ntpdate(1M)                     TCP/IP R4.11                     ntpdate(1M)


NAME
       ntpdate - set the date and time via NTP

SYNOPSIS
       ntpdate [ -bdsv ] [ -o version ] [ -p samples ] [ -t timeout ] server
       ...

   where:
       version
              Old NTP version number (1 or 2); default = 3 (latest version)
       samples
              An integer between 1 and 8 inclusive; default = 4
       timeout
              Number of seconds; default = 1.0
       server Names of hosts whose NTP servers are to be polled

DESCRIPTION
       Ntpdate sets the local date and time by polling the Network Time
       Protocol (NTP) server(s) on the host(s) given as arguments to
       determine the correct time.  It must be run by root on the local
       host.  A number of samples are obtained from each of the servers
       specified and the standard NTP clock filter, and selection algorithms
       are applied to select the best of these.  Typically, ntpdate can be
       run from time to time via cron(1M).  Note that ntpdate's reliability
       and precision will improve dramatically with greater numbers of
       servers.  While a single server may be used, better performance and
       greater resistance to inaccuracy on the part of any one server will
       be obtained by providing at least three or four servers.

       Ntpdate makes time adjustments in one of two ways.  If ntpdate
       determines your clock is off by more than 0.5 seconds, it simply
       steps the time by calling settimeofday(2).  If the error is less than
       0.5 seconds, ntpdate skews the clock's time via a call to adjtime(2).
       The latter technique is less disruptive and more accurate when the
       offset is small, and works quite well when ntpdate is run by cron(1M)
       every hour or two.  The adjustment made in the latter case is
       actually 50% larger than the measured offset, since this will tend to
       keep a badly drifting clock more accurate (at some expense to
       stability, though this tradeoff is usually advantageous).  At boot
       time, however, it is usually better to step the time.

       Ntpdate declines to set the date if an NTP server program (e.g.,
       xntpd(1M)) is running on the same host.  When running ntpdate on a
       regular basis from cron(1M) as an alternative to running a server
       program, doing so once every hour or two results in precise enough
       timekeeping to avoid stepping the clock.

   Options
         -b   Force stepping of the time.  This is useful at boot time.

         -d   Determine what ntpdate will do without it actually doing it.
              Information useful for general debugging is also printed.

         -s   Log ntpdate actions via the syslog(3C) facility rather than to
              the standard output.  This is a useful option when running the
              program from cron(1M).

         -v   Prints out the version of ntpdate that is running.

         -o   Poll using an old form of outgoing packets.  This option is
              useful, since some older software will not respond to Version
              3 queries.

         -p   Set the number of samples ntpdate acquires from each server.

         -t   Specify the time ntpdate will spend waiting for a response.
              The value will be rounded to a multiple of 0.2 seconds.  The
              default value is suitable for polling across a LAN.

SEE ALSO
       cron(1M), xntpd(1M), syslog(3C).


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