I tried factory resetting my Macbook Air following a guide on Macworld, and the first thing I did I went to Disk Utility (in Recovery Mode) and erased Macintosh HD – Data, but now it won't let me erase Macintosh HD. It says that it couldn't be unmounted because it is in use by process 712 (kextcache). Tried unmounting and it won't let me either. What should I do? Right now i can't even book an appointment at the Genius Bar because of Covid.
MacOS – Tried factory resetting the Macbook Air but won’t erase disk
disk-utilitymacosrecovery
Related Solutions
Your option is to continue letting it download. Apple does give the installer file, through Recovery Mode.
It sounds like you have an exceptionally slow Internet connection. I recommend that you do this somewhere with a better connection.
It sounds like there is a problem with the USB installer. To confirm this, restart holding Option + R to return to Disk Utility, and verify you formatted the drive as "Mac OS X Extended (Journaled).
If you have a working bootable usb, holding the "option" key should show you the Startup Manager menu:
https://support.apple.com/en-us/HT204417
Here are a few tutorials on creating Bootable USB OS X installers:
http://www.intowindows.com/how-to-create-mac-os-x-yosemite-bootable-usb-using-diskmaker-x/
Best Answer
Try erasing the entire drive, not just the volumes.
In Disk Utility, Hit Cmd ⌘ 2 (or see the View menu) to show Devices instead of just Volumes. Select the overall drive you will now see over the volumes (now in a disclosure triangle instead of separate) and Erase that, GUID/APFS.
If you aren’t following an internet recovery factory erase, here is the best one:
Click through to the erase portion.
Selecting the correct item in Disk Utility almost always gets an erase completed without reverting to the terminal app and command-line tools. Also, Apple Support is now delivered almost entirely without Genius Bar visits.