How to create a bootable installer for macOS

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

These advanced steps are primarily for system administrators and others who are familiar with the command line. You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful when you want to install on multiple computers without downloading the installer each time.

 


What you need to create a bootable installer

  • A USB flash drive or other secondary volume formatted as Mac OS Extended, with at least 14GB of available storage
  • A downloaded installer for macOS Monterey, Big Sur, Catalina, Mojave, High Sierra, or El Capitan

 


Download macOS

The installer for macOS MontereymacOS Big SurmacOS CatalinamacOS Mojave, or macOS High Sierra downloads to your Applications folder as an app named Install macOS [version name]. If the installer opens after downloading, quit it without continuing installation. To get the correct installer:

  • Download on a Mac that is compatible with that version of macOS.
  • Download on a Mac that is using macOS Sierra 10.12.5 or later, or OS X El Capitan 10.11.6.
  • Enterprise administrators: Download from Apple, not a locally hosted software-update server. 

The installer for OS X El Capitan downloads to your Downloads folder as a disk image named InstallMacOSX.dmg. To get the installer:

  • Download using Safari, and open the disk image on a Mac that is compatible with OS X El Capitan.
  • Inside the disk image is an installer named InstallMacOSX.pkg. It installs an app named Install OS X El Capitan into your Applications folder. You will create the bootable installer from this app, not from the disk image or .pkg installer.

 


Use the 'createinstallmedia' command in Terminal

  1. Connect the USB flash drive or other volume that you're using for the bootable installer. 
  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 in your Applications folder, and MyVolume is the name of the USB flash drive or other volume you're using. If it has a different name, replace MyVolume in these commands with the name of your volume.

Monterey:*

sudo /Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

Big Sur:*

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

Catalina:*

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

Mojave:*

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

High Sierra:*

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

El Capitan:

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

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument and installer path, similar to the way this is done in the command for El Capitan.


After typing the command:

  1. Press Return to enter the command.
  2. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
  3. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the volume is erased.
  4. After the volume is erased, you may see an alert that Terminal would like to access files on a removable volume. Click OK to allow the copy to proceed. 
  5. When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Monterey. You can now quit Terminal and eject the volume.
    Terminal window showing completed process

 


Use the bootable installer

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

  1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing. 
    • The macOS version that came with the Mac is the earliest version it can use. 
    • A bootable installer doesn't download macOS from the internet, but it does require an internet connection to get firmware and other information specific to the Mac model.
  2. Turn on the Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes.
  3. Select the volume containing the bootable installer, then click Continue.
  4. When the macOS installer opens, follow the onscreen instructions.

Intel processor

  1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
    • The macOS version that came with the Mac is the earliest version it can use. 
    • A bootable installer doesn't download macOS from the internet, but it does require an internet connection to get firmware and other information specific to the Mac model.
  2. Press and hold the Option (Alt) ⌥ key immediately after turning on or restarting the Mac.
  3. Release the Option key when you see a dark screen showing your bootable volumes.
  4. Select the volume containing the bootable installer. Then click the up arrow or press Return. 
    If you can't start up from the bootable installer, make sure that Startup Security Utility is set to allow booting from external or removable media.
  5. Choose your language, if prompted.
  6. Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.

 


Learn more

For information about the createinstallmedia command and the arguments you can use with it, make sure that the macOS installer is in your Applications folder, then enter the appropriate path in Terminal:

/Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia
/Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia
/Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia
/Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia
/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia
/Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia
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