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, the 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, 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).

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”, 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.

Similar areas I came across in my research were Nested X sessions and Multiseat X.