How to fix Fedora 19 “unlockable lockscreen” bug

The problem

So you’re using Fedora 19, you update yum one day, and a few days later you find some strange lockscreen behaviour. The look of your lockscreen has changed – a different background colour, clock size, and password box positioning. So far so good. But wait, why does a second lockscreen appear after you shoo away the first? Why can’t you type your password to the input field? Why can’t you get back to your desktop and unsaved work?

The explanation

This bug affects people who have the Cinnamon desktop installed in a session using Gnome. Maybe you’ve installed Cinnamon desktop environment to try it out in the past, maybe other users on your machine are using it for their sessions, or maybe you’re using an app that relies on Cinnamon and has previously installed it as a dependency. My reason for having it is Nemo – the fork of Nautilus file manager, which is the default way to browser folders on Gnome 3, and which dropped a bucket load of functionality with a recent update, causing me and many others to move to the Cinnamon-oriented aquatically-named fork.

Cinnamon has it’s own lockscreen and this conflicts with Gnome 3′s own. Basically the “unlockable lockscreen” issue is caused by these two screensaver apps competing for your attention and your password, and between them they manage to prevent you from unlocking either one or both of them at all. Although this bug has apparently been fixed for Fedora 20, we Fedora 19 users are still suffering. Indeed yesterday I lost a whole page of notes to this bug, when I had to use ctrl+alt+backspace to force a session logout (you can enable this shortcut using Gnome Tweak Tools GUI; instructions reside in the Fedora Forums).

The workaround

These instructions should save you when the bug has taken effect and you need to unlock your screen. A fix to stop the problem occurring in the first place is underneath.
Open a new virtual terminal using Ctrl+Alt+F2, login using your usual username and password, and execute:
killall cinnamon-screensaver
Make sure it worked by ensuring that this command doesn’t find the process we just killed is still running:
sudo ps -e | grep cinnamon-screensaver
And now go back to your original X-based session using Ctrl+Alt+F1

The solution

Remove Cinnamon’s screensaver. Unfortunately this will remove the Cinnamon desktop entirely, including any Cinnamon-based apps you have installed, like Nemo. Well Nemo, so long and farewell. I look forward to your smarter file sorting and expanded file-handling extension set in Fedora 20. As root:
yum remove cinnamon-screensaver
Then log out and in again (Cinnamon’s screensaver should no longer auto start with the session).
Good luck!