bdebstrap

bdebstrap is an alternative to debootstrap and a wrapper around mmdebstrap to support YAML based configuration files. It inherits all benefits from mmdebstrap. The support for configuration allows storing all customization in a YAML file instead of having to use a very long one-liner call to mmdebstrap. It also layering multiple customizations on top of each other, e.g. to support flavors of an image.

Usage examples

Minimal Debian unstable tarball

This example shows how to use a small YAML configuration to build a minimal Debian unstable tarball. Assume following configuration is stored in examples/Debian-unstable.yaml:

---
mmdebstrap:
  keyrings:
    - /usr/share/keyrings/debian-archive-keyring.gpg
  mode: unshare
  suite: unstable
  target: root.tar.xz
  variant: minbase

Then the tarball can be generated by running

$ bdebstrap -c examples/Debian-unstable.yaml --name example1
$ ls example1/
config.yaml  manifest  root.tar.xz

Debian live system

This example shows how to use a YAML configuration to build a Debian 11 (bullseye) live system. Assume following configuration is stored in examples/Debian-bullseye-live.yaml:

---
mmdebstrap:
  architectures:
    - amd64
  cleanup-hooks:
    - cp /dev/null "$1/etc/hostname"
    - if test -f "$1/etc/resolv.conf"; then cp /dev/null "$1/etc/resolv.conf"; fi
  customize-hooks:
    - cp --preserve=timestamps -v "$1"/boot/vmlinu* "$1${BDEBSTRAP_OUTPUT_DIR?}/vmlinuz"
    - cp --preserve=timestamps -v "$1"/boot/initrd.img* "$1${BDEBSTRAP_OUTPUT_DIR?}/initrd.img"
    - mkdir -p "$1/root/.ssh"
    - upload ~/.ssh/id_rsa.pub /root/.ssh/authorized_keys
    # Set 'debian' as root password. Create a secure root password with "openssl passwd -6 $password"!
    - chroot "$1" usermod -p
      '$6$ojM9XUz3tre8c/Ah$gBBIjy5zyhFMtJnQmK3YYXL8APHk9gTz.hlQP6AZnLV79bkQddUqOnTpcltEW.7l/OAq4u5.SMgDq1LL8u6BM/' root
  keyrings:
    - /usr/share/keyrings/debian-archive-keyring.gpg
  mode: unshare
  packages:
    - init
    - iproute2
    - less
    - libpam-systemd  # recommended by systemd and needed to not run into https://bugs.debian.org/751636
    - linux-image-cloud-amd64
    - live-boot
    - locales
    - openssh-server
  suite: bullseye
  target: root.squashfs
  variant: minbase

This example assumes that ~/.ssh/id_rsa.pub exists, because it will be copied into the image to /root/.ssh/authorized_keys to allow SSH access using the user's SSH key.

The squashfs image can be generated by running

$ bdebstrap -c examples/Debian-bullseye-live.yaml --name example2
$ ls example2/
config.yaml  initrd.img  manifest  root.squashfs  vmlinuz

The kernel and initrd are copied out of the squashfs image using customize hooks to allow them to be used directly by QEMU. To launch this image locally with QEMU, the root.squashfs image needs to be provided by a HTTP server:

$ python3 -m http.server -b localhost --directory example2 8080

This command exposes the generated image via HTTP on localhost on port 8080. QEMU can be started passing the TCP traffic on port 8080 to the webserver:

$ cd example2
$ qemu-system-x86_64 -machine accel=kvm -m 1G -device virtio-net-pci,netdev=net0 -monitor vc \
    -netdev user,id=net0,hostfwd=tcp::2222-:22,guestfwd=tcp:10.0.2.252:8080-tcp:localhost:8080,hostname=debian-live \
    -kernel ./vmlinuz -initrd ./initrd.img -append "boot=live fetch=http://10.0.2.252:8080/root.squashfs quiet"

To print the output on the launching terminal, add -nographic -serial stdio to the QEMU command line and console=ttyS0 to the -append parameter. Once the virtual machine is started, it can be accessed via SSH:

$ ssh -oUserKnownHostsFile=/dev/null -oStrictHostKeyChecking=no -p 2222 root@localhost

Hooks

bdebstrap ships a bunch of hook scripts that can be used to configure the produced chroot. The environment variable BDEBSTRAP_HOOKS can be used to refer to the path to the hook script. Available hooks:

• disable-units
• enable-units

Disable/enable services

The disable-units and enable-units hook script can be used to disable/enable services. Either service names or full systemd unit names should be specified. Example:

---
mmdebstrap:
  customize-hooks:
    - $BDEBSTRAP_HOOKS/disable-units "$1" apt-daily.timer cron
    - $BDEBSTRAP_HOOKS/enable-units "$1" systemd-timesyncd
  suite: bullseye
  target: root.tar
  variant: important

Prerequisites

• Python >= 3
• Python modules:
  • ruamel.yaml
• mmdebstrap (>= 0.6.0)
• pandoc (to generate the man page)
• squashfs-tools-ng (>= 0.8) for building squashfs images. Older versions of squashfs-tools-ng throw errors (bug #31) and loose the security capabilities (bug #32).

The test cases have additional Python module requirements:

• black
• flake8
• isort
• pylint
• shellcheck

Thanks

I like to thank Johannes Schauer for developing mmdebstrap and for quickly responding to all my bug reports and feature requests.

Contributing

Contributions are welcome. The source code has some test coverage, which should be preserved. So please provide a test case for each bugfix and one or more test cases for each new feature. Please follow How to Write a Git Commit Message for writing good commit messages.

Creating releases

This project uses semantic versioning. To create a release, increase the version in setup.py and document the noteworthy changes in NEWS.md. Then commit the changes and tag the release:

git commit -sm "Release bdebstrap $(./setup.py --version)" NEWS.md setup.py
git tag v$(./setup.py --version)

The xz-compressed release tarball can be generated by running:

name="bdebstrap-$(./setup.py --version)"
git archive --prefix="$name/" HEAD | xz -c9 > "../$name.tar.xz"
gpg --output "../$name.tar.xz.asc" --armor --detach-sign "../$name.tar.xz"