NAME
       ntpdate - set the date and time via NTP

       Disclaimer:  The  functionality of this program is now available in the ntpd program. See the -q command
       line option in the ntpd - Network Time Protocol (NTP) daemon page. After a suitable period of  mourning,
       the ntpdate program is to be retired from this distribution

SYNOPSIS
       ntpdate  [  -46bBdqsuv  ]  [ -a key ] [ -e authdelay ] [ -k keyfile ] [ -o version ] [ -p samples ] [ -t
       timeout ] [ -U user_name ] server [ ... ]

DESCRIPTION
       ntpdate sets the local date and time by polling the Network Time Protocol (NTP) server(s) given  as  the
       server  arguments  to  determine the correct time. It must be run as root on the local host. A number of
       samples are obtained from each of the servers specified and a subset of the NTP clock filter and  selec-
       tion  algorithms are applied to select the best of these. Note that the accuracy and reliability of ntp-
       date depends on the number of servers, the number of polls each time it is run and the interval  between
       runs.

       ntpdate  can  be run manually as necessary to set the host clock, or it can be run from the host startup
       script to set the clock at boot time. This is useful in some cases to set  the  clock  initially  before
       starting  the  NTP  daemon  ntpd.  It is also possible to run ntpdate from a cron script. However, it is
       important to note that ntpdate with contrived cron scripts is no substitute for the  NTP  daemon,  which
       uses  sophisticated  algorithms  to  maximize  accuracy  and  reliability while minimizing resource use.
       Finally, since ntpdate does not discipline the host clock frequency as does  ntpd,  the  accuracy  using
       ntpdate is limited.

       Time  adjustments  are  made  by ntpdate in one of two ways. If ntpdate determines the clock is in error
       more than 0.5 second it will simply step the time by calling the system settimeofday() routine.  If  the
       error  is less than 0.5 seconds, it will slew the time by calling the system adjtime() routine. The lat-
       ter technique is less disruptive and more accurate when the error is small, and works  quite  well  when
       ntpdate is run by cron every hour or two.

       ntpdate  will  decline to set the date if an NTP server daemon (e.g., ntpd) is running on the same host.
       When running ntpdate on a regular basis from cron as an alternative to running a daemon, doing  so  once
       every hour or two will result in precise enough timekeeping to avoid stepping the clock.

       Note  that  in contexts where a host name is expected, a -4 qualifier preceding the host name forces DNS
       resolution to the IPv4 namespace, while a -6 qualifier forces DNS resolution to the IPv6 namespace.

       If NetInfo support is compiled into ntpdate, then the server argument is optional if ntpdate can find  a
       time server in the NetInfo configuration for ntpd.

http://bashconsole.org/man.8.ntpdate