I recently upgraded my laptop from Ubuntu 17.04 to 18.04. It worked perfectly well and I have been using it without any problem, but yesterday I issued
sudo apt upgrade and it upgraded some packages.
Then I restarted the PC and it didn't boot up again. After displaying the Ubuntu logo I get a screen like below and after flashing several times it freezes.
Note that the message on the bottom line is changing for each restart. I am able to start a
tty session there log into my account.
normal boot messages usually covered by splash screen
To my knowledge, the problem is
gdm3 (GNOME display manager) fails to start, since when I issue
sudo systemctl restart gdm3 the screen flashes several times and again stays in tty session.
Can anyone suggest a solution to this without complete reinstallation of the system?