Unfortunately, the lock-screen utility
Ctrl+Alt+L shortcut uses--will also activate the blank-screen "screensaver" whenever it is told to lock the screen.
The trick then is to "fake" a keystroke immediately after the screen is locked to get rid of the blank-screen and leave the lock-screen on. We'll do this with xdotool, a small command-line utility which allows automation of keyboard and mouse clicks/movements.
sudo apt-get install xdotool
Paste the following to a file in your home directory, such as
xdotool sleep 1 key Ctrl
- This simply locks the screen normally, but one second later, sends a dummy "Ctrl" keystroke to "unblank" the screen.
- Make the file executable with
chmod +x ~/locknoblank.sh
Go to System Settings...Keyboard...Shortcuts and remove
Ctrl+Alt+L as the lock-screen shortcut so we can re-use it for our custom command. Click on "System" on the left sidebar, then click on the right of "Lock Screen" where it says "Ctrl+Alt+L"; it will now say "New Accelerator...". Press Backspace to remove the shortcut.
Now go to Custom Shortcuts on the left, and add a shortcut, naming it whatever you want to with the command as
/home/username/locknoblank.sh. Click Apply, then click on its right where it says "Disabled" to get "New Accelerator", and press
Close System Settings, and you're done!
To prevent reactivation of the screensaver (idle timeout)
Open a terminal, and type/paste:
gsettings set org.gnome.desktop.session idle-delay 7200
This sets the screensaver idle activation time to 2 hours (or 7200 seconds). You can set it to anything you want; the default is 600.