Setup per-jail configurations in an rc.conf(5) style.
See https://svnweb.freebsd.org/base/head/share/examples/jails/README
% service jail restart
You'll get the following warning at the end...
/etc/rc.d/jail: WARNING: Per-jail configuration via jail_* variables \
is obsolete. Please consider migrating to /etc/jail.conf.
% sysrc jail_confwarn=NO
% service jail restart
The warning should no longer appear.