geteltorito

geteltorito [-o output-file] iso-image

-o output-file
    Write the extracted boot image to the specified file instead of standard output.

geteltorito is a lightweight command-line tool for extracting boot images from El Torito-compliant CD/DVD ISO files. The El Torito specification enables bootable optical media by embedding floppy or hard disk images within an ISO9660 filesystem, allowing computers to boot from CDs/DVDs as if they were traditional media.

The utility parses the ISO image, locates the El Torito boot catalog (usually in the boot record volume descriptor), and extracts the primary or default boot entry. By default, it writes the raw boot image to standard output, making it easy to pipe or redirect. The extracted image can be a floppy image (1.44MB, 2.88MB), hard disk image, or no-emulation image used by modern bootloaders like isolinux, GRUB, or Windows PE.

Common use cases include converting legacy CD boot images for USB drives, inspecting bootloader sectors, embedding in custom ISOs, or testing in virtual environments like QEMU. It handles standard single-entry catalogs efficiently but skips advanced features like EFI booting or multiple alternates unless specified. The tool is fast, dependency-free, and included in major distros via the geteltorito package.

Extracts only the first/default boot entry; does not handle multi-entry catalogs, EFI images, or non-standard El Torito variants. Input must be a seekable ISO file with a valid boot catalog.

geteltorito -o boot.img disk.iso
Extracts boot image from disk.iso to boot.img.
isoinfo -i disk.iso -eltorito -no-isofs
Inspect boot catalog first.

Outputs raw images: 1.2MB/1.44MB/2.88MB floppies (emulated), hard disk images, or no-emulation (load segment:size).

Developed by Gerd Hoffmann (kraxel@bytesex.org) around 2003 as a simple C utility to address the need for extracting El Torito images without full CD authoring suites like cdrtools. Integrated into Linux distros shortly after; remains stable with minimal updates due to focused scope.

isoinfo(1), genisoimage(1), xorriso(1), isodump(8)