gdm3 not starting on ubuntu 20.04

Question

I recently upgraded from Ubuntu 18.04 to 20.04 as I was having this issue as well (with a different error). I was hoping upgrading would fix it. After upgrading Ubuntu worked a few times but now it won't start. I've been trying for ages to fix this including un-commenting #WaylandEnable=false, however when I tried that the laptop wouldn't start at all and stayed on the line dev/sda1: clean, xxxxxx/xxxxx files, xxxxxxx/xxxxxxx blocks and wouldn't go any further.

It might help to know this is a very old laptop >10years dell xps. Ubuntu works fine when it starts and is the only OS installed.

The output of systemctl status gdm is (I am typing this so might be errors):

Started GNOME Display Manager.
gdm-launch-environment [963]: pam_unix(gdm-launch-environment:session): session opened for user gdm by (uid=0)
gdm3[958]: Gdm Display: Session never registered, failing
gdm3[958]: Child process -1011 was already dead.
gdm3[958]: Child process -1011 was already dead.
gdm-launch-environment [1324]: pam_unix(gdm-launch-environment:session): session opened for user gdm by (uid=0)
gdm3[958]: Child process -1346 was already dead.

I would really like to get this fixed as it is a laptop I use a lot. I also really quickly tried to install lightdm but ubuntu told me there isn't enough disk space in /var/cache/apt/archives (which I am pretty sure is untrue last I checked I had about 9GB free) but I can delete some stuff and install lightdm if that is the best fix.

Solution

I created the file /usr/share/gnome-session/sessions/gdm-shell.session containing:

[GNOME Session]
Name=Computer

and then I could use GDM3 as the session login manager again for the first time in years.

Comments

[vanadium]

Rather than upgrading, try reinstalling fresh: that way the new system will be optimally configured, not using settings anymore that are carried over by previous installations. If such problem then still persists, then you still can start debugging.

[danbeggan]

Thanks haven't tried this as I reinstalled Ubuntu. Good to have a workaround at least

[David]

Based on what was asked in the question how does this help?

[Andrés Esteban Sampaulo]

It could be happen after upgrade or install process. May it help. Regards