How to check the log for power failures

See if this helps.

Console post see first post by Linc Davis

jayv. wrote:

What is the best key word to search for to find this information?

"shutdown cause"

as in

Sep 19 15:01:33 localhost kernel[0]: Previous shutdown cause: 5

From previous experience 0 indicates a power interruption.

Negative codes are generally associated with hardware faults, and their exact meaning is not published in any publicly available document.

The only negative shutdown code I observed not associated with an obvious hardware fault was -128, which occurred following a firmware update. Given that hardware is controlled by firmware, the "negative = hardware fault" assumption remains consistent with a hardware-initiated shutdown though.

You can confirm this yourself on any desktop Mac, by disconnecting its power cord while it's operating, and observing the system.log entries recorded upon the subsequent boot. Mine have always been 0.

I strongly recommend using a quality UPS even for sites with reliable power. For sites with less than reliable power, they're a necessity. It's pretty difficult to damage a Mac's power supply though.