Create a macOS Installer USB Without a Mac

If you don’t have access to a Mac, you can still prepare a bootable macOS installer USB from Linux or Windows. Below is a simple, practical workflow that uses OpenCore’s macrecovery.py to fetch Apple’s installer files, converts the downloaded .dmg to a raw image, and writes it to a USB drive.

What you’ll need

• A PC running Linux or Windows

• A USB drive (16 GB or larger recommended)

• Python 3 (for running macrecovery.py)

• dmg2img (Linux packages often provide it; on Windows you can use WSL or a prebuilt binary)

• A disk writer:

  • Linux: dd
  • Windows: Rufus

1) Download the macOS recovery image with macrecovery.py

OpenCore provides a small Python script that talks to Apple’s servers and downloads the official recovery image.

Get the script:

• From the OpenCorePkg repo, locate Utilities/macrecovery/macrecovery.py.
• Download the file (or clone the repo) to a local folder, e.g., ~/macrecovery/.

Example (Linux/macOS shell or Windows PowerShell/WSL):

cd ~/macrecovery
python3 macrecovery.py -h

Download a specific version (examples):

# Latest recovery for Intel Macs:
python3 macrecovery.py --latest --catalog 10.15  # or another catalog key

# Or specify product codes (see script help / repo docs)
# Example generic form:
python3 macrecovery.py -b Mac-XXXXX -m 00000000000000000 download

When it completes, you should have a file like RecoveryImage.dmg (name may vary) in the working directory.

Tip: If you’re not sure which flags to use, start with --latest and check the script’s -h help for options.

2) Convert the DMG to a raw image (.img)

Use dmg2img to convert Apple’s DMG into a raw disk image that standard imaging tools can write.

Linux (or WSL):

sudo apt-get update && sudo apt-get install -y dmg2img   # Debian/Ubuntu
dmg2img RecoveryImage.dmg RecoveryImage.img

If your downloaded file has a different name, adjust the command accordingly.

3) Write the image to a USB drive

Option A: Linux with dd

1. Insert your USB and identify its device path:

   lsblk

   Suppose it shows up as /dev/sdX (replace X with the actual letter).

2. Write the image (this will erase the USB):

   sudo dd if=RecoveryImage.img of=/dev/sdX bs=4M status=progress conv=fsync

3. Safely eject:

   sync
   sudo eject /dev/sdX

Option B: Windows with Rufus

1. Download and run Rufus.
2. Select your USB drive.
3. Click SELECT and choose RecoveryImage.img.
4. Use the default settings unless you know you need something specific.
5. Click START and wait until the write completes.
6. Safely remove the USB.

4) Boot from the installer USB

• Insert the USB into the target machine.
• Power it on and choose the USB as the boot device (use your motherboard’s boot menu key, e.g., F12/F8/F11/ESC).
• Follow the on-screen prompts to access macOS Recovery/Installer tools.

Notes & Troubleshooting

• USB size: 16 GB is usually safe; some images fit on 8 GB, but give yourself headroom.
• Write errors: If dd fails, ensure the USB isn’t mounted and that you’re using the correct device path (not a partition like /dev/sdX1).
• Rufus quirks: If Rufus complains about the image format, ensure you used dmg2img and are selecting the resulting .img, not the original .dmg.
• Hardware compatibility: Downloaded recovery images are official Apple resources; installing macOS on non-Apple hardware may require additional steps and may not be supported.

That’s it—download with macrecovery.py, convert with dmg2img, and write with dd or Rufus.