Problem erasing disk on my old iMac

Question

Level 1

6 points

Problem erasing disk on my old iMac

I want to sell or give away my old (mid 2011) iMac. But first I want to erase the disk so that my files and data can't be misappropriated. I've got as far as the Disk Utility in macOS Recovery Mode and selected the internal hard drive, clicked on Erase and then Erase again. But the process fails. When I click on Show Details it says:

Unmounting disk

Couldn't unmount disk

Operation failed

Can anyone help me with how to overcome this problem, please?

iMac 21.5″, macOS 10.13

Posted on May 25, 2020 10:42 PM

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Answer 1

BDAqua

Level 10

245,573 points

May 27, 2020 10:04 AM in response to edmundpw

You mean this part didn't work?

How to erase your disk

Start up from macOS Recovery. Then select Disk Utility from the Utilities window and click Continue.
If you're not erasing the disk your Mac started up from, you don't need to start up from macOS Recovery: just open Disk Utility from the Utilities folder of your Applications folder.

Choose View > Show All Devices from the menu bar in Disk Utility. The sidebar now shows your disks (devices) and any containers and volumes within them. The disk your Mac started up from is at the top of the list. In this example, Apple SSD is the startup disk:

https://support.apple.com/en-us/HT208496

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Answer 2

Ronasara

Level 6

15,115 points

May 26, 2020 12:06 PM in response to edmundpw

Maybe this will help you. Go to

What to do before you sell, give away, or trade in your Mac - Apple Support

This site should provide you with the specific steps to follow. Hope that helps.

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Answer 3

edmundpw Author

Level 1

6 points

May 26, 2020 10:56 PM in response to Ronasara

Thanks for the suggestion but unfortunately it doesn't help as I still get to the same point when I try to erase the disk and it says it can't be unmounted.

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