I am running a Zentyal server at home, set up to run as a gateway, file server, etc. It is running on a fairly standard computer with standard hardware (Intel i3, 8GB RAM, 300W power supply). A few nights ago, the computer randomly shut off overnight. I awoke to find that I was without internet, and discovered the computer was off. I powered it back up, checked some logs, and found surprisingly nothing interesting, besides the fact that the computer was doing routine things such as servicing DHCP requests when the log stopped abruptly at 3:00:03. No indication that a shutdown signal was sent.
There is no other indication of power outages anywhere else in the house, automatic updates are disabled, and I believe I even have the computer set in the BIOS to "Last power state" after a power outage, so I'm increasingly convinced the computer turned itself off. Is there any reason why a computer running Linux (Debian/Ubuntu/Zentyal in this case) would power itself off abruptly, especially at exactly 3am? I am baffled.