How to create a bootable USB installer for macOS High Sierra

The Mac App Store is the standard way to update or install macOS, but it doesn’t work for everyone. Perhaps you have multiple Macs, limited bandwidth, and don’t want to download the entire operating system for each system. Or maybe you want to reinstall the operating system from scratch.

Whatever your reason, installing macOS from a USB drive isn’t difficult. You just need a couple of things:

  • An 8 GB USB drive. This process will overwrite the entire drive, so be sure to back up everything that’s stored on it. If your drive is larger than 8 GB and you want to use the rest of the drive for something else, you can use Disk Utility to partition the drive: just create an empty 8 GB partition for the installer to use.
  • Access to one or more working Macs with access to the Mac App Store. This can be a friend’s machine if necessary.

That’s it! Once you have these things, we’re good to go.

First, download macOS from the Mac App Store

To get started, you’ll need the installer for the version of macOS you want on a USB stick. Go to the Mac App Store. If you’re looking for the latest version of macOS, find that operating system and click the Download or Install button.

The download takes a while. So make sure your Mac is plugged in and has a consistent connection to the internet. The installer will load when the process is complete; simple close Open the window, then go to your Applications folder to confirm that the installer is there.

If you don’t want the latest version of macOS, searching the App Store won’t help. Instead, you’ll need to go to the Purchases tab in the installer and scroll down until you find the version of macOS you want on your USB stick.

You will only find versions here that you have previously downloaded. Click the “Download” button to the left of the version you want to install and your Mac will download it. Again, the installation program will start when the download is complete; close the window when this happens. We are now ready to create our hard drive. There are two ways to do this: one using third party software and another using the terminal.

The easy way: With DiskMaker X

The easiest way to create a bootable USB drive is to Download DiskMaker X. and use it to create your drive. In general, the latest version only supports the latest version of macOS; If you’re looking to install something older than macOS High Sierra, check the List of older versions and download one that is compatible with your chosen operating system.

Installation is simple: just mount the DMG, then drag the program into your applications folder.

Launch the program and it should find the installer you downloaded above. If you placed the installer outside of the Applications folder, you can direct DiskMaker X to the file manually.

After that you will be asked which hard drive you want to use. Select the drive or partition knowing it will be completely overwritten.

Once you authorize the action, DiskMakerX will mostly run in the background. When the process is complete you will hear a loud lion roar (seriously, it freaked me out) and you will see the ride finished.

Diskmaker X also has a variety of utilities that you can find useful. The terminal method described below does not contain these.

The (somewhat) more difficult way: With the terminal

If you don’t want to rely on a third-party tool to create your hard drive, Apple offers a built-in terminal-driven method sketched here . To sum it up: there is a script called createinstallmedia included with every macOS installer, and we’re going to run it.

First, insert your USB stick and give it a name – I’ll use “Installer” for this description, but make a note of the name of the drive.

Next we look for the installation script. Open the Terminal found in Applications> Utilities and run the following command. Note that the exact command depends on which version of macOS you want to install. this one is specific to Sierra.

                      sudo /Applications/Install macOS High --volume /Volumes/Installer --applicationpath /Applications/Install macOS High

In case you are curious, this is broken down as follows:

  • To run the command as root. This means that the command must begin with sudo
  • /Applications/Install macOS High   is the location of the script. Of course, change High to the version you are installing.
  • To provide the application with a path to the volume to be overwritten. In our case it is /Volumes/Installer
  • To provide the application with a path to the installation package. For macOS Sierra, this is /Applications/Install macOS High

You will be asked to confirm that you are ready to erase the disk:

But “y”, then Enterand the process begins. First the disk is erased, then the entire installation program is copied to your disk.

The process will take a while, but when it’s done you will have a bootable drive with the installer on it.

Note that the Utilities folder offered by DiskMaker X does not exist here.

The above command is specifically for High Sierra (and a hard drive called the “Installer”). Earlier versions of macOS have slightly different names. Here is the full command for some newer versions:

  • Sierra: sudo /Applications/Install macOS --volume /Volumes/Installer --applicationpath /Applications/Install macOS
  • Captain: sudo /Applications/Install OS X El --volume /Volumes/Installer --applicationpath /Applications/Install OS X El
  • Yosemite: sudo /Applications/Install OS X --volume /Volumes/Installer --applicationpath /Applications/Install OS X
  • Outsider: : sudo /Applications/Install OS X --volume /Volumes/Installer --applicationpath /Applications/Install OS X

Hopefully you get the idea: you need to run the script in the installer yourself, point to your drive, and then point to the installer.

How to boot from your installation drive

Now that you’ve created an external installer, you’ll need to boot from it on your target Mac. Shut down the Mac, then connect your installation disk. Turn on the Mac while holding down the Option key. You will be asked which drive to boot from:

Select the drive on which you wrote the installation program. The installer for macOS will boot from it. At this point, you can update macOS or install a new version.

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