VNC HowTo

VNC allows you to open a graphical session with a remote computer. The session offers the complete display of a login session, as if you were physically sitting in front of the computer. VNC uses efficient compression techniques to send graphics over the network. These two facets of VNC make it more functional, and more efficient than running remote X Windows applications. You can read more about VNC at www.realvnc.com .

Installing VNC and SSH

1. If you are using Mac OS X or Linux, you likely have ssh already installed.
   An ssh client for Windows can be obtained from http://www.ssh.com/support/downloads/secureshellwks/non-commercial.html .

2. Obtain a VNC client for your local computer. A client for Windows or Linux may be downloaded from http://www.realvnc.com/download.html . Since the RealVNC folks don't develop a VNC client for Mac OS X, you can download a port of the client from another developer at http://sourceforge.net/projects/cotvnc/ . The name of the port is called "Chicken of the VNC."

Starting a VNC Session and connecting to it

1. Connections in VNC are established via a port number (or optionally, a display number). The display number, e.g. :12, is allocated dynamically when you start a VNC server session. The relationship between port and display is display+5900=port. You need to know the VNC display number so that you can connect from your client machine. There are 3 steps to establish a VNC session.
• Login to melodic.

  In a Windows cmd window type:

  ssh -l <userid> melodic.ucdavis.edu

  where <userid> is your login ID.

• Check to see if you already have an Xvnc server running by typing.

ps ax | grep Xvnc | grep <userid>
  
  where <userid> is your login ID. If there is an Xvnc server running under your userid, this string of ps and grep commands will return one or more lines listing the running Xvnc processes. On each line you will see Xvnc followed by :x, where x is your display number. Xvnc is the unix process that runs the VNC server session. Now that you have the display number you can either kill your Xvnc session or connect to it from your VNC client. If the ps and grep commands given above don't return any information, then you need to start a VNC server.
  
• If you are starting a VNC session on a computer in the Janata lab, do the following step:
  • If you need to start a VNC server, type :

    melodic> runvnc
5909
    
    The number that appears (in this case 5909) is the port number that your instance of the VNC server will be using. Your display number is 5909-5000, i.e. 9.

• otherwise
  • type:

  vncserver -geometry 1200x800 -depth 16 :xx
  
  where xx is the display number. Geometry defines the size of the VNC window (in pixels) and can be set to whatever you want. Depth defines the number of bits used to represent color.

• Exit the melodic shell. Log back into melodic, but this time use the command:

  ssh -l <userid> -L 59xx:melodic:59xx melodic.ucdavis.edu

  where <userid> is your login ID, and xx is your display number, in this case 09. This step established port forwarding.

• Click on the VNC client icon on the desktop, and connect to localhost:x, where x is your display number. If it is less than 10, then it is just a single digit, i.e. 9 instead of 09. Enter your password for your VNC sessions and you should be all set. If you are using Chicken of the VNC on a Mac, then only type localhost into the host field and x (your display number) into the display field.

• If you are using putty, establish an ssh connection with port-forwarding. Click here for pictures of the configuration screens you need to set. Keep in mind that your port numbers will be the 59xx number.
  
2. REMEMBER: Everytime you type 'runvnc' you will start a new VNC server, and you could end up with multiple VNC sessions. This could lead to confusion on your part, so avoid having more than one VNC session open. In principle, you can start a VNC server session and keep it open for months, never having to start another VNC session.

Connecting to an existing VNC session

• From Linux
  • Establish an ssh connection with port forwarding as described above.
  • Type:
    vncviewer <hostname> via=<hostname> :xx
    where xx is the display number, hostname is computer you are connecting to. You can optionally add Shared=1 to the command if you want to share access to the same VNC session with other computers.
    
• From Mac OS X
  • See the instructions above. Check the Shared box if you would like to share the same VNC session with other computers.

Leaving or stopping a VNC session

1. To leave your VNC session, just kill the client window on your local machine. This will terminate your connection to the VNC server but will leave your VNC server session intact so that you can connect to it at a later time.
   
2. To terminate your VNC server session, login to melodic and issue the following command:

   runvnc -kill :xx

   where xx is your display number.

3. If you have forgotten what your display number is (or to check how many VNC server sessions you might be running), type

   ps ax | grep Xvnc

   The command 'ps' will generate a list of processes you are running. The '|' sign will "pipe" the output of the ps command to the 'grep' command which will search for and display those lines containing the expression "Xvnc". On those lines, you will see Xvnc followed by :x, where x is your display number. Xvnc is the unix process that runs the VNC server session. Now that you have the display number you can either kill your Xvnc session or connect to it from your VNC client.
   
   You can further narrow the list of Xvnc process to show only yours by typing

ps ax | grep Xvnc | grep <userid>
   
   where <userid> is your login ID.