Unofficial Arch Linux images

This repository contains unofficial Docker images of Arch Linux and Arch Linux ARM for all available platforms.

The images aim to be as plain and no-thrills as possible, what you'd get from pacstrap. This does not mean they are small, however. The latest image weights in at about 100 MB, which is twice ubuntu:latest at the time of writing.

However, these images can make very convenient prototype, test and build environments in combination with Docker tooling, even on non-Linux platforms.

The images are available on Docker Hub as stephank/archlinux. Source for the build process is in the GitHub repo stephank/docker-archlinux.

Examples

Building packages

In a directory with a PKGBUILD file, run:

docker run --rm -v "$PWD":/build stephank/archlinux:makepkg

The makepkg images expect the build directory to be mounted as /build. The actual makepkg tool is invoked as makepkg --noconfirm -s. Any additional arguments passed to the image are added after the default arguments.

Before the build starts, PGP keys in the PKGBUILD validpgpkeys array are fetched from public keyservers, and the package database is refreshed.

Adding a local repository

The makepkg images have an additional repository configured:

[makepkg]
Server=file:///repo/
SigLevel=Never

When building packages that are interdependent, add them to a repo makepkg and mount it at /repo to allow them to build.

mkdir repo/
cp mydep/mydep-1.0.0-1-x86_64.pkg.tar.xz repo/
repo-add repo/makepkg.db.tar.gz repo/*.pkg.tar.xz

docker run --rm \
    -v "$PWD/repo":/repo:ro \
    -v "$PWD/myproject":/build \
    stephank/archlinux:makepkg

Creating a shared package cache

Pacman downloads can be shared between different containers to save on bandwidth. Simply create a writable mount at /var/cache/pacman/pkg, for example:

docker volume create --name pacman-pkg
docker run -v pacman-pkg:/var/cache/pacman/pkg ...

Building the images

Currently, an x86_64 host with binfmt setup for QEMU userland emulation is required to build the images. In addition, the Docker host and client must share the filesystem for the source directory containing the build scripts.

Note that building images launches a privileged container, in order to mount aufs layers.

Build all variants of the image for a specific architecture with:

./build.sh <repo> <architecture>
# e.g.: ./build.sh archlinux x86_64

During the build, the bootstrap environment and packages are cached. A script is provided to clean these intermediates:

./clean.sh

A full build of all tags and push can be performed with:

./all.sh <repo>
# e.g.: ./all.sh archlinux
# Will build and push: archlinux:x86_64-latest, archlinux:x86_64-base, etc.

Build process

The build process creates an intermediate image based on the Arch Linux bootstrap tarball, but with slight modifications. This image is primarily used to run the actual pacman command.

The bootstrap images are named archlinux-bootstrap:<version> and its rootfs is created by support/build-bootstrap.sh, which runs in an intermediate buildpack-deps:sid container. The build process automatically cleans up old bootstrap versions.

To build layers for a specific architecture, the bootstrap image is started with the support/bootstrap.sh script. This script performs steps similar to pacstrap, but calls pacman directly.

For each layer to build, pacman is invoked and an additional aufs branch is added. For each of the branches, tarballs are placed in target-*/_image. Layer metadata is written to target-*/_image/_meta.jsonl as one JSON object per line.

Once the tarballs are built, support/build-config.lua reads the metadata and builds the remaining image manifests and configs.

Finally, a tar is created for each layer and fed directly into docker load.

This process happens for each architecture, with specific settings in the target-* directories. Notably these are keyring settings in vars, and pacman configuration files.

All steps in the build process are verified with GnuPG. (This includes the ARM builds, which have signature verification enabled, unlike regular Arch Linux ARM installs.)

To-do

Add support for builds on non-x86_64 hosts. (ARM native builds.)
Prevent republish when there are no package changes.

stephank/docker-archlinux