Restart X session using Ctrl Alt Backspace in Ubuntu
You could reach to the point where nothing is responding in your session, and you have left without option except hard restart your computer, but always their was an option to restart the X session and go back to the login screen using a keyboard combination witch is Ctrl + Alt + Backspace .
To enable it in Ubuntu Unity just copy and paste the current line to your terminal :)
gsettings set org.gnome.desktop.input-sources xkb-options "['terminate:ctrl_alt_bksp']"
And you are done, you could save all your work and try it out.