— Network Time Protocol
daemon synchronizes the local clock to one or more
remote NTP servers or local timedelta sensors. ntpd
act as an NTP server itself, redistributing the local time. It implements the
Simple Network Time Protocol version 4, as described in RFC 5905, and the
Network Time Protocol version 3, as described in RFC 1305. Time can also be
fetched from TLS HTTPS servers to reduce the impact of unauthenticated NTP
The options are as follows:
- Do not daemonize. If this option is specified,
ntpd will run in the foreground and log to
- Use file as the configuration file,
instead of the default /etc/ntpd.conf.
- Configtest mode. Only check the configuration file for
- Do not set the time immediately at startup. This is the
- Try to set the time immediately at startup, as opposed to
slowly adjusting the clock. ntpd will stay in the
foreground for up to 15 seconds waiting for one of the configured NTP
servers to reply.
- This option allows ntpd to send DEBUG
priority messages to syslog.
uses the adjtime(2)
system call to correct the local system time without causing time jumps.
Adjustments of 32ms and greater are logged using
. The threshold value is chosen to
avoid having local clock drift thrash the log files. Should
be started with the -d
option, all calls to
will be logged.
After the local clock is synchronized, ntpd
adjusts the clock
frequency using the adjfreq(2)
to compensate for systematic drift.
is usually started at boot time, and can be enabled by
. See rc(8)
for more information on the
boot process and enabling daemons.
starts up, it reads settings from its configuration
file, typically ntpd.conf(5)
, and its
initial clock drift from /var/db/ntpd.drift
. Clock drift is
periodically written to the drift file thereafter.
- Default configuration file.
- Drift file.
- Socket file for communication with
David L. Mills,
Network Time Protocol (Version 3): Specification,
Implementation and Analysis, RFC 1305,
David L. Mills, Jim
Martin, Jack Burbank, and
William Kasch, Network Time
Protocol Version 4: Protocol and Algorithms Specification,
RFC 5905, June 2010.
program first appeared in OpenBSD