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debos(1) debos(1)


debos - Debian OS images builder


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.


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 more meant as a tool-chain to make common actions trivial while providing enough rope to do whatever tweaking that might be required behind the scene.

debos expects a YAML file as input and will run 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 customize 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
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:


Official debos container is available:

docker pull godebos/debos

See docker/ ( for usage.


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 suites your needs go get -u /opt/src/gocode/bin/debos --help


The following example will create a arm64 image, install several packages in it, change the file /etc/hostname to “debian” and finally make a tarball.

{{- $image := or .image "debian.tgz" -}}
architecture: arm64

- action: debootstrap
suite: "buster"
- main
- non-free
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 this name, you can provided a different name for the variable image like this:

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


This example builds a customized image for a Raspberry Pi 3.


debos read a predefined list of environment variables from the host and propagates it to fakemachine. The set of environment variables is defined by environ_vars on cmd/debos/debos.go. Currently the list of environment variables includes the proxy environment variables as documented at:

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 enviroment variable, or in other words, to prevent an environment variable to be propagated to fakemachine, use the same syntax without a value. debos accept multiple -e simultaneously.


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. Prefer using an address that is valid on your network. debos will warn if 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.


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 virtualmachine, for more information see the documentation under the fakemachine repository (

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