Mac OS bootable external installation disk

One thing that continually pops up is the need to create a bootable external installation disk so that I can install a fresh version of Mac OS on a Mac that will be reused.
I keep searching for how-to’s on how to do it and I figured it was time to start documenting it for future reference. Perhaps you can find some benefit in this guide as well.

The process is actually quite simple once you figure it out and it can be done in a few steps.

Create Mac OS Bootable drive

    1. Download the latest Mac OS installation image from the App Store.
      Here is a link to Mac OS Sierra 10.5.
      The installation image will be downloaded to your Application folder. If the installer starts automatically, quit it.
    2. Connect an external disk to your system. I am using an USB disk called PWiggers. Change PWiggers to the name of your USB disk.
    3. Open the terminal and enter the following command, don’t forget to check the name of your external drive.

      sudo /Applications/Install\ macOS\ --volume /Volumes/PWiggers/ --applicationpath /Applications/Install\ macOS\


  1. The terminal will ask for a password. This is the password of your user account, assuming you have administrator privileges.
  2. Confirm that the external disk will be erased.
    Confirm erase
  3. After the erase is complete, the installer will be copied to the external disk. This can take a few minutes. Fifteen minutes is not uncommon so you might want to grab a cup of coffee.Waiting for erase
    Copying installer to disk
  4. When the files have been copied to the external drive the terminal displays “Copy complete” and “Done”. You can now quit terminal and unmount your external drive.

Install from bootable external drive

Now that you have the bootable external drive, installing is easy. Just plug the drive into the target Mac and boot the Mac while holding down the Option button. Select the external drive from the boot manager and follow the steps from there.
You can also use Disk Utility prior to the installation to format the internal disk so you can start with a clean slate.