How to Clean Install macOS Big Sur

Apr 8, 2021 - 4 Comments

How to clean install macOS Big Sur

Mac users may occasionally find themselves wanting to clean install macOS Big Sur onto a Mac. A clean installation of macOS Big Sur basically means the entire hard drive – including the system itself, all data, all apps, user accounts, literally everything – is erased, and then a fresh clean install of macOS Big Sur is installed onto the Mac. In this way it’s sort of like a factory reset or a fresh start, or what PC users sometimes refer to as reformatting, because there will be nothing left on the Mac at all, and booting it up will be similar to booting up a new Mac, with zero user data or other stuff.

A clean install is generally for advanced Mac users only, and is otherwise not recommended unless you’re giving away a Mac or transferring ownership, and have fully backed up your data. Because it erases the entire hard disk and all data on the Mac, it will cause complete data loss intentionally, so without sufficient backups the

Before proceeding, be certain you have a full backup of the Mac, and any or all important data. Failure to have sufficient backups will result in permanent data loss.


Clean installing MacOS Big Sur 11 requires the following:

Assuming you’ve met those prerequisites, and you understand what you’re about to do and why you’re doing it, here’s how you can clean install macOS Big Sur on compatible Intel Mac or Apple Silicon Mac.

How to Clean Install MacOS Big Sur (Reformat, Erase, & Factory Reset)

Warning: This erases the entire Mac, setting it up as if it were new again. Do not proceed if you do not want to remove all data from the Mac.

  1. Be certain you have made a full backup fo the Mac
  2. Connect the MacOS Big Sur USB installer drive to a USB port on the Mac
  3. Shutdown the Mac or reboot
  4. Next, boot into Recovery Mode, which differs depending on if it’s an Intel Mac or Apple Silicon Mac:
    • Intel Mac: Immediately hold the OPTION key until the boot selection menu appears on screen
    • Apple Silicon Mac: Immediately hold the POWER button until the boot selection screen appears
  5. Select the “Install MacOS Big Sur” USB drive as the boot disk
  6. From the macOS Recovery / Utilities screen, choose “Disk Utility” from the options
  7. In Disk Utility, select “Macintosh HD” (or whatever the name of the drive to erase and clean install Big Sur onto is), then click the “Erase” button from the toolbar
  8. Choose “Macintosh HD” as the disk name (or pick another if you’re so inclined), then go to “Format” and select APFS as the file system, and choose “Erase” – WARNING: ALL DATA ON THE MAC WILL BE PERMANENTLY ERASED
  9. When Disk Utility has finished formatting the disk, quit Disk Utility
  10. Back at the ‘macOS Utilities’ screen, select “Install macOS” from the options available
  11. Select “Macintosh HD” as the destination disk to install MacOS Big Sur onto, then choose “Install” to begin the process of installing a fresh version of MacOS Big Sur

* 1: The screenshots may look slightly different from what you’re seeing on screen depending on if you’re using an Intel Mac or Apple Silicon Mac, and what version of macOS currently is on the computer – nonetheless all functionality is the same

** 2: You may need to allow external booting of startup disks on the Mac to be able to use the bootable USB drive, depending on the computer security settings.

Do not interrupt the process of clean installing macOS Big Sur onto the Mac, it will take a while, and the Mac may reboot automatically during the installation process.

When it has finished, the Mac will boot directly into a fresh, new, clean installation of macOS Big Sur, and the setup process will be just as if the Mac was brand new and being turned on for the first time. No prior data, apps, or anything else will be on the Mac.

Once you’re booted up in MacOS, it’s up to you whether or not you want to proceed with the setup process, transfer data back over to the Mac, set it up as brand new, or transfer ownership of the Mac to someone else.

Remember, a clean install is effectively the same as reformatting and factory resetting the Mac, which makes it useful for not only troubleshooting but also for transferring ownership of a computer, if you plan on selling it or giving it to someone else.

If you’re transferring ownership of the Mac, turning it off will allow the new owner to basically set it up as if it were new, able to either restore it from backups of their own, or starting fresh as they wish.

While a clean install is used for various reasons, some advanced users perform a clean install as an advanced troubleshooting approach, particularly if they’re encountering persistent issues with the system software that have not been able to be explained or resolved through typical troubleshooting methods. If you’re experiencing any issues with macOS Big Sur, you may find it useful to check out this tutorial for troubleshooting macOS Big Sur problems, to better understand why macOS Big Sur feels slow and how to speed it up, and review this guide on how to resolve wi-fi issues with macOS Big Sur if you’re experiencing wireless networking issues.

Did you clean install macOS Big Sur? What was your reason? How did it go? Did you use another approach to perform the clean install, like using internet recovery? Let us know your experiences, tips, and thoughts with erasing and reinstalling macOS Big Sur in the comments.

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Posted by: Paul Horowitz in Mac OS X, Tips & Tricks, Troubleshooting

4 Comments

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  1. JohnIL says:

    Clean installs for any OS is best. But upgrading OS doesn’t cause a lot of the issues. many times its apps that do not work with the newer OS version and the end user failed to do their homework on what is compatible. With Mac OS a lot of this stems from users having 32 Bit apps and not understanding that they are no longer supported. Clean installs are sort of the last resort when you have problems but can’t figure out where the issue is. Its a way to wipe the slate clean and start over. Apple makes a clean install of a current release mostly painless. But if you want to go back a release that’s where the trouble starts.

  2. Ian T says:

    For a “proper” Clean Install, isn’t it the case that all apps, data and the like should be manually selected from a backup even if this means re-downloading third party apps?
    After all, if you just copy back everything from Time Machine, there is a serious risk that corrupted data, apps or the like will simply be reinstalled and you may end up no better off than when you started.

    • Paul says:

      It’s up to the use case whether or not you’d want to transfer other data from manual backups, Time Machine, or nothing, after a clean install.

      If you’re transferring ownership of the Mac it’s probably best to just leave it fresh and let someone else do what they want with it.

      Some users choose to do what you mention, which is to manually backup only their data/files and then re-download and setup everything again (preferences, apps, etc). Particularly if the clean install was for performance or troubleshooting reasons, that can be a good approach.

  3. Kurt says:

    While a clean install is scary, I’m aware of a lot of junk from obsolete applications, abandoned versions and stuff like that. The other day I found a lot of email attachments from way back (both outlook and mail.app).

    So, if you know of a way to get rid of stuff now deleted programs have left behind – now that would be something I’d like to learn!

    Best /Kurt

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