Multiple X ( Desktop ) Sessions in Ubuntu

[Aruna Hewapathirane]

I was testing window managers and having a hard time comparing each due to
constantly having to log-off and sign back in as another user with a
different window manager and then something sweet happened. I came across a
article and now I am flipping back and forth between virtual terminals that
have gnome-classic, LXDE, Openbox and Awesome and it's amazing.

The article is here:
http://www.doknowevil.net/2010/10/13/multiple-x-desktop-sessions-in-ubuntu/
and for those of us who are lazy the content is right below, seriously you
should try this it blew me away :)

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This post has a lot to do with graphics but there are no graphics. It’s a
walk-through explanation and and proof of concept of some very interesting
features of Linux as a desktop operating system.

If you aren’t familiar with X, than this webpage might confuse
you<http://www.x.org>,
the X Window System <http://en.wikipedia.org/wiki/X_Window_System> is what
draws the GUI (graphical user interface) for Ubuntu. On top of this, you
may have a Window Manager or Desktop Environment <http://xwinman.org/>,
such as Gnome (Ubuntu default) or KDE (Kubuntu).

When you boot up Ubuntu, it creates a set of “virtual terminals”. These VTs
are accessible via a key combination of clt+alt+f1-12. VT7 (ctrl+alt+f7) is
the default and it handles X’s “screen 0″. If you play around, with the key
combination, you’ll notice you drop into consoles with a login prompt
(f1-6) or a blank screen (f8-f12, don’t worry if you see USB
errors<https://bugs.launchpad.net/ubuntu/+source/linux/+bug/256767>).


These virtual terminals used to be handled by X which was slower and more
prone to crash (citation needed) but since Ubuntu 8.04, this has been
handled by “Kernel Mode” <https://wiki.ubuntu.com/X/KernelModeSetting>,
where this management is handled by the kernel. You can switch to another
virtual terminal and create another X session.

Typically in Linux, you could switch to another VT, login [as another user]
and type $ *startx — :1* (special argument ‘--‘ marks the end of client
arguments and the beginning of server options, :1 defines screen 1). This
will work in Ubuntu but the part where I found it failing was switching
between this newly created X session and back to my original :0 on VT7.

The way I found to do this in Ubuntu seems a bit counter-intuitive. Before
I explain, you should create a new user, if you don’t have another already.
You can do this by going to System > Administration > Users and Groups.

To create a second X session in Ubuntu, go to your logout menu (default top
right) and select “switch user”, and login as another user (you don’t want
to create an error in the user environment). When you login as another
user, Ubuntu creates a screen :1 on VT8. This means, you can change back to
VT7 with ctrl+alt+f7, then back to VT8 with ctrl+alt+f8. I *suspect* this
is the reason VT8-12 show up as blank screens instead of login terminals.
Ubuntu seems to be leveraging the power of virtual terminals for “user
switches”.

I haven’t noticed much in performance loss doing this and the other big
question is practicality. Why would you ever do this? Perhaps you are
testing software and want isolated test cases or you want a dedicated user
for games with a more streamlined window manager and want to be able to
flip back and forth.
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