Comment # 5 on bug 934901 from Marcus R�ckert

1. as dimstar already pointed out gdm.
2. i checked /var/log/zypp/history after it killed my X session and the last
package installed was systemd
3. for testing i just logged in remotely to my laptop and ran: systemctl
try-restart systemd-logind.service

same result X session is gone. and even worse GDM does not even come up
properly afterwards.