Multiple X ( Desktop ) Sessions in Ubuntu

[John Moniz]

On 01/22/2014 09:24 PM, Bob Jonkman wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> John wrote:
>> ...a black blank screen that cannot be released, even with
>> ctrl+alt+backspace or ctrl+alt+delete.
> Ctrl+Alt+Backspace hasn't been implemented in Ubuntu for about five
> years.  Now the preferred way to restart X is with the Secure Access
> Key, SysRq+Alt+K

Thanks, this works beautifully. I had googled about the problem, but 
never found this solution. Just don't try it within Gnome, it tries to 
save a screen shot - often many times over.

>
> There's a document on the various System Request keystrokes at
> http://www.debian-administration.org/article/457/The_magic_sysreq_options_introduced
>
> And the Internet is full of documents on how to restore
> Ctrl+Alt+Backspace:
> https://ixquick.com/do/metasearch.pl?query=ubuntu+ctrl-alt-backspace
>
> - --Bob.
>
>
> On 14-01-22 03:11 PM, John Moniz wrote:
>> 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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