Several utilities for managing jails.

4.x:

killjail	shutdown or restart a jail (when used with jailer)
jails		list the jails running on a system
jstart		start up a jail securely

5.x:

jps		List processes in a jail
jid		Print id of a jail
jstart		Start up a jail securily
jkill		Shutdown a jail in an orderly fashion
jails		List running jails
injail		Determine if a process is running in a jail

WWW: http://memberwebs.com/nielsen/freebsd/jails/jailutils/