Whoo! For some reason, cinnamon freezes extremely often (multiple times a day) on my desktop, and I had been resorting to “ctrl-alt-f1” to get to a terminal and running “killall cinnamon-session”, which brings me back to login screen. Fortunately, there is a better solution, aka “ctrl-alt-esc”.
Here’s the relevant excerpt from the Cinnamon blog (http://segfault.linuxmint.com/2015/06/cinnamon-2-6/):
In case of a freeze or if you need to restart Cinnamon for any reason, you can now do so via a keyboard shortcut. The default key combination is Ctrl+Alt+Escape. Pressing this combination of keys restarts nemo and cinnamon-settings-daemon in case they had crashed, and launches a brand new instance of the Cinnamon desktop. Unlike Ctrl+Alt+Backspace which terminates your session and brings you back to the login screen, Ctrl+Alt+Escape simply restarts Cinnamon itself, which means your session is exactly as it was, you don’t lose any work and all your windows and applications remain open.