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.

The optional 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.

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. They are as follows:

listen on address
    Specify a local IP address or a hostname the ntpd(8) daemon should listen on. If it appears multiple times, ntpd(8) will listen on each given address. If ‘*’ is given as an address, ntpd(8) will listen on all local addresses. ntpd(8) does not listen on any address by default. For example:

        listen on *

    or

        listen on 127.0.0.1
        listen on ::1

sensor device
    [correction microseconds] [weight weight-value] [refid string] Specify a timedelta sensor device ntpd(8) should use. 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 example:

        sensor *
        sensor udcf0

    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 15ms behind actual time:

        sensor udcf0 correction 15000

    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, ntpd(8) will use a generic reference ID. For example:

        sensor msts0 refid GPS

server address
    [weight weight-value] Specify the IP address or the 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. If a hostname resolves 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

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

SEE ALSO
ntpd(8), sysctl(8)

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