Startup Shutdown Button Pi

[Gauner]

You could also dig into the dtoverlay=gpio-shutdown.
At least the Raspberry Pi 3B+ is prepared to just wire a button on PIN 5 and 6 which starts the Pi from halted and send a KEY_POWER Event while running.
Which (as a matter of fact) Kodi just reacts to with a shutdown menu, not an immediate shutdown process, but that's another story. (Has somebody an idea hot to make XBian shutdown on that event, but make Kodi show the shutdown menu when I press the button on the remote control?)