ntpdate(1M)                 TCP/IP 5.4 Rel. 2.01                 ntpdate(1M)


NAME
       ntpdate - set the date and time via NTP

SYNOPSIS
       ntpdate [ -bdos ] [ -a key# ] [ -e authdelay ] [ -k keyfile ] [ -p
       samples ] [ -t timeout ] server ...

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 as 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
       inserted in the /etc/rc.local startup up script to set the time of
       day at boot time and/or 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 insanity on
       the part of any one server will be obtained by providing at least
       three or four servers, if not more.

       Time adjustments are made by ntpdate in one of two ways.  If ntpdate
       determines your clock is off by more than 0.5 seconds it will simply
       step the time by calling settimeofday(2).  If the error is less than
       0.5 seconds, however, it will by default slew the clock's time via a
       call to adjtime(2) with the offset.  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 always step the time.  This can be forced in all cases by
       specifying the -b switch on the command line.  The -s switch tells
       ntpdate to log its actions via the syslog(3) facility rather than to
       the standard output, a useful option when running the program from
       cron(1M).

       The -d flag may be used to determine what ntpdate will do without it
       actually doing it.  Information useful for general debugging will
       also be printed.  By default ntpdate claims to be an NTP version 2
       implementation in its outgoing packets.  As some older software will
       decline to respond to version 2 queries, the -o switch can be used to
       force the program to poll as a version 1 implementation instead.

       The number of samples ntpdate acquires from each server can be set to
       between 1 and 8 inclusive using the -p switch.  The default is 4.
       The time it will spend waiting for a response can be set using the -t
       switch, and will be rounded to a multiple of 0.2 seconds.  The
       default is 1 second, a value suitable for polling across a LAN.

       Ntpdate will authenticate its transactions if need be.  The -a switch
       specifies that all packets should be authenticated using the key



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ntpdate(1M)                 TCP/IP 5.4 Rel. 2.01                 ntpdate(1M)


       number indicated.  The -k switch allows the name of the file from
       which the keys may be read to be modified from the default of
       /etc/ntp.keys.  This file should be in the format described in
       xntpd(1M).  The -e option allows the specification of an
       authentication processing delay, in seconds (see xntpd(1M) for
       details).  This number is usually small enough to be negligible for
       ntpdate's purposes, though specifying a value may improve timekeeping
       on very slow CPU's.

       Ntpdate will decline 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 will result in precise
       enough timekeeping to avoid stepping the clock.

FILES
       /etc/ntp.keys  contains the encription keys used by ntpdate.

SEE ALSO
       xntpd(1M).

HISTORY
       Written by Dennis Ferguson at the University of Toronto

BUGS
       The technique used for improving accuracy by compensating for clock
       oscillator errors sucks, but doing better would require the program
       to save state from previous runs.





























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