Auto restarting a Mac Mini running Ubuntu after power loss

2025-03-30 | #servers #mac | @Acidus

A few months ago, I swapped the server that runs Kennedy from a circa mid-2011 Mac Mini (Macmini5,1) to a more "modern" Mac mini from late 2014 (Macmini7,1). It has a faster (though still Intel) CPU, a larger aftermarket SSD, and a larger secondary hard drive. I put Ubuntu LTS on it and went on with my life.

However, I would get emails that Kennedy was down, and I'd look in the basement and see the server was, in fact, powered off. This was odd because I had a UPS. But even without a UPS, the Mac Mini hardware should power back on when it restores power. The 2011 Mac Mini, even with Ubuntu installed, would do this, so it seemed like a hardware feature, not an OS feature. I wasn't sure why the 2014 one was not.

Searching on the web and Stack Overflow returned a variety of complex answers that were all correct, while ChatGPT told me to install a package that didn't exist 🤖😬.

Doing some digging, I learned several things:

• That the *"turn on after power is restored"* is a flag that is set in the hardware/firmware config.

• That while many sources will tell you this setting does not persist and must be re-written after every boot, that does not seem to be the case with my model.

• There is a Stack Overflow thread that talks about using `lspci` and determining your chipset or some such, and then searching for the data sheet for that chipset to determine the hardware address you need to set the *"turn on after power is restored"* flag. I could not find the data sheet, but it didn't matter. I thought YOLO and set the flag since the poster also had a 2014 Mac Mini.

So, here is the command to tell a late 2014 Mac Mini to set the *"turn on after power is restored"* flag:

sudo setpci -s 00:1f.0 0xa4.b=0

I proceeded to test this repeatedly by yanking the cord out of it while running, waiting a period of time, and plugging it back in. I also unset the flag (=3? ), unplugged/waited/replugged, and if the server did not power back on automatically. I also confirmed that you did not need to keep setting this flag on every successful boot with a cron job or other systemd server.

Also, note to future self, since I always forget, here is how to get the model number (e.g. Macmini7,1, etc.) once Ubuntu is installed:

sudo dmidecode -t system | grep "Product Name"

Stack Overflow thread - How to reboot after power failure for Mac mini running Ubuntu?