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debos(1) debos(1)


debos -  Debian OS images builder



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


Application Options:

  -t, --template-var=   Template variables
      --debug-shell     Fall into interactive shell on error
  -s, --shell=          Redefine interactive shell binary (default: bash)
      --scratchsize=    Size of disk backed scratch space
  -e, --environ-var=    Environment variables



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
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:


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.


fakemachine at