How to make a bootable Sierra installer drive in case you want to downgrade from macOS High Sierra
macOS High Sierra is a working beta, but what if you want to keep a copy of macOS Sierra, too?
If you are preparing to test out macOS High Sierra, there is one additional set of steps you should follow. You should download a bootable copy of macOS Sierra. This allows you to use it if you partition your hard drive for dual-software installation. It is also the only way to downgrade to the older format if you decide you don't like macOS High Sierra at all.
- Before you start
- How to format your external drive for Mac
- How to make your external drive bootable for Sierra
- How to use Sierra with a bootable drive
Before you start
Before you get started, make sure you have a thumb drive with at least 8GB of storage, or a spare external hard drive (one that you don't use with anything else).
You'll also need to download macOS Sierra from the Mac App Store.
Note: After macOS Sierra has downloaded, it will automatically begin the installation process. Close the installer instead.
Please, Please, Please, backup your Mac before you do anything.
How to format your external drive for Mac
You'll need to start with a clean thumb drive or hard drive in order to get it ready to work as a bootable drive.
- Plug the USB end of the drive to a USB port on your Mac.
- Click on Finder in your Dock to open a Finder window.
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Select Applications from the list on the left side of the window.
- Scroll down and double-click on Utilities.
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Scroll down and double-click on Disk Utility.
- Select your drive under External.
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Click on the Erase tab at the top of the window.
- Note the name of your external hard drive (probably "Untitled") because you will need it when you create a bootable drive. If you have more than one external hard drive named "Untitled," you will need to rename your hard drive now.
- Select Mac OS Extended (Journaled) from the format list.
- Click Erase.
- Click Done when the process is complete.
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Close the Disk Utility window.
Your thumb drive or external hard drive is now ready.
How to make your external drive bootable for macOS Sierra
Important:You will need to be in your Mac's administrator account in order to run the sudo Terminal command
- Click on Finder in your Dock to open a Finder window.
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Select Applications from the list on the left side of the window.
- Scroll down and double-click on Utilities.
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Scroll down and double click on Terminal.
- Recall the name of your formatted external drivewhen entering the following text into Terminal. If it is not named "Untitled," you will need to change the command syntax for the pathname where it says: Volumes/Untitled. The name of the drive can't have any spaces and it is case sensitive.
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Enter the following text into Terminal (Don't forget to change the name "Untitled" if your hard drive is named something else):
sudo /Applications/Install\ macOS\ http://ift.tt/2cE0Hh4 --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Sierra.app
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Hit the enter/return key.
- Enter your administrator account password. This is the password you use to make changes on your Mac or log in. No text will appear in Terminal when you enter the password.
The process could take a very long time, depending on the drive. When it is done, the Terminal window will report "Done."
How to use macOS Sierra with a bootable drive
Once macOS Sierra is installed on your external drive, you can boot up any Mac with the drive plugged into it.
- Turn off the Mac you want to use macOS Sierra with the bootable drive.
- Connect the drive to your Mac via the USB port.
- Turn on your Mac.
- Hold down the Option key when you hear the startup chime.
- Select the external drive with macOS Sierra on it from the list of systems to start up your computer.
Do you have any questions about how to create a bootable drive for the macOS Sierra installer? Let us know in the comments.
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