---
name: "isoboot"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/isoboot"
---

# isoboot(8)

Boot code for hybrid ISO/USB images on BIOS-based computers

## NAME

**isoboot** – Boot code for hybrid ISO/USB images on BIOS-based computers

## DESCRIPTION

**isoboot** is used on BIOS-based computers to boot from an ISO image that has been written to a USB flash drive or other HDD-like device. **isoboot** is installed in a **freebsd-boot** partition with [mkimg(1)](/mkimg/1.md).

## IMPLEMENTATION NOTES

The El Torito standard for bootable CDs provides a 32KB "System Area" at the beginning of an image. To create an image that is able to be booted by the BIOS as either a CD-ROM ("ISO") and as a more HDD-like image (e.g. on a USB flash drive) it is necessary to have both a standard El Torito boot catalog containing a HDD-style partition table and boot code. **isoboot** is intended to be placed in a GPT partition to allow the system to find the standard FreeBSD [loader(8)](/loader/8.md) in the ISO filesystem later in the image.

## BOOTING

**isoboot** looks for an ISO filesystem image on the device it was booted from and seeks to read either the primary FreeBSD [loader(8)](/loader/8.md) or kernel from there.

## SEE ALSO

[mkimg(1)](/mkimg/1.md)

## HISTORY

**isoboot** appeared in FreeBSD 12.0.

## AUTHORS

This manual page written by Benno Rice ⟨*benno@FreeBSD.org*⟩.