An error occurred preparing the software update - Big Sur

Alright so I managed to get it to work without losing any data. Here are my steps.

Get an external drive. (SSD) is preferred.

Power on Mac then hold Shift, Options, Command, and R. This should bring you to a screen with a spinning globe and will ask for the wifi password.

Plug your external drive into the Mac and go to disk utility.

Click on view on top left and click show all devices

Click on your external drive and click erase. Select the following options before clicking erase again: Whatever you want to name your drive, APFS Format, GUID Scheme.

Click Erase

Afterwards go back to the macOS utilities page and select Reinstall macOS.

Accept the terms and conditions and then select the external drive as a boot device to download the OS to.

Then just wait for it to finish and then boot up following the instructions indicated.

Once in, go to Finder and then select Macintosh HD Data and navigate to user and then just open your desktop or documents folders to access your files.

Copy everything to another external device like a USB stick if the files are small in size.

Then remove at least 15gb of space remaining and turn off your laptop

Boot on your laptop again and hold the same key combination as mentioned before: Shift, Options, Command, R.

This time reinstall macOS to the Macintosh HD drive. There should be enough storage to do this. Otherwise delete more files.

Then the OS should be installed on your laptop and your external drive is no longer needed.

You now have your laptop back and your files saved.

Good Luck.

Hi,

This is very helpful, but when i hold down the option /alt key and power back on my mac, it only comes up with the macOs Installer to click, and then when I choose this, it takes me to my login page as normal, but once i’ve logged back in (this is the only time my password is accepted anymore- it is not accepted in the recovery mac) it continues with the update.

Any help would be greatly appreciated- I’m going round in circles here, and i’m clearly not the only one with this problem!

I tried restarting while pushing the Option button but I did not have the Mac HD option. It only says Mac OS Installer. So now I just keep coming back to the same error. I wanted to just go back to my old OS and free up space before updating but now I can’t do that anymore. I don’t have a recent back-up so I hope to just go back to my old OS. Help!

Please help me. I am having the same problem. Managed to boot up using the external SSD with Big Sur installed, but I cannot delete any files from the Macintosh HD.?!? How to avoid losing all my previous data in the Macintosh HD?

heya all

I also can confirm that instructions from the article can help you

https://mrmacintosh.com/big-sur-upgrade-not-enough-hd-space-serious-issue-possible-data-loss/

(or some scenarios in the comments)

we had broken update from Catalina to Big Sur on MacBook Pro 2015 and encrypted disk.

we connected to another Mac (with Big Sur) in target disk mode, couldn't mount the data volume because of the "wrong" password (probably with macOS High Sierra or Mojave it will work).

many thanks to Apple Support that they suggested to delete system volume and after that the data volume could be finally mounted and we've copied all necessary data (there is similar story in the comments of that article).

good luck to everyone

So you can see your files.

First as a backup see if you can you copy your data to the external drive you booted from?

Then try deleting a small file

if that works

Keep deleting small files to clear space

then move to larger ones.

Try Disk Drill, the basic version will allow you to see all the files (scanning takes a while, be patient).

I am able to extract the files and currently transferring 400+ GBs of data. (for me, all the (valuable) data files are in the /User, so I don't care about applications, system files etc). Just need to get that directory copy over.

I've noticed several files I've extracted are corrupted, but I guess that's the cost of screwing up update.

And for some reason Disk Drill will actually take your pwd, while Apple couldn't.....

Any way, feel really sorry for the folks who wiped the disk. Data still there, and the Macintosh HD still verify the correct pwd.

Many thanks to the guy who found Disk Drill.

Ok so I was able to follow what guysboi said. At first I could not locate the Macintosh HD - Data volume on Finder.

But I saw it on Disk Utility and right-click and chose Show on Finder, and I finally found all my files and was able to copy them to my external hard disk and delete big files to free up space.

I am now redownloading Big Sur on my Macintosh HD, now with enough space.

To find your files from Macintosh HD while booted on an external drive,

>go to Disk Utility and

>right-click on Macintosh HD - Data and

>click Show on Finder.

All your files from Macintosh HD will be there. I did and I was able to save my files, and free up space on my Macintosh HD. So happy I didn't have to lose any file at all.

Thank you for your help guysboi!

Just found a solution for those, who cant open their HD on another mac, because the FileVault password is unrecognized.

First, find another Mac who has an older OS. I used Mojave.

Now, on your "broken" mac you will have to enter the target disk mode (which is offered after the error message)

Then connect your "broken" mac to the other Mac with an older OS.

Enter the FileVault password. NOTE! This will not work if you connect your laptot to a Mac with Big Sur. Then the password will be unrecognized.

And there you go, copy all your files to a hard drive.

Next time, back up, before updating to a new OS ;) I definitely learnt my lesson...

I also had this problem, disk drill could recover some of my files, but some were corrupted. When I tried target disk mode connected to a computer running Mojave the password was recognized and I was able to delete enough space on the problem computer to let Big Sur finish installing, and the files that disk drill showed as corrupted were fine!

FIXED!!!!

after 9 hours of messing with this and 1 hr. On the phone with apple support. here’s what finally worked:

First some Details:

Machine - MBP 2018

SYMPTOM:

Update locked out halfway through install after the restart, displayed message “An error occurred preparing the software update”

FIX:

after trying every other less drastic system recovery method, I finally reformatted the hard drive by performing a hard shut down from the locked up install screen, entering disk utility recovery mode (by holding: command, option, R - during boot up). Then following the steps until coming to the screen that allows you to enter the disk utility recovery. From there Enter disk utility, erase hard drive first and then erase data drive. After that installing Big Sur from system recovery screen worked, though I later opted to restore from a backup of a previous OS using this same method.

if even the Big Sur install was so buggy, I don’t feel it bodes well for the rest of the OS, and don’t care to waste anymore time with more bugs like this. So downgrade was the clear solution to me. Maybe everything else works fine with it, but at this point I’m not taking any risks with such a time consuming bug this early I the game ;)

Hope this helps.

I couldn’t agree more. I went through almost all the same things and in order not to loose everything I have, they told me to go to an authorized store and do the procedure there, what will cost me money, which is not correct since this problem was not a result of something I did, it was indeed due to the update to BigSur.

I couldn't get into the issue Mac.

Double click the Macintosh Data and the same issue remains.

"Start your working mac in a normal manner --> login --> you will be prompted to type the password for the hard drive of the mac that's having trouble. They accepted my password finally (and any prompts from here onwards accepts my correct password)! Now delete some stuff in the hard drive of the mac that's working! I deleted some applications that are easily downloadable from the internet/are free until my drive had about 58GB of free space (no specific reason why I freed 58GB - I just wanted to play it safe). Eject the hard drive."

Can you mount the old Mac in Disk Utility?

"Start the other mac (i.e. working mac) in recovery mode --> go into disk utility --> attempt to unencrpyt the hard drive of the mac that's having trouble (I can't remember if my password was accepted then but I don't think so)"

If you have another mac running Mojave or access to a usb Mojave installer or a TM backup of a Mojave install

you could use an external drive and install Mojave to it or restore from TM backup

Then boot up to the external drive on the mac with the big sur upgrade issue.

Mount your drive with that needs some space cleared

clear some space

then reboot to the internal drive and see if the install completes.