On reboot the server time can be out of sync, because hard clock is out of sync.
This can be checked by running”hwclock; date” and comparing the results.
In Red Hat 6, the ntpdate start-up script is is separate from the ntpd start-up script and not enable by default.
ntpd does not sync time immediately, where ntpdate does a one time sync of the server clock to the ntp server.
To enable ntpdate on Red Hat 6 run “chkconfig ntpdate on”.
To sync the hardware clock with the system clock run “hwclock –systohc”.