gnome-session is broken without 3d acceleration, breaking gnome-flashback on non-3D H/W and cloud environments (Forwarded-X, VNC and NX/X2GO)

[Martin Meredith]

Gnome-Session 3.8+ enforces usage of 3D, breaking usage of all gnome-session based sessions in non-3D accelerated environments as non-3D enabled hardware, forwarded-X, VNC and NX/X2GO.

This breaks gnome-flashback, breaking upgrade path from previous LTS and removing most sane option for cloud environments!

Overriding 3D checks (sym-linking /usr/lib/gnome-session/gnome-session-check-* to /bin/true) allows to start the session but it fails few seconds later when gnome-session segfault without apparent reason.

(Sorry for hijacking this bug, but new gnome-session behavior has much broader affect then originally reported)

Original report:
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In Saucy Salamander, gdm will not start if 3d acceleration is not available. This throws an error to /var/log/gdm/:0-greeter.log

gnome-session-is-accelerated: No composite extension.
gnome-session-check-accelerated: Helper exited with code 256
gnome-session-is-accelerated: No composite extension.
gnome-session-check-accelerated: Helper exited with code 256
** (process:4142): WARNING **: software acceleration check failed: Child process exited with code 1

This is a regression from raring, and is the same if gnome-fallback is unavailable.

Possibly the same bug as #1251281, as this shows the same error.

This is preventing me from upgrading to raring, as I run 4 screens on an Nvidia Quadro NVS 450, meaning 3d is unavailable.

[Martin Meredith (mez)]

Have marked as critical as this makes saucy completely unusable as a desktop environment on non-3d machines.

[Maxim Kuvyrkov (maxim-kuvyrkov)]

Anyone has a workaround?

[Eugene San (eugenesan)]

@maxim-kuvyrkov
Please see https://bugs.launchpad.net/ubuntu/+source/gnome-session/+bug/1251281