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I upgraded my iMac from El Capitan to Sierra about 6 weeks ago and all was working well. A few days back I decided I wanted to reinstall macOS Sierra so that I had a clean installation that wasn't upgraded from El Capitan, but was 'fresh' with no old files etc.

The first problem I ran into was an endless loop during installation so I posted this question: Stuck in endless macOS Sierra installation loop . Monomeeth got me past this problem by creating a USB installer.

Then I had an issue with kernel panics upon startup after reinstalling Sierra, so I posted this question: Finally reinstalled macOS Sierra, but now I get a kernel panic and William T Froggard and Monomeeth helped me get past that.

Then I got this error message:

enter image description here

Note that is a reflection in the photo, not a GPU problem.

So I followed the advice and tested my hardware. I selected the extended test and over an hour later the test found no issues. But when I restart and try again, it keeps bring me back to the above error.

I do not believe I have a hardware issue as there were no signs of problems before I decided to reinstall macOS Sierra. As I mention in my first question, I decided to reformat the HD by doing a 2 pass secure erase and this was successful. So I think that means I have no problems with my HD right? Plus the 1hr hardware test passed also.

Note that I have already tried booting into the recovery from the recovery partition, and from the internet. I have tried both these options many times. None seem to work. If I hold down alt/option during startup I see a macOS Installer option and a Recovery option:

enter image description here

I have tried both more than once and always get stuck in some sort of loop.

  • Either I boot from the macOS Installer option and get the error in the first image above which goes round in circles because AHT finds nothing and we do it all over again.
  • Or I boot into recovery and get the whole endless loop described in my first question Stuck in endless macOS Sierra installation loop that Monomeeth helped me with.
  • Or I try and boot again from the USB installer Monomeeth helped me create, but while it worked the first time to reinstall macOS Sierra, now I get a gray screen after selecting English for my main language. I'm not sure how this is even possible! Why did it work the first time but not now?

Obviously I wish I never decided to reinstall macOS Sierra, but now that I have, what do I do from here to get it back on this computer?

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  • Does the installer give the same error when attempting to install to an external HDD? Since you've got access to another Mac, does the iMac boot successfully if you create an external bootable volume and boot from that? What model iMac do you have?
    – JMY1000
    Commented Jun 9, 2017 at 4:55
  • Thanks @JMY1000 for helping. The iMac in question is a mid-2011 27" model. I just tested it by putting a 2012 MBP in target disk mode and booting it from that. It booted fine and seems to run fine. The MBP also has macOS Sierra installed. What does this tell us?
    – user240852
    Commented Jun 9, 2017 at 7:09
  • Have you tried to reset the harddisk in your iMac?
    – Harcker
    Commented Jun 9, 2017 at 8:55
  • If by 'reset' you mean erase, then yes, I secure erased it two days ago.
    – user240852
    Commented Jun 9, 2017 at 9:59
  • @user240852 Any hardware customizations like a new HDD/SSD?
    – klanomath
    Commented Jun 9, 2017 at 14:02

2 Answers 2

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I've been looking over your other questions and the whole history of your situation and feel like we're missing something here. Not blaming you, I just think something unbeknown has happened (e.g. a power failure at some point you're not aware of that has caused some corruption).

So, I'm suggesting you do as follows:

  1. Start your iMac in Target Disk Mode
  2. Connect it to your MBP (make sure the MBP is connected to AC power)
  3. Run Disk Utility from the MBP to erase the iMac HD (no need to do another secure erase) and also run First Aid
  4. Assuming you don't encounter any errors, do a fresh download of the install macOS Sierra app from the Mac App Store (i.e. do not run the installer from the USB installer you created, but download a fresh copy from the App Store directly to your MBP)
  5. Now run the installer from the MBP
  6. Follow the steps to install macOS Sierra (ensure you select the iMac's HD to install it on)

Let me know if you run into any problems, but hopefully this will resolve the issue once and for all as it eliminates a number of possible problems.

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5

The most likely culprit is that your hard drive has failed or is in the process of failing.

You've provided lots of good info so let's see if we can digest it all...

The iMac in question is a mid-2011 27" model. I just tested it by putting a 2012 MBP in target disk mode and booting it from that. It booted fine and seems to run fine.

This means that your iMac is more than capable of running Sierra and the only component you've isolated that has eliminated your problem is your hard drive.

As I mention in my first question, I decided to reformat the HD by doing a 2 pass secure erase and this was successful. So I think that means I have no problems with my HD right? Plus the 1hr hardware test passed also.

