The FreeBSD jail mechanism is an implementation of operating system-level virtualization that allows administrators to partition a FreeBSD-based computer system into several independent mini-systems called jails. FreeBSD jails offer security, ease of delegation and os level virtualization. To upgrade your jail using make world use the following commands.
Oh, just in case you didn’t know, you can get FBSD Jail T-shirts from FreeBSD Mall ;-)
FreeBSD Jails - there's no escape