Could not create lock at /var/run/yum.pid: [Errno 28] No space left on device
df -Ph
Filesystem Size Used Avail Use% Mounted on
tmpfs 497M 497M 0 100% /run
du -h /run
447M    /run/systemd
du -h /run/systemd
447M    /run/systemd/sessions

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."

reboot
Filesystem Size Used Avail Use% Mounted on
tmpfs 497M 6.7M 490M 2% /run