Not necessarily. A two pass erase simply writes data to the drive. The trick here is to do a verification after the write (read the data back). I have seen many instances where a drive was failing but failed (pun not intended) to report that it was failing.

Many people like to "stress test" their drives in the hope that it somehow fixes things. This is roughly what you did and it ultimately doesn't make anything better.

The first problem I ran into was an endless loop during installation so I posted this question: Stuck in endless macOS Sierra installation loop . Monomeeth got me past this problem by creating a USB installer.

Again, here we are bypassing the installer by getting it on the USB and not the installer located on the hard drive. You have effectively isolated your HDD (again) and eliminated the problem (to a point).

From your previous post:

enter image description here

vfs_mountroot is what mounts your root file system that's located on your hard drive. At the risk of oversimplifying things, your kernel has loaded, but when it tries to load the rest of the OS, things break. This is the "panic" because without it, you can't do anything so it's (figuratively) throwing it's hands up the in the air "panicking."

Further down (from the same post) we have this little gem:

enter image description here

This is telling us that the kernel that got loaded was the install media but that's as far as it got. Since it couldn't mount the root file system, it stopped here. It couldn't read the drive, so it couldn't go any further.

To Summarize (and TL;DR) ....

  • You have a 2011 iMac with the original HDD, so it's at least 6 years old. If I remember correctly the lifespan of the drives installed in the iMac was rated at 3 years1. If you got 5/6 years out of it, you're pretty lucky and pretty much on borrowed time.

  • Each time you isolate your internal HDD from the equation; Target Disk Mode with a MBP and/or install from USB, it works fine.

  • If you want to further verify this, get an external USB drive and install/boot Sierra from that. If it works, then you know it's your internal drive.

Your fix...

Get a new drive; go for an SSD (I use Samsung EVO 850 in my iMac and swear by it). Your 2011 iMac has it's screen held in with magnets and Torx screws (as opposed to the 2012 and up which uses glue). Ifixit.com has an excellent tutorial on doing this drive replacement It's rated as "moderate" mostly because the screen is large and unwieldy. But, if you take your time, you can do this with no problems

1 Per iFixit.com: Installed drive was WD Caviar Blue. WD Warranty at the time was 3 years. Source: WD Warranty Policy

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  • +1 Agreed. I think this is the most likely culprit. And you've done a fantastic job of explaining how the process of elimination works and why you've narrowed it down to the HDD. My guess is the OP will get an error at Step 3 of my instructions (assuming they opt to follow them) and this will only confirm the HDD fail as well.
    – Monomeeth ♦
    Commented Jun 10, 2017 at 3:49
  • Thanks Allan. Both you & @Monomeeth were right. I tried Monomeeth's steps & did get an error at Step 3, but because it said to run First Aid from Recovery & I was running it from the MBP, I decided to keep going with Monomeeth's steps to see what would happen. This actually worked and I now have macOS Sierra installed on the iMac. But now it seems I can't always log in. If I run Disk Utility First Aid I get different results. Sometimes it's all good or I get a "File system check exit code is 8" message or I get a "Problems were found with the partition map which might prevent booting" message.
    – user240852
    Commented Jun 11, 2017 at 11:06
  • I guess this means Allan that what you said about my hard drive "is in the process of failing" is true. :( Since I was planning to sell this iMac, I do not think going with an SSD is worth it. Do you agree? I assume if it's not too hard I can replace the hard drive with a new 1TB drive? Do you agree? Any other suggestions?
    – user240852
    Commented Jun 11, 2017 at 11:07
  • @user240852 Personally, I think you've come to the right decision. However, you'd be able to install a 2TB or even 3TB hard drive at not too much more expense and this would more than pay for itself by making the iMac more desirable to potential buyers. Regardless of what you decide, I strongly suggest you make sure you get a 7200rpm model. However, if you decide to keep the iMac, then seriously consider Allan's advice to get a SSD. Or, another option is to go with a hybrid drive (basically the same thing Apple calls a fusion drive) as you can get 1TB or 2TB models for not too much.
    – Monomeeth ♦
    Commented Jun 11, 2017 at 11:17
  • If you're going to sell it, sell it now that it's working. If the HDD is too far gone, look at getting a used one from eBay - basically try to spend as little money for it as you can because you're not going to recoup the cost. If you're going to keep it; go with an SSD.
    – Allan
    Commented Jun 11, 2017 at 11:48

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