Using Apple’s “Terminal”, you can create a macOS Sierra bootable USB installer. This installer can be used to perform a clean installation of macOS Sierra on a compatible Mac.
First, download the most recent version of macOS Sierra from the App Store. While you may have retained a copy of macOS Sierra from a previous upgrade, you’ll want to download a fresh copy to ensure you have the latest version. If you use an older version, you may need to install a series of macOS Sierra updates later on.
Once you have downloaded a copy of macOS Sierra, the macOS Sierra Installer will be located in the “Applications” folder of your Mac HD. The file will be called “Install macOS Sierra”. Leave the macOS Sierra Installer in its current, default location. This is important for later on.
Next, connect a USB Flash drive to your Mac. The USB Flash drive should be at least 8GB or larger. Make sure the USB Flash drive does not contain any files or documents you wish to keep. As part of the process to create a bootable USB Flash installer for macOS Sierra, the USB Flash drive will be formatted (all data will be erased). Once the USB Flash drive is connected and has mounted onto your desktop, change the name of the drive to “Untitled”. Again, this is important for later on.
Launch “Terminal”. You can do this by going to Finder, select “Go” from the menu bar then “Utilities”. Within “Utilities” double-click on “Terminal”.
Copy and paste the command line below into the “Terminal” window (make sure to copy the command line in its entirety):
sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia –volume /Volumes/Untitled –applicationpath /Applications/Install\ macOS\ Sierra.app
After pasting the above command line into “Terminal”, press the return key on your keyboard. “Terminal” will prompt you for your computer password. Enter your password then press the return key on your keyboard.
“Terminal” will ask you to confirm that you want to erase the USB Flash drive. Enter “Y” for Yes then press return on your keyboard. “Terminal” will format the USB Flash drive and then proceed with copying over the macOS Sierra Installer files and make the Flash drive bootable. Once the process is complete, “Terminal” will display “Copy Complete” followed by “Done”. If there are no error messages, you can close out of “Terminal”.
Your macOS Sierra bootable USB Flash drive should now be ready. You can test the USB Flash drive by restarting the Mac and holding down the Option key during restart. On startup, you should be prompted to select the drive that you want to boot from (either the internal hard drive/SSD or the USB Flash drive). Select the USB Flash drive to make sure the drive works properly. After the USB Flash drive boots successfully into the macOS Sierra Installer, you can exit the installer, restart the Mac and boot normally to your internal hard drive/SSD.
- After downloading the macOS Sierra Installer, make sure to leave the installer file in its default location (Applications folder). The Terminal command line will not work if you move the installer file.
- Make sure the USB Flash drive is renamed to “Untitled”. The Terminal command line will not work if the flash drive is named differently.
- If you are having problems creating a macOS Sierra bootable USB Flash drive using the current USB Flash drive, try a different flash drive. Some USB Flash drives may be problematic.