Xephyr is a KDrive-based X Server which targets a window on a host X Server as its framebuffer. Unlike Xnest it supports modern X extensions (even if the host server doesn’t) such as Composite, Damage, and RandR.

For the best possible performance it uses SHM images and updates the shadow framebuffer via the Damage extension. It also has a visual debugging mode for observing screen updates.

Possible uses include:

Xnest replacement - Test window managers and experiment with the latest X extensions in the safety of a sandbox.

Toolkit debugging - rendundant toolkit paints can be observered easily via the debugging mode.

X Server internals development - develop without the need for an extra machine/display.

Download

Xephyr is part of the KDrive server and is now available in the regular releases of Xorg. You can get the source tarballs at http://xorg.freedesktop.org/releases/individual/xserver.

The development of Xephyr happens in the git repository of xorg and you can browse the source code.