Scroll to navigation

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


ntpd.confNetwork Time Protocol daemon configuration file


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:

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 address. 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 keyword will specify which routing table to listen on, if the operating system supports rdomains. By default ntpd(8) will listen using the current routing table. For example:

listen on *


listen on
listen on ::1
listen on rtable 4
Specify a local IP address the ntpd(8) daemon should use for outgoing queries to subsequently specified servers. For example:
query from
query from 2001:db8::1
device [correction microseconds] [weight weight-value] [refid string] [stratum stratum-value]
Specify a timedelta sensor device ntpd(8) should use, if the operating 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 example:
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 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.

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 nmea0 refid GPS

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

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 weight 5
server 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.

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 weight 5


ntpd(8) Hardened TLS for ntpd constraints, enabling server name verification, is currently not enabled on Debian due to missing LibreSSL's libtls implementation at this time.


default ntpd(8) configuration file
openntpd daemon defaults


ntpctl(8), ntpd(8), sysctl(8)


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

August 10, 2017 Debian