Using VNC to Login

To run graphical applications on RCS systems remotely, the Virtual Network Computing (VNC) application is available and provides some advantages beyond using X Windows over SSH such as a detachable session and better performance over a slow speed connection. Here is basic set up information required for this approach.

***Important Note: Please follow all of these steps with each new VNC session.***

Step 1: Install VNC on your local system

There are multiple VNC viewer programs available with unique interfaces and features. The application on RCS systems is TigerVNC.

MAC users can use the built in Apple "Screen Sharing" as a VNC client and do not have to install an additional client.

After installing the software, make sure ports 5900 and 5901 are open to allow VNC traffic through your host firewall.

Step 2: Setup port forwarding over SSH for the VNC session

On Linux or MAC systems:

local$ ssh -L 5901:localhost:5901

On a Windows system:

Setup a SSH tunnel with PuTTY on Windows.

  1. On the left side of the PuTTY dialog box when you open PuTTY, choose Connection->SSH->Tunnels

  2. in Source Port enter 5901

  3. in Destination enter

  4. Click Add and you should see the following in the list of forwarded ports: L5901

Step 3: Connect to the remote system and start the VNC server

Log onto the remote system over SSH and specify the appropriate ports for VNC client (your local system) and server (remote system) communication.

Launch a VNC server instance on the remote system. The initial vncserver instance will prompt you for a password to protect your session. Subsequent launches of vncserver will use the same password and you will not be prompted for a password.

remote$ vncserver -localhost

You will require a password to access your desktops.

New 'remote:1 (username)' desktop is remote:1

Creating default startup script /u1/uaf/username/.vnc/xstartup
Starting applications specified in /u1/uaf/username/.vnc/xstartup
Log file is /u1/uaf/username/.vnc/remote:1.log

Step 4: Open VNC on your local system

  1. Launch Apple "Screen Sharing" on a MAC.

    The Apple "Screen Sharing" connect to server dialog can be accessed with {apple key} K or Finder - Go - Connect to Server. Use "vnc://localhost:5901" as the "Server Address".

  2. Launch VNC on Windows from the menu or a launcher icon.

    On Windows, the VNC application should have installed a launcher somewhere in the menus and may have also installed an icon on the desk or start bar depending on options you chose when installing. Use the menu or icon to start VNC.

  3. Launch Linux VNC viewer from the command line

    Launch your VNC viewer program and connect to host "localhost" and port 5901. The example below shows how to launch the client using TigerVNC.

    local$ vncviewer localhost:5901

If you are using the TigerVNC GUI, enter "localhost:5901" into the "VNC server:" box then click the "Connect" button. You will then be prompted for the password created in Step 2. If your local VNC client connects successfully, you will then see your desktop on the remote system.

Your circumstances might require the use of different ports due to firewall issues or if you are running more than one VNC server session on the remote system. (Other people on the system might be running their own sessions as well and occupying the ports.) If this is the case, you may need to specify port 5902 or 5903 or ... Add 5900 to the display number to determine the correct remote port to use.

To determine whether the VNC viewer has successfully connected, check the log file noted when vncserver was started on the remote system.

After starting the server, the option exists to log out and back in again using different port forwarding parameters.

Note that some VNC viewer programs can automatically set up the SSH port forwarding through a command-line flag such as "-via" or some option in a graphical configuration menu.

Step 5: When finished, close the VNC session

To close your VNC session, view the open sessions on the remote system, then close the appropriate one.

remote$ vncserver -list
TigerVNC server sessions:
:1                    252550
remote$ vncserver -kill :1


  1. Orphaned Session

    If a previous VNC session remains open on the remote system, that old session will need to be closed prior to establishing a new connection using the same port. To identify and kill the old session, first obtain the processID of the "Xnvc" process, then issue the kill command.

    remote$ ps -elf | grep username | grep Xvnc
    0 S username    236193      1  0  80   0 - 24842 poll_s Nov09 ?        
          00:00:10 /usr/bin/Xvnc :1 -desktop remote:1 (username) 
          -auth /u1/uaf/username/.Xauthority -geometry 1024x768 
          -rfbwait 30000 -rfbauth /u1/uaf/username/.vnc/passwd 
          -rfbport 5901 -fp catalogue:/etc/X11/fontpath.d -pn -localhost
    remote$ kill 236193
  2. Locked Session

    Depending on your desktop settings on the remote system, the X screensaver may kick in and lock the session after a period of inactivity. If this happens, you'll be prompted for a password that doesn't exist. The xlock process can be killed from the command line. We recommend disabling X locking in the VNC displayed desktop settings to avoid this happening.

  3. Banish Authentication Popup

    If you get a "Authentication is required to set the network proxy used for downloading packages" dialog box constantly opening, launch a Terminal Console and type gnome-session-properties and then uncheck the PackageKit Update Applet. You may need to restart your VNC session for this to take effect.

  4. Reset Server Password

    To change the VNC server password, use the 'vncpasswd' command on the remote system.

  5. More Information

    Run 'vncserver --help' and 'man vncserver' for more information on how to use the application.

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