.\" $OpenBSD: ntpd.conf.5,v 1.22 2009/05/18 20:08:24 stevesk Exp $
.\"
.\" Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.Dd $Mdocdate: May 18 2009 $
.Dt NTPD.CONF 5
.Os
.Sh NAME
.Nm ntpd.conf
.Nd Network Time Protocol daemon configuration file
.Sh DESCRIPTION
This manual page describes the format of the
.Xr ntpd 8
configuration file.
.Pp
.Nm
has the following format:
.Pp
Empty lines and lines beginning with the
.Sq #
character are ignored.
.Pp
Keywords may be specified multiple times within the configuration file.
They are as follows:
.Bl -tag -width Ds
.It Ic listen on Ar address
Specify a local IP address or a hostname the
.Xr ntpd 8
daemon should listen on.
If it appears multiple times,
.Xr ntpd 8
will listen on each given address.
If
.Sq *
is given as an address,
.Xr ntpd 8
will listen on all local addresses.
.Xr ntpd 8
does not listen on any address by default.
For example:
.Bd -literal -offset indent
listen on *
.Ed
.Pp
or
.Bd -literal -offset indent
listen on 127.0.0.1
listen on ::1
.Ed
.It Xo Ic sensor Ar device
.Op Ic correction Ar microseconds
.Op Ic weight Ar weight-value
.Op Ic refid Ar string
.Xc
Specify a timedelta sensor device
.Xr ntpd 8
should use.
The sensor can be specified multiple times:
.Xr ntpd 8
will use each given sensor that actually exists.
Non-existent sensors are ignored.
If
.Sq *
is given as device name,
.Xr ntpd 8
will use all timedelta sensors it finds.
.Xr ntpd 8
does not use any timedelta sensor by default.
For example:
.Bd -literal -offset indent
sensor *
sensor nmea0
.Ed
.Pp
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:
.Bd -literal -offset indent
sensor udcf0 correction 70000
.Ed
.Pp
The optional
.Ic weight
keyword permits finer control over the relative 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 example,
will have five times more influence on time offset calculation
than a server with a weight of 1.
.Pp
An optional reference ID string - up to 4 ASCII characters - can be
given to publish the sensor type to clients.
RFC 2030 suggests some common reference identifiers, but new identifiers
"can be contrived as appropriate."
If an ID string is not given,
.Xr ntpd 8
will use a generic reference ID.
For example:
.Bd -literal -offset indent
sensor nmea0 refid GPS
.Ed
.It Xo Ic server Ar address
.Op Ic weight Ar weight-value
.Xc
Specify the IP address or the hostname of an NTP
server to synchronize to.
If it appears multiple times,
.Xr ntpd 8
will try to synchronize to all of the servers specified.
If a hostname resolves to multiple IPv4 and/or IPv6 addresses,
.Xr ntpd 8
uses the first address.
If it does not get a reply,
.Xr ntpd 8
retries with the next address and continues to do so until a working address
is found.
For example:
.Bd -literal -offset indent
server 10.0.0.2 weight 5
server ntp.example.org weight 1
.Ed
.Pp
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.
.It Xo Ic servers Ar address
.Op Ic weight Ar weight-value
.Xc
As with
.Cm server ,
specify the IP address or hostname of an NTP server to synchronize to.
If it appears multiple times,
.Xr ntpd 8
will try to synchronize to all of the servers specified.
Should the hostname resolve to multiple IP addresses,
.Xr ntpd 8
will try to synchronize to all of them.
For example:
.Bd -literal -offset indent
servers pool.ntp.org
.Ed
.El
.Sh FILES
.Bl -tag -width "/etc/ntpd.confXXX" -compact
.It Pa /etc/ntpd.conf
default
.Xr ntpd 8
configuration file
.El
.Sh SEE ALSO
.Xr ntpd 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
file format first appeared in
.Ox 3.6 .