An error occurred preparing the software update - Big Sur

Okay

I would try this if you have an external HDD or SSD and a spare usb flash drive

Create a mojave installer this may help big sur - How can I make a bootable USB copy of Mojave downloaded from Apple when the file is an app and not a disk image? - Ask Different (stackexchange.com)

Then install Mojave to the External Drive this may help How To Install macOS On An External Drive - Macworld UK

Boot from the Mojave external drive

Hopefully it will unlock your data drive now

Then you can backup some data and clear some space.

That is what Is basically what I did and I was able to clear the space

And after the reboot it was able to finish the big sur upgrade.

I hope this helps.

Brian

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

https://youtu.be/Qcu9o4qz2Ls

This guy figured it out (Mr. McIntosh). What a lifesaver! He saved my wife’s computer. I thought we were going to have to wipe her hard drive. You just need the right cable to connect to an external hard drive or another MacBook and then you can erase some enough data to make room for the install. Apparently you need about 35 GB for the install to work but the Big Sur will somehow let you download and go through the install if you have less than that but more than I think about 10 GB. So you somehow get stuck in this loop. I had to get an old thunderbolt cable which isn’t readily available at most electronic stores to connect my two MacBooks. His video goes through all the different scenarios that one might encounter. So helpful. Apple should pay him for finding a solution to this.

Trying to do the Bug Sur installation today and getting the error message of "an error occurred preparing the software update". Tried a couple of times, then deleted and re-downloaded the app "install Big Sur MacOS" from the Applications folder. No impact.

I am able to restart the computer holding down the option Key and selecting the original SSD, which had been renamed with a "-Data" on the end of its original name.

I've read all 13 pages of posts on this thread and most have dealt with the problem that >35Gb of free space is needed. That is not my problem as I have >250 Gb available.

I am trying to avoid the hassle of a SSD wipe and rebuild (I do have a recent Time Machine back up). I have a USB Mojave installer and can create a USB Big Sur installer if need be.

I'm not quite sure on the next logical steps so any simple advice or URLs would be appreciated.

Tracy

MacBook Pro, mid-2015, Mojave, i7/2.8 GHz processor, Mojave, 16 Gb ram, 2Tb SSD

Hi Soren and thx for reply.

I got the BS installer through the Software Update pane in Systems Preferences.

I am currently running Mojave, 10.14.6.

I will try re-downloading the BS installer from the App Store. I'll first try an install using that and it fails, I'll create a bootable USB.

Funny you ask about software updates . . . I did not update the recent Mojave Security Update or the Safari 14.03 'cause I assumed it would take care of itself under Big Sur. Are you suggesting that I update those items before attempting another BS install?

Believe me, it all helps. I ran out of ideas short of a clean wipe.

Hi Tracybjazz,

My pleasure.

I see, I think that is a good course of action going with the link I provided.

That's what I would think as well as I've upgraded the Mac operating system on clients Macs without applying software updates and usually it works but each Mac is different. I would try applying the security update and Safari update first and see what happens. It doesn't hurt to try.

Hope this helps.

Hi Tracybjazz,

Just checking in to see if the suggestions helped and if you were able to install Big Sur successfully and which method helped, the link I shared or booting directly off the USB installer.

If you have any issues don't hesitate to write back.

Hi Soren. . . . . I tried to install used the link's download installer. It got further along in the install process (had ~12 minutes to go) but it eventually stopped with the same error message that started this thread. I tried twice but stopped at the same point. I just finished creating the bootable USB installer and I'm minutes away from that install attempt. . . . Most of my time this morning has been spent making additional backups for items that I do not want to lose. Just in case Mr. Time Machine back up fails me during a disc wipe and clean install . . . . ;-). . .. . I'll will let you know. . . thx for checking . . .. Tracy

Just completed the install attempt using the USB installer . . . . same error message only this time, I was stopped at 29 minutes into the install. I may try one more dL of the installer itself with the USB approach . . . . what was that old saying about the definition of insanity? ;-)...... thx . . . Tracy

Hi Tracy,

Thanks for the two updates. I feel that’s progress that it got further along in the install.

So strange that it would stop like that even from the USB install and you having plenty of disk space.

One thing you could try doing is Safe Boot. Hold down the shift key when you boot your Mac and release it when yous see the login window and Safe boot in the menu bar. Try the install that way from your applications folder.

Yes good idea about having additional backups. You could even consider a clone via carbon copy cloner.

Hope this helps.

Hey Soren . . . . oddly, the MBPro will not let me boot in Safe mode . . . I get the symbol for 'not allowed'. . . . . so unless you've got any more rabbits in your hat, I think I've exhausted my options for getting Bug Sur installed. It may be time to start researching a restore from Time Machine (mine is on a NAS drive) or a completely fresh install of Mojave. . . thx . . Tracy

Hi Soren . . . Yes, for "not allowed", I meant the circle with the diagonal line.

I tried the 4 things . . . . 1-2 had no discernible effect. Disk First-Aid was fine.

For suggestion 4, I can start up in recovery mode (Command-R) but the only choice for OS is Big Sur, which will probably end up in a clean install/drive wipe, if it is able to complete the install, which I doubt.

There is another start up key combination (Command-R-Shift-Option) that should allow me to install the OS that came with my system (or close to it) but alas, I get the "not allowed" symbol.

I have a USB bootable Mojave around somewhere. I may dig that out and see how the MBP responds.

Thanks again for your help/suggestions . . . . but I think we are running out of options. I suppose I could call Apple or even stop by the Genius Bar but that will probably result in several hours of deja vu.

rgds . . T

Small update . . . I was able to start up in Internet Recovery mode . . . . I had to delete two extra folders that appeared after my previous Big Sur install attempt . . . one disc image was a nearly empty and the name of my actual drive (2TB-SSD) and a send disc image called "Update", which contained files for the BS install. . . .so I'll try the Internet Recovery route . . .mo' later . . . rgds . T

Hi Soren . . . the mystery keeps unfolding. I wiped the internal drive and installed a fresh Mojave. I then installed the latest Mojave updates. All installed just as expected. . . I then tried to dL Big Sur (3x) first through the Sys Pref Software update but then through the link (to the App Store that you provided). . . . but kept getting an error message at the very end of the 1-hr dL, which basically said something to the effect BS could not be verified - an error occurred while installing the BS updates. . . . Then when I do a Command-R restart, the macOS installation option shows me only a reinstall Mojave. The BS install option (that I thought should be there) is not an option. It's my MPB will do anything to avoid BS . . . . any suggestions? Maybe another complete drive wipe install? . . . thx . . Tracy

Hi Tracy,

I appreciate you getting back to me with the update.

That's good to hear you were able to do a fresh Mojave install and that you erased the internal drive. Very interesting about the mystery though.

One thing to consider would be to boot off the Big Sur USB installer you created. Hold down option when you boot your Mac, select Big Sur from the boot selector.

Next go to Disk Utility from the MacOS Utilities screen and wipe the drive again. Quit disk utility and select Install MacOS from the MacOS Utilities screen and see if that works.

Crossing both my fingers and toes that this works.

Hope this helps and keep me posted.

Hi Soren . . . that's a reasonable suggestion except that I outsmarted myself. I deleted the USB BS installer and replaced it with a USB Mojave installer, in case there was an issue during the wipe and clean install of Mojave via 'recovery' mode. . . . . . Regardless, I'm ready to move in a new direction: clean install Mojave > Time Machine restore > Catalina. . . . .. I've been a Mac user since 1989 and I've never had this much trouble with an OS upgrade. OS9 to OSX was a cakewalk compared to this . . . . thanks for all your suggestions. . . kind rgds . . T