an error occurred applying the software update

Hey I had the same problem but I have a solution. What you do is you restart your mac on the screen where is says an error occurred while applying the update and as your computer starts hold down command and "r". Then it will start macos recovery. There you choose your user and type in the password and then choole install mac os big sur. It will download a fresh copy of the update and install it. It worked for me hope it helps.

We had a similar problem with my wife's iMac (21.5" 4K). Some error, undefined, was reported and the computer kept booting to the slash circle.

So yes, first thing, do the Cmd-R boot, then open Disk Utilities and run Disk First Aid to clear up any potential problems.

Quit then go to the install screen and Big Sur should be a choice. Also make certain your drive is showing.

What I think happens sometimes is that the installer gets interrupted or corrupted and then the computer is left in an unstable state.

Hey!! I just has this issue too :(

Also a student and was mildly terrifying as I was stuck out of my laptop.

However, I did regain access

First of all I used the command R hold down upon booting up to access recovery mode I then used disk utility and did 'first aid' on my disks in case this was the issue (unsure if this was useful but might as well say). At this point I was still stuck

If I clicked startup disk it would load and load and give me no options

I then rebooted and held down alt or option key depending what laptop you have. And this boots you to a screen where you decide which disk you use to boot your laptop.

Previously it has been trying to boot using mac installer. Instead select your mac HD drive/the other option for booting.

For me this loaded me into my normal laptop interface with ALL my files.

I deleted the big sur installer as this was using up 12gb.

Currently I am backing up 40gb of my data, and will clear up some space once this is done to try again with the update

I hope this helps someone :)

I was able to fix the issue following the advice in this thread

“Restart, then hold Command - R. It will take you to Recovery Mode where you should be able to re-install Big Sur.”

https://support.apple.com/en-us/HT201314

Yes, I fixed it following the advice in this very thread:

“Restart, then hold Command - R. It will take you to Recovery Mode where you should be able to re-install Big Sur.”

Restart, then hold Command - R. It will take you to Recovery Mode where you should be able to re-install Big Sur.

Have you tried simply booting holding the Option key down?

If there are drives that can be seen this should show them. PLUS, you might also have a Choose Network below the drives listed. If you see that then select the appropriate network and log in before proceeding.

I had to do that with my wife's iMac and it showed surprisingly 2 drives named Macintosh HD and the backup external drive. If so, I selected the 2nd drive because the undefined state your computer has been left in may be trying to boot to the Data part.

Also, don't you have an external Time machine backup?

If it shows only one drive then try proceeding to boot to that.

Update: I had to scrounge around the 'net and collated useful tips found non-apple forums.

1/ Big Sur (also known as Big Sour) is full of security and privacy kinks that trips up so many apps (including Apple apps like Numbers) and devices (eg printers).

2/ Once Big Sour is embedded as the OS for your Mac device, it can't be reset to an older OS.

3/ Embedded, Big Sour does need to be recongifured. You must save all important apps (including Apple Apps like Pages, etc.) and files to a non-apple cloud account or USB drive because in Apple Store many older Apple Apps and older apps are not available for Big Sour.

4/ Reconfiguring does erase all data like factory reset. So I repeat save every important app and file because in Apple Store many older Apple Apps and older apps are not available for Big Sour.

5/ After saving the important apps and files; Click on the apple icon select Shutdown (or restart if you have quick reflexes).

6/ Start the machine at the the first appearance of the apple icon simultaneously press Command and R for 5 to 20 seconds (this varies between machines). This step is so temperamental that you may need to do a few times.

7/ When the utility box appears, you will start the dreaded process of deleting drives and doing first aid. The aim is to delete various drives and folders that may contain apps and files that were kinked by Big Sour. The kinked apps and files are corrupted and will affect running them hence crashes, app functions don't work, etc.

8/ By doing the factory reset and resinstalling Big Sour, the OS will function.

9/ Use the Apple Store to download Big Sour compatible apps.

10/ Now start reinstalling the apps and files you saved in step 3 and 4. DO NOT EXPECT ANY LOGIC TO WHERE APPLE LIST APP/FUNCTION SWITCHES. After installing them, the swearing will intensify as each app/file may have security kink that will involve going into various MAC system menus to locate the glitch switch for example Numbers apps scrolling is not logically in the Numbers app so it was #$%$%#$%#$% to find that glitch switch is in the System Preference >Touchpad. APPLE forums were difficult finding easy tips on were the swithes are. Research non-Apple forums and you will find straight forward and easy tips on where to look to the glitch switch.

11/ Printer connections are most affected as Big Sour security kinks will cause problems. Printers needs to wireless. If your printers have sleep mode and deep sleep modes, switch those modes off, or else when in those mode Big Sour security kinks will kill off the printers connections not recognise their drivers/firmwares and you will have reinstall their drivers.

12/ Some reinstalled apps and files will have minor glitches that you can find workarounds.

13/ After 3weeks of trying to find fixes for glitches, I can use some of the important apps and files. Other apps and files can only be accessed and edited through online web-accounts and Google docs (Big Sour refuse to run them). Every couple of days Big Sour printers connections are $%$^$#. Sometimes while making an urgent online bank payment and needed to print a receipt/invoice/order or to print and urgent document that needing signing that I find out the Big Sour has cut the printer connections that I have to screenshot the receipt/invoice/order, send to other apple/PC devices to print off.

No. I had to force a clean install of big sour and than recovered data from time machine backup

Did you try what was suggested above?

“restart your mac on the screen where is says an error occurred while applying the update and as your computer starts hold down command and "r". “

It worked fir me. Good luck!

Command + R Just start pressing that over and over and it reboots and it will get you into the menu.

Ah I'm sorry that happened!! All I did was as soon as i pressed power on i held down the alt key until something came up.

I'm really sorry if this doesnt work for you!

If you use Recovery Mode (Command-R) you won't lose any data. You're overwriting the OS but that being said, you should always have a fresh backup when upgrading just in case. It's not a matter of IF you need it but WHEN you need it.

Hey everyone,

I had that problem while updating for the BigSur and my computer got stück. During the initialization, the computer

was entering automatically in recovery mode (or something like this) and saying that there was a problem during the

installation of the new OSX.

I then entered in recovery mode before the installation try using (cmd + shift + r) and managed to reset the mac to factory configurations, which means back to Maverick OS and just then entering there the Apple Store and re-downloading and re-installing the BigSur. Finally, I used the Time Machine I had in an external drive to retrieve my documents and stuff.

I hope it helps someone out there that got into this inconvenient trouble.