commit de812d394d0548d96db23c50d9f1ea0464d2ca00
Author: György Balló <ballogy@freestart.hu>
Date:   Thu Sep 29 04:35:32 2011 +0200

    data: add back check for gnome-shell before running gdm-shell session
    
    Add back commit 4892c9447324f2248ce944f150abe3143f78eaa3
    
    This commit does a quick check to make sure gnome-shell is installed, and supports --gdm-mode. If either of those fail, then fall back to the old greeter.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=660409

diff --git a/data/gdm-shell.session.in b/data/gdm-shell.session.in
index 3d408c3..496cc10 100644
--- a/data/gdm-shell.session.in
+++ b/data/gdm-shell.session.in
@@ -1,5 +1,5 @@
 [GNOME Session]
 Name=Display Manager
 RequiredComponents=gnome-shell;gnome-settings-daemon;
-IsRunnableHelper=@libexecdir@/gnome-session-check-accelerated
+IsRunnableHelper=bash -c 'gnome-shell --help | grep -q gdm-mode && @libexecdir@/gnome-session-check-accelerated'
 FallbackSession=gdm-fallback
