Xephyr: preview other DE/WM in nested X-server

[Michiel]

I read in a dutch linux magazine a tip about opening a nested X-session whilst working in your main X-session with the purpose of e.g. previewing how an other desktop environment (such as XFCE or LXDE) would look like when you are using KDE4 in your main X-session.

In Pardus a nested X-server is available when you install the pisi package xorg-server-xephyr

When you enter the following code (assuming that you have GDM installed as Display Manager):

Code:

gdmflexiserver -n

you get a window with the login screen where you can choose  which session type you would like to start.

The screenshot is taken under Pardus using LXDE, in the second screenshot I have logged into a KDE4 desktop environment (as an example).

You can login in the nested X-session with the same account as in which you are already logged in in your main X-session if you want to, you can also log in with different accounts.

Of course you can also preview things with virtualisation software however the advantage of a nested X-session is that you do not have to install the entire operating system on a virtual disk.

Perhaps other people have been aware of this option (nested X-sessions) for ages, but I did not know about it untill I read the magazine  

==============http://www.freedesktop.org/wiki/Software/Xephyr ==========
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 host server doesn't ) such as Composite, Damage, randr etc (no GLX support now). It uses SHM Images and shadow framebuffer updates to provide good performance. It also has a visual debugging mode for observing screen updates.

Possible uses include;

Xnest replacement - Window manager, Composite 'gadget', etc development tool.
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.
Multiterminal with Xephyr - configuration is a single computer which supports multiple users at the same time

[Michiel]

In addition with KDM (the default displaymanager) things are a bit mroe complicated and work ONLY when the main session is an KDE4 session.
(For me this is another example that GDM had more flexibility then the IMO too tight in KDE4 bound KDM).

# kdmflexiserver -- an alternative for gdmflexiserver for KDM
# KDE, when started from KDM, allows users to start new KDM sessions or
# swith to other sessions using the "Switch User" menu item in the K menu.
#
# However, users of desktop environments other than KDE do not have an easy
# access to this KDM functionality. This script presents the user with a
# list of runing sessions and an option to start a new session. kdmctl
# is then called to switch to the selected session.
#
# (C) 2008 Jiri Bohac <jbohac@jikos.cz>
# Licensed under the GPL, version 2 or later


The full script and introducing words in it:

http://www.jikos.cz/~jbohac/goodies/kdmflexiserver