Mac Clean Install of an Operating System

This guides you through installing your existing or new macOS operating system (e.g. Sequoia‌) and removing all existing data and configuration, thus providing a "clean" installation like on a new machine. This type of clean installation ensures that there is no previous configuration that can cause issues.

Use Erase All Content and Settings (Apple Silicon and Intel with Apple T2 Chip)

⏩ TL;DR: System Settings > General > Transfer or Reset > Erase All Content and Settings

If you have an Apple Silicon or Intel with T2 Chip Mac, you can use Erase All Content and Settings for a clean installation.

With this approach you upgrade (or restore) to the desired operating system version and then use Erase All Content and Settings to "factory reset" the machine at that macOS version.

You can do this instead of having to create a bootable USB drive installer, erase the hard drive, and install macOS from that USB Installer.

🍎 Since macoS Montery (Ventura, Sequoia‌), you can factory reset and "erase" all data on your Mac's internal harddrive, restoring it as if it was "right-out-of-the-box" by using the Erase All Content and Settings feature in Mac's System Settings application. This will remove all your user data and user-installed applications without having to reinstall macOS, restoring the version that was on the machine when you reset it.

Specifically Erase All Content and Settings...

Erases all user files (data, configuration, applications)
Logs out your Apple ID
Removes your Touch ID fingerprints
Removes purchases and all your Apple Wallet items
Disables Find My and Activation Lock

This works by securely erasing all of the encrypted hard drive's encryption keys, since by default internal storage is always encrypted on all machines with Apple Silicon or Intel processors with the Apple T2 security chip.

Upgrade to the Desired macOS Version

Open the System Settings application
Navigate to General > Software Update
Click the Upgrade Now button

😞 You could start the macOS upgrade by command line, but since the reboot option is no longer supported, it will "hang" and you will still have to click the Restart button in System Settings > General > Software Update
softwareupdate --install --all

Erase All Content and Settings

Once the operating system is updated, use the Apple Silicon/T2 Erase All Content and Settings feature to erase and factory reset the machine giving you a clean install.

System Settings > General > Transfer or Reset > Erase All Content and Settings

Open the System Settings application
Navigate to General > Transfer or Reset
Click the Erase All Content and Settings... button

🔁 If your machine restarts in Recovery Activate this Mac with a message about selecting a WiFi from the menu (with none listed in the panel) and no other option but a restart, go to the WiFi icon in the Mac menu bar and join your WiFi network manually.

Use a Bootable USB Installer

If you must have a bootable USB Installer, you can do that too.

You will first need to create the bootable USB Installer and then delete your Mac's hard drive (or use Erase All Content and Settings later), and install the macOS from your bootable USB Installer.

Create a Bootable USB Drive Installer

📖 the createinstallmedia command is from the Apple Support Documentation

Format the USB Drive

From Apple Support Documentation...

A USB flash drive or other secondary volume with at least 14GB of available storage, formatted as Mac OS Extended

Mac OS Extended (Journaled) or better is fine.

Name your USB Drive macOSSequoia‌ or in the Create the installer command below, substitute macOSSequoia‌ with your USB drive's name.

Create the Bootable USB Installer

To create Bootable USB Installer

For macOS Sequoia‌...

You will first need to download the macOS update Installer Application BUT NOT LET IT INSTALL. After that you can create the bootable USB installer.

You can go to the Apple Support's page How to download and install macOS and use the link to download the macOS update from the App Store which then downloads through System Settings
⏩ You can paste this link into your browser to try to download macOS Sequoia‌ from the App Store
```
macappstores://apps.apple.com/us/app/macos-sequoia/id6596773750
```
When the download completes and the Installer Application launches, use its menu to EXIT it and DO NOT click Continue
Go to the Mac's Launchpad and you should see the Install macOS Sequoia‌ application (which is the Installer)

Now that you have macOS Installer, you can use it to create the bootable USB installer

In the terminal, execute the createinstallmedia command to create the bootable USB...

💡 You can replace macOSSequoia‌ with your USB drive's name

sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/macOSSequoia

🔒 You will probably be prompted for your password.

The output should look something like this...

Password:
Ready to start.
To continue we need to erase the volume at /Volumes/macOSSequoia.
If you wish to continue type (Y) then press return: Y
Erasing disk: 0%... 10%... 20%... 30%... 100%
Copying essential files...
Copying the macOS RecoveryOS...
Making disk bootable...
Copying to disk: 0%... 10%... 20%... 30%... 40%... 50%... 60%... 70%... 80%... 90%... 100%
Install media now available at "/Volumes/Install macOS Sequoia"

You should now have a bootable USB installer which you can list under /Volumes...

ls -al /Volumes/

The output should look something like this...

drwxr-xr-x   4 root        wheel   128 Nov  3 11:27 .
drwxr-xr-x  20 root        wheel   640 Oct 22 03:49 ..
...
drwxrwxr-x  50 someuser  staff  1768 Nov  2 12:09 Install macOS Sequoia
...

You can eject the USB drive

Install with the Bootable USB Installer

In order to have a clean install, you must delete the existing user data and configuration on your Mac.

If you have an Apple Silicon or Intel with T2 Chip Mac, you have two options to delete your existing user data and configuration.

You can use the Erase All Content and Settings feature described previously in this post. This is the easiest method; however, to save you effort, you should do this after you update the macOS version.
You can use the Mac Disk Utility application to erase your Mac's hard drive before you update the macOS version.

If you have an older Intel Mac that does not have the T2 Chip, then your only option is to use the Mac Disk Utility application to erase your Mac's hard drive before you update the macOS version

Erase Your Mac Hard Drive

How to erase your Mac hard drive depends on what type of Mac you have.

Erase Your Apple Silicon-Based Mac Hard Drive

📖 The source of truth on this is the Apple Support Documentation

To erase the hard drive on your Apple Silicon-Based Mac using the Disk Utility application...

Ensure that you are fully prepared to erase your hard drive (e.g. back up anything that you want to keep or a Apple Time Machine backup)
Shut down your Mac (power button or  Shut Down...)
Start your Mac in System Options mode by pressing and holding the power button until you see the Startup Options window
Select Options and click Continue

🔒 You will probably be prompted for your password (with admin access) and maybe your Apple ID too
In the utilities window, select the Disk Utility application and click Continue
In Disk Utility, select Macintosh HD in the sidebar
Click the Erase button
In the Erase popup, specify...
- Name: Macintosh HD
- Format: APFS
Click the Erase Button or the Erase Volume Group button if that is shown

Erase Your Intel-Based Mac Hard Drive