files

The files module can be used to copy directories from files/ to any location in your image at build-time, as long as the location exists at build-time (e.g. you can’t put files in /home/<username>/, because users haven’t been created yet prior to first boot).

The files module cannot write to directories that will later be symlinked to point to other places (typically /var/) by rpm-ostree.

This is because it doesn’t make sense for a directory to be both a symlink and a real directory that has had actual files directly copied to it, so the files module copying files to one of those directories (thereby instantiating it as a real directory) and rpm-ostree’s behavior regarding them will necessarily conflict.

For reference, according to the official Fedora documentation, here is a list of the directories that rpm-ostree symlinks to other locations:

/home/ → /var/home/
/opt/ → /var/opt/
/srv/ → /var/srv/
/root/ → /var/roothome/
/usr/local/ → /var/usrlocal/
/mnt/ → /var/mnt/
/tmp/ → /sysroot/tmp/

So don’t use files to copy any files to any of the directories on the left, because at runtime rpm-ostree will want to link them to the ones on the right, which will cause a conflict as explained above.

Example configuration

modules:
  - type: files
    files:
      - source: system   # copies `files/system/*` (* means everything inside it) into your image's root folder `/`
        destination: /
      - source: my-image/usr   # copies `files/my-image/usr/*` to `/usr/` inside the image
        destination: /usr