xdmcp

[Jim McQuillan]

LDM is really nothing more than a GUI wrapper front-end to ssh.  It then 
tunnels all X traffic through SSH.

Edubuntu can also support XDMCP.  You just need to enable remote 
connections via XDMCP in the "login screen' config applet.

There's good reasons for both LDM and XDMCP.  You'll find that with LDM, 
tunneling through SSH, that you'll run out of server horsepower much 
earlier.  It seems people get up to about 30 clients and then the 
performance degrades too much.  Whereas with XDMCP, you can run over 100 
clients on the same server hardware.  All that encrypting of the data 
imposes quite a penalty on performance.

Jim McQuillan
jam at Ltsp.org


Gavin McCullagh wrote:
> On Fri, 01 Dec 2006, Pan, Richard wrote:
>
>   
>> Is anyone running their edubuntu server as an XDMPC server?  I've been 
>> testing it out at my school.  It seems like an interesting way to deliver 
>> linux specific applications to users while retaining the mac os and 
>> windows os at my school.  Does anyone have any feedback on doing this?
>>     
>
> Edubuntu uses something quite similar to XDMCP for its thin clients.
> People have used XDMCP for quite a long time for thin clients.  However,
> one of the drawbacks of it is that all mouse-clicks, keystrokes and window
> images get sent in the clear across the network.  This means someone can
> snoop them.  
>
> Instead edubuntu uses a tunnelled ssh session.  ldm (a display manager)
> runs on the thin client, you type your username to it and it starts an X
> server and initiates an ssh connection to the server running an xsession
> displayed locally.  This means all network traffic is encrypted.  There is
> a cpu cost in the encryption but it's not too high as a cheap but
> relatively secure cypher has been carefully chosen for ldm.
>
> I'm not sure how hard porting ldm to windows would be.  It's python so it
> should be feasible -- particularly in cygwin.
>
> If you are not concerned about the security, I've used XDMCP and it works well.
>
> Another alternative might be NX, which is available freely, you can get a
> client for windows and it usually runs over ssh.  NX is mainly created to
> run over very limited bandwidth (eg a DSL server from home).
>
> 	http://www.nomachine.com/
>
> Gavin
>
>
>