Some times I want to just shut the computer down rather than to enter the password and continue. Even if that would be someone else willing to shut my computer down while I'm away he should better be able to do this peacefully rather than by just switching the power off. Can I add shutdown to the lock screen menu for such cases?
Update for those saying it's there: I use the standard Ubuntu 15.10 (not any kind of "spin-off" like KUbuntu nor a derivative like Mint or ElementaryOS) and all I have got in the upper-right corner gear menu is "Switch Account", "Guest Session" and "Suspend".
sysrq
keys , right ?