.\" $OpenBSD: ntpd.conf.5,v 1.15 2006/10/08 22:53:33 stevesk Exp $
.\"
.\" Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
.\"
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.Dd May 26, 2006
.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
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
.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 weight Ar weight-value
.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 udcf0
.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 .