VNC, Transparently

From Issue #93
January 2002

Jan 01, 2002 By Jeremy Impson

Software

Secure, transparent and ubiquitous desktops with VNC and OpenSSH, Part 1 of 2.

Configuring a VNC Server

The VNC server also must be running, and it must be configured to run your preferred window manager. This is accomplished by editing the file $HOME/.vnc/xstartup to call your preferred window manager. Use startkde & for KDE, gnome-session & for GNOME or fvwm2 & for FVWM2. Also, make sure you have run vncpasswd in $HOME/.vnc/passwd to create the password file.

Red Hat 7.1 provides an easy way to start up the VNC desktop at boot time. Use linuxconf to set the vncserver boot script (in /etc/init.d/vncserver) to come up at boot. The default bootscript, however, doesn't quite give me the flexibility that I'd prefer. Edit /etc/init.d/vncserver, looking for the line that says

"su - ${display##*:} -c \"cd && [ -f .vnc/passwd ]
&& vncserver :${display%%:*}\""

Change it to look like this:

"su - ${display##*:} -c \"cd && [ -f .vnc/passwd ]
&& vncserver ${ARGS} :${display%%:*}\""

Then edit /etc/sysconfig/vncservers so that it looks like this:

# The VNCSERVERS variable is a list of
# display:user pairs.
#
# Uncomment the line below to start a VNC server on
# display :1 as my 'myusername' (adjust this to your
# own). You will also need to set a VNC password;
# run 'man vncpasswd' to see how to do that.
#
# DO NOT RUN THIS SERVICE if your local area network
# is untrusted! For a secure way of using VNC, see
# <URL:www.uk.research.att.com/vnc/sshvnc.html>.
VNCSERVERS="1:jdimpson"
ARGS="-geometry 1024x768 -alwaysshared "

Change the value “1024x768” in ARGS to represent the size of your actual X desktop. Add any other VNC server arguments that you wish to this ARGS variable. Change jdimpson in VNCSERVERS to whatever user you wish to run the VNC Desktop. The value “1” in VNCSERVERS makes the VNC server run as display 1. You can have additional desktops come up like this:

VNCSERVERS="1:jdimpson 2:phred 3:sysadmin"

On a Red Hat system, make sure the VNC server is running by executing this:

/etc/init.d/vncserver start

At this point, you can connect to the VNC Desktop using any VNC client.

Configuring the Display Manager

On my Red Hat 7.1 system, I created a file called $HOME/.xsession. This file says which program, usually a window manager, should be run when I log in through a display manager. When logging in, the display manager checks for the existence of this file. If it exists, the display manager will then run the program listed in the file. The display manager considers this file to contain the command to start the user's desired window manager. Instead of running a window manager like GNOME or KDE, however, we'll run the VNC client. Edit $HOME/.xsession so that it looks like this:

exec vncviewer -passwd $HOME/.vnc/passwd
-fullscreen localhost:1

If you are using another Linux distribution, it is highly likely that the same mechanism will work for you, but you should double-check. One quick way to check is to put the line

exec fvwm2

in this file (assuming fvwm2 is loaded on your system). When logging in to the display manager, if fvwm2 starts up, then you have success. If not, you'll have to dive into the documentation for your system or the configuration file; try understanding what /etc/X11/xdm/Xsession does.

When you log in to the server using the display manager, it will be replaced by your chosen window manager running under the VNC server. If you have another computer on the same network, trying using the VNC client to connect to your server. You should see two copies of your desktop. When you move a window using one computer, you will see the window move on the other, too.

If, after logging into the display manager, the screen flickers and the display manager login banner returns, then something went wrong. Make sure vncserver is running, and make sure the .xsession file is correct.

Notice that in this setup you should not use any logout feature that may be part of your window manager. Doing so will end the VNC desktop, which is probably not what you want to do. Instead, just press Ctrl-Alt-Backspace to kill the X server. You'll see the display manager return to the screen. If you log back in, you'll be right where you left off. So you can turn the console over to someone else but not lose your desktop state.