Multiple X ( Desktop ) Sessions in Ubuntu

[John Moniz]

On 01/21/2014 10:25 PM, Aruna Hewapathirane wrote:
> 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 :)
>
> -------------------------------------------------------------------------------------------------------------------------------------------
> 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.
>
> -------------------------------------------------------------------------------------------------------------
We use this method at home daily for one simple task. My wife and I each 
have our own profile the first one to log on gets VT7, the next gets 
VT8. She switches to her profile using 'switch user', my prederence is 
ctrl+alt+f7/8.

One annoyance that I have with a similar task in Ubuntu, and maybe it's 
only on my machine, is that logging out of one user will result in a 
black blank screen that cannot be released, even with ctrl+alt+backspace 
or ctrl+alt+delete. Whenever more than one user is logged on, we have to 
leave them on until it's time to shut down.

The above problem does not seem to occur on my mother-in-law's machine 
using Ubuntu, or even in this one when using a different distro.

John.
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