How to create a bootable macOS installer

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The macOS Recovery partition means there’s less need to keep a bootable installer on a USB stick or external hard drive. But there are still lots of occasions when one comes in handy.

For example, if you want to downgrade to an earlier version of macOS, or you want to temporarily boot into an earlier version of the operating system. And, although the Recovery partition is excellent and works well, having a backup, just in case it doesn’t work, makes a great deal of sense.

There are two ways to make an external installation drive. The first is to use Terminal and type in a specific set of instructions. The second, much easier, method is to use software tool to do it for you. Here, we’re going to show you how to do it using Disk Drill, available in Setapp.

Download macOS installer before you start

Before you get started, you'll need:

  • Get a USB flash drive - at least 12GB for the latest versions like High Sierra, Mojave, and Catalina and 8GB for earlier versions of macOS. We recommend to use 15GB, or a spare external hard drive (one you aren't planning to use for anything else).
  • Download macOS Installer - You can get the older versions of OS on the Mac App Store. If your macOS hasn’t been publicly released yet, get the beta and launch it like any other installer.
    Note: After macOS has downloaded, it will automatically launch the installer to begin the installation process. Close the installer instead. If the version of macOS you’ve downloaded is older than the one you’re currently running, you’ll see a message saying that it’s too old to install, click Ok. The installer file will remain in your Applications folder.
  • And please, don't forget to backup your Mac before you do anything.
If you’ve previously downloaded macOS, it should still be in your Applications folder.

How to find old macOS/OS X installer

Apple has changed the way it makes previous versions of macOS available. It used to be the case that you could download the most recent version, prior to the current version, from the Mac App Store’s Purchase tab. As of the release of High Sierra, that’s no longer the case. But the good news is you can go directly to the related macOS installer pages on the App Store - macOS High SierramacOS Sierra 10.12.6 or OS X 10.11.6 El Capitan

macOS Mojave App Store page

macOS Sierra App Store page

OS X El Capitan App Store page

Here’s how you get the installation files. 

If you want to test the upcoming macOS

Sign up for the beta after you get your Mac prepared (here’s the example with Catalina). The installer will appear in your Software Update tab — it’s totally ready for the launch. 

If you want an older version of macOS and you aren’t running High Sierra or Mojave

  1. Launch the Mac App Store. 
  2. Find the older version of macOS and click on the download button. 
  3. Agree that you want to continue if you get the warning the macOS is already installed on your Mac. 
  4. Wait until the installation is completed (about 10 minutes) and quit immediately if the installer launches automatically — if you start the installation, it will delete the files. 
  5. Find your install files in the Applications folder.

The easiest way to create a bootable macOS installer

Step 1: Prepare your drive

  1. Plug a suitable USB stick or external hard drive into your Mac.
  2. Launch Disk Utility, and select the volume you want to use and click the Erase tab. 
  3. Give the disk a name and choose Mac OS Extended from the format menu. 
  4. Click Erase.

Step 2: Create boot drive

  1. Then launch Setapp, search for Disk Drill app, and run it. 
  2. Once the app has launched, click on Create boot drive, and then select OS X/macOS installer.
  3. Read the notes on the next window, then click Ok, let’s do it. Disk Drill may locate the installer file automatically. If so, it will be displayed in the window. If it’s not, click Locate installer on disk, then navigate to your Applications folder and click on the macOS installer you downloaded before start. 
  4. Click Use as Source.
  5. In the next window, click Make Bootable next to the volume you created in Step 1. 
  6. Click Yes in the dialog box that opens. Disk Drill will start creating the bootable installer drive.
  7. Wait for Disk Drill to finish. The process will take several minutes to complete, so you’ll need to be a little patient. When it’s finished, you’ll see a window appear with instructions on how to boot your Mac using the new install disk you created.

How to create a macOS bootable installer with Terminal

You don’t have to use Disk Drill to create the bootable macOS installer, though it’s much easier if you do. As we mentioned earlier, the other method is to use Terminal. Here’s how to do it.

  1. Connect your flash drive.

  2. Launch Terminal. It’s in the Utilities folder in Applications, or you can launch Spotlight and type Terminal into its window, then hit Return.

  3. When Terminal has launched, type the following, replacing ‘MyVolume’ with the exact name of the installer in your Applications folder: 

    For Mojave: 

    sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

    For High Sierra: 

    sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

    For Sierra: 

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

    For El Capitan: 

    sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

  4. Hit Return. When Terminal asks for your user password, type it in. Then, when it warns that it’s about to erase the drive, press Y. Terminal will now erase the drive and then install macOS onto it. When it’s finished, you’ll see the words ‘Copy complete’ and ‘Done’.
  5. Quit Terminal.

Create bootable installer with Terminal

Whichever method you used, you’ll now have a USB stick or external drive with a bootable version of macOS on it. The next step is to test it. Go to System Preferences, click Startup Disk and choose the install disk you just created. 

Alternatively, restart your Mac and hold down the Alt key, then select the new install disk when you’re given the option. If everything worked ok, your Mac will boot using the new installer.

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