing | i686 | testing-i686-build | /usr/share/devtools/pacman-testing.conf
testing / community-testing | x86_64 | testing-x86_64-build | /usr/share/devtools/pacman-testing.conf
staging / community-staging | i686 | staging-i686-build | /usr/share/devtools/pacman-staging.conf
staging / community-staging | x86_64 | staging-x86_64-build | /usr/share/devtools/pacman-staging.conf
multilib | x86_64 | multilib-build | /usr/share/devtools/pacman-multilib.conf
multilib-testing | x86_64 | multilib-testing-build | /usr/share/devtools/pacman-multilib-testing.conf
multilib-staging | x86_64 | multilib-staging-build | /usr/share/devtools/pacman-multilib-staging.conf

## Classic Way

### Setting Up A Chroot

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

    # pacman -S devtools

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.
Note: On btrfs disks, the chroot is created as a subvolume, so you have to remove it by removing the subvolume with `# btrfs subvolume delete $CHROOT/root`.

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

#### 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 chroot is up to date with:

    # arch-nspawn $CHROOT/root pacman -Syu

Then, to build a package in the chroot, run the following from the dir containing the PKGBUILD:

    $ makechrootpkg -c -r $CHROOT

Passing the -c flag to makechrootpkg ensures that the working chroot (named `$CHROOT/$USERNAME`) is cleaned before building starts.

### Manual package installation

Packages can be installed manually to the working chroot by using:

    # makechrootpkg -r $CHROOT -I package-1.0-1-i686.pkg.tar.xz

If done from a directory that contains a PKGBUILD, the package will then be built. Avoid being in such a directory if you want to just install the package.

### Installation after building

Tell makechrootpkg to simply install a package to the rw layer of the chroot after building by passing the -i arg. Unrecognized args get passed to makepkg, so this calls `makepkg` with the -i arg.

    # makechrootpkg -r $CHROOT -- -i

## 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 can't 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.

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