macOS Big Sur - About This Mac
I feel like I just barely updated my MacPro to macOS Catalina, and here I am getting it updated to macOS Big Sur!

Thankfully the process wasn't too bad. Of note, my MacPro was a 4,1 upgraded to 5,1 and I do not have any Bluetooth or WiFi cards.

Pre-Install Notes

  • Make sure you have or have previously run the APFS ROM Patcher.
  • At least 1 32GB+ USB thumbdrive - make sure it's a of decent quality / brand name.
  • A boot screen / boot picker.
  • SIP and authenticated root disabled.
  • Updated nvram boot-args.

It's worth noting I used 2x 16GB USB thumbdrives, but I've noted above to use a 32GB thumbdrive.

Disabling SIP and authenticated root

I figured it would be worth including this information so you don't have to dig through Google results. You'll need to either boot into recovery mode or a USB installer to do this. Either way, open Terminal and run these commands.

crsutil status # If this returns disabled you're good, move on.
csrutil authenticated-root status # If this returns disabled you're good, move on.

If either of the above commands didn't return disabled, then run the following:

crsutil disable
csrutil authenticated-root disable

You can re-run the first 2 commands to ensure the result is 'disabled'.

Update nvram boot-args

While you're also in Terminal run the following:

nvram boot-args="-v -no_compat_check"

Upgrading/Installing macOS Big Sur

Alright so first things first, we need to create a bootable USB installer. You should be able to do this all from your MacPro without needing to use any other systems, but it's possible you may need a secondary Mac.

Let's grab the tool we need to use to patch our macOS Big Sur installer. Visit this page on GitHub, click on the green button labeled 'Code'. Select the 'Download Zip' option and a zip file will download. A side-note, I have a separate adminstrator account on my MacBook Pro so I placed the unziped directory (named bigmac-master) into a directory accessible by all users - in this case I used /Users/Shared. You can put it wherever an administrative user can access it.

Next take your USB thumbdrive and erase it in Disk Utility. You can name it whatever you'd like, just make sure 'Scheme' is set to 'GUID Partition Map'. Once that has finished, you can close out of Disk Utility.

Open Next go into the directory where you've placed the patcher tool. As an example:

cd /Users/Shared/bigmac-master

Now run the following command which will setup your bootable macOS Big Sur installer on your USB thumbdrive:

sudo ./

You'll be asked (verbiage may differ slightly):

📦 Would you like to download Big Sur macOS 11.1 (20C69)? [y]:

Hit y and then Enter. This will download the macOS Big Sur Installer. It's about a 12GB so it may take a bit of time. You'll then be asked:

🍦 Would you like to create a USB Installer, excluding thumb drives [y]:

Don't worry about the 'excluding thumb drives' verbiage, but remember you should be using a thumbdrive of decent quality / brand named. Hit `y' and then Enter. It may take some time but it will do the following:

  • Create 3 partitions on the USB thumbdrive.
    • The first partition will be for a copy of the patcher tools.
    • The second partition will be for the macOS Big Sur installer.
    • The third partition will be free space.

Here's where I messed up as either I am blind or no recommendated size was given for the USB installer device so I figured my 16GB thumbdrive would be fine. It wasn't. I had to edit the script. At line 131 I had to change:

diskutil partitionDisk "$disk" GPT jhfs+ bigmac_"$disk$number" 1g jhfs+ installer_"$disk$number" 16g jhfs+ FreeSpace 0


diskutil partitionDisk "$disk" GPT jhfs+ bigmac_"$disk$number" 1g jhfs+ installer_"$disk$number" 13.5g jhfs+ FreeSpace 0

I had to readjust the partition size that was being used for the macOS installer. Nonetheless once it completes you'll see some further instructions which you'll want to follow.

According to the previously provided output it states that you should reboot the system while holding down the Option key. This gets you into your boot selector. It's worth noting that I had to hold the Esc key to get to my boot selection screen. Whatever key you hold select the 'macOS Big Sur Installer' option. Once it's loaded up open up Terminal from the menu bar. Run the following commands to patch the installer:

cd /Volumes/bigmac

Then close out Terminal so you're back at the window which has an 'Install macOS Big Sur' option. Click on that and go through the process. Since I was upgrading I selected 'Macintosh HD' as my disk. Continue on and it'll start installing/upgrading. During this process the system will reboot three times.

You may end up at the login screen once it has completed. If this is the case, reboot the system again into the boot selector. Select the 'macOS Big Sur Installer' option. Once back in the installer environment, open Terminal and run the following:

cd /Volumes/bigmac

Hopefully everything goes smoothly! However if you happen to see the following (or very similar) at the end of the script run, we'll need to create another USB key (or reuse your current key):

📸 Attempting to delete snapshot =>
diskutil apfs deleteSnapshot disk4s5 -uuid 0FFE862F-86C8-43AE-A1E0-DFFF7A6D7F79
Deleting APFS Snapshot 0FFE873F-86C8-43AE-A1E0-DFFF7A6D7F79 "" from APFS Volume disk4s5
Started APFS operation
Error: -69863: Insufficient privileges

If you see that, you won't be able to boot back into macOS Big Sur. You'll just get an endless stream of kernel panics and reboots. Thankfully there's another tool out there that can resolve this. As I couldn't boot my MacPro I had to swap over to my MacBook Pro. From there I downloaded a copy of this file to my /Users/Shared directory. I then wrote that image to my second USB thumbdrive which I had previously erased and named 'usb' and set the Scheme to GUID Partition Map.

sudo asr -source /Users/Shared/BigSurBaseSystemfix.dmg -erase -noverify -target /Volumes/usb

From there, you'll want to shutdown your MacPro, remove the first USB thumbdrive, insert the second USB thumbddrive and reboot into your boot selection screen. From there pick the 'macOS Big Sur Installer' option. Once booted into the installer, go to the menu bar and select 'Utilities', then select the 'BigSurFixes delete snapshot' option. A Terminal window will popup and you'll be asked a couple questions. To be honest I can't remember what the exact questions are and I can't find them in the tools Git repository, but they should be self explanatory. Once that has completed running. You can reboot the system. It should probably boot back into macOS Big Sur now!