While reinstalling, you may get a message that an error occurred while preparing the update.
If you erased your Mac with Apple M1 chip, you might be unable to reinstall macOS from macOS Recovery. A message might say “An error occurred while preparing the update. Failed to personalize the software update. Please try again.” Use either of these solutions to reinstall macOS.
Use Apple Configurator
If you have the following items, you can resolve the issue by reviving or restoring the firmware of your Mac:
- Another Mac with macOS Catalina 10.15.6 or later and the latest Apple Configurator app, available free of charge from the App Store.
- A USB-C to USB-C cable or USB-A to USB-C cable to connect the computers. The cable must support both power and data. Thunderbolt 3 cables aren’t supported.
If you don’t have these items, follow the steps in the next section instead.
Or erase your Mac and reinstall
Use Recovery Assistant to erase your Mac, then reinstall macOS. Before you begin, make sure that you have enough time to complete all steps.
Erase using Recovery Assistant
- Turn on your Mac and continue to press and hold the power button until you see the startup options window. Select Options, then click Continue.
- When you’re asked to select a user you know the password for, select the user, click Next, then enter their administrator password.
- When you see the utilities window, choose Utilities > Terminal from the menu bar.
resetpasswordin Terminal, then press Return.
- Click the Reset Password window to bring it to the front, then choose Recovery Assistant > Erase Mac from the menu bar.
- Click Erase Mac in the window that opens, then click Erase Mac again to confirm. When done, your Mac restarts automatically.
- Choose your language when prompted during startup.
- If you see an alert that the version of macOS on the selected disk needs to be reinstalled, click macOS Utilities.
- Your Mac will begin activating, which requires an internet connection. When your Mac is activated, click Exit to Recovery Utilities.
- Perform steps 3 through 9 once more, then continue to the next section, below.
Then use one of these methods to reinstall macOS
After erasing your Mac as described above, use one of these three methods to reinstall macOS.
Use the Reinstall macOS Big Sur utility
If your Mac was using macOS Big Sur 11.0.1 before you erased it, select Reinstall macOS Big Sur in the utilities window, then follow the onscreen instructions. If you’re not sure, use one of the other methods instead.
Or use a bootable installer
If you have another Mac and a suitable external flash drive or other storage device that you don’t mind erasing, you can create and use a bootable installer for macOS Big Sur.
Or use Terminal to reinstall
If neither of the above methods applies to you, or you don’t know which version of macOS Big Sur your Mac was using, follow these steps:
- Select Safari in the utilities window in macOS Recovery, then click Continue.
- Open the article you’re reading now by entering this web address in the Safari search field:
- Select this block of text and copy it to the clipboard:cd ‘/Volumes/Untitled’ mkdir -p private/tmp cp -R ‘/Install macOS Big Sur.app’ private/tmp cd ‘private/tmp/Install macOS Big Sur.app’ mkdir Contents/SharedSupport curl -L -o Contents/SharedSupport/SharedSupport.dmg https://swcdn.apple.com/content/downloads/43/16/071-78704-A_U5B3K7DQY9/cj9xbdobsdoe67yq9e1w2x0cafwjk8ofkr/InstallAssistant.pkg
- Bring Recovery to the front by clicking outside of the Safari window.
- Choose Utilities > Terminal from the menu bar.
- Paste the block of text you copied in the previous step, then press Return.
- Your Mac now begins downloading macOS Big Sur. When done, type this command and press Return:
- The macOS Big Sur installer opens. Follow the onscreen instructions to reinstall macOS.
If you need help or these instructions aren’t successful, please contact Apple Support.