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ntpdate(8)							   ntpdate(8)



NAME

  ntpdate - set	the date and time via NTP (Network Time	Protocol)

SYNOPSIS

  /usr/sbin/ntpdate [-bdqsuv] [-a key#]	[-e authdelay] [-k keyfile] [-o	ver-
  sion]	[-p samples] [-t timeout] server1 server2 server3...

OPTIONS

  -b  Tells ntpdate to step the	system time immediately	to match NTP. Use
      this option only when booting the	system.

  -d  Prints configuration and debugging information.

  -q  Queries the server(s) and	prints the information received; the date and
      time are not set.

  -s  Tells ntpdate to log its actions through the syslog(3) facility rather
      than to the standard output.  This is useful when	running	the program
      from cron(8).

  -u  Tells ntpdate to use an unprivileged port	to send	the packets from.
      This is useful when you are behind a firewall that blocks	incoming
      traffic to privileged ports, and you want	to synchronise with hosts
      beyond the firewall. Note	that the -d option always uses unprivileged
      ports.

  -v  Runs in verbose mode.

  -a key#
      Specifies	that all packets should	be authenticated using the key number
      provided.

  -e authdelay
      Specifies	an authentication processing delay, in seconds (see xntpd(8)
      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.

  -k keyfile
      Specifies	that authentication keys will be read from keyfile instead of
      the default /etc/ntp.keys	file.  This file should	be in the format
      described	in xntpd(8).

  -o version
      Forces ntpdate to	poll as	a version implementation. By default ntpdate
      claims to	be an NTP version 3 implementation in its outgoing packets.
      Some older software will decline to respond to version 3 queries.

  -p samples
      Acquires a specified number of samples from each server. The range of
      values for samples is from 1 and 8, inclusive.  The default is 4.

  -t timeout
      Waits timeout seconds for	a response. Any	value entered will be rounded
      to a multiple of 0.2 seconds.  The default is 1 second, a	value suit-
      able for polling across a	LAN.

DESCRIPTION

  The ntpdate command 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	sam-
  ples 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.  The ntpdate command is run from /sbin/init.d/settime to set the
  time of day at boot time, if NTP is configured.  (See	ntpsetup(8) for
  information on configuring NTP.) Note	that ntpdate's reliability and preci-
  sion will improve dramatically with greater numbers of servers.  While a
  single server	may be used, better performance	and integrity will be
  obtained by providing	at least three or four servers,	if not more.

  Time adjustments are made by ntpdate in one of the following ways:

    +  If ntpdate determines your clock	is off by more than 0.5	seconds, it
       steps 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 by	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 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).

  Ntpdate will decline to set the date if an NTP server	daemon (for example,
  xntpd(8)) is running on the same host.  When running ntpdate on a regular
  basis	from cron(8) as	an alternative to running a daemon, doing so once
  every	hour or	two will result	in precise enough timekeeping to avoid step-
  ping the clock.

				     Note

       Because of significant changes in NTP version 3,	you should check all
       scripts that use	the ntpdate command for	correct	usage and output.

ERRORS

  A common problem is polling a	server using the wrong query version number
  or wrong authentication key.	If either occurs, ntpdate prints the follow-
  ing error message:

       18 Apr 10:20:28	ntpdate(1192]: no server
	 suitable for synchronization found

  At boot time,	if NTP is not configured, the ntpdate prints the following
  message:

       WARNING:	 ntpdate cannot	succeed, please	check your
	 NTP configuration






EXAMPLES

   1.  The following command line sets the date	and time after polling server
       host1.dec.com as	a version 2 implementation:
	    /usr/sbin/ntpdate -o 2 host1.dec.com

   2.  The following command line sets the date	and time after polling server
       host2.dec.com.  All packets are authenticated using authentication key
       1.
	    /usr/sbin/ntpdate -a 1 host2.dec.com



FILES

  /usr/bin/ntpdate
      Specifies	the command path

  /etc/ntp.keys
      Contains the encryption keys used	by ntpdate

SEE ALSO

  Commands: ntpq(8), xntpd(8), xntpdc(8)

  Files: ntp.conf(4)