How to clean install macOS on your Mac

In this article, we’re going to show you how to perform a clean install of macOS. There are a number of reasons why you might want to do a clean install:

• You might want to reinstall the operating system in order to correct problems with your Mac – doing a clean install may be a good option if your Mac is running slow or otherwise misbehaving.
• Doing a clean install allows you to clear away old files that you might have been accumulating for years before installing the operating system onto a freshly formatted disk. 
• A clean install is also something you should do before selling your Mac or passing it on. It allows you to remove all your data from your Mac and return it to factory settings for the next person.
• A clean install is also something many computer users resort to when they are trying to get rid of a virus (although there is a lot of debate about whether there are viruses on the Mac).

Whatever your reason, a clean install of macOS might solve a lot of problems.

However, changes in recent years may mean that a clean install is not necessary, so we will start by explaining why you might not need to do a clean install on your Mac. 

You should also keep in mind that there are multiple ways to do a clean installation of macOS. Traditionally, the way was to make a bootable copy of the macOS installer on a USB stick and then reformat your drive before installing the bootable copy onto your Mac. There is also an even simpler method that allows you to use macOS Recovery to reinstall the Mac operating system over the web (we have a separate tutorial about doing a clean install of macOS using Recovery).

Plus, if you are running macOS Monterey or later on a M-series Mac, or an Intel Mac with a T2 chip, then a setting in System Settings/System Preferences makes wiping your Mac easier than ever. We’ll run through all of these methods below.

Should I do a clean install on my Mac?

In the past, it was helpful to reinstall the system if you wanted to correct some Mac problems, but today this solution doesn’t make as much sense.

Since macOS Big Sur (introduced in 2020), macOS has its home on its own volume, which is both read-only and cryptographically signed and sealed (referred to as a Sealed System Volume). This seal is stored either in the T2 chip of the newer Intel Macs or in the Secure Enclave of the Apple M-series chip (aka Apple Silicon).

Each component of the system is signed in hierarchical order, and any change to a component would also invalidate the seal that represents the top level. For further security, these Macs also do not start directly from the system volume, but from a snapshot of the system–and snapshots cannot be changed, even by the system itself.

So macOS itself cannot be changed by any software that you install as a user. Should a problem occur with macOS during a restart, perhaps because a storage space on the SSD is defective and thus a system component is no longer intact, this will be recognized by the startup process since the seal will now be invalid. Should this happen you will have to reinstall the system.

However, if your Mac boots up without issue then it indicates that there are no problems with the system. As long as your Mac works (which can be determined on the basis of the seal), the Mac is considered to be in working order as it complies with Apple’s specifications.

For that reason, even if you do encounter problems on Macs with T2 chip or Apple Silicon while running macOS, it makes no sense to reinstall the system yourself.

For those who want to do a clean install so that no leftovers that belong to an old system are carried along, this no longer applies because none of this information is carried over. All components are checked after installation, then signed and finally the entire system is sealed again. Again, the seal guarantees that everything is fine and that nothing untoward has crept in.

However, there is one component of the system software that is not installed on the read-only system volume. All other user-installed programs reside on the volume with the user data, including Safari. This means Apple can offer a separate update for the browser and WebKit, so that you do not have to reinstall the whole system each time.

In the case of Safari and other apps there can be benefits in cleaning up your Library folder since it may still contain remnants of old applications you no longer use.

If you feel that you have a lot of this sort of crud on your Mac then wiping your drive could be useful, just be prepared that it can be a risky business and you may end up deleting something important. Beware that a clean install can cause more problems than it fixes.

You might prefer to use an application like CleanMyMac X from MacPaw ($39.95/£34.95 a year, free trial), or one of these alternatives: Best Mac Cleaner software.

If you are happy to take the risk and still want to wipe your Mac and reinstall macOS – which you should definitely do if you are selling or passing on your Mac – read on!

Three ways to clean install macOS

As we explained above, there is more than one way to wipe your Mac and reinstall macOS:

1. Make a copy of the macOS installer on a USB stick, reformat your drive and then install the macOS onto your Mac from the installer.
2. Use macOS Recovery to reinstall macOS via the web.
3. Use the Erase All Content and Settings option setting in System Preferences (available if you are running macOS Monterey and later on a M1 or later Mac, or an Intel Mac with a T2 chip).

Not only are there three different methods (which we’ll run through below) the methods depend on the version of macOS that you are running.

