[CLUE-Tech] ssh and xwindows

[David Anselmi]

Jeff Cann wrote:
> Here's a cool, automatic trick that may not be well-known.
> 
> If I have my DISPLAY enviromental variable set and my x windows server set to 
> accept connections from remote servers (e.g., $ xhost +) when I ssh into 
> another server, SSH automatically sets DISPLAY back to the originating host.  
[...]
> Here's a simple example.  Note that in an insecure environment, you probably 
> want to pass arguments to xhost.  See the man page for xhost.
> 
> $ echo $DISPLAY
> :0.0
> 
> $ xhost +
> access control disabled, clients can connect from any host

I don't have a way to check at the moment, but the "xhost +" shouldn't 
be required and the X connection should be secure if the client and 
server allow X forwarding (and perhaps the X server allows TCP 
connections)(see ForwardX11 in the man pages).

The $DISPLAY that ssh sets up on the server is to a local (to the 
server) port.  The data the server sends there (display for the server's 
X application) gets forwarded over the ssh connection (encrypted) to the 
client.  On the client it is passed to the X server and looks like it is 
local to the client.

ssh can do this for TCP connections in general.  The X forwarding is the 
same thing, with automatic management of $DISPLAY.

Dave