/usr/share/gnome-session/sessions/openbox-gnome-fallback.session is in openbox-gnome-session 3.5.2-8+deb8u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | [GNOME Session]
Name=GNOME/Openbox fallback (Safe Mode)
RequiredComponents=gnome-settings-daemon;
RequiredProviders=windowmanager;
DefaultProvider-windowmanager=openbox
DesktopName=GNOME
|