Each deployment is grouped in exactly one "osname". From above, you can see that an osname is physically represented in the /ostree/deploy/osname directory. For example, OSTree can allow parallel installing Debian in /ostree/deploy/debian and Red Hat Enterprise Linux in /ostree/deploy/rhel (subject to operating system support, present released versions of these operating systems may not support this).

Each osname has exactly one copy of the traditional Unix /var, stored physically in /ostree/deploy/osname/var. OSTree provides support tools for systemd to create a Linux bind mount that ensures the booted deployment sees the shared copy of /var.

OSTree does not touch the contents of /var. Operating system components such as daemon services are required to create any directories they require there at runtime (e.g. /var/cache/daemonname), and to manage upgrading data formats inside those directories.