|Filesystem| Size|Used|Avail|Use%|Mounted on |---|---|---|---|---||---| tmpfs|497M|497M|0|100%|/run

TrevorH: "It would appear that updates to systemd now require a reboot to avoid this sort of problem and others related to it. The problem appears to be a known one upstream and newer systemd versions have been fixed - it's to do > with losing its dbus connection."