Overlay Filesystems

An Overlay Filesystem allows the contents of one directory to be overlaid on top of another. This means that Everest can be installed without modifying the base Celeste install, and without needing a second copy of Celeste.

Mounting a filesystem on linux usually requires superuser permissions, which would require entering the root password after every reboot. This is rather cumbersome, so a good alternative is to add an entry to ‘/etc/fstab’ for the mount point. With the ‘x-systemd.automount’ option provided by systemd, the filesystem will only be mounted when it is accessed.

If an overlay cannot be mounted without superuser permissions, an attempt will first be made to use an Unprivileged User Namespace. This can be used to create a container that has superuser privileges that are still isolated from the rest of the system.