pistop is a package that provides two services fclient and fserver.

fclient is a svscan service that waits for fserver service on a remote machine to terminate. fserver service runs on port 5555. shutdown is detected by a socket close

fserver is a svscan service that opens and binds a socket on port 5555. Clients can connect to it and give rudimentary commands. One of the command is wait. The 'wait' command will simply keep the socket open. If the service terminates, the socket gets closed and the remote client can detect this and take further action.

fserver runs as root and offers no security. It is just meant to be used on an internal network of SBC like raspberry pi and provide means to have all clients connect to it, shutdown themselves, when the socket closes.