Hello there,
after a big update yesterday, I was also greeted with the error message upon reboot:
Failed to start light display manager
I updated the Kernel (sudo mhwd-kernel -i linux510), but it did not help with the issue.
The file /var/log/Xorg.0.log contains error messages:
…
[ 5.684] (II) modesetting: Driver for Modesetting Kernel Drivers: kms
[ 5.738] (EE) open /dev/dri/card0: No such file or directory
[ 5.738] (WW) Falling back to old probe method for modesetting
[ 5.738] (EE) open /dev/dri/card0: No such file or directory
[ 5.738] (EE) Screen 0 deleted because of no matching config section.
[ 5.738] (II) UnloadModule: “modesetting”
[ 5.738] (EE) Device(s) detected, but none match those in the config file.
[ 5.738] (EE)
Fatal server error:
[ 5.738] (EE) no screens found(EE)
After many reboots I noticed, that the startup actually sometimes succeeds. In those cases the xorg-logfile does not contain errors about a missing /dev/dri/card0
A possible cause is presented in the ArchWiki:
The
amdgpukernel module is supposed to load automatically on system boot.
…
It is possible it loads, but late, after the X server requires it.
The wiki then links to the fix: Kernel mode setting - ArchWiki
In my case I added amdgpu to MODULES in the file /etc/mkinitcpio.conf and regenerated the initramfs (sudo mkinitcpio -p linux510).
Happy new year!