How to clean install macOS on your Mac

This guide explains how to perform a clean macOS installation. Before detailing the process, we'll clarify the difference between a clean install and a standard reinstall, and when a clean install is truly necessary. Is a clean install superior to a simple reinstall, or is wiping your Mac beforehand entirely unnecessary?

Traditionally, a clean install involved creating a bootable macOS installer on a USB drive and reformatting your hard drive. However, this is unnecessary for modern Macs. macOS Recovery now offers a simpler method to reinstall the operating system online (see our separate tutorial on reinstalling macOS using Recovery).

Because modern Macs install macOS on a separate, protected volume, reinstalling to fix problems is less effective than it used to be.

Should You Perform a Clean Install?

Several reasons might warrant a clean install:

• Troubleshooting Mac issues: A clean install can resolve performance problems or erratic behavior.
• Removing accumulated files: A clean install clears years of accumulated files before installing the OS on a freshly formatted disk.
• Preparing to sell or transfer your Mac: This ensures complete data removal and a factory reset.
• Virus removal (though Mac viruses are debated): Some users resort to this as a virus-removal method.

However, recent changes may render a clean install unnecessary. Since macOS Big Sur (2020), macOS resides on a sealed volume, untouched by other software. Reinstalling won't remove remnants of older macOS versions because this data isn't carried over.

A clean install risks data and setting loss. While removing excess files might seem beneficial, it's risky and could delete important data. Consider using a utility like CleanMyMac X instead. A clean install might create more problems than it solves.

If you're selling or transferring your Mac, a clean install is recommended; otherwise, proceed with caution.

How to Clean Install macOS

There are two primary methods:

1. Using the "Erase All Content and Settings" option in macOS and reinstalling via macOS Recovery.
2. Creating a bootable macOS installer USB drive, reformatting your drive, and installing from the drive.

We'll begin with the simpler method for modern Macs (all M-series and T2 Intel-powered Macs).

Before You Begin: Back Up Your Mac

Always back up your Mac before proceeding. (See our guide on backing up a Mac.) Remember, some files you think are in the cloud might actually be on your Mac. Time Machine backups might include unwanted settings; consider syncing Documents and Desktop with iCloud instead, but ensure all necessary data is in the cloud. Explore alternative Mac backup solutions for a suitable option.

The Easy Way to Wipe and Reinstall macOS

This method erases all content and settings and then installs macOS.

Requirements: Apple Silicon (M1 or later) or T2 Intel Mac; macOS Monterey or later.

1. Open System Settings.
2. Click General.
3. Click Transfer or Reset.
4. Click Erase All Content and Settings.
5. Enter your password.
6. You can skip the Time Machine backup reminder if you have another backup.
7. Review the deletion details (Apple ID, Touch ID, etc.).
8. Log out of your Apple ID and related services.
9. A final warning appears before erasure.
10. After clicking "Erase All Content & Settings," your Mac restarts.
11. Set up your Mac as new. Reinstall macOS from Recovery if desired.
12. Start up in Recovery (power button until startup options appear; on Intel Macs, hold Command R).
13. Click Options and Continue.
14. Enter your password (if needed).
15. Choose Reinstall macOS from the macOS Utilities window.

In macOS Monterey, "Erase All Content and Settings" was accessed differently but the outcome is the same.

(See our detailed guide on reinstalling macOS via Recovery.)

Clean Installing macOS Using a Bootable USB

This method uses a bootable USB drive with the macOS installer. It's ideal if you've already downloaded the installer files or are installing on multiple Macs.

Requirements: 15GB USB drive, admin privileges, a backup.

1. Format the External Drive:

<code>1.  Plug in the USB drive.
2.  Open Disk Utility (Applications > Utilities).
3.  Select the drive and click Erase.  (Rename it "Untitled" if necessary.)
4.  Choose Mac OS Extended (Journaled) format and GUID Partition Map.
5.  Click Erase.
6.  Click Done.</code>

2. Get the macOS Install File:

<code>*   **Via Software Update:**  (For installing a newer macOS version) Open System Settings > General > Software Update and download the installer (don't install it yet).
*   **From the Mac App Store:**  Download the desired macOS version from the Mac App Store.  (See our guide on installing older macOS versions if needed.)  After downloading, *do not* run the installer; quit it using Command   Q.  Locate the installer file (usually in Applications).</code>

3. Create a Bootable USB Disk:

<code>Use Terminal to create the bootable drive:

1.  Open Terminal.
2.  Use the `sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia –volume /Volumes/MyVolume` command (replace `MyVolume` with your drive's name).  For other macOS versions, adjust the command accordingly.
3.  Enter your password.
4.  Type 'Y' to confirm erasure.
5.  Wait for the process to complete.</code>

4. Wipe Your Mac:

<code>For modern Macs (Catalina, Big Sur, or later), use "Erase All Content and Settings."  For older Macs, use Disk Utility to delete the Macintosh HD and Macintosh HD – Data volumes.</code>

5. Install macOS:

<code>*   **M-series Macs:**  Plug in the bootable installer, turn off your Mac, press the power button until the startup options appear, select the installer, and follow the instructions.
*   **Intel Macs:**  Hold Option/Alt during startup, choose the installer, and follow the instructions.</code>

Reasons Not to Clean Install macOS

On Macs with T2 chips or Apple Silicon, a clean install is often unnecessary due to the sealed system volume. The system's integrity is verified by a cryptographic seal; if the Mac boots normally, the system is considered healthy. Reinstalling won't resolve issues unless the system volume itself is damaged. Cleaning up the Library folder might be beneficial for removing old app remnants.

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