There is also the even trickier business of installing a clean copy of an older version of macOS on your Mac (e.g. Ventura, Monterey, Big Sur, Catalina, High Sierra, Sierra, El Capitan, Mojave, Yosemite or an even old version of OS X). Speaking of which, if an old version is what you’re looking for, it may be worth taking a look at another article where we focus on that entirely: How to download and install old versions of OS X on a Mac.

Before you begin: Back up your Mac

Before you begin we recommend that you make a backup, just in case something goes wrong. Full instructions here: How to back up a Mac. It’s entirely possible that there will be something on your Mac that you thought was in the cloud but was actually on your Mac (we speak from experience!)

Note that with regard to backups, you probably won’t want to recover a Time Machine backup if you don’t want to copy over all the settings and preferences associated with your old system. You could alternatively sync all your Documents and Desktop with iCloud rather than run a full backup, but make sure that everything you need is in the cloud and be aware that you may lose your settings and applications. We have some alternative Mac Backup solutions here.

Option 1: Erase All Content and Settings (macOS Monterey and later)

Before the arrival of Monterey, it was necessary to create a bootable USB drive or use Recovery Mode to wipe your disk. However, since macOS Monterey Apple has made it easy to get a factory-fresh installation.

An Erase All Content and Settings option arrived with macOS Monterey (in 2021) that allows you to reset your Mac to factory settings without having to work through the many steps to wipe and format your drives.

The new option wasn’t available on every Mac running Monterey though. An M1 or later Mac, or an Intel Mac with a T2 chip inside was required to use the Erase All Content and Settings option.

These Intel Macs have the T2 security chip:

• MacBook Air from 2018
• MacBook Pro from 2018
• Mac mini from 2018
• iMac 27-inch from 2020
• iMac Pro
• Mac Pro from 2019

In macOS Ventura and later

In Ventura System Preferences became System Settings, so the method slightly changed and things look completely different, so we will run through both methods.

Here’s how to find Erase all Content and Settings in macOS Ventura or later.

1. Open System Settings.
2. Click on General.
3. Click on Transfer or Reset.
4. Choose Erase all Content and Settings.

In macOS Monterey

If you are running macOS Monterey the Erase All Content and Settings option is much easier to find.

1. Open System Preferences.
2. Click on System Preferences in the menu bar at the top of your screen.
3. Click on Erase All Content and Settings.

Now that you have located the Erase All Content and Settings option, follow the steps below to wipe your Mac.

1. Select Erase All Content and Settings
2. Enter your password.
3. You’ll be reminded to do a backup with Time Machine before you begin deletion, but you can skip that step.
4. A window will show you what will be deleted, including Apple ID, Touch ID, accessories, and Find My settings.
5. Finally, you will need to log out of your Mac and all related services using your Apple ID.
6. Before your Mac is erased you receive a final warning, so if you have second thoughts at least you can stop at this point!
7. Having clicked the second Erase All Content & Settings your Mac will restart. Eventually, you will see a black screen while it restarts.
8. Once your Mac restarts you can go through the steps to set it up as new, or you can leave it at this stage for the next owner to set up. Just turn the Mac off first.

Option 2: Do a clean install via Recovery

We explain how to reinstall macOS via Recovery here: How to reinstall macOS, but we will summarise the steps here.

How you enter recovery mode depends on the Mac you own.

If you want to enter recovery mode on an M1 or later Mac follow these steps:

1. Press and hold the power button when you start up your Mac.
2. Continue to press and hold the button until you see a startup options window appear with an Options icon.
3. Select Options.
4. Click Continue.

To enter Recovery on an Intel Mac press Command+R.

1. Once Recovery starts up you’ll see a macOS Utilities window with options to Restore From Time Machine Backup, Reinstall macOS [version], Safari (or Get Help Online in older versions) and Disk Utility. If you want to wipe the Mac before reinstalling choose Disk Utility. 
2. Using Disk Utility run through the steps to erase your Mac as detailed in our How to reinstall macOS guide.
3. After you have erased your drive click on Disk Utility > Quit Disk Utility. Or just Command + Q.
4. Now choose Reinstall macOS from the options.
5. Wait while macOS is reinstalled. Expect this to take a while.

Option 3: Do a clean install macOS using a bootable USB

Now for the method that involves using a bootable USB with the macOS installation on it. This might be the best method if you already have the installation files downloaded and don’t want to wait for hours for Recovery to download the files.

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