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Help reinstalling macOS

Hi everyone,


I tried to format my old MacBook air (later 2013) by rebooting into recovery mode > disk utility


I erased the main MacOS partition and I think where I made a mistake is that I also erase the MacOS recovery partition


So my Macbook won't boot up and the internet recovery gives me a -2001f error message.


So I figured the only way to fix this would be to create a bootable flash drive with a MacOS installer.


To make things a little bit more complicated, since my Macbook Air is not working I'm using a PC to create the bootable flash drive.


With a PC I can't just download MacOS High Sierra from the appstore so I had to find it online.


I managed to download MacOS High Sierra but for some reason in an .iso file and not a .dmg.


I used TransMAC to create a MacOS bootable USB installer then installed (following these steps https://www.winytips.com/mac-os-usb-bootable-installer-windows-pc/)


The USB installer was successfully created, I connect it to my mac and hold down the key OPTION to boot on the USB drive. Install MacOS Sierra appears on the screen, but when I click on reinstall MacOS High Sierra in the MacOS Utilities to said that the installation file was damaged?


Then I proceeded to go to diskpart, highlighted the SSD and clicked on restore which seemed to work as now under my SSD I can a partition called OS X Base System


I reboot my laptop, this time normally, not booting on the USB installer and yeah I get the Apple logo (before I would get the folder icon with a question mark).


However, MacOS doesn't boot. It's taking me to MacOS utilisies.


I thought I just needed to reinstall MacOS, so I click on reinstall Mac OS, but when I'm asked to select the disk where I want to install MacOS, my disk is greyed out and when I click on my disk it says "This disk is locked"


So yeah I'm stuck there. Cannot reinstall MacOS. Online I see people saying to go to Diskpart and erase the partition but erase is greyed out for me




I ran out of ideas at this point.


Would someone know how to unlock my disk so I could reinstall MacOS?


Many thanks



MacBook Air

Posted on Sep 10, 2021 3:28 AM

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Question marked as Top-ranking reply

Posted on Sep 10, 2021 5:58 AM

So I tried using another wifi network, I created a hotspot with my phone and somehow the internet recovery mode worked straight away.

MacOS Big Sur installer launched after 5 min.

Clicked on install MacOs, my disk was greyed out and it said that my disk was not formatted in Mac OS X Extended.

So I went back into diskpart, selected my SDD, this time the erase button wasn't greyed out. Selected Mac OS X Extended and clicked erase.

Erase successful

Went back to the main menu, tried to install MacOS Big sur and this time around I could select my disk.

MacOS is now being installed now


So it seems like the issue was internet provider which didn't connect to Apple servers hence giving me the 2002 error.


Go figure.



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Question marked as Top-ranking reply

Sep 10, 2021 5:58 AM in response to Sephirote

So I tried using another wifi network, I created a hotspot with my phone and somehow the internet recovery mode worked straight away.

MacOS Big Sur installer launched after 5 min.

Clicked on install MacOs, my disk was greyed out and it said that my disk was not formatted in Mac OS X Extended.

So I went back into diskpart, selected my SDD, this time the erase button wasn't greyed out. Selected Mac OS X Extended and clicked erase.

Erase successful

Went back to the main menu, tried to install MacOS Big sur and this time around I could select my disk.

MacOS is now being installed now


So it seems like the issue was internet provider which didn't connect to Apple servers hence giving me the 2002 error.


Go figure.



Sep 10, 2021 4:05 AM in response to Sephirote

User wrote " So my Macbook won't boot up and the internet recovery gives me a -2001f error message. " The error message -2001f indicates there is a very weak or No Internet Connection


To achieve the Internal Recovery Mode - command + Option + r key and Immediately look for the Wifi Icon.


You will have to click click on the Icon and Manually Input the wifi Password. To avoid this tricky method better to connect via Ethernet Cable to Router.


Further, even if you can download the Full Installer ( doubtful ) on a Windows PC - the Create a Bootable Installer can not be done on any other platform but from an Apple Computer

Sep 10, 2021 4:10 AM in response to Sephirote

The first mistake was to erase your macs hard drive without having a means to reinstall the OS,

you should not rely on Apples Recovery Servers.


