macOS

1. Open Terminal and create a staging directory:

   mkdir ~/USBEFR_STAGING
   cd ~/USBEFR_STAGING

2. Copy the downloaded EFR image to the staging directory.
3. Verify the SHA-256 checksum of the EFR image:

   shasum -a 256 <EFR_IMAGE_FILE.img.gz>

   Compare the output against the checksum from the Customer Support Portal.
4. Extract the compressed EFR image:

   gunzip <EFR_IMAGE_FILE.img.gz>

   This produces an uncompressed file: <EFR_IMAGE_FILE.img> (approximately 8 GB).
5. Connect the USB flash drive to your Mac.
6. Identify the USB drive device identifier:

   diskutil list

   Identify your USB drive by its size and note the disk identifier (for example, /dev/disk4).
7. Unmount all partitions on the USB drive:

   diskutil unmountDisk /dev/diskX

   Replace diskX with your disk identifier.
8. Write the EFR image to the USB drive:

   The dd command will overwrite all data on the target USB drive. Double-check the disk identifier before running the command. Targeting the wrong disk can permanently overwrite your file system.

   sudo dd if=<EFR_IMAGE_FILE.img> of=/dev/rdiskX bs=4m

   Use /dev/rdiskX (raw disk) rather than /dev/diskX for faster write speeds. Replace diskX with your disk identifier. The operation may take several minutes. When it completes, dd displays a summary of records transferred.

   After writing completes, run:

   sync

9. If macOS displays a dialog that the disk is unreadable, click Ignore — do not click Erase. The EFI partition written by dd is not recognized by macOS.
10. Verify the USB drive file structure by mounting the USBEFR volume and listing its contents:

    ls -R /Volumes/USBEFR

    The USB drive should contain the following directory structure:

    EFI/
      BOOT/
        BOOTX64.EFI
        grubx64.efi
      centos/
        SHIMX64.EFI
        grubx64.efi
      fonts/
        unicode.pf2
    boot/
      resusys.vmlinuz
      resusys.cpio
      resusys.cpio.sig
    IMAGES/
      README