isohybrid

isohybrid [options] <isoimage>

-d DEPTH, --depth=DEPTH
    Set MBR depth in sectors from image start (default: autodetect)

-D, --no-clobber
    Do not overwrite if image already hybrid

-h, --help
    Display usage help

-l LENGTH, --length=LENGTH
    Set image length in sectors (default: autodetect)

--interval=SECTORS
    Force sectors per track in partition table (default: autodetect)

--offset=SECTORS
    Force partition table offset in sectors (default: autodetect)

--uefi
    Add x86-64 EFI System Partition support

-u, --update
    Update existing hybrid; preserve boot track

-V, --version
    Show version information

isohybrid, from the Syslinux project, converts standard ISO 9660 images into hybrid bootable media. It embeds a Master Boot Record (MBR) and DOS-compatible partition table directly into the ISO, enabling direct writing to USB drives or hard disks while retaining CD-ROM compatibility.

This allows a single image to boot via legacy BIOS as either optical media or block device. The --uefi option adds EFI firmware support by installing an EFI System Partition (ESP), making it suitable for modern x86/x64 systems.

Commonly used by Linux distributions (e.g., Fedora, Debian live ISOs) for versatile installers. It works on unmodified ISOs with El Torito boot catalog from tools like mkisofs or xorriso. Modifies file in place; detects image size automatically.

Modifies ISO in place; backup first. Requires write access and sufficient space. UEFI mode needs GPT-compatible tools for full ESP. Not for ARM/other arches without syslinux variants. May conflict with non-standard ISOs.

isohybrid distro.iso (BIOS hybrid)
isohybrid --uefi distro.iso (BIOS+UEFI)

Write to USB: dd if=distro.iso of=/dev/sdX bs=4M status=progress oflag=sync
Supports ventoy or Rufus for multi-boot.

Developed by H. Peter Anvin for Syslinux project. Introduced in Syslinux 4.00 (2009) for BIOS hybrids; UEFI support added in 6.xx (2014+). Evolved with isolinux for El Torito integration; widely adopted for distro ISOs post-2010.

syslinux(1), extlinux(1), genisoimage(1), xorriso(1), isohybrid.efi(8)