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Taken from the Linux Cookbook, Part 2 by Carla Schroder
Problem
You have all these great window managers and desktop environments installed— KDE, Gnome, Enlightenment, Fluxbox, XFce, and such—and you would like to run some of them simultaneously. You know you can start up separate additional X sessions, or log out of X and start up in another window manager, but you wonder if there isn't a way to run them at the same time. Solution
Xnest, the "nested X server," is just the tool for the job. Xnest allows you to run additional X sessions inside of already running X sessions.
Open a command shell in any X session—let's say you're running IceWM—and fire up Xnest:
$ Xnest -ac :1
You should see a blankscreen with an X cursor in the middle. Now you can open a window manager. This example starts up WindowMaker:
$ wmaker -display :1
Now you can start up another one. From a command shell on IceWM, enter:
$ Xnest -ac :2
Some window managers or desktop environments, such as Gnome, need to start from an xterm in the Xnest window. First start up an xterm:
$ xterm -display :2
Then start Gnome from the xterm:
$ gnome-session
You can start up yet another Xnest session from any available terminal in any of the windows:
$ Xnest -ac :3
You can continue to open more window managers until your system resources are exhausted and everything slows to a crawl. Figure 15-1 shows Gnome inside of IceWM, on KDE. Discussion
X sessions are numbered from 0, so the default X session is always :0. The -ac option to Xnest specifies the session number for the new display. Keep trackof your whereabouts by checking the DISPLAY value:
$ echo $DISPLAY :0.0
The -ac option disables access controls. Otherwise, X will not let you open any applications. Xnest uses the same options as the X command—see xserver(1x). When you get several window managers going, you might see an error message like this, and the new one won't start:
$ gnome-session gnome-session: you're already running a session manager
No problem. Just track it down and kill it:
$ echo $SESSION_MANAGER local/windbag:/tmp/.ICE-unix/2774 $ rm /tmp/.ICE-unix/2774
and now Gnome will start.