If you want the ability to perform a fresh and clean install of macOS Sierra, then you should consider creating a macOS Sierra USB install disk. Not only will this walkthrough work for the macOS Sierra Developer Preview, but it will also work for the public beta and future final releases. In the following video tutorial, we’ll show you how.
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A note on flash drives: You will need a USB flash drive to make this work. Your USB drive should be at least 8GB, and a USB 3.0 drive is preferred. Kingston sells an 8GB USB 3.0 drive for less than 6 bucks. Make sure that the disk you choose to use doesn’t contain anything that you want to keep, because the following tutorial will purge everything on the drive.
Step 1: Download macOS Sierra from the Mac App Store. Since macOS is currently only available for developers, you’ll need to first redeem a download code via Apple’s developer website. Once the public beta for macOS Sierra opens, anyone who signs up will be able to redeem a download code and install the beta.
Step 2: Once macOS Sierra is downloaded, close the install pop-up that appears using Command (⌘)+Q
Step 3: Open Finder → Applications and right-click on Install 10.12 Developer Preview and select Show Package Contents.
Step 4: Open Contents → Resources.
Step 5: Open a Terminal window via Applications → Utilities → Terminal.
Step 6: In the Terminal window type sudo followed by a space.
Step 7: Drag the createinstallmedia file from the Finder window opened in Step 4 to the Terminal window.
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Step 8: Type
--volume followed by a space.
Step 9: Connect your USB drive and drag the USB drive into the Terminal window.
Step 10: Type
--applicationpath in the Terminal followed by a space.
Step 11: Open Finder → Applications and drag the Install 10.12 Developer Preview into the Terminal window.
Step 12: Press Return on the Keyboard to submit the full command.
Step 13: Type a ‘Y’ to continue when prompted to do so, and press Return on your keyboard.
Step 14: The install process will begin by erasing the contents of your USB disk and copying the installer files to disk. The entire process is quite lengthy; it can take around 20-30 minutes, so you’ll need to show patience.
Once the process is finished, you’ll have a working macOS Sierra USB install disk that can be used to reinstall the macOS Sierra beta on a freshly wiped Mac. If you’re looking to perform a clean install of macOS, then this is the best way to do so.