Comment # 6 on bug 939594 from Egbert Eich

gdm in SLE12 still starts the Xserver as root. gdm in 42 doesn't do that any
more but relies on systemd-logind to make sure access to devices is possible.
This is nothing we can resolve from the X side.

I assume that starting the Xserver as root (runlvl 3 -> log into text console
as root -> '/usr/bin/Xorg -retro') works - Olaf?