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NAME

ntpd — Network Time Protocol (NTP) daemon

SYNOPSIS

DESCRIPTION

The ntpd daemon synchronizes the local clock to one or more remote NTP servers or local timedelta sensors. ntpd can also 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 man-in-the-middle attacks.

The options are as follows:

-d

Do not daemonize. If this option is specified, ntpd will run in the foreground and log to stderr.

-f file

Use file as the configuration file, instead of the default /etc/ntpd.conf.

-n

Configtest mode. Only check the configuration file for validity.

-v

This option allows ntpd to send DEBUG priority messages to syslog.

ntpd uses the adjtime(2) system call to correct the local system time without causing time jumps. Adjustments of 32ms and greater are logged using syslog(3). The threshold value is chosen to avoid having local clock drift thrash the log files. Should ntpd be started with the -d or -v option, all calls to adjtime(2) will be logged.

At boot, ntpd will stay for a maximum of 15 seconds in the foreground and make efforts to verify and correct the time if constraints are configured and satisfied or if trusted servers or sensors return results, and if the clock is not being moved backwards.

After the local clock is synchronized, ntpd adjusts the clock frequency using the adjfreq(2) system call to compensate for systematic drift.

ntpd is started at boot time by default via ntpd_flags in /etc/rc.conf. See rc(8) and rc.conf(8) for more information on the boot process and enabling daemons.

When ntpd 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.

FILES

/etc/ntpd.conf

Default configuration file.

/var/db/ntpd.drift

Drift file.

/var/run/ntpd.sock

Socket file for communication with ntpctl(8).

SEE ALSO

date(1), adjfreq(2), adjtime(2), ntpd.conf(5), ntpctl(8), rc(8), rc.conf(8), rdate(8)

STANDARDS

David L. Mills, Network Time Protocol (Version 3): Specification, Implementation and Analysis, RFC 1305, March 1992.

David L. Mills, Jim Martin, Jack Burbank, and William Kasch, Network Time Protocol Version 4: Protocol and Algorithms Specification, RFC 5905, June 2010.

HISTORY

The ntpd program first appeared in OpenBSD 3.6.