OK, this is a cascade of issues and I don't know what to do anymmore.
- My screen was staying black for too long (maybe 10 seconds) after logging in on Ubuntu 18.04 with regular gnome3 desktop. So I decided to check my graphics drivers. I had nvidia 390 drivers and I read online there were some issues with them, so I tried to switch back to the 340 drivers which were apparently available in "additional software".
- That didn't work. I rebooted and the display still took a long while to come on. I checked which drivers were in use, and it actually reverted to the Nouveau drivers. Apparently there was a problem with 'installing/selecting' the 340 drivers because some file could not be modified because of permission issues. I thought "hey OK but if it only reverted to Nouveau just now it might boot fine next time" so I rebooted again.
- That didn't work either and now the screen just remains black permanently (can't even try to log in). So I try to change TTY to fix this graphical problem.
- That doesn't work either, because for some reason after about 3 seconds every time the TTY is automatically switched back to... TTY7 I guess? and for 0.5 seconds the following text is shown (see image) before it blanks again.
- As a last resort I would just reinstall the whole OS BUT I can't do that either because I have no USB stick (it broke) and no CD drive. I installed from an ISO on disk which I loaded manually, but I cant do that again because well, the GRUB menu timer is set to 0 seconds. And I can't change that easily because every 3 seconds my TTY changes back to TTY7 which is blank and useless.
Please help, I'm all out of ideas. What can I do? I'd prefer very much to just revert to the nvidia 390 drivers and just accept the long login time. Is there a command for that which doesn't take painstakingly long to type while you constantly have to switch TTYs?
UPDATE: OK, suddenly my TTY stopped switching automatically and I could restore usage of the Nouveau drivers (apparently somehow they weren't really selected after all) using information from this post: How to change proprietary video driver using the command line?. I'm now back at square 1 but at least I can still use my computer.
Option "NoAccel" "True"
in the xorg.conf device section for your NVIDIA graphics card (the one which uses the "nouveau" driver). That's all there is to it. – Nimrod Nov 30 '18 at 20:48