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Trying to reset my iMac to factory to give as gift. When in Disk utility and pressing erase for the main internal it won’t do it and pop up says “couldn’t in mount disk”!!? What’s up? How can I erase? Thanks
iMac 27″, macOS 10.12
1. In the Disk Utility app on your Mac, choose View > Show All Devices.
Note: If you’re checking your startup disk or startup volume, restart your computer in macOS Recovery, select Disk Utility in the macOS Utilities window, then click Continue.
1. In the Disk Utility app on your Mac, choose View > Show All Devices.
Note: If you’re checking your startup disk or startup volume, restart your computer in macOS Recovery, select Disk Utility in the macOS Utilities window, then click Continue.
I have the same problem. I restarted in Recovery Mode, tried to erase the startup disk and got the messages "Unmounting disk; Couldn't unmount disk; Operation failed...". How do I erase this disk before giving the computer away. It is an iMac 27 inch, mid 2011, running High Sierra.
I just started up the iMac in target disk mode and tried to erase the startup disk from my other iMac. It started, then gave me the messages "Unmounting disk; Couldn't open device. : (-69877); Operation failed...". What now?
Except I made a mistake. I erased the startup volume and hard disk which apparently erased the hidden recovery mode partition. The correct way was to just erase the startup volume. I ended up having to restore everything using an ethernet connection to the computer. Good luck.
Any luck yet?
Finally successful. I erased the volume within the hard disk and then was able to erase the startup disk.
Whew, great to hear, was it just waiting for fsck to finish before it could unmount it?
Ah, take care my friend! :)
Trying to erase disc, getting “couldn’t I mount disk” error message?
