|NTPD.CONF(5)||File Formats Manual||NTPD.CONF(5)|
Network 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:
listen onaddress [
rtablekeyword will specify which routing table to listen on. By default ntpd(8) will listen using the current routing table. For example:
listen on *
listen on 127.0.0.1 listen on ::1 listen on 127.0.0.1 rtable 4
query from 192.0.2.1 query from 2001:db8::1
sensor * sensor nmea0
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
sensor udcf0 correction 70000
ID-string of 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
stratum keyword can be used to
change the stratum value from the default of 1.
trusted keyword indicates the time
learned is secure, trustworthy, and not vulnerable to man-in-the-middle
constraints validation is skipped.
This is useful for boot-time correction in environments where
constraints cannot be used.
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.
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.
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
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 information falling outside of a range near the constraint will be discarded and such NTP servers will be marked as invalid.
constraint fromurl [ip...]
constraint fromis 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 constraint from "https://22.214.171.124" "2620:fe::9"
constraint from, specify the URL, IP address or the hostname 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/"
ntpd.conf file format first appeared
in OpenBSD 3.6.
|March 31, 2022||OpenBSD-current|