“Oh No” screen, and can’t startx after Ubuntu 24.04 upgrade from 22.04

If you get the "Oh No" screen during a major version upgrade, likely the upgrade was aborted, and you will need to play with apt to complete the upgrade process.

Very frequently, when the video driver does not load correctly on nvidia cards, the partially initialized GUI hangs and leaves the keyboard in an unusable state, so the ctrlaltFkey sequence doesn't work (actually, even caps lock wouldn't work). There are several ways to get out of this, but the easiest is to add nomodeset in the kernel command line from grub. (I have detailed that process at Why Ubuntu 24.04.1 only works on on one computer, but shows black screen after installation on several other computers? )

One possible cause for this is that your video driver did not build correctly (or was interrupted and didn't finish), and by changing video driver versions, you have forced it to rebuild successfully.

There are two possible routes to get past the next error. You can look for a log file (likely in your home directory) to find out what is crashing when you attempt to log in and then fix that. (If you find more errors this way that you can't correct, add them to the question.)

Alternately, with prior knowledge of how you got in this state, you can try to repair it. With the assumption this was caused by an aborted upgrade, you can complete the upgrade with dpkg --configure -a followed by apt full-upgrade and fix errors and repeat until everything finishes without error and it says there are no updates to install. (That might have fixed the video driver too.)

Since you say you are getting to the login prompt now, there are a few more possibilities.

• Possibly your desktop GUI got (partially?) uninstalled, and something like apt install ubuntu-desktop may fix it.

• Possibly even though your GUI is now working at the login prompt, it isn't actually working well enough to support gnome because you still have the wrong video driver. It may be possible to install a non-gnome desktop or failsafe GUI to test this. However if nvidia-smi sees your video card then this is probably not the issue.

• You may have something corrupt in your user profile that is crashing when you log in. The easiest way to test this is to log in as a different user and see if it's just your account. (Maybe create a temporary account to test?) If you confirm it is your account, or don't have another account to try, you can try renaming the configuration directories. Something like:

  mkdir oldconfig

  mv .gnome* .local oldconfig/

Note that this is destructive and may damage other parts of your account profile, but is reversible.

Destroying your user profile config is kind of a last resort. It would be better to dig through config files and find the actual error unless you have prior knowledge that your profile might have gotten corrupted.

First a recap of the issue:

1. accepted System upgrade from 22.04->24.04 via UI. There were no errors, but at the end before reboot my background went black.
2. After reboot went straight to "Oh No" Screen of death.

Logged in as root via recovery menu (press escape during boot up)

Assumed the issue was nvidia drivers, spent a long time trying all sorts of options, and blacklisting nouveau via configs and kernel parameters. It was not nvidia driver issue, nvidia-smi worked but it was confusing since the Xorg logs would frequently say things about loading Nouveau, even though it was blacklisted etc. Some sort of driver conflict like that seemed a reasonable explanation but this was a goose chase: 560 drivers are working for the RTX 3060, and I tried to create new users to login with but that was no help.

Solution:

1. log in as root with network enabled (or if you can get to a log in with ctl atl f3 just do that, i couldnt)
2. install lightdm
3. edit /etc/gdm3/custom.conf and uncomment WaylandEnable=true
4. install or reinstall gnome-desktop, genome-session, ubuntu-desktop
5. reboot
6. hopefully the login GUI shows up
7. using a mouse that works (i had to plug one in as my trackpad wouldnt click, and couldnt find a keyboard way) change the log-in session to Gnome-Wayland
8. If you see a black screen with a little rectangle on the upper left, dont worry, you are in Gnome but with a blank background!
9. right click and select a background photo
10. reboot
11. now selecting "ubuntu-desktop on wayland" should work.

Now everything basically looks the same as it did in 22.04 except there is a trashcan icon with an x through it on my desktop complaining about some permissions thing...shrugs

Not 100% sure that this was fixed by changing the background image in gnome, but i tried multiple times to login to ubuntu-wayland only to get sent into the Oh No screen before I made that change. I was actually planning on just settling with Gnome3, but decided to try one last time after I couldnt get the dash to show up on my desktop, and it worked...