- 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.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Sierra.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.