Comment 6 for bug 391117

I think there is a missing quotation mark (") in the description of the line to be added. The following worked for me:

add to the file
/etc/gdm/PostSession/Default
the following line (inserted in line just before last line "exit 0"):

/usr/bin/canberra-gtk-play --file=/usr/share/sounds/ubuntu/stereo/desktop-logout.ogg