How to Create a Bootable macOS Installer on a USB Flash Drive using Terminal

The Need for a Physical Installer

While Apple provides macOS Recovery over the internet, a physical, bootable USB installer is an indispensable tool for Mac administrators and power users. If a Mac’s hard drive has completely failed, if you need to install macOS on multiple machines without downloading the 12GB installer each time, or if you simply prefer performing a completely clean, offline format and reinstallation, a bootable USB drive is the most reliable method.

You do not need third-party software like Rufus or BalenaEtcher to create this drive. Apple includes a hidden command-line utility called createinstallmedia inside every macOS installer application.

Prerequisites

1. A USB Flash Drive: It must be at least 16GB in size. Warning: The process will completely erase the drive. Ensure there is no important data on it.
2. The macOS Installer: You must download the full installer app from the Mac App Store (e.g., “macOS Sonoma” or “macOS Ventura”). When the download finishes, the installer will automatically open; quit the installer without proceeding. The file (e.g., “Install macOS Sonoma.app”) must remain in your /Applications folder.

Step 1: Format the USB Drive

The createinstallmedia tool requires the USB drive to be formatted as Mac OS Extended, not APFS.

1. Connect the USB drive to your Mac.
2. Open Disk Utility (found in Applications > Utilities).
3. In the left sidebar, select your USB drive (ensure you select the physical drive, not a volume underneath it).
4. Click the Erase button at the top.
5. Name the drive exactly MyVolume (this makes the terminal command easier later).
6. Set the Format to Mac OS Extended (Journaled).
7. Set the Scheme to GUID Partition Map.
8. Click Erase. Once finished, close Disk Utility.

Step 2: Execute the createinstallmedia Command

Now we will use the Terminal to write the installer files to the USB drive and make it bootable.

1. Open the Terminal application (found in Applications > Utilities).
2. You will need to use the specific command that corresponds to the version of macOS you downloaded. Assuming your USB drive is named MyVolume, copy and paste the appropriate command below.

For macOS Sonoma:

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

For macOS Ventura:

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

For macOS Monterey:

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

3. Press Enter.
4. Terminal will prompt you for your administrator password. Type it (the characters will not appear on screen) and press Enter.
5. You will receive a warning that the volume will be erased. Type Y and press Enter to confirm.

The terminal will now display the progress as it erases the disk, copies the massive installer files, and makes the disk bootable. This process can take anywhere from 10 to 30 minutes depending on the speed of your USB drive. Do not remove the drive or close the terminal until you see the words Install media now available and the terminal prompt returns.

Step 3: Booting from the USB Drive

The process for booting from the newly created drive depends on the type of Mac you are repairing.

On a Mac with Apple Silicon (M1/M2/M3)

1. Turn off the Mac completely.
2. Press and hold the power button until you see “Loading startup options” appear on the screen.
3. You will see your internal hard drive and the bootable USB installer. Click the USB installer and select “Continue.”

On an Intel-based Mac

1. Turn off the Mac completely.
2. Press the power button, then immediately press and hold the Option (Alt) key.
3. Release the key when you see a dark screen showing your bootable volumes.
4. Select the USB installer and press Enter.

Note: For Intel Macs with the T2 Security Chip, you may need to boot into macOS Recovery first and use the “Startup Security Utility” to allow booting from external media.

Conclusion

Creating a bootable macOS installer using the terminal is a straightforward process once you understand the createinstallmedia syntax. Keeping one of these drives in your desk drawer ensures you can always recover a failing Mac, regardless of your internet connection status.

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