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-   -   Multiseat dualhead with 2 SCREENs (http://www.nvnews.net/vbulletin/showthread.php?t=130885)

Shambler0 03-30-09 08:21 PM

Multiseat dualhead with 2 SCREENs
* I have 2 monitors, mice and keyboards, and a dual-head nv6200.

* I want me and my friend to work independedly on the same computer without additional hardware.

* I need accelerated 3D to work at least on one monitor, but both seats with 3D is my goal. It would be great it I could change both monitor resolutions at runtime.

Links: What is mutiseat / multiterminal * How to do it in linux (see also other links in the article) * 100% working solution for windowsXP

Btw, I have 2 seats with full functionality under windowsXP via shareware proprietary software. I had a quake duel with my friend on a single computer and it worked without a flaw. It is very stable (I only sometimes see visual glitches, and only if two DirectX windows are active, OpenGL works fine)

I am trying to get along with the configuration with 2 independed Xorg servers using one same videocard. I don't care about the overhead from 2 Xorgs.

I am able to independedly control input devices through evdev. That is, keyboard1 affects only with monitor1, and so on.

Xorgs launch and work, but only one at a time: when one initializes, the other turns itself off (but X still runs - that is, it is not killed).

Twinview also works fine (but I don't need it in the current configuration).

I *was* able to somehow get them to work simultaneously: X started on first monitor, then it turned itself off and the second one was initialized. If I then pressed Ctrl+Alt+Backspace, Xorgs would restart showing both of screens active at once (due to a problem with evdev, both X reacted on any of my keyboards - it was like typing on two computers with one keyboard). It looked like a bug to me, but a useful one. But evdev didn't work, so I had to upgrade everything, and two simultaneous X did not work from then on. I can post my configuration at that moment, if anyone wants it.

So, I need nvidia driver to somehow only initialize only one of two heads. Does anyone have a clue, how could that be possible?

Any other tips on how may able to I archive my goal are welcome. (Xephyr will likely work over TwinView, but I need the 3D which it doesn't support, AFAIK.)

Thank you in advance!

JaXXoN 03-30-09 08:35 PM

Re: Multiseat dualhead with 2 SCREENs
The current nvidia driver doesn't support two instances of Xorg running
in parallel directly accessing a single GPU at the same time.

Xephyr might support 3D in the mean time:

Maybe this helps to get you started

If you get 3D working with Xephyr, please write up a tutorial :-)



Shambler0 03-31-09 05:08 PM

Re: Multiseat dualhead with 2 SCREENs
Well, it did work with 180.37 - even if it was a bug, and I'm not sure if I can reproduce it again, it showed that it is at least possible. (I should have tried rendering 3D back then...)

It also seems that it is just a matter of not resetting the monitor modes - you see, when two X servers recieved Ctrl+Alt+Backspace in sync, 2 copies of the driver were loaded almost syncroneously. Maybe the driver first turns off all the monitors, then turns on only the one it uses? So, they both disabled both monitors, then each of them enabled their "own" monitor, leaving the other one running? It makes sense that way.

By the way, is there a way to completly disable "green" monitor power management such as DPMS?
It is so that the drivers couldn't disable the monitors even if they wanted to, and all they could do is to paint their VRAM black (which is not a problem)?

3D with xephyr is experimental, even if it works at all.

michael wolf 08-23-09 07:44 AM

Re: Multiseat dualhead with 2 SCREENs
i would love to see your xorg.conf.
i have the same problem actually. i just bought an overpowered machine for home hoping that both my wife and i could use it at the same time thus saving power/cash/etc...

with regards to dpms look at the xset command. is this what you are talking about when you say "monitor modes"? if not, and you can clarify it, ill be happy to do more research.

did you ever try this trick with 185?


p.s. if you haven't already found this solution, you can set up two screens without xinerama so one is :0 and the other :0.1. then open xephyr full screen in either. unfortunately this still sucks because:

xephyr has a "crash with gimp" problem
xephyr has a dumb screen rotate policy (hers is a pivot monitor)
no 3d on xephyr
no hotplugging kbrd/mouse on xephyr
no dpms on second screen, that is either all monitors are in standby or none are
gksudo password requests block both screens

but it works and is stable. and for now it is enough for what we do.

michael wolf 08-23-09 10:17 AM

Re: Multiseat dualhead with 2 SCREENs
xset -dpms
xset dpms force on - on the first screen after i started the second
and restarting the first after the second is running

all results are the same. whichever monitor comes up last kills the other.


Fiable.biz 10-01-09 10:08 PM

Re: Multiseat dualhead with 2 SCREENs

Originally Posted by JaXXoN (Post 1971633)
The current nvidia driver doesn't support two instances of Xorg running
in parallel directly accessing a single GPU at the same time.

I don't understand every thing in this discussion. But is the above assertion still true? and sure?
I have a 9500 GT video card on Mandriva Linux 2009 Spring.

kauos 10-16-10 08:02 AM

Re: Multiseat dualhead with 2 SCREENs
It IS possible, but it is a little bit fiddly.

I have a single Nvidia Geforce 6200 AGP, with a standard VGA connector, DVI-d connector, and a TV-OUT connector.

I am using Ubuntu 10.04 on an AMD Athlon 2700+ 32bit.

My particular solution required the VGA and the TV-OUT to have a separate X instance each (I'm running a Freevo DVR alongside a standard X session).

The key for me was that I start both servers as close to instantaneously as possible.

Get your xorg.conf file to the point where you can start each seat one at a time.

Then the following shell scripts will wait until both are run before then starting both X servers at the same time.




chmod 777 $LOCAL_FLAG

while [ ! -f $REMOTE_FLAG ]
 echo "Waiting for $REMOTE_FLAG"


/usr/bin/xinit -- /usr/bin/X :0 -sharevts -layout seat0




chmod 777 $LOCAL_FLAG

while [ ! -f $REMOTE_FLAG ]
 echo "Waiting for $REMOTE_FLAG"


/usr/bin/xinit /usr/bin/freevo -- /usr/bin/X :1 -sharevts -layout seat1

It is not perfect. There is a thin line (about 5 pixels) at the top of screen 0 which contains corrupted pixels. But apart from that it works and appears stable so far.

Yes I could have used Xephyr (but the touchscreen support tended to crash, something that this native multi-seat solution fixes).

I could probably have used Userful as well, but they didn't have support for Ubuntu 10.04 32 bit version. Also Userful is not guaranteed to work with the TV-OUT according to their support.... but then again according to NVidia, this solution isn't supposed to work either.

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