You should have downloaded a copy of macOS High Sierra and created a bootable USB flash drive installer,

and used that to erase your drive and install macOS High Sierra.


Transmac does not work for creating bootable flash drives for macOS.


Are you able to borrow another mac, and download macOS High Sierra and then create a bootable

USB installer on that mac. Then use that to install macOS High Sierra.


Mac OS X Base System is Apples Servers.


If you can't borrow a mac, then you may have to try the Apple Recovery Servers.


Boot to your Recovery HD, restart the mac while pressing and holding down the Command and R keys.


Open Disk Utility, click on View in the menubar and select Show All Devices.(Select All Devices will be on macs running

High Sierra or newer)


Highlight the Disk not any of the indented Volumes (Disk is called Apple SSD SM0....)


Click Erase.

Give the Disk a name.

Format: APFS (for macOS High Sierra) or Mac OS X Extended (Journaled) {for macOS Sierra or earlier}

Scheme: GUID Partition Map.

Click Erase.

When Done quit Disk Utility.


The certificates for several of Apples OS's expired in October 2019, Apple haven’t bothered getting these updated on 

their Recovery Servers with valid certificates. 


This may be the problem you are experiencing. 


Try this workaround, we are going to set the time and date on your mac to a date previous to the expiry date of the certificates.


Connect your mac to your router via cable, not WiFi


Boot to your Recovery HD, click on Utilities in the menubar select Terminal.


Make sure WiFi is switched off, it can reset the date back to today.


Enter a new date, for example or just copy and paste


sudo date -u 011421002017


press Return

enter your password

press Return


If Terminal returns an error saying sudo : command not found, then try again without sudo.

just enter 


date -u 011421002017


press Return


You won't be prompted for a Password if you did not need to use sudo


Once the date has changed you can quit Terminal.


Now try downloading the OS.

Click on Install OS X, press Continue.


If this works then when the OS is installed and booted up you can Open System Preferences> Date & Time

and reset the time back to today.

Sep 10, 2021 5:12 AM in response to PRP_53

Thanks for your reply.


Helpful to know what the -2021f error is.

Though I doubt that a weak signal was the issue. I'm 2m away from the router and my PC have a strong signal exactly in the same location.


Though I think it's a good idea to try to connect to internet via ethernet. It's a MacBook air so it doesn't have a ethernet port but I do have a Apple USB to ethernet adaptor. Just connected my MacBook to my router via ethernet and booted in internet recovery mode.

It's still showing the Wifi icon. I'm not sure if it's connected via ethernet? It says I'm connected to my wifi (I can see the name of my wifi displayed below the rotating earth)


Does the Apple USB to Ethernet adaptor works in recovery mode?


EDIT: I'm sorry, the error was -2002f not -2001f.

I just got the error again now

Sep 10, 2021 5:24 AM in response to Eau Rouge

"Boot to your Recovery HD, restart the mac while pressing and holding down the Command and R keys.


Open Disk Utility, click on View in the menubar and select Show All Devices.(Select All Devices will be on macs running

High Sierra or newer)


Highlight the Disk not any of the indented Volumes (Disk is called Apple SSD SM0....)


Click Erase."


When I boot while pressing and holding down the command and R key, it boots into Internet recovery mode.

CMD+R no longer works to boot the Recovery mode (it used to boot the recovery mode, but since I erased the partitions, CMD+R takes me straight to the Internet recovery mode now)


So I just booted the mac normally without holding down any key. Apple logo appears, it thinks for 30s and then boots into Recovery mode.

I go into Disk utility> View> Show All Devices


It gives me the below:


Apple SSD SM12XXXX

OS X Base system


When I select Apple SSD, the erase button is greyed out as shown in my screenshot above. I cannot follow your instructions because I cannot erase the partition

Sep 10, 2021 5:40 AM in response to PRP_53

In the internet recovery mode, I don't see any option to turn off wifi?

There is no option to use an ethernet connection either.

It only says choose a network and it's only showing wifi networks. I turned off my router's wifi and now it's just showing my neighbor's wifi networks.

I booted into recovery mode, turned off the wifi on the utility page.

Booted back into internet recovery mode and still no options to choose an Ethernet network.



Help reinstalling macOS

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