Create an external bootable installer for Apple macbook,imac or macOS

The way we install our operating system has changed with the introduction of macOS Mojave. Most notably, imaging and installing via target disk mode have been dropped. We can still download the installer from the app store but we can also install the latest supported macOS via internet recovery. Two great options but this might not be the most efficient way.

This is where having an external bootable installer comes in very handy!

Using Apple’s createinstallmedia to create your own bootable installer makes installing much easier and quicker. Let’s see how this is done.

Firstly you need to download the version of macOS you wish to use as the bootable installer. This can be done via the app store or from the Apple downloads website. Once this downloads it will sit in the Applications folder. Do not run the installer as doing so will not only install macOS but also remove the installer itself.

You then need an external hard drive, SSD or USB stick which has at least 12GB of available storage space. You also need to make sure this is formatted Mac OS Extended. This can be done via Disk Utility

The next step involves the command line using the Terminal app. Don’t worry if you are not an avid user of the command line as Apple has this covered for us by providing the commands needed to create the bootable installer. Terminal can be found in the Utilities folder within your Applications folder. This can also be searched via Spotlight.

The command relies on the macOS installer being in your Applications folder so double check it’s in there.

You can either type the command out yourself or copy and paste directly into the Terminal window. The only consideration is what you are going to name your bootable installer. The standard name would be ‘Install macOS Mojave’ for example, but you are free to name this whatever you like.

The command looks complicated but let’s break this down to see exactly what’s going on.

sudo /Applications/Install\ macOS\ --volume /Volumes/Install\ macOS\ Mojave

The sudo part is used to execute the command with elevated privileges. This is sometimes referred to as the superuser.

The next part is pointing to the installer application. Remember the installer is sitting in the Applications folder. So we are going to:

Applications -> Install macOS -> Contents -> Resources -> createinstallmedia

The installer app can be control clicked (or right clicked) to show a pop-up menu. Selecting ‘Show Package Contents’ allows you to explore the app resources. Following the path above you can find the createinstallmedia file within the app:

The next part of the command is pointing to our external volume. As this is classed as an external volume we type this as /Volume in the command line. As the name of our USB stick has spaces in it (Install macOS Mojave) this is specified as a backslash in the command line so the command looks like this:

/Volumes/Install\ macOS\ Mojave

So now everything is in place we can run the command. You can either type the command out yourself or copy and paste into Terminal. Just make sure you have the correct name of your external volume at the end.

Once we have typed the command you will be prompted to provide the password for the admin on the computer. You will also need to confirm if you want to go ahead with the command as this will erase the USB stick so make sure you have backed up any data that is on the USB!

Once this has been confirmed by pressing the Y key the command will erase the USB stick and begin copying the files across. You can track the progress visually on the screen:

And once this has completed Terminal will display a message letting you know your bootable installer is now ready to be used.

Here you go! You now have your own external bootable installer for macOS. Make sure to test this by firstly ejecting the volume then restarting the device, holding down the option key and selecting your new macOS installer. When booted this will look just like the recovery so should have a familiar look.

You can check the Apple Support Article (HT201372) which has commands for other versions of macOS. Just make sure you change the name at the end of the command from /MyVolume to the name you want to give to your installer.