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While my Ubuntu 20.04 (Focal) PC was at the lock screen, I inadvertently left an object on the keyboard for over an hour. It repeatedly pressed who knows how many buttons. When I found it, it was repeatedly pressing Esc over and over again.

When I tried logging into my account, it gave a generic "Authentication Error" kind of message, and would not allow me to type in a password. I assumed this was an account timeout / lockout issue, so I waited several hours and tried again — to no avail. It showed the same error, and acted the same way.

I was able to login on a terminal (Ctrl+F4) with the same account, and I successfully restarted gdm (following this excellent answer, but substituting systemctl instead of service). That removed the error message and allowed me to type my password; however, it locked up on a black screen with no error message for at least 20 seconds.

Next, I tried restarting the PC, which resulted in the screen transitioning (as if to log me in), but transitioning to the very same login screen.

Finally, I went to the terminal (Ctrl+F4), and ran startx, which did start the GUI. It prompted me for my password for the login keyring, which did not complain about an authentication error.

Generally, it works okay, although some of my settings seem to be missing or changed. The dock is now smaller, and only shows up when I press Super (Win).

Next, I logged out from there, and tried logging in the normal, GUI way again (Ctrl+F1), but it still didn't work, and transitioned to the login screen again.

What's going wrong here? My account does not appear to be locked, but the GUI login method won't work.

Where can I look for more information? Here's the result of running tail -f /var/log/syslog during one of my attempts to login normally.

The only fishy thing I see is the line

Jan  9 10:17:38 asrock gdm3: GdmDisplay: Session never registered, failing
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  • Do you have (or can you create, via the terminal) another user account you can try?
    – steeldriver
    Commented Jan 9 at 22:15
  • Read man 5 shadow, the "encrypted password" section: A password field which starts with a exclamation mark means that the password is locked. The remaining characters on the line represent the password field before the password was locked.. Read man sudoedit to see how to edit /etc/shadow.
    – waltinator
    Commented Jan 10 at 1:32
  • @steeldriver I created a new account graphically (since startx is working), and was able to login successfully. It brought up the account setup wizard that Ubuntu normally has, and looked like a normal desktop.
    – jpaugh
    Commented Jan 10 at 5:55
  • @waltinator If it were an account issue, then how am I able to login via the terminal? I think it's more likely that GDM got screwed up because of something else.
    – jpaugh
    Commented Jan 10 at 5:57

1 Answer 1

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I was able to workaround this issue by using a different display manager. The easiest way to configure the display manager is during the install process.

Typing sudo apt install lightdm will install the lightdm display manager, and — during the install process — it will ask you which display manager you want to use by default. Just pick the new one, and reboot the computer

This also (thankfully) restored my dock.

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