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NTPD.CONF(5)		  FreeBSD File Formats Manual		  NTPD.CONF(5)

NAME
     ntpd.conf -- Network Time Protocol	daemon configuration file

DESCRIPTION
     This manual page describes	the format of the ntpd(8) configuration	file.

     ntpd.conf has the following format:

     Empty lines and lines beginning with the `#' character are	ignored.

     Keywords may be specified multiple	times within the configuration file.
     The basic configuration options are as follows:

     listen on address [rtable table-id]
	     ntpd(8) has the ability to	sync the local clock to	remote NTP
	     servers and, if this directive is specified, can act as NTP
	     server itself, redistributing the local clock.

	     Specify a local IP	address	or a hostname the ntpd(8) daemon
	     should listen on to enable	remote clients synchronization.	 If it
	     appears multiple times, ntpd(8) will listen on each given ad-
	     dress.  If	`*' is given as	an address, ntpd(8) will listen	on all
	     local addresses using the specified routing table.	 ntpd(8) does
	     not listen	on any address by default.  The	optional rtable	key-
	     word will specify which routing table to listen on, if the	oper-
	     ating system supports rdomains.  By default ntpd(8) will listen
	     using the current routing table.  For example:

		   listen on *

	     or

		   listen on 127.0.0.1
		   listen on ::1
		   listen on 127.0.0.1 rtable 4

     query from	address
	     Specify a local IP	address	the ntpd(8) daemon should use for out-
	     going queries to subsequently specified servers.  For example:

		   query from 192.0.2.1
		   query from 2001:db8::1

     sensor device [correction microseconds] [weight weight-value] [refid
	     string] [stratum stratum-value]
	     Specify a timedelta sensor	device ntpd(8) should use, if the op-
	     erating system supports sensors.  The sensor can be specified
	     multiple times: ntpd(8) will use each given sensor	that actually
	     exists.  Non-existent sensors are ignored.	 If `*'	is given as
	     device name, ntpd(8) will use all timedelta sensors it finds.
	     ntpd(8) does not use any timedelta	sensor by default.  For	exam-
	     ple:

		   sensor *
		   sensor nmea0

	     An	optional correction in microseconds can	be given to compensate
	     for the sensor's offset.  The maximum correction is 127 seconds.
	     For example, if a DCF77 receiver is lagging 70ms behind actual
	     time:

		   sensor udcf0	correction 70000

	     The optional weight keyword permits finer control over the	rela-
	     tive importance of	time sources (servers or sensor	devices).
	     Weights are specified in the range	1 to 10; if no weight is
	     given, the	default	is 1.  A server	with a weight of 5, for	exam-
	     ple, will have five times more influence on time offset calcula-
	     tion than a server	with a weight of 1.

	     An	optional reference ID string - up to 4 ASCII characters	- can
	     be	given to publish the sensor type to clients.  RFC 2030 sug-
	     gests some	common reference identifiers, but new identifiers "can
	     be	contrived as appropriate."  If an ID string is not given,
	     ntpd(8) will use a	generic	reference ID.  For example:

		   sensor nmea0	refid GPS

	     A stratum value other than	the default of 1 can be	assigned using
	     the stratum keyword.

     server address [weight weight-value]
	     Specify the IP address or the hostname of an NTP server to	syn-
	     chronize to.  If it appears multiple times, ntpd(8) will try to
	     synchronize to all	of the servers specified.  If a	hostname re-
	     solves to multiple	IPv4 and/or IPv6 addresses, ntpd(8) uses the
	     first address.  If	it does	not get	a reply, ntpd(8) retries with
	     the next address and continues to do so until a working address
	     is	found.	For example:

		   server 10.0.0.2 weight 5
		   server ntp.example.org weight 1

	     To	provide	redundancy, it is good practice	to configure multiple
	     servers.  In general, best	accuracy is obtained by	using servers
	     that have a low network latency.

     servers address [weight weight-value]
	     As	with server, specify the IP address or hostname	of an NTP
	     server to synchronize to.	If it appears multiple times, ntpd(8)
	     will try to synchronize to	all of the servers specified.  Should
	     the hostname resolve to multiple IP addresses, ntpd(8) will try
	     to	synchronize to all of them.  For example:

		   servers pool.ntp.org
		   servers pool.ntp.org	weight 5

CONSTRAINTS
     ntpd(8) can be configured to query	the `Date' from	trusted	HTTPS servers
     via TLS.  This time information is	not used for precision but acts	as an
     authenticated constraint, thereby reducing	the impact of unauthenticated
     NTP man-in-the-middle attacks.  Received NTP packets with time informa-
     tion falling outside of a range near the constraint will be discarded and
     such NTP servers will be marked as	invalid.

     Support for constraints is	only available if ntpd(8) has been linked with
     libtls from LibreSSL. Configuring a constraint without libtls causes
     ntpd(8) to	log a warning message on startup.

     constraint	from url
	     Specify the URL, IP address or the	hostname of an HTTPS server to
	     provide a constraint.  If constraint from is used more than once,
	     ntpd(8) will calculate a median constraint	from all the servers
	     specified.

		   server ntp.example.org
		   constraint from www.example.com

     constraints from url
	     As	with constraint	from, specify the URL, IP address or the host-
	     name of an	HTTPS server to	provide	a constraint.  Should the
	     hostname resolve to multiple IP addresses,	ntpd(8)	will calculate
	     a median constraint from all of them.  For	example:

		   servers pool.ntp.org
		   constraints from "https://www.google.com/"

FILES
     /usr/local/etc/ntpd.conf	  default ntpd(8) configuration	file

SEE ALSO
     ntpctl(8),	ntpd(8), sysctl(8)

HISTORY
     The ntpd.conf file	format first appeared in OpenBSD 3.6.

FreeBSD	13.0			August 10, 2017			  FreeBSD 13.0

NAME | DESCRIPTION | CONSTRAINTS | FILES | SEE ALSO | HISTORY

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