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MacOS Big Sur Installation failed

Hi all,


I am unable to start my homescreen/desktop after trying to install macOS Big Sur (MacBook Air 2015). Error Message: „An error occured preparing the software updates“. I can only choose between the options target disk mode or restart or shut down. No options available to get back to my homescreen. And I cannot select a system (startup disk) to start up my computer.

What can I do to get out of this?

MacBook Air

Posted on Feb 3, 2021 4:08 PM

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Question marked as Top-ranking reply

Posted on Feb 10, 2021 4:58 AM

Hello all,


for me it helped that I put my Mac in Target Disk Mode and connected it to another Mac via a Thunderbolt cable. Now it is possible to use the Mac as an external hard drive. "Macintosh HD Data" was still locked. But after deleting the "Macintosh HD" drive, I had access again after entering the usual password. Then I could backup my data from „Macintosh HD Data“ and set up my Mac again by reinstalling macOS. I can't guarantee it will work, but it worked for me.


Best regards

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11 replies
Question marked as Top-ranking reply

Feb 10, 2021 4:58 AM in response to Holmesley72

Hello all,


for me it helped that I put my Mac in Target Disk Mode and connected it to another Mac via a Thunderbolt cable. Now it is possible to use the Mac as an external hard drive. "Macintosh HD Data" was still locked. But after deleting the "Macintosh HD" drive, I had access again after entering the usual password. Then I could backup my data from „Macintosh HD Data“ and set up my Mac again by reinstalling macOS. I can't guarantee it will work, but it worked for me.


Best regards

Feb 6, 2021 11:38 AM in response to LukeTheKing

Hello LukeTheKing,


We see your Mac is not showing a startup disk after trying to install Big Sur. We'd be happy to help.


Could you tell us which macOS you had before performing the upgrade?


Since seeing this message, have you tried the restart option?


Do you have any peripherals connected to your Mac? If so, we'd like you to disconnect them when trying to update.


Have you tried running First Aid? Let's give that a try with these steps: How to repair a Mac disk with Disk Utility


Take care.

Feb 6, 2021 12:38 PM in response to jdo_apple

Hi jdo_apple,


I have tried several options like safe mode, internet recovery or recovery mode. Nothing’s working for me.


Before performing the update I had macOS Catalina (10.15.7) installed.


In the meantime I am able the click on my startup disk, but my Password gets rejected all the time. Even though it‘s 100% right. I can log in to my account (not to encrypt the disk) without being rejected, but the systems loops and tries to restart itself many times. Therefore I cannot use the Disk Utility repair option.


What du you think about the target disk mode? Seems to be my last option.


Feb 7, 2021 6:25 AM in response to jdo_apple

Hi, i have had the exact same problem as they guy you responded too and i’m wondering if you could help me. I have a 2020 macbook air that was previously in catalina. I’ve been putting off doing the big air update because i’ve had disk storage issues but i’ve now got around to it because i’ve deleted files, on Friday i started doing the update and i got passed the apple logo and went onto ‘choose startup disk’ and ‘macOS update assistant’ that had an updating bar that didn’t move at all. Got no idea what’s going on it’s been a few days now??!

Feb 7, 2021 8:51 AM in response to jdo_apple

Hi there

I have the exact same issue too. I’ve tried restarting in recovery mode but it wouldn’t accept my password (which was definitely correct), ran diagnostics by holding D on reboot and it reported no issues, and cannot see another disk on startup disk to select, just a continuous loading icon. Please can you advise what we need to do here


i have a MacBook Air 2019


thanks


Feb 26, 2021 11:52 AM in response to LukeTheKing

I have a 27" iMac (late 2014, 3TB Fusion drive) and had this exact same issue upgrading from Catalina 10.15.7. I don't have second Mac laying around to support target disk mode. However, I did a Time Machine backup just prior this Big Sur install error. After trying multiple restarts, shutdowns, ..., all in an effort to recover Big Sur update, I gave up and pressed command-R on a restart to enter recovery mode. After selecting Time Machine, it first erased "Macintosh HD", then restored backup. Backup was 2.45TB, so it took about 8-hours (RAID drive using Thunderbolt).


I once again have a functional iMac, but still using Catalina 10.15.7. Lots of anxiety and wasted time. I will wait for something more positive from Apple before reattempting Big Sur install.

MacOS Big Sur Installation failed

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