Remove old temporary snapshots, but only at boot. Ideally we'd have
"self-destroying" btrfs snapshots that go away if the last last
reference to it does. To mimic a scheme like this at least remove the
old snapshots on fresh boots, where we know they cannot be referenced
anymore. Note that we actually remove all temporary files in
/var/lib/machines/ at boot, which should be safe since the directory has
defined semantics. In the root directory (where systemd-nspawn
--ephemeral places snapshots) we are more strict, to avoid removing
unrelated temporary files.
This also splits out nspawn/container related tmpfiles bits into a new
tmpfiles snippet to systemd-nspawn.conf
Given that this is also the place to store raw disk images which are
very much bootable with qemu/kvm it sounds like a misnomer to call the
directory "container". Hence, let's change this sooner rather than
later, and use the generic name, in particular since we otherwise try to
use the generic "machine" preferably over the more specific "container"
or "vm".
Create /var/lib/containers so that it exists with an appropriate mode. We want
0700 by default so that users on the host aren't able to call suid root
binaries in the container. This becomes a security issue if a user can enter a
container as root, create a suid root binary, and call that from the host.
(This assumes that containers are caged by mandatory access control or are
started as user).
Management of /var/cache/man should move to the distribution package
owning the directory (for example, man-db). As man pages are a
non-essential part of the system and unnecessary for minimal setups,
there's no point in having systemd ship these lines.
Distribution packages should make sure the appropriate package for their
distribution adopts this line. Ideally, the line is adopted by the
upstream package.
For Fedora I have filed this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1110274
Lennart Poettering