isoboot8
Boot code for hybrid iso/usb images on bios-based computers
Overview
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).
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) 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) or kernel from there.
Releases
23 releases since FreeBSD 11.2-RELEASE; the text changed 10 times.