is anybody aware of a method to move an application from one X session to a different X session ?

more specifically, i work with several VNC screens on the same workstation which i access and display remotely. now, instead of opening n-times the same application (let's say emacs) in each VNC screen i would like to move the emacs application to the VNC screen 'of focus' = the VNC screen i work in at a given moment. as said, we speak here about the same workstation (a VPS) which runs numerous VNC screens (virtual X sessions), so it's the same machine (CPU) the emacs application runs on in my scenario.

i read about xpra, shifter, GuiEvite and other tricks - which one is generic enough to work also on a slackware box ?

when i don't need X i switch to tmux which is great as i can access the same tmux session as many times i want - which is kind of equivalent to what i want to achieve here in X : to see the content of a running application in any VNC screen i want without having to restart it.

any input appreciated !

can anybody help here ? i couldn't get xpra installed on my slackware 14.2 box, so i decided to go with x2go where the installation this time worked fine using SlackBuilds scripts.

but now even the simplest "single application" using /usr/bin/xterm doesn't want to show up on my fvwm screen when testing x2go with host:localhost or with host:<local_IP>... it just pumps my CPU load up to the sky while the x2go client window remains grayed out till i kill all x2go processes. x2go doesn't seem to like known_hosts file and also doesn't recognize my passwordless ssh setup. needless to say that ssh and rsa keys are in place and work smoothly including passwordlessly. the x2go server appears to be running with a x2gocleansessions process on the same localhost.

what do i do here wrong ? any suggestions ?

I don't think it's possible with X. But it might be in the near future, because the replacement for X is coming and it can do much more. I seem to remember reading about what you're trying to do, and it will be possible.

wow, a replacement for X - huge news - thanks for your reply !

in any case, i gave up on getting xpra and x2go running on by slackware boxes as i found another solution for my problem :

the reason i was looking into such a xdummy solution as i didn't know how to rescale the page or virtual desktop size in fvwm inside a running VNC session. it turned out to be a simple button press à la "Restart fvwm". so, now i need only one single fvwm VNC screen which i can scale and adjust and re-use for any remote connection without losing running X applications - just as i do it with tmux on the terminal level.

Do you have to have several different VNC screens or could you do with multiple VNC views of a single much larger screen? Because if you do the latter, then you can simply drag the window across the larger screen.

I personally use x11vnc on the server side, which serves up the display on my graphics card (which has the advantage of 3d graphics hardware acceleration, for what it's worth, as well as clean integration with the local desktop). Then, I use a command like the following to serve up a portion of the screen canvas:

So, if I set up a 2048x1536 screen on VGA (even if the attached monitor or null cable can't display it), I could serve up four separate 1024x768 VNC sessions with:

interesting thought, similar to what x0vncserver would do. i used x11vnc years ago but i wasn't aware of the -clip option.
in fact, i use for work a beautiful 4K Philips monitor, which would allow to load quite a few instances of such x11vnc 'clips' at once.
thank you for this suggestion !