Creating a Bootable macOS Installer: Step-by-Step Guide

Introduction / Why This Is Needed

A macOS bootable installer on a USB flash drive is an essential tool for:

• Clean installation of macOS on a new or formatted disk.
• System recovery in case of critical errors when booting into Recovery Mode is impossible.
• Updating/installing on multiple Macs without repeated internet downloads.
• Installing older versions of macOS (if the image is available) on compatible computers.

This guide works for Macs with Apple Silicon (M1/M2/M3) and Intel, as well as for the latest versions of macOS Ventura and Sonoma.

Requirements / Preparation

Before you begin, ensure you have:

1. A working Mac with an internet connection (to download the image).
2. A USB flash drive or external SSD with a capacity of at least 16 GB. USB 3.0+ is recommended for speed.
3. A stable internet connection (the image download is ~12 GB).
4. Administrator privileges on the target Mac (a password for sudo in Terminal will be required).
5. The name of the future macOS version (e.g., Sonoma or Ventura) you plan to use.

⚠️ Important: The process completely erases all data on the selected flash drive. Make sure it does not contain any important information.

Step-by-Step Guide

Step 1: Preparing the USB Drive

1. Connect the flash drive to your Mac.
2. Open Disk Utility (via Spotlight Cmd+Space or in Applications → Utilities).
3. In the left sidebar, select the flash drive itself (not the partition), and click "Erase".
4. Set the parameters:
   • Name: Any short name without spaces (e.g., MyVolume). Remember it.
   • Format: APFS (for macOS Sonoma/Ventura) or Mac OS Extended (Journaled) (for older macOS versions).
   • Scheme: GUID Partition Map.
5. Click "Erase". Once finished, the flash drive will appear in Finder and on the Desktop.

Step 2: Downloading the macOS Installer Image

1. Open the App Store.
2. Search for the required version:
   • For macOS Sonoma — simply search for "Sonoma".
   • For macOS Ventura — search for "Ventura".
   • For other versions (e.g., Monterey) use direct links from the Apple website.
3. Click "Get" or "Download". The image (~12-14 GB) will start downloading to the Applications folder.
4. Do not run the downloaded installer! The process of creating the bootable media uses its internal files.
5. Wait for the download to complete. The file will be named Install macOS <Version>.app.

Step 3: Creating the Bootable Media via Terminal

1. Open Terminal (Applications → Utilities → Terminal).
2. Enter the command, specifying exactly your flash drive's name and macOS version:

# Example for macOS Sonoma and a flash drive named 'MyVolume'
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

How to form the command:

• Replace Sonoma with your version (Ventura, Monterey, etc.).
• Replace MyVolume with your flash drive's name (case-sensitive!).
• The space in the .app path is escaped with a backslash \.

3. Press Enter. The system will ask for the administrator password (typed characters will not be displayed).
4. The process will begin. You will see a progress bar and messages:

   Erasing /Volumes/MyVolume: 0%... 10%... 100%
   Copying to /Volumes/MyVolume: 0%... 50%... 100%
   

5. Do not interrupt the process! It takes 10-25 minutes depending on the flash drive's speed.
6. Upon completion, you will see:

   Copy complete. Done.
   

   The flash drive is ready.

Step 4: Booting from the Created Media (Verification)

1. Eject the flash drive from your Mac.
2. For Macs with Apple Silicon (M1/M2/M3):
   • Shut down your Mac.
   • Hold the power button until the startup disk selection menu appears.
   • Select the flash drive (usually Install macOS Sonoma).
3. For Intel-based Macs:
   • Turn on your Mac and immediately hold the Option (Alt) key.
   • In the menu, select the yellow Install macOS icon with your flash drive's name.
4. The macOS Installer should load. If it appears — the media was created successfully.

💡 Tip: After verification, you can restart your Mac into normal mode. The flash drive will be preserved for future use.

Verifying the Result

Successful creation of the bootable media is confirmed by:

1. Launching the macOS Installer when selecting the flash drive in the startup menu (see Step 4).
2. In Disk Utility, the flash drive will be displayed with the name Install macOS <Version>.
3. In Finder, files like Install macOS <Version>.app and com.apple.recovery.boot will appear on the flash drive.

If the startup menu does not show the flash drive, recheck the formatting (GUID + APFS) and repeat Step 3.

Potential Issues

Error "Not enough space" or "Insufficient free space"

• Cause: The flash drive is too small (less than 16 GB) or not formatted correctly.
• Solution: Use a flash drive of 16 GB or more and reformat it via Disk Utility (GUID + APFS).

createinstallmedia command not found

• Cause: The path to the .app file is specified incorrectly or the file was not downloaded.
• Solution: Ensure the file Install macOS <Version>.app is in the Applications folder. Check the name using the command ls /Applications/ | grep Install.

"The volume could not be unmounted" or "Unable to erase"

• Cause: The flash drive is in use by the system or is damaged.
• Solution: Restart your Mac, connect the flash drive immediately, and try again. If that doesn't work — check the flash drive in Disk Utility and use "First Aid".

Booting from the flash drive does not start on an Apple Silicon Mac

• Cause: The flash drive was created for an Intel Mac, or there is an issue with the port.
• Solution: Ensure you used the official image for your macOS version. Try a different USB port (preferably USB-A/USB-C directly, without hubs).

No "Install macOS" icon in the startup menu

• Cause: The flash drive is formatted incorrectly (e.g., in exFAT) or the copying process did not complete.
• Solution: Recheck the formatting (GUID + APFS) and ensure Terminal showed "Copy complete. Done.". If necessary, repeat Step 3.