438 lines
11 KiB
Groff
438 lines
11 KiB
Groff
.\"-
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.\" Copyright (c) 1980, 1990, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the Institute of Electrical and Electronics Engineers, Inc.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)date.1 8.3 (Berkeley) 4/28/95
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.\" $FreeBSD$
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.\"
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.Dd November 1, 2005
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.Dt DATE 1
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.Os
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.Sh NAME
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.Nm date
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.Nd display or set date and time
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.Sh SYNOPSIS
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.Nm
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.Op Fl ju
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.Op Fl r Ar seconds
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.Oo
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.Fl v
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.Sm off
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.Op Cm + | -
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.Ar val Op Ar ymwdHMS
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.Sm on
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.Oc
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.Ar ...
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.Op Cm + Ns Ar output_fmt
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.Nm
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.Op Fl jnu
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.Sm off
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.Op Oo Oo Oo Oo Ar cc Oc Ar yy Oc Ar mm Oc Ar dd Oc Ar HH
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.Ar MM Op Ar .ss
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.Sm on
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.Nm
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.Op Fl jnu
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.Fl f Ar input_fmt new_date
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.Op Cm + Ns Ar output_fmt
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.Nm
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.Op Fl d Ar dst
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.Op Fl t Ar minutes_west
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.Sh DESCRIPTION
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When invoked without arguments, the
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.Nm
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utility displays the current date and time.
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Otherwise, depending on the options specified,
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.Nm
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will set the date and time or print it in a user-defined way.
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.Pp
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The
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.Nm
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utility displays the date and time read from the kernel clock.
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When used to set the date and time,
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both the kernel clock and the hardware clock are updated.
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.Pp
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Only the superuser may set the date,
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and if the system securelevel (see
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.Xr securelevel 8 )
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is greater than 1,
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the time may not be changed by more than 1 second.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl d Ar dst
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Set the kernel's value for daylight saving time.
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If
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.Ar dst
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is non-zero, future calls
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to
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.Xr gettimeofday 2
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will return a non-zero for
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.Fa tz_dsttime .
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.It Fl f
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Use
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.Ar input_fmt
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as the format string to parse the
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.Ar new_date
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provided rather than using the default
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.Sm off
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.Oo Oo Oo Oo Oo
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.Ar cc Oc
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.Ar yy Oc
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.Ar mm Oc
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.Ar dd Oc
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.Ar HH
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.Oc Ar MM Op Ar .ss
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.Sm on
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format.
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Parsing is done using
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.Xr strptime 3 .
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.It Fl j
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Do not try to set the date.
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This allows you to use the
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.Fl f
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flag in addition to the
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.Cm +
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option to convert one date format to another.
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.It Fl n
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By default, if the
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.Xr timed 8
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daemon is running,
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.Nm
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sets the time on all of the machines in the local group.
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The
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.Fl n
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option suppresses this behavior and causes the time to be set only on the
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current machine.
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.It Fl r Ar seconds
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Print the date and time represented by
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.Ar seconds ,
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where
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.Ar seconds
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is the number of seconds since the Epoch
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(00:00:00 UTC, January 1, 1970;
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see
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.Xr time 3 ) ,
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and can be specified in decimal, octal, or hex.
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.It Fl t Ar minutes_west
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Set the system's value for minutes west of
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.Tn GMT .
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.Ar minutes_west
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specifies the number of minutes returned in
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.Fa tz_minuteswest
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by future calls to
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.Xr gettimeofday 2 .
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.It Fl u
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Display or set the date in
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.Tn UTC
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(Coordinated Universal) time.
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.It Fl v
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Adjust (i.e., take the current date and display the result of the
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adjustment; not actually set the date) the second, minute, hour, month
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day, week day, month or year according to
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.Ar val .
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If
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.Ar val
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is preceded with a plus or minus sign,
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the date is adjusted forwards or backwards according to the remaining string,
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otherwise the relevant part of the date is set.
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The date can be adjusted as many times as required using these flags.
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Flags are processed in the order given.
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.Pp
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When setting values
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(rather than adjusting them),
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seconds are in the range 0-59, minutes are in the range 0-59, hours are
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in the range 0-23, month days are in the range 1-31, week days are in the
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range 0-6 (Sun-Sat),
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months are in the range 1-12 (Jan-Dec)
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and years are in the range 80-38 or 1980-2038.
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.Pp
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If
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.Ar val
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is numeric, one of either
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.Ar y ,
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.Ar m ,
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.Ar w ,
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.Ar d ,
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.Ar H ,
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.Ar M
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or
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.Ar S
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must be used to specify which part of the date is to be adjusted.
