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High Sierra Upgrade fails with: An error occurred while verifying firmware

I've tried a number of times to upgrade my iMac 2011 21.5" to High Sierra and each time it fails with the message:


macOS could not be installed on your computer

An error occurred while verifying firmware


My machine was "fixed" by Apple about 10 months ago after a failed disk drive. It was a dual "fusion" drive with 1TB HDD and 128 GB SSD. Now is the same. Has loads of free space and seems to work well.

iMac (21.5-inch, Late 2012), macOS Sierra (10.12), null

Posted on Sep 28, 2017 9:53 PM

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Posted on Sep 29, 2017 1:07 PM

Here is the fix -- thanks to petterihiisila of Finland posting on the MacRumors site:

Firmware error with High Sierra?! | MacRumors Forums


I booted into rescue mode, checked the partitions with "diskutil list" and "verifydisk" (terminal), and fixed the EFI partition. "diskutil repairdisk <your EFI disk/partition>".


You can find more details of the error in the ia.log file, in the installation directory. Look for lines related to firmware, it might refer to inability to mount the MS-DOS EFI partition. That's what I had. But I don't have the logs anymore.

I did the fix above without booting into rescue mode. High Sierra install went without a hitch afterwards.

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Question marked as Best reply

Sep 29, 2017 1:07 PM in response to stentor007

Here is the fix -- thanks to petterihiisila of Finland posting on the MacRumors site:

Firmware error with High Sierra?! | MacRumors Forums


I booted into rescue mode, checked the partitions with "diskutil list" and "verifydisk" (terminal), and fixed the EFI partition. "diskutil repairdisk <your EFI disk/partition>".


You can find more details of the error in the ia.log file, in the installation directory. Look for lines related to firmware, it might refer to inability to mount the MS-DOS EFI partition. That's what I had. But I don't have the logs anymore.

I did the fix above without booting into rescue mode. High Sierra install went without a hitch afterwards.

Nov 11, 2017 10:00 PM in response to desnjm

Here’s the layman’s guide 🙂


Step1: Open Terminal (press cmd+space then type terminal to open terminal)


Step2: Type sudo diskutil verifyDisk disk0

(you may be prompted for a password)


Step3: If an error is listed proceed to step 4

(The error I got was - “Problems were found with the partition map which might prevent booting

Error: -69766: The partition map needs to be repaired because there's a problem with the EFI system partition's file system

Underlying error: 8: Exec format error”)


Step4: Type sudo diskutil repairdisk disk0


Step 5: type y

(Repairing the partition map might erase disk0s1, proceed? (y/N) y - AFAIK the chance of it erasing is 0% however perform a backup if worried, I risked it aha)


Step 6: Install High Sierra!



Good luck!

Nov 15, 2017 2:05 PM in response to KingPinUK

I did tis, and I get an error repairing disc0.

Started partition map repair on disk0

Checking prerequisites

Checking the partition list

Adjusting partition map to fit whole disk as required

Checking for an EFI system partition

Checking the EFI system partition's size

Checking the EFI system partition's file system

Repairing the EFI system partition's file system

Updating boot support partitions for the volume as required

Creating a new EFI system partition

Checking the EFI system partition's folder content

Problems were encountered during repair of the partition map

Error: -69854: A disk with a mount point is required

Dec 11, 2017 4:16 PM in response to stentor007

Hm, I don't think this is applicable when the hard drive is blank. I've replaced my hard drive, booted the High Sierra installer from a USB drive, formatted the hard drive, and started the installation to it. I ran Disk Utility's First Aid on it beforehand, which found no errors.


I know the installer is good, because I used it to update a different computer.

High Sierra Upgrade fails with: An error occurred while verifying firmware

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