Remote assistance for X

Warren Block wblock at
Sat Jan 2 05:58:49 UTC 2010

On Fri, 1 Jan 2010, Karl J. Runge wrote:
> On Fri, 1 Jan 2010, Warren Block <wblock at> wrote:
> Here are some examples that should work, I provide "prompt>" to indicate
> which machine the command is run on (and I skip your -c preference):
>   supportee_host> ssh -t -N -f -L 5500:localhost:5500 $supporter_host && \
>                   x11vnc -display :0 -connect_or_exit localhost:0 -rfbport 0
> which should be the same as:
>   supportee_host> x11vnc -display :0 -proxy ssh://$supporter_host \
>                   -connect_or_exit localhost:0 -rfbport 0
> i.e. x11vnc has a built-in -proxy that already does what you want it
> to do; it runs ssh(1) for you:
> Note how I use -connect_or_exit instead of -connect to try to avoid
> problems if the connection fails:
> I also use the '-rfbport 0' described there to prevent x11vnc from listening
> for any connections (which I think is what you want.)
> Aside: Originally I thought you could ssh into supportee_host, for anyone
> looking to do that here is the analogous command:
>   supporter_host> ssh -t -N -f -R 5500:localhost:5500 $supportee_host \
>                   x11vnc -display :0 -connect_or_exit localhost:0 -rfbport 0

Yes.  In fact, I first tried the x11vnc_ssh script and it worked great. 
The only catch is that it needs ssh access into the supportee machine.

[SSL mode for x11vnc]

>> That looks more elegant.  Are the security and speed comparable to ssh?
> Speed shouldn't be a problem; I believe both ssh and 'x11vnc -ssl' use
> OpenSSL for encrypting the session traffic.  If a machine is *really*
> slow the choice of encryption cipher may be noticable (I don't see a
> big effect even on a 300MHz test machine I have.)

I've tried it now and it does just what is needed for my setup!

Finally, a little feedback:

On a Windows Vista system, AVG screamed that the netcat.exe from was a virus (don't think it is, just 
mentioning it).  The TightVNC server on that Vista machine will connect 
with the FreeBSD ssvncviewer, and the ssvncviewer console window shows 
status information, but no graphic window opens on the FreeBSD system.

The FreeBSD TightVNC vncviewer opens a window but has real trouble 
keeping the display updated, no doubt due to Vista. Finally, the 
UltraVNC server with special Vista video drivers works usably with 
ssvncviewer.  Can SSL be used with a Windows VNC server?

x11vnc talking to ssvnc-gui works noticeably better than all of those 
combinations.  Thanks for your work and your help!

-Warren Block * Rapid City, South Dakota USA

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