rootfs.md

Getting a rootfs

There are many ways to produce a directory to pass to the rootfs config field, here are a couple of potential solutions.

From a container image

OCI images can be turned into tarballs which can be extracted into a rootfs. For example:

❯❯ mkdir $rootfs_dir && cd $rootfs_dir
❯❯ cat > Containerfile
FROM docker.io/library/debian
RUN apt update
RUN apt install -y qemu-guest-agent

❯❯ podman build -t deb-qga  # Docker would work exactly the same
❯❯ podman export -o deb.tar $(podman create deb-qga)
❯❯ tar xf deb.tar
❯❯ rm Containerfile deb.tar

Using mkosi

mkosi is a more advanced tool for building OS images, as well as just producing a rootfs it can build full disk images with a bootloader, plus many other features. You'll need to refer to the full documentation to really understand mkosi, but here's a minimal example. This will only work if you host system has apt (on Ubuntu you'll also need to install the debian-archive-keyring package), otherwise you'll need to adapt it for your host distro or run it in a container.

mkosi.conf:

[Output]
Format=directory

[Distribution]
Distribution=debian
Release=bookworm

[Content]
Packages=
        mount
        qemu-guest-agent

Then from the directory containing that file, run mkosi -f. This should produce a directory named image that you can use for your rootfs config field.