setting ntp daemon

1.single machine use ntpdate at boot time
#ee /etc/rc.conf
add one line as below
ntpdate_enable="YES"

2.most machine use ntpd daemon
#ee /etc/ntp.conf
server asia.pool.ntp.org prefer
server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org
server 3.pool.ntp.org
driftfile /var/db/ntp.drift

3.modify /etc/rc.conf to start ntpd daemon
#ee /etc/rc.conf
add one line as below
ntpd_enable="YES"

4.restart ntpd daemon without reboot machine
#ntpd -p `cat /var/run/ntpd.pid`