Customising the rootfs

You can customise the rootFS with different packages, included files, USE flags - even different init systems. This page will give a small overview of what you can change.



This page will reference files and directories relative to your catalyst directory. On foxbuild, this will be a fork of the catalyst repo.


This guide uses the spec name stage4-openrc.spec as a placeholder for any spec name. Replace it with the spec being edited.


To add, change or remove packages in Xenia, edit stage4-openrc.spec:


You can add your own packages here. Make sure they are spelled correctly and you include the package category.

USE flags and other portage config

Global USE flags

To add a global USE flag, edit stage4-openrc.spec:


You can add USE flags here as well as removing USE flags with -.

Package specific USE flags

To add package specific USE flags, edit config/package.use/stage4:

sys-boot/grub device-mapper

You can add USE flags here the same way you do in a typical package.use. You can also change package masks, licenses and keywords here (for example to enable testing on a specific package).

Adding services

To add services to Xenia (the equivalent of rc-update), edit stage4-openrc.spec:


You can specify the service here alongside the runlevel in the format service|runlevel.

On systemd specs, this is defined in the fsscript. See below for more details.

Custom shell script

To run custom script at the end of the build process, edit


You can add your own custom script at the end of this file.

Filesystem overlay

To add arbitrary files to Xenia, such as new backgrounds or configuration for packages, open overlay and add any files you want here. For example, to edit /etc/fstab, edit overlay/etc/fstab.

Multiple overlays can be added. See stage4-systemd.spec for an example. It applies both the common overlay that is shared amongst all spec files and a GNOME specfic overlay.

These files will be added after catalyst has completed emerging the system.

Submitting changes to Xenia

If you make a change and you want it merged into Xenia, please follow these guidelines:

  • Have a defined purpose to all your changes and reasoning for why it should be added to the base system

  • Make sure added files, packages and USE flags are not specific to your system

  • Put the services, packages and global USE flags in alphabetical order

You can then submit an MR to the catalyst repository with your changes.