In this article we'll run through the steps necessary to create a bootable installer of the Mac operating system, whether it's so you can install the latest version of the macOS on multiple Macs; perform a clean instal of the macOS; or just to be prepared with a handy emergency disk if your Mac experiences problems and you don't want to connect to the internet.

You can also use your bootable installer to install the MacOS on a separate partition of your hard drive, it's also a hassle-free way to go back to the previous version of the MacOS.

Luckily, making a bootable installation of the Mac operating system became a whole lot easier when Apple launched Mavericks back in 2013. With that version of Mac OS X, and all versions since, itis been possible to use the Terminal command createinstallmedia to create a bootable installer of the macOS, in this article we'll show you how.

What you’ll need

12GB Flash Drive

  • You’ll need a drive with at least 12GB storage available (it used to be 8GB, but Apple now recommends 12GB - although we say ideally 32-64GB.)
  • We recommend a Flash memory stick if you are planning to boot from the drive as it will be quicker.  
  • If you have data on the drive that you need you will need to find another drive as this will be completed formatted.

The MacOS installation files

  • You will need to get the installation files from the Mac App Store. If you already have the software on your Mac you will find it in the Mac App Store under your purchased tab.
  • It goes without saying that you will need an internet connection to download the software.
  • Download the software but don’t start the process of installing it on your Mac because doing so will delete the installers - and it’s the installers you need. If it opens, close the installer.
  • You will find the installation files in your /Applications folder. Access it from the Finder.

Using Terminal to create a bootable installation of MacOS

Note, the createinstallmedia tool doesn’t work under OS X 10.6 Snow Leopard - it requires OS X 10.7 Lion or later.

Also, the processes have changed slightly since Mavericks so if your looking to create an installation of one of the ‘Cat’ versions of Mac OS X you should read this instead.

Creating a bootable installation of MacOS requires a single command in Terminal. The createinstallmedia command makes it possible to create a bootable copy of an installer on any drive that’s connected to your Mac.

Note that the createinstallmedia command erases anything on your external disk though, so make sure there’s nothing on it that you need.

  1. Download the installation files from the Mac App Store
  2. Don’t start the installation process.
  3. Plug in your external drive.
  4. Change the drive’s name to something memorable. For the sake of this tutorial we’ll call it Name.
  5. Open Terminal, which you will find in Applications > Utilities (or just search using Spotlight cmd+space bar)
  6. Type (or paste) the following in to Terminal, replacing Name with the name you gave your drive. (If it’s Sierra you are installing the words will be as below, alternatively, if it’s Yosemite.app, Mavericks.app type it thus, if it’s El Capitan: you need to type El\ Capitan.app

    sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Name --applicationpath /Applications/Install\ macOS\ Sierra.app --nointeraction &&say Done
  7. Click Enter
  8. Enter your password and wait - The process can take a while, you'll see “Erasing Disk: 0%… 10%… 20%… 30%…100%… Copying installer files to disk… Copy complete.” and so on.
  9. Wait until you see Done in the command line

You can also run the Mac operating system directly from an external drive rather than your built-in startup disk, this is handy if you are testing new versions of the Mac OS. The process is different to the one described above though, and we cover it here: Read about How to run macOS on an external hard drive here.