From Settings -> Privacy, I got

  • Automatic Screen lock -> turned on
  • Lock Screen on Suspend -> turned on

None of them locks my screen. But the manual lock option works fine. (I did get some error message about Auto-lock while installation)

Any thoughts on how to fix it? And I'm using lightdm instead of gnome-gdm3

  • Auto-lock? Is this a package you installed? – UnKNOWn May 17 '20 at 15:32
  • No. I meant the installation of ubuntu-20.04. And got an error message about auto-lock functionality but didn't understand. – MI Nayan May 19 '20 at 7:35
  • error msg you got during lightdm installation?? – UnKNOWn May 19 '20 at 7:41
  • Got error while upgrading to ubuntu-20.04 from 19.10. And by default I use lightdm. – MI Nayan May 20 '20 at 7:17
  • I am trying gnome-screensaver with my updated ubuntu-20.04/gnome/lightdm. – veo May 31 '20 at 8:01

Screen lock is disabled by default with lightdm on Ubuntu 18+ due security issues.

check more here:

You can check you display manager with: sudo systemctl status display-manager

If you still want to lock your screen with lightdm - you can use dm-tool lock. Also you can add it to keyboard shortcut as command (e.g. Super+L).

Switching to gdm3 helped: sudo dpkg-reconfigure gdm3

  • Switching to gdm3 worked. Be aware though, when you receive an error message that the switch was not successful, you need to restart. That's what did it for me. – SlideM Jul 23 '20 at 16:42

What's the timeout set to? Previous experience may point to a very unexpected hardware related cause which I call "mouse jitter": It could be that your mouse has a slight malfunction and 'jiggles' by itself a bit, causing your computer to stay awake. Try unplugging your mouse and see what gives.

  • I don't think so. – MI Nayan May 19 '20 at 7:32

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