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I have this strange problem of my Mac rebooting. Everything was normal until I started syncing photos from iCloud (this could be coincidental, maybe not). First time I noticed a problem after 1-2 days as my system fan started going crazy, with CPU utilization at a max, several minutes later followed by system shut down. I traced the 100% CPU to Spotlight reindexing constantly; I temporarily disabled indexing:

sudo mdutil -a -i off

Problems with fans went away, but now photos service was going at very high CPU, accelerating fans again. I disabled Photos app (as much as I knew how) to avoid performing any analysis. This solved the fans and CPU going crazy problem. I could live without Photos on this Mac, no problems here.

Photos/Spotlight searching might just be coincidental, this part I'm not sure. Just so my system was more or less stable for at least several month before this addition.

But, here's the problem:

As soon as I leave my computer alone, after several minutes of inactivity, something happens that my computer goes into sudden reboot. I can't even leave it for 5 min for bathroom break. For information: putting computer to sleep was always disabled on my Mac, only screen saver and later on monitors were to trigger. Now I disabled it all, with no difference. I tried: 'caffeinate' with no difference as well.

Also, working on my Mac, performing various tasks has no effect whatsoever, but leaving it idle, goes to reboot soon.

Please help. What I was trying to find is if there's some kind of log that I could dump of a system on freeze, some entry to trace of what was the final activity before my Mac reboots. Any idea?

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    The symptoms you describe indicate an abnormal condition; using software or “hacks” to get around the problem could potentially make it worse. First step in diagnosing the problem is to boot into safe mode or to a clean install (you can do this from an external USB so as to not overwrite your existing drive). If the problem persists, it’s likely hardware. Start there and post your results
    – Allan
    Commented Dec 28, 2019 at 7:48
  • Thank you Klanomath for your response. I swapped my drive to an old system's drive, booted from it successfully, let my computer on for this night, without problem. I just switched back to my problematic drive, and tried to find a hack - opened Powerpoint presentation and put it in presentation mode. This allowed me the entire hour of breakfast without shutting down. So, this is hack for sure, but now I have something. I narrowed the timing down to, and the process that kills my system on inactivity consistently starts between 5 and 6 minutes after screensaver kicks in. Is there a trace dump?
    – QRrabbit
    Commented Dec 29, 2019 at 17:23
  • And the results of running in Safe mode or a clean install?
    – Allan
    Commented Dec 30, 2019 at 2:55

2 Answers 2

Reset to default
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Go to System Preferences | Security & Privacy | Click on "Advanced" on bottom right (unlock padlock first) | Uncheck "Logout after 10 minutes of inactivity"

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    This is an intuitive solution - the reboot could simply be the system logging the user out. +1. Oh, and welcome to Ask Different!
    – Allan
    Commented Aug 25, 2020 at 16:44
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Could not find a perm solution for above.

Using caffeinate -d command in terminal to keep the system awake.

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  • The issue isn't the computer going to sleep, it reboots after inactivity with all screen savers and power saving disabled.
    – Allan
    Commented Aug 15, 2023 at 23:56
  • Yeah, it did not work for me too. Looks like some hardware problem to me.
    – user2677679
    Commented Aug 22, 2023 at 22:47

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