This service won't use much resources, but it's certainly nicer to see
it attached th the user's slice along with user@.service, so that
everything we run for a specific user is properly bound into one unit.
We use systemd-user-sessions.service as barrier when to allow login
sessions. With this patch user@.service is ordered after that too, so
that any login related code (which user-runtime-dir@.service is) is
guaranteed to run after the barrier, and never before.
Unfortunately this needs a new binary to do the mount because there's just
too many special steps to outsource this to systemd-mount:
- EPERM needs to be treated specially
- UserRuntimeDir= setting must be obeyed
- SELinux label must be adjusted
This allows user@.service to be started independently of logind.
So 'systemctl start user@nnn' will start the user manager for user nnn.
Logind will start it too when the user logs in, and will stop it (unless
lingering is enabled) when the user logs out.
Fixes#7339.
Lennart Poettering