GDM shows black screen with blinking white cursor
After booting, GDM may present you with a black screen with a blinking white cursor in the top left. This may be caused by GDM starting up before the graphics drivers are fully initialized. One possible workaround is to start KMS early. Another possible workaround is to edit the systemd service and either set its type to “idle” or add a small delay:
[Service] ExecStartPre=/bin/sleep 2
If a longer delay is required, increase the delay time.
to do so:
The easiest way to do this is to run:
sudo systemctl edit gdm.service
This opens the file
/etc/systemd/system/unit.d/override.conf in your text editor (creating it if necessary) and automatically reloads the unit when you are done editing.