[Fixed] Can't log in after suspending Xubuntu 20.04

Published: 2021-01-01

Tagged: learning linux

(It's funny that this will be my first post of 2021)

My laptop at home is a Thinkpad T470 running Xubuntu 20.04, upgraded from 18.04 after that was upgraded from 16.04. Everything worked fine, including the printing service(!), except...

Except I couldn't log in after suspending the system. I just refrained from ever using the suspend feature. Until today.

Here's how the problem manifested:

1. Hit the suspend button from the GUI.
2. After a few seconds, screen goes blank and the power button begins pulsing slowly, signalling the machine is suspended.
3. Press the power button, get a log in screen. It has a password input and three buttons: switch user, cancel, and unlock.
4. Enter password, hit unlock. Screen goes blank for a second.
5. I'm back at the prompt, but now I can't input anything into the password field.

Here's what a I tried:

1. Trigger the bug. Hit ctrl+alt+F3 to get a terminal. Turn on tmux and tail the following logs: /var/log/syslog, /var/log/auth.log, /var/log/lightdm/seat0-greeter.log, and /var/log/lightdm/lightdm.log. See a few warnings and errors, investigate, but come up with nothing related to my problem.
2. Remove lightdm-gtk-greeter and lightdm-gtk-greeter-settings: apt-get remove lightdm-gtk-greeter lightdm-gtk-greeter-settings. Trigger bug: same thing happens. Except now the login prompt looks different. Eh.
3. Trawl through launchpad bugs and ubuntu forums and notice someone having a similar problem with light-locker and xscreensaver. Decide to uninstall light-locker and reinstall xfce4-screensaver: apt-get remove light-locker xfce4-screensaver && apt-get install xfce4-screensaver. Trigger bug, input password and... success!.

I'm not sure what was the exact problem was, but I strongly suspect that it has something to do with light-locker. Anyway, hope this helps anyone else that gets stuck on this issue.