How to create a bootable installer for macOS

You can use an external drive or secondary partition as a startup disk from which to install the Mac operating system.

A bootable installer can be useful when you want to install macOS on multiple computers without downloading the installer each time. When your Mac starts up from a bootable installer, it starts up directly to the macOS installer, and doesn't require an Internet connection to complete the installation.

These advanced steps are primarily for system administrators and others who are familiar with the command line. It isn't necessary to create a bootable installer to install macOS.

Download macOS from the App Store

  1. Download macOS from the App Store. To download, use a Mac that is compatible with the version of macOS you're downloading. 
    If you're downloading macOS High Sierra, use a Mac with High Sierra, Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators: Please download from Apple, not a locally hosted software-update server.
  2. When the macOS installer opens, quit it without continuing installation.
  3. Find the installer in your Applications folder as a single ”Install” file, such as Install macOS High Sierra.

Use the 'createinstallmedia' command in Terminal

  1. After downloading the installer, connect your Mac to the USB flash drive or other volume that will be used as the bootable installer. Make sure that it has at least 12GB of available storage.
  2. Open Terminal, which is in the Utilities folder of your Applications folder.
  3. Type or paste one of the following commands in Terminal. These assume that the installer is still in your Applications folder, and the name of your volume is MyVolume. If it's named differently, replace MyVolume accordingly.

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

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

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

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

    Mavericks:
    sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ Mavericks.app
  4. Press Return after typing the command.
  5. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
  6. 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. 
  7. Quit Terminal when done.

Use the bootable installer

  1. Connect the volume containing the bootable installer to a compatible Mac.
  2. Use Startup Disk preferences or Startup Manager to select that volume as the startup disk. Learn about selecting a startup disk, including what to do if your Mac doesn't start up from it.
  3. Your Mac then starts up directly to the macOS installer. Follow the onscreen instructions to install macOS.

Learn more

For more information about the createinstallmedia command used in the examples above, make sure that the macOS installer is in your Applications folder, then enter the appropriate path in Terminal:

High Sierra:

/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia

Sierra:

/Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia

El Capitan:

/Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia

Yosemite:

/Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia

Mavericks: 

/Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia
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