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.Dd March 30, 2018
.Dt ISOBOOT 8
.Os
.Sh NAME
.Nm isoboot
.Nd Boot code for hybrid ISO/USB images on BIOS-based computers
.Sh DESCRIPTION
.Nm
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.
.Nm
is installed in a
.Cm freebsd-boot
partition with
.Xr mkimg 1 .
.Sh 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.
.Nm
is intended to be placed in a GPT partition to allow the system to find
the standard
.Fx
.Xr loader 8
in the ISO filesystem later in the image.
.Sh BOOTING
.Nm
looks for an ISO filesystem image on the device it was booted from and
seeks to read either the primary
.Fx
.Xr loader 8
or kernel from there.
.Sh SEE ALSO
.Xr mkimg 1
.Sh HISTORY
.Nm
appeared in FreeBSD 12.0.
.Sh AUTHORS
This manual page written by
.An Benno Rice Aq benno@FreeBSD.org .