Re: multiple gdm

["Jasper St. Pierre" <jstpierre mecheye net>]

You cannot run two different X servers at the same time which act on different monitors. At least, it's not possible with the open-source stack, and I highly doubt it's possible with NVIDIA proprietary either.

The syntax for ":0.0" and ":0.1" is composed of two parts: the X Display (":0") and the X Screen (".0"). These are two different resources inside the X server.

GNOME *might* support using syntax like DISPLAY=:0.1 to run on a specific X11 screen (you can test it with something bare like `DISPLAY=:0.1 gnome-shell` while logged in), but it's an unsupported configuration.

Unfortunately, GNOME doesn't allow the same user to log in twice, even if on different X11 screens. Most applications, especially ones like Firefox, use the user's home directory as a place to store settings and configuration, and if two Firefox instances are running, it will get confused and your settings will become corrupt.

A lot of other GNOME applications work the same way (a system known as "dconf" saves settings in your home directory, and we have a per-session writer which makes sure that the database is serialized to disk. If there are two writer instances, your database becomes corrupt).

Hopefully that explains things and answers your question.

On Thu, Jan 15, 2015 at 10:08 AM, Stephen Adler <adler stephenadler com> wrote:

Thanks, just to be clear, I don't want one gnome session running on two
X servers. I want to run two different instances of gnome, each with its
own X server. The idea would be, if all is working, when I boot my
system, I'll get two gdm login screens, one for each monitor. I could
then have to log in twice, perhaps under different user names. It may
sound like a bad hack, but I'm just wondering if somehow I could
configure gdm to work of some specified display, like :0.0 or :0.1 or
something like that.

On Thu, 2015-01-15 at 09:45 -0800, Jasper St. Pierre wrote:
> GNOME does not support multiple X11 screens. My understanding is that
> recent versions of nvidia proprietary added XRandR as a feature, which
> is what we require for multi monitor support.
>
> On Jan 15, 2015 6:31 AM, "Stephen Adler" <adler stephenadler com>
> wrote:
>         Guys,
>
>         I'm not sure if this is the right mailing list to ask this
>         question so
>         forgive if I miss-posted...
>
>         I have a system with two video cards, quadro K2200 and a K620
>         and the
>         nvidia propriatary driver will not configure a single desktop
>         (X server)
>         using both cards. It will configure two separate X servers or
>         X
>         displays, one for each card. So I thought maybe I could run
>         two versions
>         of gdm, one for each X server or X display (I'm not sure the
>         terminology
>         here.) :0.0 and :0.1 would be the -display syntax to use. This
>         way I
>         could have two separate sessions a bit like a KVM switch
>         expect I'd have
>         two monitors with one keyboard and mouse, and I would move my
>         mouse over
>         from one monitor to another to switch from one gnome session
>         to another.
>
>         so... how would I configure gdm to run on two X displays or
>         servers?
>
>         Thanks!
>
>         Steve.
>
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--

  Jasper