ntpdate man page on FreeBSD

Man page or keyword search:  
man Server   9747 pages
apropos Keyword Search (all sections)
Output format
FreeBSD logo
[printable version]

NTPDATE(8)		  BSD System Manager's Manual		    NTPDATE(8)

NAME
     ntpdate — set the date and time via NTP

SYNOPSIS
     ntpdate [-46bBdoqsuv] [-a key] [-e authdelay] [-k keyfile] [-o version]
	     [-p samples] [-t timeout] server ...

DESCRIPTION
     Note: The functionality of this program is now available in the ntpd(8)
     program.  See the -q command line option in the ntpd(8) page.  After a
     suitable period of mourning, the ntpdate utility is to be retired from
     this distribution.

     The ntpdate utility sets the local date and time by polling the Network
     Time Protocol (NTP) server(s) given as the server 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 a subset of
     the NTP clock filter and selection algorithms are applied to select the
     best of these.  Note that the accuracy and reliability of ntpdate depends
     on the number of servers, the number of polls each time it is run and the
     interval between runs.

     The following options are available:

     -4	     Force DNS resolution of following host names on the command line
	     to the IPv4 namespace.

     -6	     Force DNS resolution of following host names on the command line
	     to the IPv6 namespace.

     -a key  Enable the authentication function and specify the key identifier
	     to be used for authentication as the argument key.	 The keys and
	     key identifiers must match in both the client and server key
	     files.  The default is to disable the authentication function.

     -B	     Force the time to always be slewed using the adjtime(2) system
	     call, even if the measured offset is greater than +-128 ms.  The
	     default is to step the time using settimeofday(2) if the offset
	     is greater than +-128 ms.	Note that, if the offset is much
	     greater than +-128 ms in this case, it can take a long time
	     (hours) to slew the clock to the correct value.  During this
	     time, the host should not be used to synchronize clients.

     -b	     Force the time to be stepped using the settimeofday(2) system
	     call, rather than slewed (default) using the adjtime(2) system
	     call.  This option should be used when called from a startup file
	     at boot time.

     -d	     Enable the debugging mode, in which ntpdate will go through all
	     the steps, but not adjust the local clock.	 Information useful
	     for general debugging will also be printed.

     -e authdelay
	     Specify the processing delay to perform an authentication func‐
	     tion as the value authdelay, in seconds and fraction (see ntpd(8)
	     for details).  This number is usually small enough to be negligi‐
	     ble for most purposes, though specifying a value may improve
	     timekeeping on very slow CPU's.

     -k keyfile
	     Specify the path for the authentication key file as the string
	     keyfile.  The default is /etc/ntp.keys.  This file should be in
	     the format described in ntpd(8).

     -o version
	     Specify the NTP version for outgoing packets as the integer
	     version, which can be 1 or 2.  The default is 3.  This allows
	     ntpdate to be used with older NTP versions.

     -p samples
	     Specify the number of samples to be acquired from each server as
	     the integer samples, with values from 1 to 8 inclusive.  The
	     default is 4.

     -q	     Query only - do not set the clock.

     -s	     Divert logging output from the standard output (default) to the
	     system syslog(3) facility.	 This is designed primarily for conve‐
	     nience of cron(8) scripts.

     -t timeout
	     Specify the maximum time waiting for a server response as the
	     value timeout, in seconds and fraction.  The value is rounded to
	     a multiple of 0.2 seconds.	 The default is 1 second, a value
	     suitable for polling across a LAN.

     -u	     Direct ntpdate to use an unprivileged port for outgoing packets.
	     This is most useful when 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	     Be verbose.  This option will cause ntpdate's version identifica‐
	     tion string to be logged.

     The ntpdate utility can be run manually as necessary to set the host
     clock, or it can be run from the host startup script to set the clock at
     boot time.	 This is useful in some cases to set the clock initially
     before starting the NTP daemon ntpd(8).  It is also possible to run
     ntpdate from a cron(8) script.  However, it is important to note that
     ntpdate with contrived cron(8) scripts is no substitute for the NTP dae‐
     mon, which uses sophisticated algorithms to maximize accuracy and relia‐
     bility while minimizing resource use.  Finally, since ntpdate does not
     discipline the host clock frequency as does ntpd(8), the accuracy using
     ntpdate is limited.

     Time adjustments are made by ntpdate in one of two ways.  If ntpdate
     determines the clock is in error more than 0.5 second it will simply step
     the time by calling the system settimeofday(2) routine.  If the error is
     less than 0.5 seconds, it will slew the time by calling the system
     adjtime(2) routine.  The latter technique is less disruptive and more
     accurate when the error is small, and works quite well when ntpdate is
     run by cron(8) every hour or two.

     The ntpdate utility will decline to set the date if an NTP server daemon
     (e.g., ntpd(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 stepping the clock.

     Note that in contexts where a host name is expected, a -4 qualifier pre‐
     ceding the host name forces DNS resolution to the IPv4 namespace, while a
     -6 qualifier forces DNS resolution to the IPv6 namespace.

     If NetInfo support is compiled into ntpdate, then the server argument is
     optional if ntpdate can find a time server in the NetInfo configuration
     for ntpd(8).

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

SEE ALSO
     ntpd(8)

BUGS
     The slew adjustment is actually 50% larger than the measured offset,
     since this (it is argued) will tend to keep a badly drifting clock more
     accurate.	This is probably not a good idea and may cause a troubling
     hunt for some values of the kernel variables kern.clockrate.tick and
     kern.clockrate.tickadj.

BSD				 May 17, 2006				   BSD
[top]

List of man pages available for FreeBSD

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
...................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net