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How to Clean Install macOS Big Sur 11.0

Written by John

A clean install of macOS Big Sur is required when there are problems you’re troubleshooting or when you face catastrophic internal disk failures. When you are troubleshooting and need a fresh installation of the macOS Big Sur, you can use an external drive with a macOS Big Sur installer to get the job done.

For you to clean install macOS Big Sur, you need to erase your hard disk first. Before erasing the hard disk, make sure to have backups of data you may need after the new installation of the operating system.

While there are processes to clean install macOS Big Sur with an internet connection, you can also install the latest OS without an internet connection. You will need an external drive with a macOS Big Sur installer to make this possible.

By following the steps in this tutorial, you will able to fix a problem you run into when installing macOS Big Sur from a bootable USB drive.

An error occurred while preparing the update. Failed to personalize the software update. Please try again”.

A software update is required to use this startup disk”.

Users run into this error message when making a clean installation of macOS Big Sur with USB Drive. Follow the steps in this tutorial and you will be able to have a fresh installation of the latest macOS without any problems.


During WWDC20, Apple announced that the new macOS Big Sur will not be available for macs dated 2013 and below. Unlike macOS Catalina that supported every standard configuration Mac that Mojave supported, Big Sur drops support for various Macs released in 2012 and 2013. The following are the Big Sur compatible macs

  • 2015 and later for MacBook
  • 2013 and later for MacBook Air
  • 2013 and later for MacBook Pro
  • 2014 and later for Mac Mini
  • 2014 and later for iMac
  • 2017 and later for iMac Pro
  • 2013 and later for Mac Pro

USB-C External Drive

We recommend you choose a good USB-C flash drive to use as your external drive for the clean install of macOS Big Sur.

Steps to Clean Install macOS Big Sur 11.0 for M1 and Intel Chip

Step 1: Backup your Mac with Time Machine

Backup your Mac with Time Machine

As you already know, clean install macOS Big Sur completely erases your Macintosh drive. Make sure that you have backed up your Mac with Time Machine. The Time Machine is the in-built backup feature of your Mac. To create backups with Time Machine, all you need is an External Storage device. After you connect the device and select it as your backup disk, Time Machine automatically makes hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for all previous months. The oldest backups are deleted when your backup disk is full.

Step 2: Download macOS Big Sur Installer

You will need to download the macOS Big Sur installer to begin the installation process. This process can be different based on the operating system that is running on your Mac.

If you’re running Big Sur on your Mac computer, follow these steps to download the installation package.
1. Click on the Apple menu icon and open System Preferences
2. Choose Software Update
3. Download the macOS Big Sur installation files

If in case you’re running an older version of macOS, you can get the Big Sur installer from the Mac App Store.

Here is the link to macOS Big Sur on the Mac App Store.

Know that the download can take some time because of the file size. The Big Sur installer is 12.6 GB in size and takes a while to download. Find the installer file in your Application folder.

Step 3: Format the USB Flash Drive

We will be moving the Big Sur installer file to the USB flash drive we will be using for the clean installation. You need to format the flash drive to be used for installing macOS Big Sur.

Format USB External Drive

1. Plug the USB-C drive into the Mac
2. Go to Applications > Utilities
3. Double-click and open Disk Utility
4. Choose the drive and click on Erase
5. And Name "Flash Drive"
5. Pick APFS as the format type
6. Choose the GUID Partition Map from the Scheme menu
7. Click on Erase

Wait for Disk Utility to create the partition and set up the external drive. This process may take a while. Once this is completed, click on Done.

Step 4: Move macOS Big Sur Installer to the USB Drive

Note that you do not need to turn your USB drive into a bootable drive if your Mac computer uses the latest M1 chip. This is because you cannot use a USB bootable drive to install macOS Big Sur on the latest MacBook Air M1, MacBook Pro M1, and Mac mini M1. Simply copy the Big Sur installer you have downloaded on your Mac computer to the formatted USB flash drive. Now, we are all set to clean install macOS Big Sur from an external drive, without any internet connection.

Copy Install macOS Big Sur to Flash Drive

Step 5: Allow Mac to Use External Disk

You will need to allow your Mac computer to use external disks. Both T2 Intel Macs and M1 Macs do not allow you to boot from external media. You need to allow booting from external media from the Startup Security Utility screen.

You can check out our in-depth tutorial for Macs to allow using external disks.

Step 6: Erase Hard Disk from Recovery Mode

You have to erase the hard disk on your Mac computer from the Recovery Mode. To access Recovery Mode, press and hold the power button on M1 Macs during startup. For Intel-based Macs, press the Command + R key combination during startup.

  • M1 Macs

  • intel mACS

Erase M1-based Macs with Recovery Assistant

1. Press and hold the Touch ID / Power Button while booting up your laptop. Keep pressing the button until you see ‘Loading Startup Options’ appear below the logo.

Boot to Recovery Assistant

2. You will see the screen to select the admin user and enter the admin password. However, you can erase the hard disk by using the Recovery Assistant. Click on ‘Recovery Assistant’ near the Apple logo in the top-left corner. Choose ‘Erase Mac’ from the dropdown options.

Erase Mac with Recovery Assistant

3. In the Erase Mac screen, click on ‘Erase Mac…’ and then choose ‘Erase Mac’ in the popup option.

You can also use the Recovery Assistant on Intel-based Macs to erase the hard disk. However, to do that, you need to enable FileVault. To enable FileVault on Intel Macs, go to System Preferences and choose Security & Privacy. From here you can turn on FileVault for the hard disk. After you’ve turned on FileVault, follow the steps mentioned for M1-based Macs to erase the hard disk with Recovery Assistant.

Step 7: Use Terminal to Open Install Assistant

You have to open Big Sur Install Assistant from the Terminal. Follow the steps to open macOS Big Sur Install Assistant.

1. Click on Utilities from the top menu bar and choose Terminal.

Open Terminal in Recovery Mode

2. Paste this block of code into the Terminal and press return

Go to USB Drive (My USB name is "Flash Drive")
cd /Volumes/Flash\ Drive

Open the macOS Big Sur Install Assistant with this command
./Install\ macOS\ Big\

Open InstallAssistant on Flash Drive

Follow the instructions on the screen to complete the clean installation of macOS Big Sur.

Install Clean macOS Big Sur with Flash Drive

Keep Your macOS Big Sur Clean

The most common reason why users need to clean install macOS Big Sur is to troubleshoot problems. You can avoid most problems on your macOS Big Sur by keeping it clean and thus avoiding the need to go through the time-intensive process of a fresh installation.

It may seem like a daunting task to keep your computer clean and free of all clutter considering the various tasks you do on a daily basis. This is exactly the reason why we recommend the Clean My Mac X app.

Clean My Mac X removes all the clutter on your Mac computer by scanning, detecting, and removing unwanted files. In three quick steps, you can make sure your computer remains clean and performs optimally.

Clean Up System Junk and App Junk in macOS Big Sur

When you clean install macOS Big Sur, you will get a fresh version of the latest operating system without any problems you may have had previously. By following the steps in this tutorial, you will be able to install macOS Big Sur without an internet connection and without encountering a common installation error with USB bootable drives. You may choose to retain a copy of the latest macOS Big Sur on your USB flash drive for times when you need to erase the hard disk and clean install macOS Big Sur.

Next Tutorial to help you clean install macOS Big Sur with Internet Connection.
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