Clean installation of macOS, this is how you do a ‘clean install’

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Clean Mac installation

When a new version of macOS becomes available, there are a lot of people who consider doing a clean install, a so-called clean install. Something related to this is a factory reset of the Mac. You then make a fresh start on your Mac, without taking all previous problems with you. If you’ve taken over a Mac from someone else, a clean installation is often the best option so that the Mac really becomes yours. In this tip you can read how to do it.


Note: make sure you always have a backup of all your files and data should something go wrong! You can do this for example via a Time Machine or another external hard drive.

Clean Mac Install or Not?

macOS Big Sur is the latest version of macOS. If you want to install this update, you can find it in the System Preferences.

With a normal update, all user data is retained. The big advantage is that you don’t have to worry about it: you just have to press a button and have some patience. But you also take all the junk from previous installations with you. If you want to start over with a clean Mac, you will need to perform a factory reset and a clean install. In doing so, the entire contents of your discs will be deleted.

Clean installation: two methods

There are two ways to perform a clean install of your Mac:

  • Directly on your Mac’s startup disk
  • From an external USB stick or external drive (recommended).

Have you already installed Big Sur? Then you can also start over. You first erase your hard drive and then install macOS Big Sur. You can also reinstall your Mac directly using a USB stick with macOS Big Sur installed.

Before you start, it is important that you ‘park’ all documents and other files that you want to keep on an external hard drive, a hard drive or with an online storage service such as iCloud Drive, Google Drive or Dropbox. You are going to erase your hard drive and all your personal files will also be deleted.

Method 1: Clean install on the Mac startup disk

You can choose to install Big Sur directly on your Mac’s startup disk. This means that you first completely erase the current startup disk and then install macOS 11. For this you need one bootable version of the Big Sur installation file.

All data on your startup disk is erased, so you can also get rid of all kinds of problems that have accumulated over the years, such as a slow Mac, sudden freezes and crashing apps. Reformatting the boot disk and performing a clean installation can solve everything in one fell swoop.

The main difference between the two clean install methods mentioned is the amount of work. When installing on the boot disk, you must first install a bootable version of the installer, restart your Mac via this bootable installer, erase the startup disk, and then install macOS. If you are installing from a USB stick or external hard drive, you can skip most steps and start the installation almost immediately.

Do you have a Mac with Fusion Drive? Then you can also perform the following steps, but many things are already arranged for you.

That is how it works:

  1. Restart your Mac.
  2. Immediately hold down the Cmd + R key combination.
  3. Release the keys when you see the Apple logo.
  4. Recovery mode is now active.
  5. Then you are going to completely erase the hard drive.
  6. Click in the menu bar and connect to your Wi-Fi network.
  7. click on Disk Utility> Continue.
  8. Choose Macintosh HD – Data in the column. Not visible? Then choose first Activate.
  9. Enter the password for administrator and unlock.
  10. Then click the Minus (-) button to delete the volume.
  11. Confirm that you want to delete.
  12. Click in the toolbar Wis.
  13. Choose the structure. If you used APFS before, choose it again. If this is not an option, you choose Mac OS Extended (journaled).
  14. Enter a name and click on Wis.
  15. The disk will now be completely erased and after that you can close the Disk Utility.

Install or reinstall macOS Big Sur

When you’re done wiping the drive, install macOS Big Sur (for the first time or again):

  1. In the utility, select Reinstall macOS> Continue.
  2. Follow the instructions on the screen.
  3. Choose the newly formatted macOS storage drive.
  4. The Mac will now download and reinstall Big Sur. All data will be deleted.

Once you are done with this, you can copy all the loose documents back to your Mac. It makes no sense to restore a Time Machine backup in this case, because then you also get all the junk back.

Method 2: clean install macOS from a USB stick

You can also choose to install macOS via a (bootable) USB stick. This is useful if you are having problems with your Mac. This gives you the option to physically reinstall macOS, just like you used to install from a CD. The method we discussed above with a clean install requires you to have a good internet connection. This is not necessary when installing a USB stick, because you first ensure that all files are local.

What do you need? A USB stick or external hard disk / SSD of at least 16 GB and a Mac with OS X 10.6.8 or higher.

For this method you will need:

  • A Mac with OS X 10.6.8 or later.
  • An empty USB stick with at least 16GB of storage space (any files left on it will be deleted).
  • A backup of your current Mac. For example, use Time Machine or Carbon Copy Cloner to make a full backup. With that you can always go back to the last working situation.
  • It is also wise to store your important documents and files somewhere, for example on Dropbox.

Before you get started, you will first need to install a version of macOS on a separate USB stick. You need a USB stick with at least 16GB of storage for this. Follow these steps to put macOS on a USB stick:

  1. Download macOS Big Sur (or any other version you want), when it’s available.
  2. After the download is complete, close the installation screen that appears with Command + Q to prevent the installation from starting. After all, you don’t want Big Sur on your Mac just yet.

You now have two options: create a USB stick with the Terminal app or a simpler method with the MacDaddy app.

Option 1: MacDaddy

For this option you do not have to enter complicated commands and it is therefore somewhat easier for novice users.

  1. Download ‘Install Disk Creator’ from MacDaddy from this link.
  2. Open the zip file you downloaded.
  3. Connect the USB stick to the Mac.
  4. Start the program and select the USB stick at the top.
  5. Choose now Choose a macOS installer.
  6. In Finder, browse for the installation file.
  7. Click Open and add macOS Big Sur.
  8. click on Create installer.

Option 2: with Terminal

For this option you should be more familiar with using commands in the Terminal application.

  1. Start de Terminal-app.
  2. Type the following command and press Enter.

sudo /Applications/Install macOS Big Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/BigSurStick

  1. Terminal asks for your password. Fill this in.
  2. Confirm your choice with Y and Enter.

Have some patience now, as it can take up to half an hour for your bootable USB stick to be ready. You can see the progress in Terminal. In the meantime, leave the window open. The end result is a USB stick that allows you to safely install macOS on a clean Mac.

Run clean installation

Installing a clean install of macOS is the next step in the process. Follow the steps below carefully so that nothing can go wrong.

  1. Insert the USB stick with the installer into your Mac and restart it with the Alt / Optn key pressed.
  2. The macOS Startup Manager will appear with all bootable drives and devices attached. Select the USB stick you prepared for installation and press Enter.
  3. The Mac will now boot from the installer on the USB stick. This can take a few minutes, depending on the speed of the USB port and the USB stick. Once this is done, the Mac will return to the macOS Utility startup window. You get a number of options there, such as Recover from a Time Machine backup. Choose Disk Utility.
  4. In the following steps, your startup disk will be completely erased, so you can start with a clean slate. Choose the desired startup disk. This is usually Macintosh HD.

Clean installation with Disk Utility

  1. Then click Knowledge to erase the entire disk. Also make sure the format is set to APFS (if available). Otherwise you choose macOS Extended (Journaled).
  2. Disk Utility will now erase the entire disk. Once this is done, you can exit this program. After this, you come back to macOS Utility.
  3. Select now Install macOS and the installation of Big Sur will now take place.
  4. During the installation process, choose the correct drive you just erased, such as Macintosh HD.

After these final steps, you will be guided through the standard macOS installation procedure. Once everything went well, you will have a completely clean Mac with the latest version of macOS.

Of course you have not lost everything. When you log in with your Apple ID, all personal data such as calendars and email will be synced back to iCloud. Programs downloaded from the Mac App Store can be re-downloaded free of charge from the Purchases overview. Any other programs downloaded outside of the Mac App Store can be re-downloaded from the creators’ website. In most cases this can be done free of charge by logging in again with your data.

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