An error occurred preparing the software update - Big Sur

Hi LizethBo,

What you need to do is boot off of a USB stick of MacOS to try to restore from back up to Catalina if you can. You might need to use a second Mac to create the USB stick.

Once restored, you need to create a new container in the APFS volume for the installation. Download the installer again under Catalina and it should allow you to install on the other volume.

Hope this helps.

Hi LizethBo,

What you need to do is boot off of a USB stick of MacOS to try to restore from back up to Catalina if you can. You might need to use a second Mac to create the USB stick.

Once restored, you need to create a new container in the APFS volume for the installation. Download the installer again under Catalina and it should allow you to install on the other volume.

Also, see my comment you earlier for additional details.

Hope this helps.

Hi LizethBo,

Thanks for the photo. I assume you are entering your correct user password.

Do you know if you have a firmware password enabled?

What happens if you click forgot all passwords?

Hope this helps.

Hi shaobo626,

The prohibitory symbol means that your Mac contains an operating system but it's not able to boot to it.

Are you able to boot into recovery mode? After you hear the startup chime, hold down command r to boot into recovery mode. Once in Recovery mode select reinstall MacOS and you should be good to go. This will not touch your data but reinstall the operating system and address the issue.

If you are not able to boot into recovery mode, you might need to use another Mac to create a USB stick with a bootable copy of Big Sur to reinstall the operating system on the said Mac.

Hope this helps.

Hi mohammadskhv,

You should have read my comment about this to save you the hassle.

You didn't need to erase your Mac and you wouldn't have had to loose anything.

You could have used another Mac to create a bootable USB stick of Big Sur or even Catalina and used that to reinstall just the operating system and you would have been up and running in no time.

I'm glad you had a backup.

If you wish, I would consider upgrading to Catalina if you want to hold off on Big Sur as Catalina has been out longer.

Hope this helps.

Hi Brandontjo,

If you didn't erase your drive you should be fine and your files are safe.

The prohibitory symbol means that your Mac contains an operating system but it's not able to boot to it.

If you have another Mac and a 16GB USB drive you should be able to reinstall MacOS onto the said Mac from the flash drive and be good to go. How to create a bootable USB drive of MacOS.

Once the USB drive is created, put it into the USB port of the Mac having issues. If it's on turn it off by holding down the power button.

Next, press the power button to turn it on normally and then hold down the option key and let go when you see a screen showing a few volumes. In the boot selector, you would choose the drive Install MacOS Big Sur with the arrow keys and hit enter to boot from it.

When it's booted off the USB, click reinstall MacOS Big Sur and follow the prompts to continue.

The data is restored from a time machine back up.

Hope this helps.

Hi Brandontjo,

Thanks for your reply and glad what I said was helpful.

How did you reinstall the stock OS, recovery mode by holding down command r

If you partitioned your drive and ended up deleting a partition in the process all data is lost. With Catalina or Big Sur Apple changed the way the drive is structured. For example there will be a drive that says Macintosh HD - Data and Macintosh HD for the operating system.

If I were you, I would try to upgrade to MacOS Catalina, it's been around longer and more stable or Big Sur if you feel like it.

Hope this helps.

I am encountering this error on an Intel-based Mac. Insufficient disk space without warning. The last OS was Catalina.

Upon error, it asked to choose a startup disk, in which only the Bootcamp drive was the only option. There is no option to return to the regular login or my original macOS drive.

I have entered the recovery mode through [Option-R], the menu reinstall macOS only gave the choice of Big Sur version. Surely if I proceed with this, I will still get the same error since the disk space is not enough. Disk utility can still detect and mount the drive of my macOS.

I have then tried the recovery mode to reinstall the macOS that came with the Mac through [ Shift-Option-Command-R ], this brings me to Maverick OS installation. However, it cannot detect a disk to install at all. Disk utility is not able to mount those partitions as well.

At this stage, how can I go back to Catalina or install Catalina? Will the bootable installer solve this? Which partition has my actual data, the one with ending "Data" or the one without?

