So I have a Xubuntu box, an old PC that was running Windows previously. All is peachy with the Linux install bar one thing: every time I shutdown the system, it shuts down fine, but immediately restarts again. This wasn't happening with Windows and appeared to be an issue particular to Linux or Ubuntu.
I tried a variety of variants of the
shutdown command with and without
sudo. This included
shutdown -H -P +0. I even tried adding
acpi=force to grub. Nothing worked. Instead the fix was to go into the BIOS and look for anything that says "wake" and disable it. In my case, I had to turn off "Wake on LAN" which did the trick!
Considering the amount of time I wasted on this and the general annoyance of the issue, this was very satisfying to resolve. I hope it helps someone else out there too.