How to Perform a Clean Install of macOS Sierra

The OS supports two clean install options

macOS Sierra supports the same install and upgrade install methods familiar to most Mac users.

In this guide, we cover the clean install option. If you would rather perform an upgrade installation, visit our complete guide to upgrading to macOS Sierra.

The clean install process outlined in the guide works for both the Golden Master release as well as the fully released version of macOS Sierra.

macOS Sierra: Clean vs. Upgrade Install

The upgrade install is the easiest way to upgrade your Mac to macOS Sierra. This method preserves your current user data, documents, and apps while upgrading the existing macOS startup drive to macOS Sierra. The advantage is that once you upgrade, your Mac is ready to go, with your data intact and ready to use.

On the other hand, the clean install option wipes existing data on the target drive and replaces it with a pristine copy of macOS Sierra. A clean install is a good choice if you experience software problems with your Mac and cannot resolve them. While a clean install may solve the issue, you're starting from scratch; your current user data and applications will be gone.

Before continuing, you should verify that your Mac can run macOS Sierra.

Types of Clean Installs With macOS Sierra

The macOS Sierra installer on your Mac can perform two types of clean installs. The main difference between the two clean install methods comes down to the target for the clean install. Each has slightly different requirements, but the result is a pristine version of macOS Sierra installed on your Mac.

Clean Install on a Non-Startup Drive

The first option is a clean install on an empty volume or drive or on a target drive with data you don't mind losing. This method is the easiest type of clean install to perform. You don't need to make a bootable copy of the installer since you can run the installer directly from your Mac's startup drive.

For this method to work, you need to have an available second drive or volume. For most Macs, that means an external drive of some type. This drive will be the target for the installation and become the startup drive whenever you choose to boot into macOS Sierra.

Use a clean install on a non-startup drive when you want to try out a new version of macOS and want to continue using the older version. It's also a common method of installation for trying a beta software version of macOS.

Clean Install on a Mac Startup Drive

The second type of clean install involves first erasing your Mac's current startup drive and then installing macOS Sierra. This method requires you to make a bootable copy of the macOS Sierra installer, which you can use to boot from and then erase your Mac's current startup drive.

This method results in the complete loss of data on the startup drive. It might be a good choice if your Mac has accumulated a lot of data debris, which happens when you install and uninstall a lot of software over time. Such problems can cause your Mac to run slowly, create startup issues and shutdown issues, or result in crashes and apps not running correctly.

As long as the problem isn't hardware-related, reformatting the startup drive and performing a clean install of an OS can help revive your Mac.

What You Need to Perform a Clean Install of macOS Sierra

Once you've determined that your Mac is capable of running macOS Sierra and your clean install method, follow these foundational steps:

  • Download macOS Sierra installer: Download the installer from the Mac App Store.
  • Get a 16 GB USB flash drive: You need a flash drive for a clean install on your Mac's startup drive. If you plan to use the clean install on a non-startup drive, you don't need the USB flash drive.​
  • Backup your Mac: We highly recommend making a clone of your Mac before performing the update. This step will allow you to easily return your Mac to the condition it was in before you installed macOS Sierra. At the very least, you should have a current Time Machine backup or the equivalent, even if your clean install target is a non-startup drive.

If the macOS Sierra installer launches automatically once the download is complete, quit the installer immediately without performing the installation. If you install the OS without creating a bootable installer, you will lose access to the installer files.

Preliminary Steps for a Clean Install on a Non-Startup Drive

To perform a clean install on a non-startup drive, you will need to erase the target drive if it contains any other Mac operating systems. If the non-startup drive is empty or only contains personal data, you can skip the erase process.

Disk Utility being used to erase a drive for macOS Sierra install

To erase the non-startup drive, use these guides on Disk Utility in OS X Yosemite or earlier and how to format your Mac's drives in OS X El Capitan and later.

After you erase the non-startup drive, you can jump to the clean install process.

If you're going to perform a clean install on a non-startup drive, you can skip most of the preliminary steps and jump to the installation. We suggest reading through all of these steps before starting the install to familiarize yourself with the process.

Preliminary Steps for a Clean Install on a Mac Startup Drive

To perform a clean install on the startup drive, first create a bootable copy of the installer, boot from it, and erase the startup drive before installing macOS Sierra.

  1. Follow the instructions for how to create a bootable macOS Sierra installer on a USB flash drive.

  2. Connect the bootable flash drive containing the macOS Sierra installer to your Mac.

  3. Execute the Startup Manager shortcut by restarting your Mac while holding down the Option key.

  4. After a short wait, your Mac displays the macOS Startup Manager, which lists the bootable devices your Mac can start up from. Use the arrow keys to select the macOS Sierra installer on the USB drive, then press Enter or Return on your keyboard.

  5. Your Mac starts up from the USB flash drive. This process can take time, depending on how fast the USB port is and how fast the USB flash drive is.

