Hya

Set up
Debian buster amd64. This desk top is as average as it can be.

What happens
It turns on without power button touched, shortly after it is shut off. It does not happen every time, only every once in a while.

Troubleshooting 1
Power surge, hardware failure are very unlikely. Software -cron setting, malicious program- must be irrelevant, because no program is running after shut down.

Culprit
After a long investigation, including invisible penguin , I found that mouse (not rodent, but USB connected one) triggers power on. Only when mouse moves after shut down, comp turns on. But, now question is how?

Troubleshooting 2
Kernel options for USB checked to find nothing.

Found
It is outside Linux setting. BIOS has "USB mouse power on" setting.

I remember Mac SE/30, when power on was on its keyboard. ACPI may or may not be related, but I did not check (reason, I thought it is related to power'SAVE'.

Happy Penguins

Nice job of detective work.

And here I was thinking a mouse walked up and pushed the power button with its nose.

I mean, that's what your thread title says.

Have a great April Fools Day!

Hya,

Thanks for your post.

Yes, I also ruled out the possibility you mentioned.

cheers

update after long interval.

The mouse went south, new mouse does not behave like the old one. (nothing happens with buttons)