Comment 6 for bug 1716639

Same here. Ubuntu 18.04 on Dell E7440.
I was forced to switch to switch to lightdm, because gdm3 simply won't start.

Here're some logs:
Jul 06 00:04:07 HOSTNAME dbus-daemon[2769]: [session uid=116 pid=2769] Activating service name='org.gnome.ScreenSaver' requested by ':1.12' (uid=116 pid=2771 comm="/usr/lib/gnome-session/gnome-session-binary --auto" label="unconfined")
Jul 06 00:04:07 HOSTNAME org.gnome.ScreenSaver[2769]: Unable to init server: Could not connect: Connection refused
Jul 06 00:04:07 HOSTNAME gnome-screensav[2777]: Cannot open display:
Jul 06 00:04:07 HOSTNAME dbus-daemon[2769]: [session uid=116 pid=2769] Activated service 'org.gnome.ScreenSaver' failed: Process org.gnome.ScreenSaver exited with status 1
Jul 06 00:04:07 HOSTNAME gnome-session[2771]: gnome-session-binary[2771]: CRITICAL: Unable to create a DBus proxy for GnomeScreensaver: Error calling StartServiceByName for org.gnome.ScreenSaver: GDBus.Error:org.freedesktop.DBus.Error.Spawn.ChildExited: Process org.gnome.ScreenSaver exited with status 1
Jul 06 00:04:07 HOSTNAME gnome-session-binary[2771]: CRITICAL: Unable to create a DBus proxy for GnomeScreensaver: Error calling StartServiceByName for org.gnome.ScreenSaver: GDBus.Error:org.freedesktop.DBus.Error.Spawn.ChildExited: Process org.gnome.ScreenSaver exited with status 1