How to Make a Bootable Flash Installer of OS X or macOS

A simple Terminal command makes the process easy

With the arrival of OS X Lion in 2011, Apple changed its software-delivery method to a download model with the Mac App Store instead of using physical DVDs and other media. While downloading an OS X or macOS version offers instant gratification, it means you're left without an installer. This is problematic if you need to reinstall OS X or macOS on a newly formatted hard drive, if you're in an emergency booting situation, or if you need to repair your Mac's hard drive.

Fortunately, it's easy to create a bootable USB flash drive with OS X or macOS. We'll look at how to do this using Terminal, the command-line utility included with all copies of OS X and macOS.

This article addresses the creation of a bootable USB drive for OS X Mavericks and later as well as macOS. macOS refers to Apple operating systems starting with version numbers 10.12 and later. OS X describes version numbers 10.8 through 10.11.

Illustration of a person using a laptop to create an OS X Mountain Lion bootable USB drive
Lifewire / Alex Dos Diaz

What You Need

First, you'll need the OS X or macOS installer on your Mac. Ideally, download the installer, but don't use it. When you download and use the OS X or macOS installer, the installer deletes itself as part of the installation process. If you've already installed OS X or macOS, redownload the installer.

If you download the installer and find that it starts up on its own, quit the installer the way you would with any other Mac app.

Once downloaded, the installer resides in the Applications folder. It will be called "Install OS X [your version]" or "Install macOS [your version]."

You'll also need a USB flash drive. Make sure that it has at least 12 GB of available storage and is formatted as Mac OS Extended.

It's also important that your Mac meets the minimum requirements for the OS you're installing. Apple's website offers the exact system requirements for each version.

How to Use the Createinstallmedia Terminal Command

From OS X Mavericks forward, within the installer packages is a hidden command that you can enter into Terminal to easily create a bootable copy of the installer.

This Terminal command, called createinstallmedia, creates a bootable copy of the installer using any drive connected to your Mac. In this example, we're using a USB flash drive. Here's how to do it:

The createinstallmedia command will erase the content of your USB drive, so back up any data on the drive if it's important.

  1. Locate the Mac OS installer file in your Applications folder.

  2. Plug your USB flash drive into your Mac.

  3. Change the flash drive's name. In this example, we're calling it FlashInstaller. Double-click the drive's name to select it, and then type in the new name.

    Rapid double-clicking the name of a drive can open that drive in a window on Finder, so if this step isn't working for you, try clicking once on the file name, pausing for a second, and then clicking a second time.

  4. Launch Terminal, located in Applications/Utilities.

    Alternatively, enter Terminal into Spotlight Search to quickly start up the utility.

  5. In the Terminal window that opens, enter one of the following commands, depending on which OS X or macOS installer you're working with. Note that we're using the name FlashInstaller for our USB drive, so if you named it something else, use that name.

    For macOS Catalina:

    sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/FlashInstaller



    For macOS Mojave:

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

    For macOS High Sierra:

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

    For OS X El Capitan

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

    For OS X Yosemite:

    sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/FlashInstaller --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --nointeraction

    For OS X Mavericks:

    sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/FlashInstaller --applicationpath /Applications/Install\ OS\ X\ Mavericks.app --nointeraction
  6. After you enter the command, press Return.

  7. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.

  8. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the bootable installer is created.  

  9. When Terminal is finished, the volume will have the same name as the installer you downloaded, such as Install macOS Catalina. Quit Terminal and eject the volume.

  10. You now have a bootable installer for your OS X or macOS version.