How to Create a Fresh Internal Boot Drive for an erased iMac

Question

How to Create a Fresh Internal Boot Drive for an erased iMac

I have a 2018 iMac with fusion drive which I have been booting from an OWC external SSD for faster computing. I erased the internal drive in the [apparently mistaken] belief that the OS was locked of and couldn't be erased. I now find that internet recovery is impossible.

I have the SSD external boot drive, and also Time Machine and Carbon Copy Cloner backups on a Western Digital Elements drive. I also have a MacBook Pro (13-inch, 2017)

What options do I have for getting the iMac back in working order and able to boot from the latest Mac OS? Can anyone offer links with step by step procedures?

Any help will be appreciated.

iMac 21.5″, macOS 10.15

Posted on Sep 24, 2021 5:24 AM

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Answer 1

padams35

Level 4

3,613 points

Sep 24, 2021 8:19 AM in response to BillfromPyrmont

Option one: with the time machine connected hold option to enter the boot selector, then select the time machine’s recovery partition.

Option two: create a bootable USB installer. https://support.apple.com/en-us/HT201372

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Answer 2

Sep 25, 2021 12:12 AM in response to BillfromPyrmont

By connecting bluetooth keyboard to iMac by cable the Cmd R is able to work.

I'm now able to commence recovery.

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Answer 3

rkaufmann87

Level 10

148,470 points

Sep 24, 2021 8:23 AM in response to BillfromPyrmont

I would recommend restarting the iMac in the Recovery Partition (hold down Command + R on startup) and install Mac OS on the internal drive.

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Answer 4

Sep 24, 2021 11:31 PM in response to padams35

Thanks for those options. I followed your first suggestion, which seemed to proceed as expected. However, when I returned to the computer after the predicted recovery time had expired, an error window [see image attached] said " Unrecoverable err. SecurityAgent was unable to create requested mechanism builtin:prelogin."

I have tried to reboot with the external SSD both attached, an not attached, but the same message appears.

I've attempted recovery with CMD + R, but the message also appears.

The iMac seems to be attempting to boot from the internal drive, and I have no way to direct it to the external drive.

It may not be relevant to the "SecurityAgent" message, but the internal logic board was replaced under warrantee, early in the life of the computer. Could this be interferring?

Any thoughts on what to do next? Or, where to repost the question?

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How to Create a Fresh Internal Boot Drive for an erased iMac

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