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.\" $OpenBSD: ntpd.8,v 1.40 2015/10/30 16:41:53 reyk Exp $
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.\"
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.\" Copyright (c) 2003, 2004, 2006 Henning Brauer <henning@openbsd.org>
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER IN
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.\" AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
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.\" OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.Dd $Mdocdate: October 30 2015 $
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.Dt NTPD 8
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.Os
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.Sh NAME
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.Nm ntpd
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.Nd Network Time Protocol daemon
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.Sh SYNOPSIS
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.Nm ntpd
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.Bk -words
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.Op Fl dnSsv
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.Op Fl f Ar file
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.Ek
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.Sh DESCRIPTION
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The
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.Nm
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daemon synchronizes the local clock to one or more remote NTP servers
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or local timedelta sensors.
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.Nm
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can also act as an NTP server itself,
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redistributing the local time.
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It implements the Simple Network Time Protocol version 4,
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as described in RFC 5905,
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and the Network Time Protocol version 3,
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as described in RFC 1305.
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Time can also be fetched from TLS HTTPS servers to reduce the
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impact of unauthenticated NTP
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man-in-the-middle attacks.
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.Pp
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The options are as follows:
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.Bl -tag -width "-f fileXXX"
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.It Fl d
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Do not daemonize.
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If this option is specified,
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.Nm
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will run in the foreground and log to
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.Em stderr .
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.It Fl f Ar file
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Use
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.Ar file
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as the configuration file,
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instead of the default
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.Pa /etc/ntpd.conf .
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.It Fl n
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Configtest mode.
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Only check the configuration file for validity.
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.It Fl S
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Do not set the time immediately at startup.
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This is the default.
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.It Fl s
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Try to set the time immediately at startup, as opposed to slowly adjusting the
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clock.
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.Nm
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will stay in the foreground for up to 15 seconds waiting for one of the
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configured NTP servers to reply.
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.It Fl v
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This option allows
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.Nm
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to send DEBUG priority messages to syslog.
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.El
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.Pp
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.Nm
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uses the
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.Xr adjtime 2
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system call to correct the local system time without causing time jumps.
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Adjustments of 32ms and greater are logged using
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.Xr syslog 3 .
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The threshold value is chosen to avoid having local clock drift
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thrash the log files.
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Should
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.Nm
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be started with the
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.Fl d
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or
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.Fl v
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option, all calls to
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.Xr adjtime 2
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will be logged.
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.Pp
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After the local clock is synchronized,
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.Nm
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adjusts the clock frequency using the
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.Xr adjfreq 2
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system call to compensate for systematic drift.
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.Pp
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.Nm
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is usually started at boot time, and can be enabled by
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setting
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.Va ntpd_flags
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in
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.Pa /etc/rc.conf.local .
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See
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.Xr rc 8
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and
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.Xr rc.conf 8
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for more information on the boot process
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and enabling daemons.
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.Pp
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When
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.Nm
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starts up, it reads settings from its configuration file,
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typically
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.Xr ntpd.conf 5 ,
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and its initial clock drift from
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.Pa /var/db/ntpd.drift .
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Clock drift is periodically written to the drift file thereafter.
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.Sh FILES
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.Bl -tag -width "/var/db/ntpd.driftXXX" -compact
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.It Pa /etc/ntpd.conf
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Default configuration file.
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.It Pa /var/db/ntpd.drift
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Drift file.
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.It Pa /var/run/ntpd.sock
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Socket file for communication with
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.Xr ntpctl 8 .
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.El
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.Sh SEE ALSO
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.Xr date 1 ,
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.Xr adjfreq 2 ,
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.Xr adjtime 2 ,
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.Xr ntpd.conf 5 ,
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.Xr ntpctl 8 ,
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.Xr rc 8 ,
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.Xr rc.conf 8 ,
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.Xr rdate 8
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.Sh STANDARDS
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.Rs
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.%A David L. Mills
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.%D March 1992
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.%R RFC 1305
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.%T Network Time Protocol (Version 3): Specification, Implementation and Analysis
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.Re
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.Pp
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.Rs
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.%A David L. Mills
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.%A Jim Martin
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.%A Jack Burbank
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.%A William Kasch
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.%D June 2010
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.%R RFC 5905
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.%T Network Time Protocol Version 4: Protocol and Algorithms Specification
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.Re
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.Sh HISTORY
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The
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.Nm
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program first appeared in
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.Ox 3.6 .
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