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On boot, iMac Apple logo blinks red after update to Mac OS Sierra

After upgrading to MacOS Sierra, my 2015 iMac 21.5 Retina has a blinking red Apple logo and then a brief splash of screen flicker when booting. Once booted, the computer seems to run fine, with no obvious flakiness. I'm not sure why the logo blinks red and then the screen flickers -- bad drivers; a software fault in the boot phase; some issue with the fusion drive; or perhaps some other gremlin? A quick internet search reveals that at least a few others have the same issue with this OS version, and it seems to have happened in years past with other MacOS version upgrades. But there are no good answers on how to fix it. I've rebooted several times hoping it would clear itself, but no luck.

iMac, macOS Sierra (10.12), iMac 2015 21.5 4k Retina

Posted on Sep 22, 2016 7:48 PM

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2 replies
Question marked as Helpful

Oct 15, 2016 1:11 PM in response to Mike Rose1

Finally upped to Apple second level support after I found that starting in safe mode eliminated the red box flash, and had a long discussion and help from a very knowledgeable support person. Tried eliminating dozens of extensions, startup items etc and many restarts none of which eliminated the issue of the red box. Notably did not eliminate any Apple extensions. So suggest that problem is a bug in an Apple extension that is immobilized with a safe boot.

Question marked as Helpful

Nov 1, 2016 8:46 AM in response to Headhunter06

So, I tookmy imac to the Apple store on saturday....and something seemed to work...though, it blows my mind. The initial clean install of seirra wouldn't work....but going back to el capitan did. The guy I worked with seems to think the problem has to do with the 2TB Fusion drive in the imac.....something about breaking it apart...and sierra not being able to put it back together. I don't know that much about fusion drives...but that might be a reason...and might be the common denominator in this thread. So, for now....I'm not upgrading back to Sierra....I'm staying with El Capitan for at least 6 months. Why would anyone release an update like that? Now I need to disable the annoying...."DO YOU WANT TO UPGRADE?" notification.

74 replies

Sep 22, 2016 7:52 PM in response to Headhunter06

A Safe Mode boot deletes system caches that can help after an update or upgrade.


Follow these steps to start up into safe mode.

  1. Start or restart your Mac.
  2. Immediately after you hear the startup sound, press and hold the Shift key.
  3. Release the Shift key when you see the Apple logo appear on the screen.

After the Apple logo appears, it might take longer than usual to reach the login screen or your desktop. This is because your Mac performs a directory check of your startup disk as part of safe mode.

To leave safe mode, restart your computer without pressing any keys during startup.

Sep 25, 2016 12:53 PM in response to Headhunter06

Same problem, after several calls to Apple they were not aware of this. Tried several re-installs etc and tried usual repairs, removed virus checker and pruned Little Snitch. No significant issues as yet but red box still appears. Time Machine slow and slight problem with mail but neither show stoppers.

Apple suggested I take to Repair as issue does not show on Booting from El Cap on attached disk and first level support suspected damaged disk. S.M.A.R.T. checks show disk ok. I suspect some bug that will be fixed on next update.

Sep 25, 2016 4:21 PM in response to Mike Rose1

Well, my problems went from bad to worse, and now I have a repair appointment scheduled. So, since the red square thingy didn't seem to effect performance, I got all my files reinstalled after clean install and then went to setup Bootcamp for Windows. Unfortunately, Bootcamp hung during the "partitioning" stage. After 2+ hours stuck and making no progress I tried to kill it, but the "stop" button was greyed out. Left it to run for another hour hoping it would clear, but no luck. So then I killed the process manually. But now there is 300gb of space missing from my hard drive -- does not show as Bootcamp and does not show as available (or not) anywhere. Tried Disk Utility First Aid. No luck with that. So.... Now I will head over to my Apple Store tomorrow to see what they can do. I'm wondering if there is a gremlin with the Fusion drive and Sierra causing both the red box and the inability to partition. Sure would hate to have Apple replace the hard drive. But if that's what it takes, so be it. (Its still less than a year old, under warranty, and the red box/Bootcamp issues aren't my fault.)

Oct 11, 2016 6:21 AM in response to Headhunter06

I had/have this problem too with a mid 2015 iMac retina running Sierra. I worked with level 2 to no avail. I sent him a slo-mo video of the flash just to prove that I wasn't hallucinating. Otherwise it's running fine with the exception of some apps aborting when quitting. The Level 2 said he was forwarding my video to Engineering to see what they think is wrong. That was two weeks ago.


Some programmer in Apple dropped into some condition where he/she use the "red flash" to signify that they are in a situation that they should never be in but just in case they get there flash the logo red.

Oct 15, 2016 10:52 AM in response to plumsteadbb

Same problem, after several calls to Apple they were not aware of this. Tried several re-installs etc and tried usual repairs, removed virus checker and pruned Little Snitch. No significant issues as yet but red box still appears. Time Machine slow and slight problem with mail but neither show stoppers.

Apple suggested I take to Repair as issue does not show on Booting from El Cap on attached disk and first level support suspected damaged disk. S.M.A.R.T. checks show disk ok. I suspect some bug that will be fixed on next update.

Question marked as Helpful

Oct 15, 2016 1:11 PM in response to Mike Rose1

Finally upped to Apple second level support after I found that starting in safe mode eliminated the red box flash, and had a long discussion and help from a very knowledgeable support person. Tried eliminating dozens of extensions, startup items etc and many restarts none of which eliminated the issue of the red box. Notably did not eliminate any Apple extensions. So suggest that problem is a bug in an Apple extension that is immobilized with a safe boot.

On boot, iMac Apple logo blinks red after update to Mac OS Sierra

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