  6. The installer displays a welcome screen asking you to choose a country and language to use. Make your selection and select Continue.

  7. Once the startup process completes, your Mac displays the macOS Utilities window. Select Disk Utility, then select Continue.

    The macOS Utilities allows you to use Disk Utility to erase a drive

  8. Disk Utility launches and displays the drives and volumes currently attached to your Mac.

    In the left pane, select the volume you wish to erase. It will likely be named Macintosh HD if you never changed the Mac's default name for the startup drive.

  9. With the startup volume selected, select Erase from the Disk Utility toolbar.

    You are about to erase the entire contents of your Mac's startup drive, including the current version of the OS, your media, apps, and data. Make sure you have a recent backup of the startup drive before continuing.

  10. In the next window, give the volume a name and select a format to use. Make sure to choose OS X Extended (Journaled) in the Format drop-down menu. You can also enter a name for the startup volume if you wish or use the default "Macintosh HD."

  11. Select Erase. The drop-down window changes to display the erase process. Typically, this is quick.

  12. Once the erase process is complete, select Done.

  13. You're finished with Disk Utility. Select Quit Disk Utility from the Disk Utility menu.

  14. The macOS Utilities window reappears. Select Install macOS, and then select Continue to start the installation process.

Clean Install macOS Sierra

After you complete the preliminary steps for your chosen clean install location, use the macOS installer to install macOS Sierra.

  1. Once the macOS installer launches, select Continue.

  2. The macOS Sierra licensing agreement appears. Read through the document and select Agree twice, acknowledging that you've read and agree to the terms, to continue.

  3. The installer displays the default target for the installation of macOS Sierra. The target is usually the startup drive (Macintosh HD). If this is correct, select the startup drive, then select Install.

  4. If you wish to install on a non-startup volume, select Show All Disks. The installer displays a list of attached volumes that you can install macOS Sierra on. Make your selection, then select Install.

    macOS installer's choose disk option

The installer displays a progress bar and time estimate for the installation process. While the process bar is displayed, the installer is copying needed files to the target volume. Your Mac restarts after the process finishes.

macOS Sierra Installation process bar

Use the macOS Sierra Setup Assistant to Complete the Installation

Once your Mac restarts, you're guided through the macOS Sierra setup process, where you create user accounts, set time and date preferences, and perform other housekeeping chores.

macOS Sierra Setup Assistant welcome page

Choose Your Country

At this point, you should see the macOS Sierra Setup Welcome screen. From the list of available countries, select your location, then select Continue.

The setup assistant makes its best guess on the keyboard layout to use. You can accept the suggested layout or select one from the list.

Transfer Data

Setup can now transfer your old account and user data from a Time Machine backup, startup disk, or other Mac device. In addition, you can transfer data from a Windows PC. You can also forgo transferring any data at this time.

We suggest selecting Don’t transfer any information now. Once you have macOS Sierra set up, you can always use the Migration Assistant to bring over old data.

Turn on Location Services

Choose to turn on Location Services, which allows apps to determine your Mac's location. This service can be helpful for applications such as Maps and Find my Mac.

Manage Your Apple ID and Account Settings

Next, choose to sign in with your Apple ID whenever you log in to your Mac. Choosing this option also signs you in to iCloud, iTunes, the App Store, FaceTime, and other services. You can also choose not to use your Apple ID and sign in to the various services as needed.

To set up the administrator's user account, enter or confirm the following:

If you selected the Apple ID option, you might find that some of the account fields are complete. You can treat the partially filled-in form as a suggestion to use or replace as you see fit.

  • Full name: Enter your full name.
  • Account name: This name will be the name of your home folder.
  • Password: You need to enter this twice to verify the password.
  • Password hint: While optional, it's a good idea to add a hint, just in case you have trouble remembering the password in the future.
  • Password reset: You can choose to allow your Apple ID to reset your password. This setting can be a handy fallback should you ever forget your Mac's password.
  • Time zone: Request automatic time zone settings based on the current location.

Manage Passwords and Files

Once the account is in place, you can set up iCloud Keychain. iCloud Keychain allows you to sync login and password information from one Mac to other Apple devices you may use. Syncing happens through iCloud, and all information is encrypted, preventing prying eyes from being able to intercept and make use of the data.

The setup process offers to keep your files on your Mac safely stored in iCloud, making them available to any device that can access your iCloud account.

If you would like files in your Desktop and Documents folder automatically copied to iCloud, place a check mark in the box labeled Store files from Documents and Desktop in iCloud. We suggest deferring this option until after you have your Mac set up and know how much data this would require.

Diagnostics and Final Steps

You can have your Mac send Diagnostics and Usage information to Apple to help find and fix bugs. If you change your mind, control Diagnostics and Usage data from Security & Privacy in System Preferences.

The setup assistant finishes the setup process and then displays your Mac's desktop, which signals that the setup is complete. You're ready to explore your new macOS Sierra operating system.

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