Ubuntu 18.04 refuses to use lock screen

Solution 1:

Try the default lock screen (screen lock) key combination on Ubuntu 18.04 and Fedora 28 first:

• Super+L (that is Windows+L). On terminal try xdg-screensaver lock.

• If that did not work then check whether the following command returns true:

   gsettings get org.gnome.desktop.lockdown disable-lock-screen 
  

• If the command above returned true then do the following:

   gsettings set org.gnome.desktop.lockdown disable-lock-screen false 
  

Check whether the lock screen (screen lock) works now.

Had a similar problem and this helped me solve my issue.

Solution 2:

Here's one thing you can try.

1. First of all, make sure gnome-screensaver is installed

   sudo apt install gnome-screensaver
   

2. Try to issue lock command in the terminal:

   gnome-screensaver-command -l
   

   then see if there's any text output in the terminal, such as "Screensaver is not running!"

   If it's the case, run the daemon:

   gnome-screensaver &
   

   then retry the previous lock command. Let's hope it will work now.