How To Make A Bootable USB Flash Disk For macOS

We all know that using a USB flash drive to install the operating system is the most stable and flexible, and it is the same for the macOS system. But how to use a macOS computer to create a USB boot disk? Let me tell you how to do it.

1. Preparation And Conditions.

1.1 Download macOS.

  1. Choose the corresponding macOS system version according to your computer model.
  2. Make sure that the downloaded installation package is in the “Applications” folder.
  3. Apps downloaded in the Mac App Store will be automatically saved in the “Applications” folder.
  4. Packages in DMG or ISO format need to be opened and dragged to the “Applications” folder.
  5. Click the package in PKG format will automatically install it to the “Applications” folder according to the prompts.

1.2 Prepare Boot Media.

  1. You can use one of the following three media, U-Disk, USB Portable Hard Drive, Create A New Partition.
  2. U Disk: Catalina and above versions require a U disk with a capacity of 16G and above, and other versions require a U disk with a capacity of 8G.
  3. USB Portable Hard Drive: such as USB SSD portable hard disk is better.
  4. Use the system “Disk Utility” to create a new partition, which is suitable for experienced users. It is recommended to use USB external storage to avoid erasing the entire internal disk for major version updates.
  5. Use “Disk Utility” to erase the above-mentioned media or partitions, the requirements are as follows.
  6. The disk format should be Mac OS X extension (Journaled).
  7. GUID Partition Map.
  8. Partition name: boot_partition (this name is used in this example, you can customize it, please note that boot_partition in the terminal command below should also be changed to your customized name).

2. Use The “createinstallmedia” Command In The Terminal.

  1. Connect the USB flash drive or other volumes to be used to save the bootable installer.
  2. Open the Applications —> Utilities—> Terminal app.
  3. Type or paste one of the following commands in the Terminal. These commands assume that the installer is in your macOS “Applications” folder and that “boot_partition” is the name of the USB flash drive or other volumes you are using.
  4. macOS Big Sur 11 corresponding command: sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/boot_partition.
  5. macOS Catalina 10.15 corresponding commands: sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/boot_partition.
  6. macOS Mojave 10.14 corresponding commands: sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/boot_partition.
  7. macOS High Sierra 10.13 corresponding commands: sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/boot_partition.
  8. macOS Sierra 10.12.X corresponding commands: sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/boot_partition --applicationpath /Applications/Install\ macOS\ Sierra.app --nointeraction.
  9. OS X El Capitan 10.11.X corresponding commands: sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/boot_partition --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app.
  10. OS X Yosemite 10.10.X corresponding commands: sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/boot_partition --applicationpath /Applications/Install\ OS\ X\ Yosemite.app --nointeraction.
  11. Press the Return key to run the above command, when there is a prompt, type your administrator password, then press Return again. When you type the password, the terminal will not display any characters.
  12. It will prompt you another message, type Y to confirm that you want to erase the volume, then press Return. In the process of erasing the volume, the “terminal” will display the progress.
  13. After the volume is erased, you may see a reminder that the “terminal” wants to access files on the removable volume. Click “OK” to allow the copy to continue.
  14. When the “Terminal” shows that the operation is complete, the corresponding volume will have the same name as the installer you downloaded, such as “Install macOS Big Sur”. You can now exit the “terminal” and eject the volume.
  15. If there is a “mount of outer dmg failed” error, please execute the below command in the terminal to repair the permission (below command use Big Sur as an example): sudo chmod 777 /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia.

3. Use The Bootable Installer (macOS System Startup Disk).

Before using the system startup disk to install the macOS system, first make sure whether you are using a Mac equipped with an Apple chip, and then follow the below corresponding steps.

3.1 Install macOS System On Apple Chip Steps.

  1. Insert a bootable installer (USB flash drive) into a Mac that is connected to the Internet and compatible with the version of macOS you want to install.
  2. Turn on your Mac and continue to hold the power button until you see the startup options window, which will display the bootable volume and a gear icon labeled “Options“.
  3. Select the volume containing the bootable installer and click “Continue
  4. Once the macOS installer opens, follow the instructions on the screen.

3.2 Install macOS On Intel Processor Steps.

  1. Insert a bootable installer (USB flash drive) into a Mac that is connected to the Internet and compatible with the version of macOS you want to install.
  2. After turning on or restarting your Mac, immediately hold down the Option (Alt) ⌥ key.
  3. When you see a black screen showing a bootable volume, release the Option key.
  4. Select the volume that contains the bootable installer. Then click the up arrow or press the Return key.
  5. If you cannot start from the bootable installer, make sure the external boot setting in the launch security utility is set to allow boot from external media.
  6. Follow the prompts to select your language.
  7. Select Install macOS (or Install OS X) from the Utilities window, then click continue and follow the onscreen instructions.

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