- Connect to your Mac remotely via SSH or telnet.
- Become root ('su' and enter your root password)
- Type sync to clear the buffer (may not be necessary with the next command, but I'm cautious!)
- Type halt to shut down the machine.
I just tried this from my PC to my Mac, and it did exactly what it was supposed to do ... my Mac shut down cleanly. No errors of any sort on restart, but I did lose my '3 day, 4:54' uptime! I'm not quite sure why one would want to do this, but it is possible.

