To start slapd, configure it in /etc/openldap/slapd.conf then add
the following line to /etc/rc.conf.local:

slapd_flags="-u _openldap"

and to /etc/rc.local (be sure to start it _before_ any daemon that may
need it):

if [ "$slapd_flags" != "NO" -a -x /usr/local/libexec/slapd ]; then
    install -d -o _openldap /var/run/openldap
    /usr/local/libexec/slapd $slapd_flags
    echo -n ' slapd'
fi
