My goal is to use three monitors with my Linux system. It is a laptop, so adding another video card is not the easiest solution. (I have investigated a number of such options: getting a docking station with a PCI slot, USB/Cardbus vga adapters, etc, and for the time being don't want to go that way.)

I am wondering if using an older desktop+screen I have lying around as the third "monitor" might be the easiest solution, if only there is a way to get it to work as a seamless, integrated desktop.

I was wondering if I can use VNC or perhaps X itself (?) to achieve the following:

  • computer A is my main computer; it has all my files, etc.
  • computer B is used just to display on an additional screen
  • keyboard+mouse are connected to computer A
  • use VNC or X to connect the two so that computer B shows a X screen that is just as if it was a third physical screen connected to computer A.

I don't know if the last point is clear, but what I mean is that I would like to be able to:

  • be able to have my window manager assign/move around virtual desktops on all three screens
  • move windows back and forth between the screens attached to computer A and the screen of computer B
  • be able to copy something in an app being shown on a screen of computer A and paste it into an app being shown on the screen attached to computer B
  • access the filesystem on my main computer (A) when using applications that are being shown on the screen attached to computer B

Basically, I would like X to treat computer B just like it was nothing but a third physical screen...

Is this doable? : )


  • 1
    If you want to avoid buying extra hardware due to the costs, you should also take the power consumption of computer B into account. If B is quite power hungry, special hardware may be an economically better solution.
    – foraidt
    Mar 2, 2010 at 8:55

3 Answers 3


That's what DMX: Distributed Multi-head X is designed to do, unfortunately it's been broken in several X.Org releases, so you may have to work a bit to get it working.


Looking for an answer for myself (using an iPad instead of a computer), I found the best option to be using VNC, specifically tightvnc. See here: https://help.ubuntu.com/community/VNC/Servers#tightvncserver


Consider plugging a physical cable into an unused port on the second monitor and then switch the input (monitors usually have DVI, HDMI, and VGA).

In principle, it should be possible to do the same thing via VNC. That is, configure the X11 server to have one real display and a second simulated display that isn't connected to any output, and then use x11vnc (or equivalent) to access the contents of the second display via VNC. Unfortunately, I'm not enough of an X11 configuration wizard to know how to do this. Any ideas?

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