Seen on ubuntu 22.04 after do-release-upgrade the xdm Login Manager fails to start,
cause a old xdm.pid file hangs from last shutdown on “/run/xdm.pid”.
XDM prevent start on a old PID File!!
Workaround edit Roots crontab to purge it:
sudo crontab -e
@reboot rm -rf /run/xdm.pid > /dev/null 2>&1
quit and save with “:wq!”
..reboot