I have not erased my drive so hope the files are safe. I do have back up but it is not up-to-date. Thanks!

Dongsun

You will need to use another mac to make the usb installer

Here is the apple link to making a usb installer

https://support.apple.com/en-us/HT201372

here is the program i use but it only works well if you are still running mojave

https://diskmakerx.com/

Here is a good article for installing to the external drive

https://www.macworld.co.uk/how-to/macos-external-drive-3659666/

Be sure to use an external drive that is large enough to backup your data to

Brian

I've struggled a lot prior to this solution, and possibly messed up even more with erasing NVRAM and SMC.

I recall before I struggled I could still mount the Macintosh HD but not completely could not.

When turned into TDM this showed up:

Following the Youtube video of Mr. Macintosh, one step I noticed that is different is, in Disk Utility Terminal Window, I could only list 'OS X Base Systems .Trash'

Where the Macintosh HD is not mounted. This is consistent.

The other two methods I've not tried yet:

1. Convert another Mac into Mojave using external boot. And then supposedly I could access easily in TDM
2. Erase the System Portion on 'Macintosh HD - Data', I guess all the data is in 'Macintosh HD - Data - Data'.

Hi Tracybjazz,

How did you first obtain the installer for Big Sur, from Software Update?

Are you currently using Mojave or Catalina? When updating to Catalina a data disk is created. You can read more about it here: About the read-only system volume in macOS Catalina.

I would delete the application "Install MacOS Big Sur" from your applications folder and redownload it from the App store again and then use the USB stick and try it from that.

I've had situations where the software update installer didn't work or show up but when using the direct link it would show up fine and download. If the direct link doesn't work from your Mac again then try the USB stick.

How to create a USB installer for MacOS

Dowonload MacOS Big Sur - App store link.

Somehow it's not letting you do it from the computer itself.

I assume you are fully up to date via Software Update?

Hope this helps.

Tracy,

Thanks for the two updates.

Resetting SMC and PRAM may not show a visible effects but they do help in a small way. Good to know your disk is in good shape.

Regarding the key combinations, you are correct that one is able to reinstall the OS that came with the machine. There is also one to upgrade to the latest version that is compatible with your Mac which is option command r

I wouldn't bother calling Apple or stopping by the genius bar as that will take time and probably go over some of the same steps. Just my thoughts.

Do you happen to have FileVault enabled or a firmware password set?

Glad you were able to start up in Internet Recovery, that's good news. Since you were able to start up in Internet recovery you could try reinstalling the operating system this way, I assume it's Mojave. If you can find your USB of Mojave you could try that as it will save the download time, I don't know how fast your internet connection is. If you can't find your Mojave USB then use Internet Recovery.

Hope you are able to reinstall MacOS Mojave successfully and then upgrade to Big Sur afterwards. If somehow you aren't, there is one last step we can try but will share that later as I've wrote a lot already.

Hope this helps and let me know how it goes.

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

After few attempts I manage to access my data (running on Mojave before trying to upgrade) without erasing the disk. I did not have my mac backed up on an external driver, so here the steps I took:

– access recovery mode by pressing shift+cmd+alt+r at the same time before clicking the power button. You will see a world graphic spinning. Insert your internet password and after about 15mins you will see a prompt with different options.

• select the last option ‘disk utility’
• under the folder ‘internal’, you will see the disk ‘Update’. I tried erasing but it did not work, so I unmounted it by selecting it and clicking on ‘unmount’. That disk will be light grey now. You could see that I only had 15gb free so it is probably what caused the issue.
• Now I run the disk ‘Macintosh HD’ by selecting and clicking on the run option via the top left menu. Be aware i had another disk greyed out ‘macintosh HD-data’, which I haven’t touched. A prompt appears where you have to ‘unlock’ the disk. You will ask to insert your password (this time it works!). The system will reboot and voilà. All my files were there!
• note: before trying to run the ‘’macintosh HD’ try to ‘first-aid’ and see if it allows you to unlock it. I always had errors, so i try running it again.

I will now make sure to backup and free some space before attempting the upgrade.

Hope this helps!