Reinstall macOS after factory resetting my 2015 MacBook Air

Question

Reinstall macOS after factory resetting my 2015 MacBook Air

Hi! I have decided to sell my old 2015 MacBook Air, and so I performed a factory reset on the laptop. However, I am now unable to reinstall macOS from macOS Utilities. After initialling resetting it, my screen popped up with the spinning globe prompting me to do an internet recovery. My computer shut down immediately after connecting to my WiFi network, and when I powered it back on, the prohibitory symbol (circle with dash through it) appeared on the screen. I then followed the steps to press Command + R , in order to access the Disk Utility page. I am now unable to reinstall macOS when I try due to error messages appearing on the screen. I have absolutely no idea how to fix this issue. The laptop was working perfectly fine before I decided to do a factory reset.

Another note, before I did a factory reset on my device, it was running macOS Big Sur, but now when I attempt to reinstall macOS, it shows macOS Sierra and not Big Sur. Why would this be happening?

Posted on Jan 15, 2021 8:17 PM

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Answer 1

HWTech

Level 9

60,554 points

Jan 17, 2021 4:43 PM in response to sarahfromarmidale

If you are attempting to install macOS 10.12 Sierra, then you need to erase the entire physical SSD. You have highlighted the physical SSD in your second screenshot. Erase the physical SSD as GUID partition and MacOS Extended (Journaled). Once properly erased you should be able to select "Install macOS".

If Internet Recovery Mode gives you problems, then create a bootable macOS USB installer using another Mac. Or connect the MBAir 2015 directly to the router using an Ethernet Cable & a Thunderbolt to Gigabit Ethernet Adapter.

Also here are all the steps you should have performed before erasing the SSD whenever you are selling an Apple computer:

https://support.apple.com/en-us/HT201065

Edit: Even though macOS 10.12 Sierra is able to recognize an APFS volume it is only very basic support. Sierra cannot be installed to an APFS volume. Even if it could be installed to an APFS volume you should still erase the whole physical drive.

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Answer 2

Jan 17, 2021 6:13 PM in response to HWTech

Hi! Thank for you the reply! I have tried to erase the physical SSD (AppleAPFSMedia) as GUID partition and MacOS Extended (Journaled), however it says the erase process has failed. When I click "details", it says it couldn't unmount the disk and so the operation failed. Is there any way to fix this?

Thank you for all the help!

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Answer 3

HWTech

Level 9

60,554 points

Jan 17, 2021 7:44 PM in response to sarahfromarmidale

Are you booted into Recovery or Internet Recovery Mode or from a USB installer? If so, then you may need to launch the Terminal app from the Utilities menu and force unmount all the volumes on the internal SSD. In theory the internal SSD should be "disk0" (you can confirm by checking Disk Utility) so the following command should unmount all volumes on the internal SSD:

diskutil  unmountDisk  force  disk0

If this command completes successfully, then quit the Terminal app and launch Disk Utility to erase the whole physical SSD before installing macOS. I had to do this recently because even in Recovery Mode macOS would not unmount the disk normally.

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Reinstall macOS after factory resetting my 2015 MacBook Air

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