ntpdate(8)						      System Manager's Manual							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 version] [-p samples] [-t timeout] server1 server2 server3...

OPTIONS

       Tells  ntpdate  to  step  the system time immediately to match NTP. Use this option only when booting the system.  Prints configuration and
       debugging information.  Queries the server(s) and prints the information received; the date and time are not set.  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).  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.  Runs
       in verbose mode.  Specifies that all packets should be authenticated using the key number provided.  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 specify-
       ing a value may improve timekeeping on very slow CPU's.	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).  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.   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.  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 suitable 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 deter-
       mine 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.  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  precision 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 timekeep-
       ing to avoid stepping 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 following 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

       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 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

       Specifies the command path Contains the encryption keys used by ntpdate

SEE ALSO

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

       Files: ntp.conf(4)

																	ntpdate(8)