Gnome - Lock screen - What's this button?

In lock screen of Debian or Ubuntu Gnome, I got the following button:

It looks like a "pause" icon. When I clicked on it , I got a black screen and no way to get back to the work space except of restarting. It seems to similar to a hibernate mode, but from hibernate mode I can restore everything by pressing a key.

Solution 1:

Sorry, but what it normally does is to hibernate the system.

On my system (Ubuntu GNOME) this works perfectly. It should turn off your monitors after time but let yourself into the system again after one click on a keyboard or mouse button (movement). This looks like an error in your System.

Solution 2:

I had the same problem, it was pretty annoying. You need to change the settings in the terminal by:

sudo -H gedit /etc/systemd/logind.conf

Your current setting is this:

HandleLidSwitch=suspend

To fix this behaviour, change suspend to either hibernate or poweroff.

Credits: http://tipsonubuntu.com/2018/04/28/change-lid-close-action-ubuntu-18-04-lts/