How to determine random shutdown

[illusiumd]

My hack keeps randomly shutting down. When I go to console > sys log -- the last/previous entry before I booted back up is some common safari TCP error. If the CPU overheated would that be a reason why sys log wouldn't contain any info?

 

[brpc]

Tl;dr - Test your memory.

Bust out memtest86 usb stick and test your memory. I got new memory a few months ago and it was working fine until last Wednesday. Windows 10 and Sierra both experienced abrupt, complete shutdowns, then the system booted on its own 5 seconds later. Thought it was PSU based on behavior (no bsod, no logged errors, etc), but because I didnt test memory... well, same problem came back with new PSU.

Tested memory and it was 1 bad stick in a set of 4. Must have been a gradual problem, though, because it took 3 months to fail hard.

 

[iMacRo]

I had a similar problem and it turned out to be a failing power supply. The computer had worked properly for over a year and then began randomly shutting down. It did not reboot nor was there ever a consistent message in the error log.