How to create a bootable macOS Big Sur USB installer ?

Creating a bootable official macOS Big Sur USB install drive is a reliable way to install or repair macOS Big Sur (version 11.x) on a compatible Mac using built-in macOS tools.

This process uses the Install macOS Big Sur.app and the createinstallmedia command to transform a USB drive into a bootable installer.

Below are the detailed, step-by-step instructions to create a bootable macOS Big Sur usb installer

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Prerequisites

• macOS Big Sur Installer: The full Install macOS Big Sur.app (approximately 12-13GB), located in /Applications. See the note at the end if you need to download it.
• USB Drive: Minimum 16GB capacity (32GB recommended for reliability). A USB 3.0 drive is faster but not required.
• Mac with Admin Access: You’ll need a Mac to run the commands and an admin password.
• Time: About 20-30 minutes, depending on USB speed.

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Step-by-Step Instructions to create a bootable macOS Big Sur USB installer

1. Obtain the macOS Big Sur Installer

• Check /Applications:
  • Open Finder and look for Install macOS Big Sur.app in /Applications.
  • Verify its size (should be ~12GB):
    du -sh /Applications/Install\ macOS\ Big\ Sur.app
• If Missing:
  • On a compatible Mac (e.g., 2013 MacBook Pro or later), download it from the Mac App Store:
  • Open the App Store, search “Big Sur,” click “Get,” and let it download to /Applications.
  • On an unsupported Mac or if unavailable, use gibMacOS:
    git clone https://github.com/corpnewt/gibMacOS.git cd gibMacOS python3 gibMacOS.command
  • Select “macOS Big Sur” (11.x), download the .pkg, and extract Install macOS Big Sur.app to /Applications.

2. Prepare the USB Drive

• Insert the USB Drive:
  • Plug the USB into your Mac. It will appear in Finder or on the Desktop.
• Open Disk Utility:
  • Go to Applications > Utilities > Disk Utility, or use Spotlight (Command + Space, type “Disk Utility”).
• Erase the USB Drive:
  • In Disk Utility, select the USB drive from the left sidebar (top-level device, e.g., “16.0 GB SanDisk,” not a partition).
  • Click Erase and set:
  • Name: BigSurUSB (or any name you prefer).
  • Format: Mac OS Extended (Journaled) (required for Big Sur’s bootable installer).
  • Scheme: GUID Partition Map.
  • Click Erase. This wipes the drive—back up any data first.
• Verify Mount Point:
  • After erasing, it mounts as /Volumes/BigSurUSB. Confirm:
    ls /Volumes/

3. Create the Bootable Installer

• Run the createinstallmedia Command:
  • Open Terminal (Applications > Utilities > Terminal).
  • Enter this command, replacing BigSurUSB with your USB’s volume name if different:
    sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/BigSurUSB --nointeraction
  • Breakdown:
  • sudo: Runs with admin privileges.
  • --volume: Targets the USB drive.
  • --nointeraction: Automates without prompts.
• Enter Admin Password:
  • Type your password (it won’t display) and press Enter.
• Wait for Completion:
  • The process erases the USB, copies the installer files, and makes it bootable. It takes 10-20 minutes.
  • Terminal will show progress (e.g., “Copying to disk…”), ending with:
    Install media now available at "/Volumes/Install macOS Big Sur"

4. Verify the Bootable USB

• Check the Result:
  • The USB will be renamed to Install macOS Big Sur and mounted at /Volumes/Install macOS Big Sur.
  • In Finder, it should appear with a Big Sur installer icon.
• Inspect Contents:
  • Run:
    ls /Volumes/Install\ macOS\ Big\ Sur/
  • You’ll see files like InstallESD.dmg and boot components.

5. Eject the USB

• Safely Remove:
  • In Finder, click the eject icon next to Install macOS Big Sur.
  • Or in Terminal:
    diskutil eject /Volumes/Install\ macOS\ Big\ Sur
• Unplug the USB once ejected.

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Using the Bootable USB

• Install Big Sur:
• Insert the USB into the target Mac.
• Restart while holding Option (⌥) until the boot menu appears.
• Select Install macOS Big Sur and follow the prompts to install on the internal drive.
• Unsupported Macs: For pre-2013 Macs, use OpenCore Legacy Patcher (OCLP) to patch the installer post-creation for compatibility.

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Troubleshooting

• “Command not found” or “Permission denied”:
• Verify the installer path (/Applications/Install\ macOS\ Big\ Sur.app). If renamed (e.g., with “Beta”), adjust the command.
• Ensure sudo is used correctly.
• “Volume not found”:
• Check the USB’s mount point:
  ls /Volumes/
• Update the command with the exact name (e.g., /Volumes/MyUSB).
• Process Hangs:
• Use a USB 3.0 port/drive if available. Cancel with Control + C and retry if needed.

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Notes

• Space: The USB must be empty and properly formatted—16GB is the minimum, but 32GB avoids potential issues.
• Speed: USB 3.0 cuts creation time significantly (e.g., 5-10 minutes vs. 20+ on USB 2.0).
• Reusability: This USB can install Big Sur on multiple Macs or be reformatted later.

You now have a bootable macOS Big Sur USB installer.