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Re: Two computers in one: two users each with their own accounts, monitor, and keyboard?

On Wednesday 06 January 2010 02:58:48 Dotan Cohen wrote:
> I have a desktop computer with onboard VGA and option to add a
> discrete video card. It has plenty of spare USB ports for mice and
> keyboards.
> Does Debian support using this computer for _two_ workstations, each
> with their own user accounts, monitor, and keyboard?

From what I understand about Linux in general, no.  At the very least, doing 
so your be overly complicated.

The first problem to solve is getting two separate X sessions to run at the 
same time, but using separate hardware.  It should be possible, but I've never 
tried it.  You'd have to write two fairly complex xorg.conf files to make sure 
the inputs and outputs are explicit and that X completely ignores the other 
hardware -- neither session can (e.g.) try to "turn off" the unused 
inputs/outputs.  Then you'd want to start them on the same "virtual terminal", 
something which will only work if your xorg.conf files are correct AND Xorg 
and the kernel don't actively try and prevent this.

If you can get that working, you should be able to run a login manager on each 
session.  Then two different (or the same) user could login to each session.  
I guess the login manager is actually responsible to starting the X session, 
but once you could get two sessions running at the same time on the same vt, 
it should be relatively easy to start two login managers -- one for set of 
hardware / xorg.conf.

If you even got that far, you'd still have some interference issues.  Things 
like Ctrl+Alt+Fx or Alt+SysRq+x would still affect all of the hardware by 
switching to another virtual terminal.  Modern login managers probably even 
have some facility for using and switching to other virtual terminals, which 
would switch both sets of hardware.  I'd wager that all of these could be 
disabled, for either all keyboards or all but one, but I don't know how off 
the top of my head.

I think it would be easier simply scale the second computer down to a "thin 
client".  It would need it's own CPU, RAM, and I/O but it should be able to 
mount most file-systems via ro-nfs with a few filesystems mounted with rw-nfs 
(or nbd/iscsi/eata) after netbooting.  It would run its own Xorg instance, but 
use XDMCP to (graphically) login to the primary computer, such that all the X 
programs would run on the primary computer, and all the user settings/data 
would be on the primary computer -- users wouldn't even need a login to the 
thin client.

Without hard disks, and needing only enough CPU power to run X, the second 
system could be *very* small.  Since it could share (at least) /usr with the 
main system, it wouldn't need to be separately updated much.

This post turned out a lot longer and a lot less informative than I had hoped.

TLDR: No; look into something like LTSP, but small-scale.
Boyd Stephen Smith Jr.           	 ,= ,-_-. =.
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