Below are some useful command for VNC server
 
1. Start a vncserver
     Command : vncserver
      You will prompted to provided the password.
 
2. Changing the password for VNC
     Command: vncpasswd : n (e.g. vncpasswd : 1)
      n- The port on which the vnc is running.
 
3. Killing a VNC server
     Command: vncserver -kill :n (e.g. vncserver -kill :n)
      n- The port on which the vnc is running.
      As a good practice we should use above command to clear vnc server. Killing a OS    level process will not release the lock on the vnc port which was used previously for running vnc . So next time we will not be able to start on that locked vnc port.