Don’t worry if the drive isn’t formatted for the Mac. The drive will be reformatted automatically as part of the process. Change the name of your drive to Untitled; you need to do this for the steps below.
Use the Terminal to create a boot disk
So you have your external drive, and the Sierra beta installer is in place. Now you’re going to use Terminal to create a boot drive. If you’ve never used Terminal before, don’t worry. This is pretty easy. (If your really don’t want to use Terminal, there’s a free app called Diskmaker X that will make a boot drive. As of this writing, it supports El Capitan and older versions of OS X. I tried a workaround to see if I could use DiskMaker X to create a Sierra boot disk, and I got error messages. Keep an eye on DiskMaker X to see if/when it will support macOS Sierra.)
Here are the steps to create a macOS Sierra beta boot disk. (Apple also has these instructions.)
- Connect the external drive to your Mac. (In the Terminal command you will use, I use
Untitledto represent your external drive. If your drive is named something else, you need to change
Untitledto the name of your drive.)
- Launch Terminal (/Applications/Utilities/Terminal.app).
- Copy the following:
sudo /Applications/Install\ macOS\ Sierra\ Public\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Sierra\ Public\ Beta.app
- Go back to Terminal and paste the copied code at the prompt.
- Terminal will ask for a password. This is your user password. Terminal doesn’t display characters when you type it in. Hit Return.
- Terminal will tell you that it will erase your drive. To confirm that you want to continue, type Y and hit Return.
- You’ll see that Terminal erases your drive. When that part is done, your Mac may ask you if you want to use the drive for Time Machine. Click Don’t Use.
- Terminal will copy the installer file to your drive. This will take a few minutes.
- After copying, Terminal is done. You should see Terminal display a “Copy complete” and Done notice. You can quit Terminal and your drive is ready for use.
How to boot from the installer drive
- Plug your external drive into your Mac.
- Power up (or restart) your Mac. Press down on the Option key while the Mac boots.
- After a few moments, your Mac should display the Startup Manager, which will show you the available boot drives. Click on the external drive and hit Return. (You don’t need to select a network to proceed.)
- Your Mac will display an OS X Utilites window. If you want to install the beta and leave the data intact, select Install OS X. If you want to start over and wipe out the data, you need to go into Disk Utility to reformat the internal drive first, and then install macOS Sierra.
Macworld also has bootable-install-drive instructions for El Capitan (OS X 10.11), Yosemite (OS X 10.10), Mavericks (OS X 10.9), Mountain Lion (OS X 10.8), and Lion (OS X 10.7).
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