debos - Debian OS image builder

Synopsis

debos [options] <recipe file in YAML>
debos [--help]

Application Options:

  -b, --fakemachine-backend=   Fakemachine backend to use (default: auto)
      --artifactdir=           Directory for packed archives and ostree repositories (default: current directory)
  -t, --template-var=          Template variables (use -t VARIABLE:VALUE syntax)
      --debug-shell            Fall into interactive shell on error
  -s, --shell=                 Redefine interactive shell binary (default: bash) (default: /bin/bash)
      --scratchsize=           Size of disk backed scratch space
  -c, --cpus=                  Number of CPUs to use for build VM (default: 2)
  -m, --memory=                Amount of memory for build VM (default: 2048MB)
      --show-boot              Show boot/console messages from the fake machine
  -e, --environ-var=           Environment variables (use -e VARIABLE:VALUE syntax)
  -v, --verbose                Verbose output
      --print-recipe           Print final recipe
      --dry-run                Compose final recipe to build but without any real work started
      --disable-fakemachine    Do not use fakemachine.

Description

debos is a tool to make the creation of various Debian-based OS images simpler. While most other tools focus on specific use-cases, debos is designed to be a toolchain making common actions trivial while providing enough rope to do whatever tweaking which might be required behind the scenes.

debos expects a YAML file as input and runs the actions listed in the file sequentially. These actions should be self-contained and independent of each other.

Some of the actions provided by debos to customise and produce images are:

• apt: install packages and their dependencies with 'apt'
• debootstrap: construct the target rootfs with debootstrap
• download: download a single file from the internet
• filesystem-deploy: deploy a root filesystem to an image previously created
• image-partition: create an image file, make partitions and format them
• ostree-commit: create an OSTree commit from rootfs
• ostree-deploy: deploy an OSTree branch to the image
• overlay: do a recursive copy of directories or files to the target filesystem
• pack: create a tarball with the target filesystem
• pacman: install packages and their dependencies with pacman
• pacstrap: construct the target rootfs with pacstrap
• raw: directly write a file to the output image at a given offset
• recipe: includes the recipe actions at the given path
• run: allows to run a command or script in the filesystem or in the host
• unpack: unpack files from archive in the filesystem

A full syntax description of all the debos actions can be found at: https://godoc.org/github.com/go-debos/debos/actions

Installation (Docker container)

An official debos container is available:

docker pull godebos/debos

See docker/README.md for usage.

Installation from source (under Debian)

sudo apt install golang git libglib2.0-dev libostree-dev qemu-system-x86 \
     qemu-user-static debootstrap systemd-container
export GOPATH=/opt/src/gocode # or whatever suits your needs
go install -v github.com/go-debos/debos/cmd/debos@latest
/opt/src/gocode/bin/debos --help

Simple example

The following example will create an arm64 image, install several packages in it, change the file /etc/hostname to "debian" and finally make a tarball of the complete system.

{{- $image := or .image "debian.tgz" -}}

architecture: arm64

actions:
  - action: debootstrap
    suite: bookworm
    components:
      - main
      - non-free-firmware
    mirror: https://deb.debian.org/debian
    variant: minbase

  - action: apt
    packages: [ sudo, openssh-server, adduser, systemd-sysv, firmware-linux ]

  - action: run
    chroot: true
    command: echo debian > /etc/hostname

  - action: pack
    file: {{ $image }}
    compression: gz

To run it, create a file named example.yaml and run:

debos example.yaml

The final tarball will be named "debian.tgz" if you would like to modify the fileame, you can provided a different name for the variable image like this:

debos -t image:"debian-arm64.tgz" example.yaml

Other examples

Example recipes are collected in a separate repository:

https://github.com/go-debos/debos-recipes

Environment variables

debos reads a predefined list of environment variables from the host and propagates them to the fakemachine build environemnt. The set of environment variables is defined by environ_vars in cmd/debos/debos.go. Currently the list of environment variables includes the proxy environment variables documented at:

https://wiki.archlinux.org/index.php/proxy_settings

The list of environment variables currently exported to fakemachine is:

http_proxy, https_proxy, ftp_proxy, rsync_proxy, all_proxy, no_proxy

While the elements of environ_vars are in lower case, for each element both lower and upper case variants are probed on the host and if found propagated to fakemachine. So if the host has the environment variables HTTP_PROXY and no_proxy defined, both will be propagated to fakemachine respecting the case.

The command line options --environ-var and -e can be used to specify, overwrite and unset environment variables for fakemachine with the syntax:

$ debos -e ENVIRONVAR:VALUE ...

To unset an environment variable, or in other words, to prevent an environment variable being propagated to fakemachine, use the same syntax without a value. debos accepts multiple -e simultaneously.

Proxy configuration

While the proxy related environment variables are exported from the host to fakemachine, there are two known sources of issues:

• Using localhost will not work from fakemachine. Use an address which is valid on your network. debos will warn if the environment variables contain localhost.

• In case you are running applications and/or scripts inside fakemachine you may need to check which are the proxy environment variables they use. Different apps are known to use different environment variable names and different case for environment variable names.

Fakemachine Backend

debos (unless running debos with the --disable-fakemachine argument) creates and spawns a virtual machine using fakemachine and executes the actions defined by the recipe inside the virtual machine. This helps ensure recipes are reproducible no matter the host environment.

Fakemachine can use different virtualisation backends to spawn the virtual machine, for more information see the fakemachine documentation.

By default the backend will automatically be selected based on what is supported by the host machine, but this can be overridden using the --fakemachine-backend / -b option. If no backends are supported, debos reverts to running the recipe on the host without creating a fakemachine.

Performance of the backends is roughly as follows: kvm is faster than uml is faster than qemu. Using --disable-fakemachine is slightly faster than kvm, but requires root permissions.

Benchmark times for running pine-a64-plus/debian.yaml on an Intel Pentium G4560T with SSD:

Backend	Wall Time	Prerequisites
--disable-fakemachine	8 min	root permissions
-b kvm	9 min	access to /dev/kvm
-b uml	18 min	package user-mode-linux installed
-b qemu	166 min	none