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+''' $Header
+''' 
+.de Sh
+.br
+.ne 5
+.PP
+\fB\\$1\fR
+.PP
+..
+.de Sp
+.if t .sp .5v
+.if n .sp
+..
+.de Ip
+.br
+.ie \\n.$>=3 .ne \\$3
+.el .ne 3
+.IP "\\$1" \\$2
+..
+'''
+'''     Set up \*(-- to give an unbreakable dash;
+'''     string Tr holds user defined translation string.
+'''     Bell System Logo is used as a dummy character.
+'''
+.tr \(bs-|\(bv\*(Tr
+.ie n \{\
+.ds -- \(bs-
+.if (\n(.H=4u)&(1m=24u) .ds -- \(bs\h'-12u'\(bs\h'-12u'-\" diablo 10 pitch
+.if (\n(.H=4u)&(1m=20u) .ds -- \(bs\h'-12u'\(bs\h'-8u'-\" diablo 12 pitch
+.ds L" ""
+.ds R" ""
+.ds L' '
+.ds R' '
+'br\}
+.el\{\
+.ds -- \(em\|
+.tr \*(Tr
+.ds L" ``
+.ds R" ''
+.ds L' `
+.ds R' '
+'br\}
+.TH NTPDATE 8 LOCAL
+.SH NAME
+ntpdate - set the date and time via NTP
+.SH SYNOPSIS
+.B ntpdate
+[
+.B -bdos
+] [
+.B -a
+.I key#
+] [
+.B -e
+.I authdelay
+] [
+.B -k
+.I keyfile
+] [
+.B -p
+.I samples
+] [
+.B -t
+.I timeout
+]
+server ...
+.SH DESCRIPTION
+.I Ntpdate
+sets the local date and time by polling the Network Time Protocol
+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,
+.I ntpdate
+can be inserted in the
+.I /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
+.IR cron (8).
+Note that
+.IR 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.
+.PP
+Time adjustments are made by
+.I ntpdate
+in one of two ways.  If
+.I ntpdate
+determines your clock is off by more than 0.5 seconds it will simply
+step the time by calling
+.IR 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
+.IR adjtime (2)
+with the offset.  The latter technique is less disruptive and more
+accurate when the offset is small, and works quite well when
+.I ntpdate
+is run by
+.I cron (8)
+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 -b
+switch on the command line.  The
+.B -s
+switch tells
+.I ntpdate
+to log its actions via the
+.IR syslog (3)
+facility rather than to the standard output, a useful option when
+running the program from
+.IR cron (8).
+.PP
+The
+.B -d
+flag may be used to determine what
+.I ntpdate
+will do without it actually doing it.  Information useful for general
+debugging will also be printed.  By default
+.I 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
+.B -o
+switch can be used to force the program to poll as a version 1 implementation
+instead.
+.PP
+The number of samples
+.I ntpdate
+acquires from each server can be set to between 1 and 8 inclusive
+using the
+.B -p
+switch.  The default is 4.  The time it will spend waiting for a
+response can be set using the
+.B -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.
+.PP
+.I Ntpdate
+will authenticate its transactions if need be.  The
+.B -a
+switch specifies that all packets should be authenticated using the
+key number indicated.  The
+.B -k
+switch allows the name of the file from which the keys may be read
+to be modified from the default of
+.I /etc/ntp.keys.
+This file should be in the format described in
+.IR xntpd (8).
+The
+.B -e
+option allows the specification of an authentication processing delay,
+in seconds (see
+.IR xntpd (8)
+for details).  This number is usually small enough to be negligible for
+.IR ntpdate 's
+purposes, though specifying a value may improve timekeeping on very slow
+CPU's.
+.PP
+.I Ntpdate
+will decline to set the date if an NTP server daemon (e.g.
+.IR xntpd (8))
+is running on the same host.  When running
+.I ntpdate
+on a regular basis from
+.IR cron (8)
+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.
+.SH FILES
+.nf
+/etc/ntp.keys\0\0contains the encription keys used by \fIntpdate\fP.
+.fi
+.SH SEE ALSO
+xntpd(8)
+.SH HISTORY
+Written by Dennis Ferguson at the University of Toronto
+.SH 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.