man systemd-sysextman systemd-sysext -- System extensions are searched for in the directories /etc/extensions/, /run/extensions/ and
/var/lib/extensions/. The first two listed directories are not suitable for carrying large binary images,
however are still useful for carrying symlinks to them. The primary place for installing system extensions is
/var/lib/extensions/. Any directories found in these search directories are considered directory based
extension images; any files with the .raw suffix are considered disk image based extension images. When
invoked in the initrd, the additional directory /.extra/sysext/ is included in the directories that are
searched for extension images. Note however, that by default a tighter image policy applies to images found
there, though, see below. This directory is populated by systemd-stub(7) with extension images found in the
system's EFI System Partition.