I use a 2014 Intel Mac mini as a home server running Ubuntu Server. After a power outage, it did not start automatically when power came back.
The fix was in a power-management setting on the Intel 8 Series chipset. The AFTERG3_EN bit in the GEN_PMCON_3 register controls what the system does when power returns after a complete power loss. Intel's documentation says a value of 0 boots the system when power returns, while a value of 1 leaves it in the soft-off state.
Apple identifies the Late 2014 Mac mini configurations as Macmini7,1. The PCI address used below, 00:1f.0, corresponds to D31:F0 in Intel's chipset documentation. I changed the setting on Ubuntu Server with this command:
sudo setpci -s 00:1f.0 0xa4.b=0:1The command clears bit 0 in register 0xa4 for that chipset function. I then cut the power and restored it. The Mac mini started automatically.
I tested this on one Late 2014 Mac mini (Macmini7,1); I have not tested every configuration in that model family. Do not apply it directly to other Mac mini generations, which may use different chipsets or register mappings. Check the exact model and its chipset documentation first. An AI tool can help find relevant information, but verify any suggested register and command against a reliable source before running it.