How To Make A Bootable macOS Installer On An External Drive

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; install the latest macOS beta, perform a clean install of the macOS; or just to be prepared with an emergency disk if your Mac experiences problems and you don’t want to connect to the internet or in Recovery mode, or can’t access Recovery mode.

If you want to find out how to make a bootable install of the macOS Catalina beta, macOS Mojave, or an older version of Mac OS X or macOS, you’ve come to the right place.

You can also use your bootable installer to install the MacOS on a separate volume of your hard drive (or on a partition if you are running an older version of the Mac OS), it’s also a hassle-free way to go back to an older version of MacOS X or MacOS.

Luckily, making a bootable installation of the Mac operating system became a whole lot easier when Apple launched OS X Mavericks back in 2013. With that version of Mac OS X, and all versions since, it’s been possible to use the Terminal command createinstallmedia to create a bootable installer of the macOS, in this article we’ll show you how. Before we do, we run through getting the installation files. If you already have them you can jump straight to how to make a bootable installer and which createinstall code to use.

If you want to run macOS from an external drive, which is slightly different, read this.

What you need to make a bootable install drive

There are two main things you’ll need to make your bootable install. The whole process shouldn’t take very long.

A 12GB Flash Drive (at least!)

We recommend a 12GB (or more) drive, this may be more than you need, for example, the installer for the beta of Mojave was 5.68GB while High Sierra’s installer was 4.3GB.

We recommend a Flash memory stick as it will be quicker. You’ll also benefit from USB 3, or USB Type C – this may be your only choice if you have a newer Mac.

If you have data on the drive that you plan to use you will need to transfer it to another drive, or get a new drive, as it will be completely formatted and erased.

The installation files

Depending on which version of macOS you are running, and the version you want to to install, you will either be able to get the installation files from the Mac App Store, or you will have to obtain them from elsewhere. The former is easier, but even if you have updated your machine it’s still possible to get older installation files – we show you how here Getting older versions of macOS.

It goes without saying that you will need an internet connection to download the software and you may need it while installing the version of macOS if it needs to check for firmware or similar.

How to get MacOS Catalina beta installation files

If it’s an installer for the Catalina beta you are after, follow these steps. You’ll need to sign up for the beta if you want to test and try out new Catalina features before they are released.

We go into more details about gettingand installing the Catalina beta here. We do mention the code for installing the Catalina beta below though.

How to get MacOS Mojave installation files

With either macOS Mojave or High Sierra installed it’s a little tricky to get the installation files. This is because when High Sierra launched Apple stopped making older versions of the OS available to download via the Mac App Store, and in Mojave it changed it so that updates to macOS came via Software Update rather than the Mac App Store.

Luckily it can still be done, and we explain how to get old versions of macOS here.

How to get MacOS installation files from Mac App Store

As explained above, if you are already running Mojave or High Sierra on your Mac you won’t be able to use the following method to get hold of the installation files, but if you are – or you have access to a Mac that is – follow these steps.

Here’s how to get the MacOS installation files for if you are after an older version of the MacOS, and you aren’t currently running Mojave or High Sierra.

    1. Launch the Mac App Store on your Mac.
    2. Look for the version of macOS you want in the store (if you have previously downloaded the version search under your Purchased tab).
    3. Click on the Download button. If you have already installed this version of macOS, you will see a message warning that the version of macOS is already installed on this computer. Click on Continue to confirm that you still want to download the full installer.
  1. Your Mac will download the installer to your Applications folder. This process may take some time depending on the speed of your connection and whether you are using a wireless network. It took us about 10 minutes over Ethernet.
  2. If it automatically launches after download, quit – you don’t want to 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.
  3. You will find the installation files in your Applications folder, which you can access via the Finder.

How to make a bootable macOS installer

Now you have the installation files, we can move onto the process of making the bootable installer.

Note, the createinstallmedia method described here doesn’t work under OS X 10.6 Snow Leopard or earlier – 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 older article instead.

Since Mavericks, 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.

These are the instructions to follow if it’s the macOS High Sierra installer you require, although if you wanted a different version of a post-Mavericks OS, or the Mojave beta, the instructions will be similar.

  1. Plug in an external drive with at least 8GB space (preferably 12GB) as that’s how much the installer will require.
  2. Launch Disk Utility (press Cmd + spacebar and start to type Disk Utility).
  3. Before this next step, note: if you are running High Sierra or newer you will need to click on the View drop down below the close minimise buttons. Choose Show All Devices from the options. Now you will see the external root drive in addition to the volume below it.
  4. Select the root drive in the sidebar (the next step won’t with if you only select the volume).
  5. Click on Erase.
  6. Choose Mac OS Extended (Journaled) as the Format.
  7. Choose GUID Partition Map as the Scheme.
  8. Your drive will be called Untitled by default, you could give your drive a name such as “macOS” or “USB”. (Note you just need to replace the term USB in the Terminal command with the name of your drive).
  9. Click on Erase.
  10. Wait while Disk Uitlity creates the partition and sets up the drive (this can take a few minutes).
  11. Then click Done.
  12. Open Terminal (the easiest way is to press cmd+space bar and then start typing Terminal).
  13. Copy the following text that corresponds to the version of macOS you are installing into Terminal, you’ll find the text in the section below.
  14. Click Enter/Return.
  15. Terminal will ask for a password. This is your user password. Note you won’t see characters appear as you type it in, that’s fine. After typing in your password, press Enter.
  16. Terminal will warn that it is about to erase the drive (so make sure there wasn’t anything important on it!). If you want to continue press Y and then Return. The process can take a while, you’ll see “Erasing Disk: 0%… 10%… 20%… 30%…100%…
  17. Now Terminal will spend a few minutes copying the installer file to your drive. “Copying installer files to disk… Copy complete” and so on will appear in the Terminal window.
  18. When Terminal has finished copying the installer you will see the words Copy complete and Done appear.
  19. Now you have the installer on the external drive you can use that to install multiple copies of macOS. Plug the external drive into the Mac that you want to install the macOS on.
  20. Start up the Mac, holding down the Option/Alt key while it is booting up.
  21. Your Mac will display the Startup Manager, click on your external drive to select that as the startup disk. Your Mac will start up in Recovery Mode.
  22. Click on Install macOS and then click on Continue. The version of macOS should start to install on your Mac now.

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.

Note that older versions of macOS used “applicationpath” while newer ones don’t – if you use the command you will get an error (we have the code for the all versions of macOS and Mac OS X below).

createinstallmedia commands

The createinstallmedia command will be slightly different depending on which version of macOS you are wanting to use.

Note MyVolume may have a different name for you, for example it might be USB or similar. Check in Disk Utilities, it’s the name of the external disk you are using.


sudo /Applications/Install macOS Catalina –volume /Volumes/MyVolume –nointeraction –downloadassets


sudo /Applications/Install macOS –volume /Volumes/MyVolume

High Sierra

sudo /Applications/Install macOS High –volume /Volumes/MyVolume


sudo /Applications/Install macOS –volume /Volumes/MyVolume –applicationpath /Applications/Install macOS

El Capitan

sudo /Applications/Install OS X El –volume /Volumes/MyVolume –applicationpath /Applications/Install OS X El


sudo /Applications/Install OS X –volume /Volumes/MyVolume –applicationpath /Applications/Install OS X


sudo /Applications/Install OS X –volume /Volumes/MyVolume –applicationpath /Applications/Install OS X

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