NAME
ntpd
—
Network Time Protocol daemon
SYNOPSIS
ntpd |
[-dnSsv ]
[-f file] |
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.
-S
- Do not set the time immediately at startup. This is the default.
-s
- 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. -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.
After the local clock is synchronized,
ntpd
adjusts the clock frequency using the
adjfreq(2) system call to compensate for systematic drift.
ntpd
is usually started at boot time, and
can be enabled by setting ntpd_flags in
/etc/rc.conf.local. 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.
When ntpd
(engine) receives a
SIGINFO
signal, it writes its peer and sensor status
to syslog(3).
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.