Comment 70 for bug 214370

Nelux

it works but it's not the optimal solution, it doesn't allow you to change the logout sound or the sound theme unless you manually modify your scripts or name your new sound theme "ubuntu" and move or erase the original one.

The clean way would be to execute /usr/share/gnome/shutdown/libcanberra-logout-sound.sh, but when the scripts in PostSession or init.d are executed everything Gnome is already killed, including canberra.

There is no way in Gnome to execute a script BEFORE Gnome itself logs out and kills everything, that is the problem, the code does not exist (it does exist and work in KDE though). The script for the logout sound is already there, it's the one I mentioned above, but nothing calls it. That is a long standing upstream bug but nobody can be bothered to write the code.

Incidentally, for the same reason, you cannot execute anything upon logout in Ubuntu, only AFTER logout, and probably only as root.