An error occurred preparing the software update - Big Sur

I contacted Apple and got it to work. It’s because the computer doesn’t have enough space. So back up your laptop to an external hard drive and free up space.

to bypass the update and go back to regular log-in:

turn the computer off by holding down the power button

press and hold the option button BEFORE turning back on the computer

keep pressing option and turn the computer on

once the computer is on, you should be at the screen that says 2 options for Mac

select Mac HD

log into your wifi

now it should start up again and log back to Home Screen.

Hi LizethBo,

Ok, if you have another Mac you might need to create a bootable USB of MacOS Big Sur or even Catalina. Here is a direct link to the installer for Big Sur if you need it. Just run the pkg file and it will create an installer in your applications folder on the second mac which you can use to boot off the USB on the said Mac with issues.

If you hold down command r at boot, are you able to boot into recovery mode? If so can you go to Disk Utility and post a screenshot of the window for me?

Please report back with your findings and I will be able to help you further.

Hope this helps.

tartangear wrote:

I tried to do the Big Sur update and near the end of the installation i get the message

"An error occurred preparing the software update "

and then i'm asked to select a startup disk.

I've tried rebooted a few times and it always happens.

I assume i'll need to do a recovery of some sort.

I tried to reboot with CMD+r and then i was asked to enter the user password, which wasn't accepted (even through it's definitely the correct password).

Can anyone suggest what i should do next?

https://discussions.apple.com/content/attachment/5304c99c-3ed2-408b-b6a4-222640aef9c1

https://discussions.apple.com/content/attachment/61e88eb9-6f02-4267-8c93-c209a5f3045d

You do not say what exact Mac this is?

What macOS are you currently running before the upgrade/update?

I suspect this is a server issue being overload— slow downloads can cause corruption in the installer.

If you have the full installer, you can see it in your Applications folder "Install macOS Big Sur.app"

If it is there— reboot into Safeboot mode an click open the installer in your Applications and see if it goes without issue.

If no resolve delete thjat installer/empty the trash and try anew.

You can always Call Customer Support (800) MY–APPLE (800–692–7753)

I recently had this issue, and found the solution from this website (all credit to Mr. Macintosh for solving my problem!):

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

My issue was that the Big Sur update didn't check whether there was enough free space on the hard drive before trying to install. So you need to free up some space for the update to complete. Here is the extract to retain your data:

13. How to fix this issue + retain your data!

This section is divided into 2 parts. Part one is for if your Mac is encrypted with FileVault 2. The 2nd section is for if your Mac is not encrypted.

FileVault 2 Enabled

When FileVault is enabled on macOS Catalina or Big Sur, you are required to enter your account password before entering macOS recovery. This is critical because the only way to recover (retain user data) a FileVault enabled Mac will be with the help of a 2nd Mac.

If your Mac is encrypted and you need to recover your data, you have 2 options. One with just your mac and a USB Drive and the other with a 2nd Mac and a Thunderbolt or USB Cable using Target Disk Mode.

Option #1 – Install macOS Mojave on a external USB, SD Card or Hard drive.

1. You can boot from this external version of macOS. This will allow you to clear enough space from “Macintosh HD – Data”
2. Use an external USB flash drive or external hard drive. You install macOS on an external USB, SDCard or hard drive. Once Mojave is installed from recovery to the external drive boot to it by holding down Option after reboot. Once booted to mojave, you will see your drives on the desktop. You can then mount “Macintosh HD – Data” from Disk Utility. Now you can delete files from the “Macintosh HD – Data” then reboot. The Big Sur upgrade will finish.

Option #2 – 2nd Mac Required – Target Disk Mode

1. You need a 2nd Mac running macOS High Sierra or Mojave. (Big Sur & Catalina Mac fix instructions coming soon)
2. One of the following cables are required. USB-C to USB-C 3.0 Cable, or a ThunderBolt 3 Cable.
3. Once you have the target Mac in Target Disk Mode, you can use the host mac running 10.14 or 10.13 to mount the disk after entering your encryption password. > https://support.apple.com/guide/mac-help/transfer-files-mac-computers-target-disk-mode-mchlp1443/mac
4. As soon as you plug in your cable from the target mac to the host mac, you will get a pop-up window asking you to enter the password for your problem Mac.

Hi Tracy,

That's strange it won't boot into safe mode. You mentioned the symbol for not allowed, you mean the circle with the line through it? It looks like this:

I have four things things you can try:

1. Reset the SMC
2. Reset NVRAM or PRAM
3. Search for Disk Utility in Mojave and open it. Next, click First Aid in the menu bar to see if it finds anything wrong with your drive.
4. Reinstall MacOS. Boot into recovery mode by holding down command r at boot and double click reinstall MacOS. This will reinstall just the operating system which should be Mojave and not touch your files.

After reinstalling MacOS Mojave you can the installation for Big Sur and hope it works.

Hope this helps.

Hi Tracy,

Thanks for getting back to me.

That's strange it won't boot into safe mode when holding down the Shift key at boot. You mentioned the symbol for not allowed, you mean the circle with the line through it? It looks like this:

I have four things things you can try:

1. Reset the SMC
2. Reset NVRAM or PRAM
3. Search for Disk Utility in Mojave and open it. Next, click First Aid in the menu bar to see if it finds anything wrong with your drive.
4. Reinstall MacOS. Boot into recovery mode by holding down command r at boot and double click reinstall MacOS from the MacOS utilities window. This will reinstall just the operating system which should be Mojave and not touch your files. Having a backup is a good thing and based on what you've said you have one which is good.

