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I have a system with a single monitor, I would like to test the an xmonad configuration that is designed for multiple monitors. Is there any way to emulate a system with 3 monitors using something like Xephyr to test my configuration?

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up vote 4 down vote accepted

I found the solution using Xephyr and Xdmx

First create the Xephyr displays

Xephyr -screen 1920x1080 -ac :1
Xephyr -screen 1920x1080 -ac :2
Xephyr -screen 1920x1080 -ac :3

This creates 3 windows 1920x1080, each of these will act as a monitor

Next add the xinerama layer onto these virtual displays

Xdmx +xinerama -xinput local -display :1 -display :2 -display :3 -ac :4

Next create a fresh terminal and start your window manager or application like so


or if you just wanted to test an applications xinerama support instead of xmonad you could run xterm or thunar.

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You only need a single instance of Xephyr.

Xephyr +xinerama -screen 1920x1080 -screen 1920x1080 -screen 1920x1080 -ac :1

If you need RANDR extension, add +extension RANDR args.

Xephyr +extension RANDR +xinerama -screen 1920x1080 -screen 1920x1080 -screen 1920x1080 -ac :1

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While this answers the question it is not a full-blown solution. These solutions place the three screens in a horizontal row (well, at least according to xinerama (xdpyinfo -ext XINERAMA -display :1), the actual window placement will be taken care of by the window manager). If you want to have any other placement of the screens this will not help.

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