RootFS generation

To make custom Xenia images, the tool foxbuild can be used on a Gentoo system/container or as its own container.

Xenia setup

As Xenia is immutable and it is advised to not install to the base system when necessary, distrobox will be used. This can also be followed on any system with distrobox.

First, setup a Gentoo distrobox and enter it:

distrobox create --root --image --name gentoo
distrobox enter --root gentoo

Setup the container:

emerge --sync

The remainder of this guide takes place from within the Gentoo distrobox.

foxbuild installation

First, install the Xenia overlay.

Next, allow for foxbuild to be emerged:

echo "xenia-tools/foxbuild **" >> /etc/portage/package.accept_keywords/foxbuild

Install foxbuild:

emerge foxbuild

Initial setup

Run the following commands:

mkdir -p /var/foxbuild/output
touch /var/foxbuild/output/Manifest.toml

Creating a root image

foxbuild pulls from a git repo to get the required files to build. First, we will use the existing repo that Xenia builds from.

Run foxbuild:


Configuration options will appear.


Set the git repo to pull from here. Here, we will use the default of


The git branch from the repo set above to use. Here, we will use the default of unstable.


Here, the target set to be built can be specified. This will typically be a spec file such as stage4-systemd.spec, but can also be a comma seperated list of spec files, changed to only rebuild spec files that have changed in the last commit and * to build all targets. We will leave this at the default stage4-systemd.spec.

Using a config file

foxbuild can also take a config file instead of running interactively.

To do this, write a config file, here called build.toml:

catalyst_repo = ""
git_branch = "unstable"
target = "stage4-systemd.spec"

Then, run foxbuild with -c specified:

foxbuild -c build.toml

Now, foxbuild will start setting up the build envionment, generating a Portage snapshot and downloading the required seed stage3 for the spec selected. It will also show where it is logging. To see the log in real-time, open another terminal and run tail -f on the log:

tail -f /var/foxbuild/stage4-systemd.spec.log

Testing the image

foxbuild creates a repo in /var/foxbuild/output. First, expose the repo over a web server:

cd /var/foxbuild/output
python3 -m http.server

Next, from the installer or using foxupdate on a Xenia system, set the repository to http://localhost:8000/ (or replace localhost with the IP/domain of the system hosting the repo).

Then, you can select the available targets that foxbuild has built.

Updating the build environment

foxbuild generates a Portage snapshot if there isn’t already one on the system, but doesn’t create a new one every time it is run. If the git_repo is changed, foxbuild will not pick this up until the build environment has been updated. To update the build environment, run foxbuild with -u:

foxbuild -uc build.toml

Customising the image

First, create a fork of the catalyst repo. Then, follow the customisation guide here to customise the root.

Once changes have been made, push them to the repo. Then, set the repository in foxbuild config to match the repo created.