This started happening after 2018-07-23 updates. I have Debian Testing with xfce4. I had some custom configs, though it might be the problem, but I was already prepared for OS reinstall, so I did just that. It didn't help. Login loops back after successful login. `~/.xsession-errors` contains something about "X server already running on display :0", "Fatal IO error 11 (Resource temporarily unavailable) on X server :0.0". Note this happens on clean Debian Testing install with all partitions formatted, choosing XFCE4.
However I have also tried installing only base system, and then `apt-get --no-install-recommends install xfce4-session lightdm xinit xserver-xorg-video-nouveau xserver-xorg-input-libinput` and I could login to GUI but it was completely empty without panel, clear desktop, mouse couldn't even select empty space. After adding some more XFCE4 packages on VT1 and reboot I'm stuck again on lightdm login. Same problem if running apt-get without --no-install-recommends flag and nothing else on base system installation. Links to possibly same problem in OpenSuse: https://forums.opensuse.org/showthread.php/532345-login-screen-coming-up-again-and-again-(maybe-lightdm-)-after-a-recent-daily-update https://forums.opensuse.org/showthread.php/532318-X-server-fatal-errors Karolis M.
