I'm trying to use the disk utility to erase my iMac but get Erase process has failed unmounting disk Couldn't open device.: (-69877) What steps do I need to take to initiate an erase and clean install?
iMac with Retina 5K display, macOS 10.15
In order to erase your disk it should be inactive. That means that you can't erase the disk you are currently booted from.
Boot from the external disk and then erase your internal one - there should be way to go.
How to create a bootable installer for macOS - Apple Support
You may also use Recovery Mode from the Internet:
Hey there!
Make sure you are erasing the Boot Disk while you are in recovery mode. See How to erase a disk for Mac – Apple Support for steps on how to erase your disk.
If you are still encountering issues erasing the disk, you may need to try running first aid on the disk. See Repair a storage device in Disk Utility on Mac - Apple Support for steps on running First Aid in Disk Utility (do this while in Recovery Mode).
Best of luck! Let us know how you go.
I'm trying to use the disk utility to erase my iMac but get Erase process has failed unmounting disk Couldn't open device.: (-69877) What steps do I need to take to initiate an erase and clean install?
