An error occurred preparing the software update - Big Sur

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.

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,

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.

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 Tracy,

I see, that sounds like a reasonable way to go. I agree it shouldn't be that hard to upgrade an OS. I've been a Mac user just as long, since the early 1990s.

You could even do this, clean install Mojave > restore your data from Time Machine > upgrade to Catalina and then apply the Big Sur upgrade once you install Catalina. It shouldn't matter though but somehow it's not liking Mojave for whatever reason.

Hope this helps and do keep me posted.

Hi Tracy,

I appreciate you updating me.

That's good news that Apple was able to get Big Sur installed from their own server. I believe the installer does a hardware check which could be why the install failed. Failures don't usually become apparent until one upgrades MacOS or the firmware is updated during install.

Interesting about the memory degrading, one thing you can run and would have recommend was Apple diagnostics. It can be run by holding down the D key when you boot your Mac. The diagnostics at the store could be more thorough but apple diagnostics does check the hardware and gives you an idea of something is amiss.

Good luck getting your RAM taken care of by your local Mac guy. Rossmann Repair Group is another place if you need it.

Hope the apple store appointment wasn't costly.

My pleasure and it was great helping you out.

I called Apple support. I’ve gone through a series of steps and re-installed Big Sur. It was due to low memory that the problem has occurred.

Hi Amy1150,

Have you tried restoring from backup, downloading the installer and updating again to Big Sur?

Hope this helps.

Hi dddeeennn,

Yes, boot back into your Mac normally if you able to and then perform a time machine back up.

Also, refer to my post that I just shared for additional information.

Hope this helps.

Hi Sasha331,

What exactly are you experiencing, are you able to boot your Mac?

What operating system are you currently running, how much disk space do you currently have?

Frstrtd21 Did you look at my article?

G_Unit5913 this means that you have filevault enabled. Did you read the section about how to recovery when filevault is enabled?

I have this same problem and I don’t not have any other computed to connect it to in order to use target disk mode. I don’t know what to do because every time I restart/shutdown and turn on the computer it comes up with the same error. I believe I have a 2018 MacBook Pro. I do not know what else I can do at the moment. I am also a college student and need my computer for classes so this is a huge problem at the moment...

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

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

I have the exact same problem since yesterday. Please if someone knows a step by step guide through this mess.... I made a time machine backup of my Macbook Air 2018 128gb before i started the upgrade from Mojave to Big Sur.

can't follow Cfred2020 advice because when in macOS Recovery my mac does not recognize my password although it is the correct one.