start or stop a VNC server

-kill :display#
       This  kills  a  VNC  desktop  previously started with vncserver.  It does this by killing the Xvnc
       process, whose process ID is stored  in  the  file  "$HOME/.vnc/host:display#.pid".   It  actually
       ignores  anything preceding a ":" in its argument.  This can be useful so you can write "vncserver
       -kill $DISPLAY", for example at the end of your  xstartup  file  after  a  particular  application
       exits.