Comment 36 for bug 1280300

The issue still persists in Ubuntu 20.04. Running mate with lightdm and light-locker configured to lock-on-suspend enabled. After resuming, the desktop contents before suspend are visible for roughly 5 seconds, before the lock screen appears.

As this is absolutely unacceptable in terms of security and privacy, I'm using the following script to suspend (thanks to gethin for the pointer!):

#!/bin/bash
mate-screensaver-command -l
systemctl suspend