$ grep jail /etc/rc.conf

jail_enable="YES"

jail_interface="fxp0"                      # Interface to create the IP alias on
jail_devfs_enable="YES"                 # mount devfs in the jail
jail_procfs_enable="YES"                # mount procfs in jail

jail_list="ducky"

jail_ducky_rootdir="/usr/home/jails/ducky"       # Jail's root directory
jail_ducky_hostname="ducky.unixathome.org"     # Jail's hostname
jail_ducky_ip="10.55.0.20"                 # Jail's IP number