The ctrl-alt-backspace key combination was used to restart X-server and was recently disabled because of a upstream (X.org) design decision:
The Ctrl-Alt-Backspace key combination currently "zaps" (hard-restarts) the X server, and thus loses any unsaved data in applications, etc. This key combination is also largely undocumented, so users (probably ex-Windows users) may press this key combination without expecting data loss. This spec proposes to follow upstream's lead and disable this key combination by default in order to prevent this usability issue from occurring in normal installs.
There are two ways of still using the Ctrl Alt Backspace behavior:Full story »