xlock locks the X server till the user enters their pass-
word at the keyboard.  While xlock is running, all new
server connections are refused. The screen saver is disabled.
The mouse cursor is turned off.  The screen is blanked and a
changing pattern is put on the screen.  If a key or a mouse
button is pressed then the user is prompted for the password
of the user who started xlock.

If the correct password is typed, then the screen is
unlocked and the X server is restored.  When typing the
password Control-U and Control-H are active as kill and
erase respectively.  To return to the locked screen, click
in the small icon version of the changing pattern.