Transfer display of active windows remotely

[Matthieu Herrb]

Magnus Kessler wrote:
> On Saturday 11 October 2008, Prasad H.L. wrote:
>> This is what I have in mind.
>>
>> - Consider display :0 on machine 1 (m1) and display :0 on machine 2 (m2).
>> - Let us say, a process 'p1' running under privileges of user 'u' opens a
>> window on :0 of m1. - I do an 'ssh -X u at m1' in xterm on :0 of m2 and
>> login to m1.
>> - Now, from that xterm window, is there any way by which I can make that
>> window of process 'p1' appear on :0 of m2.
>>
>> This kind of situation regularly occurs to me and some of my friends. We
>> have multiple terminals at our disposal. On one terminal, I start some
>> xterm which is, let us say, showing output of some process. I go to some
>> other department in the institute and do an ssh to that terminal. Now, I
>> have no way of seeing what is going on in that xterm. Well, this is a
>> simple example, of course.
> 
> This particular use case, seeing the terminal output of a process on a 
> different terminal, can be achieved quite easily using "screen" [0]. No 
> support from X required at all.
> 
> In a first terminal (or even on the console without any X) run screen. Then 
> run any non-graphical process in the screen session. When you move to a 
> different computer, log into the first one through ssh and grab the screen 
> session (screen -dr). You will see the output of the still running process 
> there.
> 
>> Another example (though childish). Consider a case where I have a browser
>> window with many tabs open in it, the window being displayed on :0 of m1.
>> I would like to export it to :0 of m2 when I go and sit in front of m2.
>> Before closing ssh on m2, I re-export the window back to :0 of m1 and
>> then quit the ssh. Such a feature would be really great to have. Since,
>> any way, currently the only dependency on the remote machine is that it
>> should have an X server running, I believe this feature should be
>> implementable if not already present.
> 
> Have you looked into NX [1]? NX can be considered the "screen" for running X 
> sessions. I usually run an NX session on one machine (in the background, 
> without any access to the graphics hardware), then connect to it using the 
> nxclient software from either machine on the network. I can disconnect from 
> a running session and pick it up later from somewhere else.
> 

In addttion to NX or other similar setups (using Xvnc for instance), Let 
me add that there is nothing anymore in the X protocol that prevents 
doing what Prasad H.L. suggests directly (without a proxy).

It is an application (or maybe toolkit) level problem: handle the event 
that the X display connection is being closed better than by killing the 
application and allow it to reconnect to a new display later (through 
some communication protocol).

The gnuserv/gnuclient code in XEmacs for instance implements that (with 
some bugs and limitations, but it works for me everyday).
I've heard rumors that Gtk and/or Qt have support for this kind of 
things. It's just application that fail to implement the required support.

With Xft and XRandR the 2 major difficulties that may have prevented 
more applications to implement that in the past are gone.

It would definatly be nice to see more apps supporting that, but I don't 
thing that Xorg can do a lot in this area.
-- 
Matthieu Herrb