/etc/rc.conf: 
<snip>
ifconfig_nfe0_alias0="192.168.100.34/32"
jail_enbable="YES"
jail_list="jail1"
jail_jail1_rootdir="/jailhouse/jail1"
jail_jail1_hostname="jail1.clermont.cc"
jail_jail1_ip="192.168.100.34"
jail_jail1_devfs_enable="YES"
jail_jail1_devfs_ruleset="devfsrules_jail"

desktop# ls /jailhouse/jail1
.cshrc          boot            lib             proc            sys
.profile        dev             libexec         rescue          tmp
COPYRIGHT       etc             media           root            usr
bin             home            mnt             sbin            var

desktop# /etc/rc.d/jail start
desktop# jls
desktop#