Bug#718686: gnome-session: GNOME3 Shell does not support multiple X11 screens ("Zaphod mode not supported")

[Rafael Varela Pet]

Package: gnome-session
Version: 3.4.2.1-4
Severity: important
Tags: upstream, wheezy

I'm opening this report following Josselin Mouette's advice to file
against gnome-session the problem described in #678011.

My setup is the same as the one described by one of the participants
in #678011, Norbert Veber: I have a single nvidia video card with two
outputs connected to two monitors. My prefered way to set it up is so
that they are two separate displays :0.0 and :0.1.

This worked great in debian 6 and gnome 2.x. Each screen would get its
own gnome panels, and its own separate virtual desktops that could be
switched independantly. In wheezy and gnome 3 this no longer works.
You should see a message like this in your ~/.xsession-errors:

gnome-session-is-accelerated: Zaphod mode not supported.

So I'm getting the gnome-fallback session, and rather than starting a
gnome panel on each display as expected, it starts two of everything
on just one screen. It starts nothing on the second screen.

The workaround is to switch to xinerama/twinview mode instead which
extends a single display :0 to both monitors.

See also:

https://bugzilla.gnome.org/show_bug.cgi?id=648156

-- System Information:
Debian Release: 7.1
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.2.0-4-amd64 (SMP w/2 CPU cores)
Locale: LANG=es_ES.utf8, LC_CTYPE=es_ES.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages gnome-session depends on:
ii  gnome-session-bin      3.4.2.1-4
ii  gnome-session-common   3.4.2.1-4
ii  gnome-settings-daemon  3.4.2+git20121218.7c1322-3+deb7u1
ii  gnome-shell            3.4.2-7

Versions of packages gnome-session recommends:
ii  gnome-power-manager     3.4.0-2
ii  gnome-session-fallback  3.4.2.1-4

Versions of packages gnome-session suggests:
ii  desktop-base      7.0.3
ii  gnome-keyring     3.4.1-5
ii  gnome-user-guide  3.4.2-1+build1

-- no debconf information