Usage of vnc

A. Server machine

  1. First set a password with vncpasswd. The password is stored encrypted in the .vnc directory in the file passwd.
  1. Start a vnc session with e.g: 
	vncserver -geometry 1600x1200 -depth 24
You can choose a different window size (e.g. 1024x768), the depth specifies the color depth.
  1. The session can be killed with:
	vncserver -kill :1
The :1 indicates that the session made use of screen 1. This is the default value you get when starting a session. If there is another user running VNC you will get another screen number, at the start of the VNC session the number is specified. Note that the server continues to run at logout. At any time one can disconnect from the server while the session continues to run, the connection can be re-established again later and from another client machine as needed.
  1. After starting the session the X window manager specified in ~/.vnc/xstartup will be started. The xstartup file could contain this:
        #!/bin/sh
	xrdb $HOME/.Xresources
	startxfce4 &
The xstartup file as listed above causes starting of the XFCE environment. Replace "startxfce4 &" by "startkde &" to start up the complete KDE environment, by "exec gnome-session &" to start up GNOME or by "mvm &" and "konsole &" to start the Motif Windows manager and the KDE terminal (on a solid grey background if "xsetroot -solid grey" is added to the xstartup file)
  1. In case of problems with fonts add this to the xstartup file: 
	xset +fp /usr/share/X11/fonts/misc
        xset +fp /usr/share/X11/fonts/75dpi
         The paths specified may need to be adapted, the paths above are correct for SLC5.

B. Client machine

     vncviewer xxx:N
with xxx the name of the machine to connect to and N the screen number
In all cases the machine running the server should be specified as well as the screen number.

C. Tunneling

A direct connection to the server program may not be possible, in that case tunneling via ssh can be used. This also provides more safety, as the connection via ssh is encrypted. To make clear how this works consider the following example: a VNC connection to a machine with name tarfa should be established via a login server with name "login" in the domain nikhef.nl:

Login to login.nikhef.nl as follows:
     ssh -l username -L 5901:tarfa.nikhef.nl:5901 login.nikhef.nl
Then ssh to tarfa and open a VNC session there, as explained under A. Next connect your viewer to localhost and everything should work, if the VNC session is on screen 1. If it is on screen N instead of 5901 5900+N (that is the result of adding N to 5900) should be specified in the ssh command shown above. Note that under Windows the ssh command cannot be given directly, one can use either a special ssh program or install Cygwin and use the Cygwin console to give this command. MacOS X comes with a VNC server which uses screen 0, to switch the server on go to "System Preferences", "Sharing" and select "Screen Sharing".

D. Useful scripts

On the server machine:

startvnc: starts a vnc sesssion
stopvnc: stops vnc session usng screen 1
stopvncn N: stops vnc screen N

Contents of these scripts (geometry defines the maximum size if the window in pixels, depth refers to the number of bits used for defining colors):
startvnc: vncserver -geometry 1880x1160 -depth 24
stopvnc: vncserver -kill :1
stopvncn: vncserver -kill :$1

On the client machine:

For setting up a tunnel to Nikhef:
vnc tarfa: sets up a tunnel to machine tarfa, screen 1, localhost screen 1
vncn tarfa N: sets up a tunnel to machine tarfa, screen N, localhost screen N
vnc2 tarfa: sets up a tunnel to machine tarfa, screen 1, localhost screen 2

Contents of these scripts:
vnc: ssh -l user -L 5901:$1.nikhef.nl:5901 login2.nikhef.nl
vncn ssh -l user -L 590$2:$1.nikhef.nl:590$2 login2.nikhef.nl
vnc2: ssh -l user -L 5902:$1.nikhef.nl:5901 login2.nikhef.nl