An error occurred preparing the software update - Big Sur

Is there any update to this issue? Also happening to my Macbook Pro 2017 13"

The only answers I can see is to accept complete data loss and reinstall original OS via Recovery.

One would like to think that there is surely a more appropriate solution, especially given it went through fine on my works older MacBook Pro (2014).

Same exact issue.

After a ton of time and research; I figured out my laptop didn't have enough space (9.5gb) and big sur was 13gb; sooo; I am making a story out of it here: https://ibhuman.com/an-error-occurred-preparing-the-software-update-macbook-pro/ - normally, the update checks space first, but big sur is messing up there.

Copy and Paste from Apple Upgrade to Big Sur support page. Note the space requirements for UpGrading from which ever existing macOS to Big Sur

" If upgrading from macOS Sierra or later, macOS Big Sur requires 35.5GB of available storage to upgrade. If upgrading from an earlier release, macOS Big Sur requires up to 44.5GB of available storage. To upgrade from OS X Mountain Lion, first upgrade to OS X El Capitan, then upgrade to macOS Big Sur. "

After spending 3 days going back and forth with Apple Customer Service, I’m slightly regaining faith with the support I have been provided so far knowing that erasing my HD was not an option.

So far, my iMac used to have Catalina 10.15.7 and had 640GB space available. After figuring out some cause of the issue, it appears that the Wifi would be the cause as I live in rural area and use a SIM Wifi with a range of 5 to 15Mb speed on good weather.

A slow speed would affect a lost of packet data which would render the failure to install the OS on the device because it would have incomplete information of the OS.

As some of you I have tried Recovery booting Cmd+Option+R. I tried internet recovery Cmd+Opt+Alt+R. When I managed to access OS recovery utilities, it couldn’t find any backup on my TimeCapsule nor in the TimeMachine. Like for some, my admin password was refused. Connecting to with my AppleID wouldn’t find any iCloud account connected to the HD.

As last resort, I have been recommended to use an external HD which I would accept to erase and format to MacOS extended journaled. Then once I had access to OS utilities, to recover from the last OS installed. For some reason it only recognised Yosemite as last OS installed. But never mind.

So now the OS Yosemite is installing on the external HD and the iMac will work from an external bootable drive.

The following steps which I have now to take once it’s done will be (as recommended by Customer Support)

• Go to finder and find the internal HD
• Select user account represented by a folder with a house on it
• Copy and paste the folder to the external hard drive which may take a long time ( a 500GB or 1TB external HD would be recommended).

These are the steps I need to take and because my external HD seems to be slow, I am yet to complete these step.

I believe the next step will be to then erase completely the iMac, format the HD to OS extended journal and transfer the external HD back to the iMac which would make sense for me. But don’t take my word for it, I might skip steps that I need to learn from. But I hope the first three steps as mentioned above will help some of you.

Good luck to any of you who have issues with installing Big Sur.

Fred

After following the first few steps from Apple Support and continuing with the last step I am please to say that I have now BigSur installed and running on my iMac.

As I was speaking to a different senior customer service representative at Apple who I told I had a backup on my time capsule, she advised me to install the last OS on the iMac, from Os Recovery Utilities and after having deleting its hard drive and formatted it.

So that's what I did. And these are the steps:

• Start the computer in recovery mode Cmd+R and keep your fingers on the keys until Apple logo appears.
• Go to Disk Utilities
• Select the Apple HD drive
• Go to the tab 'erase'
• Rename your HD drive and click erase
• Once done close disk utilities
• in OS recovery utilities chose 'Reinstall last MacOS'
• Once installed (take about 1h30 to 3h) open AppStore
• Search "Big Sur" and click 'get'
• it will take around 3h for the full installation to complete.
• Once installed open finder
• Again , top left menu in finder, choose 'File' and select 'open new finder window'
• On second window , find and select your backup. (mine was on a Time Capsule) Right click on it for info and select 'Mount'
• It will check the volume first which may take a while if the backup is large or very large... Though I was informed that mounting a the backup as is would mean also copying the faults contained in it if there are any. So I was also advised to go quicker to select folders individually.
• So from the second window again I explored the content from my backup and selected individually the folders that I really needed back on the iMac. I was scared when he showed '35 days remaining' for the folders 'Pictures'. But don't stress out, time is theoretical and not real. The only advise is not to use the computer while all the transfer are made as it will need all the memory it needs for it.

I hope these informations will help those who are still struggling installing Big Sur.

Good luck

Fred

Thanks for your suggestions Fred. Seems a little extreme for me to consider at this stage though. I don't think Big Sur is for me if it's this challenging to to a simple upgrade. Catalina is motoring along just fine.

What are you seeing, when you try to install, Macintosh HD doesn't show up as an option?

How are you installing it, Software Update from System Preferences?

What Mac Model do you have.

The more information I have, the better I can assist.

Hi, I have the MacBookPro Touch Bar 13" 2017.

This happened to me also, so initially, the only option I had was to restart as a target disk or restart from the menu as it did not display any startup disk, so I went for a restart.

The install came back up and went through without any errors the 2nd time round.

I now get the Big Sur welcome screen. So far - all is well.

Hope this helps. Thanks

I have the same issue. Any ideas? Hello Apple?

try resetting or erasing your Mac using iCloud or Find My on your iPhone.

Now after you do this, please back up your computer and free space by using an external drive. then if you want, upgrade your Mac !

I am posting my findings here.

https://ibhuman.com/an-error-occurred-preparing-the-software-update-macbook-pro/

Interesting, does it not show up via the boot loader or refuse to boot when you click enter to boot from the selected volume?

Please see my comments, get into target disk mode and copy over the data through Disk Drill.

Then safe to wipe out disk and install OS.

Please see my comments.

I've tried a lot of things and nothing worked.

Then Disk Drill helped.

The key is to have you Macintosh HD take your pwd. Disk Drill does that fine.