Ubuntu – Ubuntu 20.04 not work lock screen after update


I had Ubuntu 18.04 LTS and I upgraded to 20.04. The lock screen to ask password after some time it was working perfectly. After the upgrade stopped working. I tried to go to Ubuntu settings and check if it’s enabled and yes is enabled to lock screen ifor 5 minutes but the screen is never locked again after the upgrade. Any idea how to fix it?

The computed is a Lattepanda 864s. But that is not an issue. It was working everything perfect but after the update to the 20.04 stopped working. All the rest of the system works very well. It’s just is not,locking the screen to give password.

Thank you

Best Answer

  • I had this problem as well, and after not finding a solution on S.O. / AskUbuntu, I went over to Luanchpad to poke around for related bugs or questions.

    It seems this issue is specific to LightDM, and is perhaps part of a bigger security issue, and switching to GnomeDM (gdm) fixes the issue. Here are the steps I followed:

    Install GDM if not already installed:

    sudo apt-get install gdm3

    Switch from LightDM to GDM3:

    sudo systemctl status display-manager

    Reset/reinstall some stuff:

    sudo dpkg-reconfigure lightdm
    sudo apt install --reinstall ubuntu-session

    Reboot, and you should be good. Note that I don't know if switching back from GDM to LightDM will maintain the fix. From the links below it sounds like it may be part of a broader security issue and the Super+L keyboard shortcut is disabled for a reason.

    More links to background:
    Can't lock screen with shortcut on Ubuntu 20.04 gnome

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