My base system is Gentoo amd64, up to date. Before the upgrade, I have the shutdown button in the KDE menu. But after the upgrade, this button is gone...I think it is because of the permission settings are wrong. The user account I used is in the user group. But I have no idea how the set the permission. I even tried to delete the KDE configuration files in the user directory and try to re-configure everything, but does not work.
The configuration file /etc/config/kdm/kdmrc has the following section:
Un-comment the "AllowFifo=true" line, then the system shutdown as it used to before the latest upgrade. Source and info As long as this is correct you can add a shutdown launcher.