How to Clean Install macOS Sierra

Some advanced Mac users may like to perform a clean install of macOS Sierra, which is essentially the process of erasing a hard drive and then starting fresh with a new clean installation of macOS Sierra 10.12. After the clean install is complete, a separate backup of any necessary files is manually transferred back over to restore personal data. A clean install can be desirable for many reasons, including to start anew, or as a troubleshooting method to extreme problems, but it’s really not appropriate for all Mac users.

Because the clean installation process involves manually backing up important files and data from a Mac (not just using Time Machine), formatting the hard drive and erasing everything in the process, using a boot installer disk to perform a clean installation of Sierra, and then manual file transfers to restore personal data, this is best reserved for advanced users. The vast majority of Mac users will be better served updating to macOS Sierra using the standard install and update method via the Mac App Store.

If you understand the objective and are comfortable with the clean installation process, you will need the following:

• Bootable macOS Sierra installer drive
• A Mac compatible with macOS Sierra (see list of Sierra compatible Macs here)
• A manual backup of your personal files, data, photos, and important information

Important note: a clean install will erase everything on the Mac and then install macOS Sierra, nothing else will be on the Mac. Wiping over and starting over clean is the entire point of this. Therefore you must backup your data manually beforehand, using a method of your choice. This is NOT the same as using Time Machine and restoring. If you don’t know what you’re doing with making manual file backups or with a clean install of macOS Sierra, don’t proceed, you will lose all data on the Mac. 

How to Clean Install macOS Sierra

1. Complete a backup to Time Machine before beginning. We recommend having a full Time Machine backup in addition to your manual file backup which you intend to manually restore data from. Be sure to back up your important files, pictures, data, or whatever else – do not skip this. Performing a clean install will erase the Mac and you will lose any data you do not save to an external volume
2. Attach the boot macOS Sierra install drive to the Mac
3. Reboot the computer, as soon as you hear the boot chime start holding the OPTION key during boot up
4. Continue holding OPTION key until you see a boot menu appear, choose the “Install macOS Sierra” volume from this menu
5. When the “macOS Utilities” screen loads, choose “Disk Utility” from the list
6. Select “Macintosh HD” (or the name of your target Mac drive to format and clean install Sierra onto), then choose the “Erase” button
7. Keep the drive named “Macintosh HD” (or rename it if you want), and go to “Format” and choose “Mac OS Extended (Journaled)”, then click on “Erase” – ALL DATA ON THE MAC WILL BE REMOVED AND ERASED, THIS IS IRREVERSIBLE
8. After the drive is finished formatting, quit out of Disk Utility to return to the macOS Utilities screen
9. Choose “Install macOS Sierra” from the menu options 
10. Click on “Continue” and agree to the terms, then select “Macintosh HD” (or the target drive name) from the drive list and then choose “Install”
11. Let macOS Sierra install, the entire installation process can take a while so be prepared to wait

When macOS Sierra has completed installing, it will boot back into a clean install of macOS Sierra and directly into the Mac OS setup process. 

The Mac will have nothing on it, just macOS Sierra. There will be no third party apps, no data, no personal files, no pictures, no music, no personal information, it’s much like getting a brand new Mac in that sense, which is the entire purpose of the clean install process. 

Once you’re at the mac OS 10.12 desktop, you’re ready to manually copy your files, apps, and personal data back over to the Mac, or you can start fresh with nothing on the computer at all. Enjoy! And don’t miss checking out some of the best macOS features.

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