It's a pretty basic client-server application. The server just listens for a connection, authenticates the client, and then does a reboot. It avoids the following to get added reliability:
  1. It doesn't use any existing client-server application, because then it would have the same problem as that application.
  2. It doesn't go through init for the reboot - it just issues a reboot system call
  3. It doesn't sync the disks (some would say this is risky, though with journaling filesystems it's less so than it used to be. Also it's easy to change it to sync if you prefer that)
  4. It doesn't fork - it does its job entirely in a single process
  5. It doesn't exec - it does its job entirely in a single process
  6. It doesn't use virtual memory. It only uses physical memory. It gets this advantage via mlockall on most machines.
It doesn't piggyback on /bin/login or sshd or telnetd or anything like that, because that would decrease the effectiveness of the program.

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