openntpd-openbsd/src/usr.sbin/ntpd/ntpd.8

.\" $OpenBSD: ntpd.8,v 1.40 2015/10/30 16:41:53 reyk Exp $
.\"
.\" Copyright (c) 2003, 2004, 2006 Henning Brauer <henning@openbsd.org>
.\"
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.Dd $Mdocdate: October 30 2015 $
.Dt NTPD 8
.Os
.Sh NAME
.Nm ntpd
.Nd Network Time Protocol daemon
.Sh SYNOPSIS
.Nm ntpd
.Bk -words
.Op Fl dnSsv
.Op Fl f Ar file
.Ek
.Sh DESCRIPTION
The
.Nm
daemon synchronizes the local clock to one or more remote NTP servers
or local timedelta sensors.
.Nm
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.
.Pp
The options are as follows:
.Bl -tag -width "-f fileXXX"
.It Fl d
Do not daemonize.
If this option is specified,
.Nm
will run in the foreground and log to
.Em stderr .
.It Fl f Ar file
Use
.Ar file
as the configuration file,
instead of the default
.Pa /etc/ntpd.conf .
.It Fl n
Configtest mode.
Only check the configuration file for validity.
.It Fl S
Do not set the time immediately at startup.
This is the default.
.It Fl s
Try to set the time immediately at startup, as opposed to slowly adjusting the
clock.
.Nm
will stay in the foreground for up to 15 seconds waiting for one of the
configured NTP servers to reply.
.It Fl v
This option allows
.Nm
to send DEBUG priority messages to syslog.
.El
.Pp
.Nm
uses the
.Xr adjtime 2
system call to correct the local system time without causing time jumps.
Adjustments of 32ms and greater are logged using
.Xr syslog 3 .
The threshold value is chosen to avoid having local clock drift
thrash the log files.
Should
.Nm
be started with the
.Fl d
or
.Fl v
option, all calls to
.Xr adjtime 2
will be logged.
.Pp
After the local clock is synchronized,
.Nm
adjusts the clock frequency using the
.Xr adjfreq 2
system call to compensate for systematic drift.
.Pp
.Nm
is usually started at boot time, and can be enabled by
setting
.Va ntpd_flags
in
.Pa /etc/rc.conf.local .
See
.Xr rc 8
and
.Xr rc.conf 8
for more information on the boot process
and enabling daemons.
.Pp
When
.Nm
starts up, it reads settings from its configuration file,
typically
.Xr ntpd.conf 5 ,
and its initial clock drift from
.Pa /var/db/ntpd.drift .
Clock drift is periodically written to the drift file thereafter.
.Sh FILES
.Bl -tag -width "/var/db/ntpd.driftXXX" -compact
.It Pa /etc/ntpd.conf
Default configuration file.
.It Pa /var/db/ntpd.drift
Drift file.
.It Pa /var/run/ntpd.sock
Socket file for communication with
.Xr ntpctl 8 .
.El
.Sh SEE ALSO
.Xr date 1 ,
.Xr adjfreq 2 ,
.Xr adjtime 2 ,
.Xr ntpd.conf 5 ,
.Xr ntpctl 8 ,
.Xr rc 8 ,
.Xr rc.conf 8 ,
.Xr rdate 8
.Sh STANDARDS
.Rs
.%A David L. Mills
.%D March 1992
.%R RFC 1305
.%T Network Time Protocol (Version 3): Specification, Implementation and Analysis
.Re
.Pp
.Rs
.%A David L. Mills
.%A Jim Martin
.%A Jack Burbank
.%A William Kasch
.%D June 2010
.%R RFC 5905
.%T Network Time Protocol Version 4: Protocol and Algorithms Specification
.Re
.Sh HISTORY
The
.Nm
program first appeared in
.Ox 3.6 .