How to Perform a Clean Install of macOS Sierra

The OS supports two clean install options

The same install and upgrade install methods familiar to most Mac users are supported by macOS Sierra.

In this guide, we will 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 all of your current user data, documents, and apps while upgrading the existing operating system on your Mac's startup drive to macOS Sierra. The advantage is that once the upgrade is complete, your Mac is ready to go, with all of your personal data intact and ready to use.

The clean install option, on the other hand, replaces the contents of the target drive, wiping away any existing data on the drive and replacing it with a pristine copy of macOS Sierra. A clean install is a good choice if you are experiencing software problems with your Mac and unable to resolve them. While a clean install may solve the issue, you are starting from scratch; all of your current user data and applications will be gone.

Before continuing, you should verify that your Mac is able to run macOS Sierra.

What You Need to Perform a Clean Install of macOS Sierra

macOS Sierra Installation process bar

Once you've determined that your Mac is capable of running macOS Sierra, you will need the following:

  • MacOS Sierra Installer - This can be downloaded from the Mac App Store.
  • A 16 GB USB flash drive - The flash drive is needed 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.​
  • A current backup of your Mac - We highly recommend making a clone of your Mac before performing the update. This 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.
macOS Utilities

There are two types of clean installs that can be performed with the macOS Sierra installer on your Mac. Each has slightly different requirements, but the end result is a pristine version of macOS Sierra installed on your Mac.

Clean Install on a Non-Startup Drive

The first type is to install the OS on an empty volume or drive, or on a target drive whose data you don’t mind losing. This 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, which will become the target for the installation and will also become the startup drive whenever you choose to boot into macOS Sierra.

This type of installation is often used when you want to try out a new version of the Mac OS, but don't wish to totally commit to the new OS and want to be able to continue to use the older version. It's also a common method of installation for trying out a public beta of macOS.

Clean Install on a Mac Startup Drive

The second type of clean install is performed by 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 will result in complete loss of all data on the startup drive but might be a good choice for some people. This is a good option true 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 to revive your Mac.

Installing macOS Sierra: An Overview

The main difference between the two clean install methods comes down to the target for the clean install. If you're going to perform a clean install on the startup drive, you need to do the following:

  1. Create a bootable copy of the installer.
  2. Boot from the bootable installer.
  3. Erase the startup drive.
  4. Install macOS Sierra.

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

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

Before continuing, make sure you have done the following:

  1. Backed up your Mac with Time Machine or the equivalent, and if possible, created a clone of your current startup drive. We suggest doing this even if your clean install target is a non-startup drive.
    1. Downloaded the macOS Sierra Installer from the Mac App Store.
      Hint: you can quickly find the new OS by using the search field within the Mac App store.

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

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

To erase the non-startup drive, use the instructions found in the following guides:

After the non-startup drive is erased, you can jump to the section titled, "Clean Install of macOS Sierra."

Preliminary Steps for a Clean Install on a Mac Startup Drive

  1. Follow the instructions for how to make a bootable flash installer of OS X or macOS. This will make the bootable flash drive you need.

  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.

    After a wait, your Mac will display the macOS Startup Manager, which will display all of the bootable devices that 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.

  4. Your Mac will start up from the USB flash drive. This can take time, depending on how fast the USB port is, and how fast the USB flash drive is.

  5. The installer will display a welcome screen asking you to choose a country/language to use. Make your selection and select Continue.

  6. Once the startup process completes, your Mac will display the macOS Utilities window, with the following options:

    • Restore from Time Machine Backup
    • Install macOS
    • Get Help Online
    • Disk Utility
  7. Select Disk Utility, then select Continue.

  8. Disk Utility will launch and display the drives and volumes currently attached to your Mac.

    In the left-hand pane, select the volume you wish to erase. It will likely be named Macintosh HD if you never bothered to change 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 completely erase the contents of your Mac’s startup drive. This can include the current version of the OS, as well as all your personal data, such as music, movies, pictures, and apps. Make sure you have a current backup of the startup drive before continuing.

  10. A window will appear, allowing you to give the volume a name, as well as select a format to use. Make sure the Format drop-down menu is set to OS X Extended (Journaled). 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 will change to display the erase process. Normally, 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 will reappear. Select Install macOS, then select Continue. The installation process will begin.

Clean Install macOS Sierra

macOS installer's choose disk option
  1. The macOS installer has been launched, and the installer window is now open. Select Continue.

  2. The macOS Sierra licensing agreement will appear. Read through the document if you like, then select Agree to continue.

  3. A sheet will drop down, asking if you have read and agree to the license. Select Agree once again.

  4. The installer will display the default target for the installation of macOS Sierra. This is usually the startup drive (Macintosh HD). If this is correct, you can select the startup drive, then select Install and proceed to step 6.

    If, on the other hand, you wish to install on a non-startup volume, select Show All Disks.

  5. The installer will display a list of attached volumes that you can install macOS Sierra on. Make your selection, then select Install.

  6. The installer will display 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. Once the files have been copied, your Mac will restart.

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

Use the macOS Sierra Setup Assistant to Complete the Installation

Welcome to the macOS Sierra Setup Assistant
  1. At this point, you should be seeing the macOS Sierra Setup Welcome screen. From the list of available countries, select your location, then select Continue.

  2. The setup assistant will make its best guess on the keyboard layout to use. You can accept the suggested layout or select one from the list. Once you've made your selection, select Continue.

  3. 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. For now, let's take care of the basic setup. Make a selection, then select Continue.

  4. You can turn on Location Services, which allows apps to determine where your Mac is located. This can be helpful for applications such as Maps and Find my Mac. Make a selection, then select Continue.

  5. You can choose to sign in with your Apple ID whenever you log into your Mac. This will also sign you into 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. Depending on the choice you make here, you'll have slightly different install options going forward. We'll make a note where the installation process differs. Make a selection, then select Continue.

  6. You'll be presented with the terms and conditions for using macOS Sierra and the other basic OS services on your Mac. Select Agree. When the window drops down asking you to confirm agreement, select Agree once again.

  7. You will be asked to set up the administrator’s user account. If you selected the Apple ID option above, you may find that some of the account fields are already filled out. You can treat the partially filled in form as a suggestion to use or replace as you see fit. Enter or confirm the following:

    • Full name.
    • Account name. This 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.
    • You can choose to allow your Apple ID to reset your password. This can be a handy fallback should you ever forget your Mac's password.
    • You can also have the time zone automatically set based on the current location.
  8. Enter the requested information, then select Continue.

    If you chose to sign in with your Apple ID, you can perform the next two steps. If you chose to skip the Apple ID sign-in, you can jump ahead to step 11.

  9. 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. The syncing is performed through iCloud, and all information is encrypted, preventing prying eyes from being able to intercept and make use of the data. Make a selection, then select Continue.

  10. The setup process will offer to keep all of your important 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 checkmark 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 you know how much data this would require. (iCloud only offers a small amount of free storage space.) Make a selection, then select Continue.

  11. You can have your Mac send Diagnostics and Usage information to Apple to help in finding and fixing bugs. The Diagnostics and Usage data can be controlled from Security & Privacy option in System Preferences, should you change your mind later on. Select Continue.

The setup assistant will finish the setup process, and then display your Mac’s desktop. The setup is complete, and you're ready to explore your new macOS Sierra operating system.

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