How To Fix A Randomly Rebooting Mac (OS X 10.8 – Mountain Lion)

Image representing Apple as depicted in CrunchBase
Image via CrunchBase

My iMac was rock stable, right up until I installed Mountain Lion on it.  Then, at random times, it would suddenly reboot.  Fortunately, most of it seemed to happen at night – I’d get up in the morning and find my Mac had rebooted.


So, I finally got around to investigating the problem – I had’t seen any good blog posts on it (most of them were things like take it to a Mac Genius).  Finally, I found a hint buried in an Apple forum:  the problem stems from Spotlight.  The indexes for Spotlight get corrupted, and that causes the reboot.  Ah-ha!  So the solution is pretty simple – have Spotlight dump all it’s current stuff, and build up again from new.  Of course, there’s not an obviously marked way to do this 🙂

Go into System Preference, and select Spotlight.  Click on the Privacy tab.  There probably isn’t anything listed under “Prevent Spotlight from searching these locations:”  We’re going to add one. Hit the “+” at the bottom, and select your Mac’s hard drive, and click Choose.  It’s now in the list.

Close System Preferences, and reboot your Mac once.  Then, go back into System Preferences -> Spotlight -> Privacy, and remove the drive you added.  Just click on the drive in the list, then click “-” at the bottom of the list.

After that, everything had been going great! 🙂  No more random reboots for me 🙂

Intel-CPU based iMac with a 27 inch 16:9 aspec...
Intel-CPU based iMac with a 27 inch 16:9 aspect ratio screen, released by Apple in October 2009. (Intel based iMac models released prior to October 2009 used screens with a 16:10 aspect ratio. PowerPC-based iMacs released 1998–2005 used screens with a 4:3 or 16:10 aspect ratio.) (Photo credit: Wikipedia)

One additional bit:  Having Mountain Lion randomly reboot is a lot less painful than when versions older than Lion would reboot.  Most of the apps I use are state aware, so for the most part when the iMac comes back up restores all my workspaces to what it was before 🙂

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18 thoughts on “How To Fix A Randomly Rebooting Mac (OS X 10.8 – Mountain Lion)”

  1. My MacBookPro (mid 2010) has been stable as hell since I got it. Never felt the need to upgrade from SnowLeopard. But last week I upgraded and I got two kernel panics already. So hope your method works, would be awesome.

  2. ill give it a try lets see in a few days if this works???!! coz it reboots atleast 5 times in an hr sometimes. i took it to apple care and they said there is nothing wrong with it…i wish i cud downgrade back to snow leopard…at least it was running smoothly..i cant get nethng done on this computer..

  3. I was searching for weeks and finally came across and article that mentioned how these random restarts are a glitch in mid-2010 Macbooks that Apple will replace free of charge. Being that I had already tried every logical other alternative out there with no success, I went into the the Apple store (for a second time, the first, they were clueless), showed them the article and they were like “oh yeah” must be the glitch.

    Replaced my logic board for free. Issue has not occurred since. Happy days! Apple evidently didn’t want to make the glitch knowledge readily available because they thought too many people would claim the fix. I think that’s pretty shady, but I’m happy my computer finally works correctly. 😐

  4. Glad that Apple fixed it for ya! There’s nothing that drives me more nuts than a machine that randomly reboots!!! 🙂

  5. I faced the same things as mentioned by you.. It all started after upgrading my OS from Snow Leopard to Mountain lion. Hope this strategy works! Thanks man!

  6. Any idea why my mid 2010 i5 MBP with ML would be restarting every time Time Machine wants to do a backup?

    Everything crapped out due non Apple RAM installed from a year ago. Had to do a full restore from TM, which worked. It wants to do a long backup now, and restarts my comp every time after an hour or so.

  7. Worked like a champ — at first.

    For the past three days my iMac would not only reboot, but immediate shut down. It took three days to get the iMac to actually boot up — and stay on — long enough to get into the the System prefs to monkey around. It worked at first, but as soon as I removed the HD from the “ignore” list, the iMac’s rebooting began again. Updates appreciated.

  8. the fix worked for about three days, then the rebooting resumed. fixed again with the ‘spotlight’ method but wondering if i should upgrade to mavericks?

  9. thanks sir..
    you did a really great job. thanks for searching, my macbook was rebooting after 5 mint. i have done your steps. i will wait and see. but i think its stable now. thanks again

  10. Thanks for charing! So far so good! I had problems with rebooting but I did what you suggested and it seems to work for me. I have been ok for some days now. I will work tomorrow and then the big test will come… 🙂

  11. Im running Yosemite 10.10.1 on a Hackintosh build. These builds are prone to have issues, but I was somewhat pleased to see regular Macs were having this issue as well, so it’s not just entirely a Hackintosh error.

    Just tried your fix on my build, hope it works! Its super frustrating to lose a bunch of progress on photoshop ._.

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