Why Can't I Upgrade to Big Sur, Even After A Clean Install of Catalina?

Question

Why Can't I Upgrade to Big Sur, Even After A Clean Install of Catalina?

I tried to upgrade to Big Sur about 2 days after general release. No issues at all on my 2016 MBP, but on my 2017 iMac I was left stuck in a 'bootloop'. By this I mean that the installation process started, first reboot occurred, then the progress bar would reach about 10%, never enough to even show the "Estimated Time Remaining" text, then it would reboot and repeat that process every 2 mins 10 seconds (yes I timed it to see if there was any sign of progress). This would continue forever, or at least overnight which is the longest I tested it.

Safe mode didn't work, nor did removing any software that seemed a likely problem, or launch daemons and the like (I guess those two things are about the same).

So I finally bit the bullet and erased my drive, installed Catalina totally fresh, and tried the upgrade. Result: Exactly the same boot loop.

So I'm back on Catalina and reinstalling all my stuff and pretty much resigned that this iMac will never progress to Big Sur.

Anybody have any ideas?

Thanks.

iMac 27″ 5K, macOS 10.15

Posted on Dec 16, 2020 7:00 AM

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Answer 1

Best reply

rkaufmann87

Level 10

141,366 points

Dec 20, 2020 10:39 PM in response to burglarbill

Turn off the computer, then restart it and hold down the power button for about 15 seconds and then release. If that does not work, please restart in Safe Mode per the direction in the following link and then restart normally.

Use safe mode to isolate issues with your Mac

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Answer 2

Dec 21, 2020 3:30 AM in response to simon.ward@mac.com

I might be a little pre-emptive with this because it's still restoring files from Time Machine, but I'm pretty sure I've found the fix. You need to install from USB. You will probably need to erase everything in order to actually do the install by wiping the disk in recovery mode, because it didn't work for me until I did this.

You'll need a 16gb usb stick. I was able to use a standard USB-A one with an adapter, but USB-C is obviously quickest for Macs with only USB-C ports.

I'll update this reply when it's actually up and running, but so far it's looking good.

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Answer 3

Dec 21, 2020 9:59 AM in response to burglarbill

Decided not to restore Time Machine in order to hopefully avoid these future problems and have a fresh start. So no advice on whether that works or not. But it was surprisingly easy to get everything set back up. One thing I will do in future before updating is make a cloud back up of some key Application Support files, because digging around in the Time Machine for them is a bit slow.

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Answer 4

Dec 20, 2020 9:57 PM in response to simon.ward@mac.com

Exact same problem for me, except this is on a MacBook Pro.

Progress bar gets to 10%, then reboots and starts again. Did a clean install and had the same problem.

Let me know if you find a fix!

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Why Can't I Upgrade to Big Sur, Even After A Clean Install of Catalina?

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