After reinstalling MacOS Mojave you can try the installation for Big Sur and hope it works.

Hope this helps and keep me posted.

The following will make it easier for you to make and include screenshots in future posts:

How to take a screenshot on your Mac 

(⌘⬆︎3) Command-Shift-3         Capture the screen to a file

(⌘⬆︎⌃3) Command-Shift-Control-3 Capture the screen to the Clipboard

(⌘⬆︎4) Command-Shift-4         Capture a selection to a file

(⌘⬆︎⌃4) Command-Shift-Control-4 Capture a selection to the Clipboard

(⌘⬆︎5) Command-Shift-5         Invoke new screen grabber

I've been stuck with this issue for more than a week now. I have spare 19' MBP16 with Big Sur and connectors/cables.

There is a new way of releasing enough space for upgrade, if you know/have worked with some linux/unix commands and you know which files to delete, follow the instructions of John Grundback's at https://mrmacintosh.com/big-sur-upgrade-not-enough-hd-space-serious-issue-possible-data-loss/#comment-14106

It's very simple, but be careful.

To sum up, I've manually mounted /dev/*my_ssd_disk* at '/', and by doing that I can access all my files. Perform 'rm -r $DIR$' or 'rm $Files$' to release spaces. I released 50GBs.

I've not tried yet, but maybe if the system level instruction set is still fine, maybe we can plug in a hard drive, format it, mount both drives of Macintosh HD and /dev/$your_mac_disk$, and copy the files over?

I guess if you have not messed up with the system too much (by purging NVRAM, SMC, etc like I did), by releasing enough space you've already solved the problem. Supposedly with enough space the 'upgrader' will go on and finish the job.

As I have wiped NVRAM, multiple times, I am currently stuck at:

Boot up then 'Command + R' Recovery: Do not take pwd, can not verify with iCloud, so dead end

Boot up then 'Option + Command + R' Internet Recovery: Do not take pwd, can not verify with iCloud, so dead end

Boot up then 'Shift + Option + Command + R' Recovery: Finally got into recovery mode, but: 1. disk utility refuse to mount the Macintosh HD Data, 2. I can not select any disk to reinstall the OS. (Install the Yosemite on a flash drive worked for me though. My Mac is a 2014 MacPro 15 so this Basic MacOS X installer might come with the Mac).

Boot up then 'Option': If I select Installer, then I ended up in infinite loop of rebooting... (doubt it might be messed up by resetting NVRAM, SO DO NOT RESET NVRAM). For once I've seen a question mark, where Apple told me to wipe NVRAM according to: https://support.apple.com/en-us/HT204323, kind of funny.

Boot up then 'Option': If I select to boot from Macintosh HD, then it shows a prohibited symbol: https://support.apple.com/en-us/HT210901. This is consistent since the upgrade.

At this point, with most of my data already been copied over using Disk Drill (apparently if you have a Mojave or lower the problem will become a lot easier, just follow previous posts), I am trying my best to recover the OS while avoid wiping out the old OS (either formatting the entire disk or formatting the System Volume Portion of Macintosh HD - Data).

Also, sometimes the servers are very busy or have outages. This can cause the updates to not download & install. The same thing happened on November 12, 2020, when Apple had released BigSur.

You can check the Apple System Status at: https://www.apple.com/support/systemstatus/

Hi

I had the exact same errors. MacBook Air late 2018. 128gb

Im not clued up on all the workings of a Mac for when things go wrong but had to teach myself

In the end I did the following it meant I lost everything on the MacBook but I was lucky and everything was stored elsewhere. I still don't have Big Sur installed but Ive got a working MacBook. I followed the section for selling on your Mac

1) erased and removed the MacBook via the "find my" app

2) Forced shutdown by pressing the on/off button

3) Command R which installed the original OS - Mojave in my case

I did have issues where it didn't recognise the disk to install it on but I clicked on the partition button and followed that

I then updated to Catalina via the App Store.

https://apps.apple.com/gb/app/macos-catalina/id1466841314?mt=12

Hope this helps

Same issue. 2018 MacBook Pro 2.3Ghz, Upgrading from Catalina to Big Sur

1. bigsur downloads
2. restarts then tries to install and gets stuck at 10%, giving the error you see below
3. trying to start in recovery then asks for my password, which the Mac tells me is incorrect
4. trying to enter my vault key from iCloud doesn’t work either because it tells me my iCloud account cannot unlock this volume
5. there is no way to get to the main screen or any screen; no way to recover or enter my password for anything
6. i took it to a Mac specialist locally and they said they have no idea but they would have to wait 3-5 days likely at minimum before Apple released a resolution, also a lot of people are having this issue
7. I work online, this is debilitating

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. "

Hi dddeeennn,

Restoring from backup means that once you have a time machine back up you can restore your data from the previous back up.

I would do a time machine back up and then try seeing if you can download the installer for Big Sur either from the app store or the direct link normally from your own user account. delete the previous installer for MacOS Big Sur from your applications folder or drag it to the trash.

Run the installer and see if you get the same error, if you do, try running the installer again from safe mode

Report back and then I'll provide more instructions. Step by step and don't want to overwhelm you.

Hope this helps.

Hi Sabueno,

If you have access to another Mac, I would download the installer for Big Sur, run the .pkg file and Install MacOS Big Sur will appear in your Applications folder. Then create a bootable installer and try booting the said Mac off the USB installer and try the install that way.

Hope this helps.

jecoycoy,

See if you can boot into safe mode by holding down the shift key when you start your Mac.

If you hold down down command r when you start your Mac, are you able to boot into recovery mode?

Hope this helps.