Big Sur reboots back into Catalina

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Big Sur reboots back into Catalina

iMac 21.5" 2017 - Big Sur 11.1 reboots back into Catalina 10.15.7

(This machine is not my own and it is in a relatives house.)

Upgrading via System Preferences it says 3 hrs for 12Gb, I go away for an hour and come back and it is installing with white progress bar at approx 95% complete with no estimate to completion. I go away and come back 15 min's later and it has rebooted and all looks normal except 'About this Mac' says I still have Catalina 10.15.7 on board and System Preferences says there is the Big Sur 11.1 awaiting download and install. Did this twice with same result. There is no Big Sur install icon in dock or applications folder.

Should I try any or all of the following:

Shut off sleep mode
Install from Safe Mode
Reset SMC & PRAM
How do I find a partial Big Sur install folder/file if any
If found should I delete and have another go
Run 3rd party app Onyx to clean up any flotsam and jetsam and any other detritus
Or should I wait for Big Sur 11.2

Thank you for your feed back

Posted on Jan 19, 2021 6:03 PM

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Answer 1

Top-ranking reply

FineWine Author

Level 1

63 points

Mar 9, 2021 8:18 PM in response to Owl-53

Thank you all for your advice.

Today I successfully upgraded my relatives machine to Big Sur 11.2.3

This is a 21.5" iMac 2019 base model.

I turned off Wifi and forced it to use the Ethernet connection to the router

I started in Safe Mode and upgraded from that state.

It took 3½ hours with 2 hours of those just for the 12.*Gb download via UFB over optic.

It was very slow to install with long (10min) black screens - very disconcerting.

Anyway it is done now and all is good 🤞

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Answer 2

Owl-53

Level 10

107,303 points

Feb 27, 2021 2:09 PM in response to FineWine

Please check this link on the Apple Support page specific to UpGrade to Big Sur especially Empty Space Requirements. Then have a Read over Here for tips for upgrading to Big Sur.

Since the attempts have not been successful - suggest shutdown the Router hen same to computer. Connect to router via Ethernet connection ( Wifi is iffy at best ) Restart Router and then computer and immediately hold - Shift - to startup is Safe Mode. It will do a Repair Disk, clear cache files and only load Apple Software and Fonts so load slowly - Normal. The computer will look and perform differently - Normal

Open Apple Apps Store and download the full installer of Big Sur ( 12.14 GB ). This will take time with several pauses usually at 15 minutes but in Real Time 45 minutes, again at 10 minutes but real time 30 minutes etc. Once totally downloaded it will attempt to launch. Do not allow it to do so - just quit it. There will be a new Application in Application folder called install Big Sur - copy it to an external drive for future purposes like Bootable Installer. Make a Time Machine Backup Now. Once done - launch the installer.

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Answer 3

sterling r

Community Specialist

Jan 21, 2021 3:21 PM in response to FineWine

Hello FineWine,

It sounds like you are experiencing issues when updating to macOS Big Sur. We understand how important this is to you and we are here to help.

First, let’s remove all peripherals from the iMac.

Next, let’s remove any 3rd party ram that may be installed in the iMac. This article should help: Install memory in an iMac

Also, let’s try to test in a new user account as well. This article can help: Set up users, guests, and groups on Mac

Let us know if the issue persists.

Cheers!

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Answer 4

Owl-53

Level 10

107,303 points

Feb 27, 2021 5:09 PM in response to vtewari

Are there any AntiVirus, Disk Cleaner, Optimizers, Defrag, VPNs etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS. The Built-in Security of Big Sur is all that is required.

Any of the above will cause issues even if not active during the installation process

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Answer 5

FineWine Author

Level 1

63 points

Jan 23, 2021 2:49 PM in response to sterling r

Thank you. I have decided to wait for the next macOS Big Sur GM update 11.2. I will do a manaul Time Machine backup, run Onyx pre update and do a SMC & PRAM reset. The only peripheral, apart from her wireless keyboard & mouse, is her ext drive for Time Machine. I will reset her modem/router and ensure connection via Ethernet cable not WiFi.

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