No password input field on lock screen

Reloading unity restores the password input on the login screen for me (Ubuntu 14.04 with a Nvidia GPU).

1. Switch to an alternate terminal using Ctrl+Alt+F1.

2. Reload unity with:

   nohup unity --replace &
   

3. Switch back to your graphical terminal using Ctrl+Alt+F7. You may have to wait several seconds if you see a black screen.

Unity sort of works after this but you can at least save your work in progress:

• The compiz grid plugin seems to think multiple monitors are now a single monitor.

• The global menu bar no longer works.

• Menus in window title bars no longer work (if enabled).

• Custom global keyboard shortcuts don't work.