Sharing an X server (session) across computers

kvmxorg

I have 2 computers (both running linux) and I'm currently using synergy to use them. This is great, but now I'm wondering, is there any way (is it possible? being worked on? tried and failed? definitely not possible?) to not only share a mouse/keyboard/clipboard between the computers, but to share an X session? What I'm thinking is being able to drag X windows between monitors.

I realize that this is extremely non-trivial to do and I know enough about linux (though not about xserver) that I'd like to pursue this idea even if there's nothing that does this for you.

Also, I don't need to be able to just "install this and it works". I'm completely willing (and would be surprised if it didn't require) to install custom kernals, or mount partitions between machines, or whatever it takes. Since I assume it would require the same instance of xorg server running on both machines.

Best Answer

You could look into xpra - it's not quite as smooth as you describe (no dragging between X servers) but it will give you the ability to start a program on one machine and then later detach it and reattach it on another machine. (Think of it as screen for GUI applications.)

It's difficult to get tighter integration than that, because the process is still tied to the machine you start the program on, and process migration is a really hard problem.

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Unique synergy monitor setup

What if you switch client screen1 with 2 ?

------------  -----------  ------------  -------------   
|  client  |  | server  |  | server   |  | client    |   
|  screen2 |  | screen1 |  | screen2  |  | screen1   |   
|----------|  |---------|  |----------|  |-----------|

This way you are able to set the right of cl scr2 to left of srv scr1 and leftof cl scr1 to right of srv scr 2. Then, if you need, you can just move your taskbar to the desired screen and set the DE's behavior to open new windows on the screen where the mouse cursor is located.

I had a similar setup, with the only exception that in the middle was a client with a single display and server with 2 screens on left and right... or something like this.

Possible to move a window from one X screen to another on same host

You cannot move an X application started directly with the X server the application is ultimately displayed on, this is due to an X client being "tied to the X server (X display) it was started on for its lifetime"[1] This is most likely to do with metadata that the X server holds about a client's windows that cannot be easily transferred between X servers.

The same is true of separately configured screens (when not using extensions such as Xinerama or Twinview) for programs that don't have multi-screen support explicitly written in - "With this configuration it is not possible to move windows between screens, apart from a few special programs like GIMP and Emacs which have multi-screen support."[2]

In theory if an application was designed to cope with an X server context switch, it could be provided with the new display/screen number, save the state of it's windows, connect to the new X server/screen and resurrect it's windows, but few applications would be designed in this way and would necessarily involve either a lot of boilerplate or the inclusion of a library that would facilitate this somehow.

The best option for you is probably to use other applications that can act as a proxy between an X client and the displaying X server in a similar way that GNU screen can be used for console applications and the terminal. Xmove and Xpra [3&4] seem to be the most widely used implementations for doing this. The caveat of using those is that the applications that you start have to register with Xmove or Xpra as their X server in order to be able to context switch between different display servers.

Finally there is another question, on SuperUser, that is asking a similar question for a slightly different purpose (reconnect to X after X crash, rather than deliberate disconnect/reconnect of client)[5]

Best Answer

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Unique synergy monitor setup

Possible to move a window from one X screen to another on same host

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