Mount an ISO:

Taken from freebsd-questions list by Christian Hiris:
http://lists.freebsd.org/pipermail/freebsd-questions/2004-May/046942.html
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attach md:
# mdconfig -a -t vnode -f /yourpath/your.iso 
# mount -t cd9660 /dev/md0 /yourmountpoint

list configured mds:
# mdconfig -l

unmount and detach:
# umount /yourmountpoint
# mdconfig -d -u 0

There are some examples listed in 'man 8 mdconfig'. 
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Previously, you'd use 'vmconfig', which is now depreciated:
	vnconfig /dev/vn0c /yourpath/your.iso
	mount -t cd9660 /dev/vn0c /mnt/iso

	umount /mnt/iso
	vnconfig -u /dev/vn0c