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.Pp
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The week day or month may be specified using a name rather than a
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number.
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If a name is used with the plus
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(or minus)
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sign, the date will be put forwards
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(or backwards)
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to the next
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(previous)
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date that matches the given week day or month.
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This will not adjust the date,
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if the given week day or month is the same as the current one.
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.Pp
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When a date is adjusted to a specific value or in units greater than hours,
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daylight savings time considerations are ignored.
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Adjustments in units of hours or less honor daylight saving time.
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So, assuming the current date is March 26, 0:30 and that the DST adjustment
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means that the clock goes forward at 01:00 to 02:00, using
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.Fl v No +1H
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will adjust the date to March 26, 2:30.
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Likewise, if the date is October 29, 0:30 and the DST adjustment means that
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the clock goes back at 02:00 to 01:00, using
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.Fl v No +3H
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will be necessary to reach October 29, 2:30.
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.Pp
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When the date is adjusted to a specific value that does not actually exist
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(for example March 26, 1:30 BST 2000 in the Europe/London timezone),
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the date will be silently adjusted forwards in units of one hour until it
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reaches a valid time.
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When the date is adjusted to a specific value that occurs twice
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(for example October 29, 1:30 2000),
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the resulting timezone will be set so that the date matches the earlier of
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the two times.
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.Pp
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Adjusting the date by months is inherently ambiguous because
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a month is a unit of variable length depending on the current date.
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This kind of date adjustment is applied in the most intuitive way.
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First of all,
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.Nm
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tries to preserve the day of the month.
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If it is impossible because the target month is shorter than the present one,
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the last day of the target month will be the result.
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For example, using
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.Fl v No +1m
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on May 31 will adjust the date to June 30, while using the same option
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on January 30 will result in the date adjusted to the last day of February.
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This approach is also believed to make the most sense for shell scripting.
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Nevertheless, be aware that going forth and back by the same number of
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months may take you to a different date.
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.Pp
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Refer to the examples below for further details.
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.El
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.Pp
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An operand with a leading plus
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.Pq Sq +
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sign signals a user-defined format string
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which specifies the format in which to display the date and time.
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The format string may contain any of the conversion specifications
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described in the
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.Xr strftime 3
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manual page, as well as any arbitrary text.
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A newline
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.Pq Ql \en
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character is always output after the characters specified by
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the format string.
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The format string for the default display is
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.Dq +%+ .
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.Pp
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If an operand does not have a leading plus sign, it is interpreted as
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a value for setting the system's notion of the current date and time.
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The canonical representation for setting the date and time is:
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.Pp
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.Bl -tag -width Ds -compact -offset indent
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.It Ar cc
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Century
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(either 19 or 20)
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prepended to the abbreviated year.
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.It Ar yy
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Year in abbreviated form
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(e.g., 89 for 1989, 06 for 2006).
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.It Ar mm
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Numeric month, a number from 1 to 12.
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.It Ar dd
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Day, a number from 1 to 31.
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.It Ar HH
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Hour, a number from 0 to 23.
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.It Ar MM
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Minutes, a number from 0 to 59.
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.It Ar ss
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Seconds, a number from 0 to 61
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(59 plus a maximum of two leap seconds).
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.El
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.Pp
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Everything but the minutes is optional.
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.Pp
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Time changes for Daylight Saving Time, standard time, leap seconds,
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and leap years are handled automatically.
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.Sh ENVIRONMENT
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The following environment variables affect the execution of
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.Nm :
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.Bl -tag -width Ds
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.It Ev TZ
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The timezone to use when displaying dates.
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The normal format is a pathname relative to
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.Pa /usr/share/zoneinfo .
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For example, the command
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.Dq TZ=America/Los_Angeles date
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displays the current time in California.
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See
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.Xr environ 7
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for more information.
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.El
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.Sh FILES
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.Bl -tag -width /var/log/messages -compact
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.It Pa /var/log/wtmp
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record of date resets and time changes
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.It Pa /var/log/messages
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record of the user setting the time
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.El
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.Sh EXIT STATUS
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The
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.Nm
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utility exits 0 on success, 1 if unable to set the date, and 2
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if able to set the local date, but unable to set it globally.
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.Sh EXAMPLES
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The command:
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.Pp
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.Dl "date ""+DATE: %Y-%m-%d%nTIME: %H:%M:%S"""
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.Pp
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will display:
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.Bd -literal -offset indent
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DATE: 1987-11-21
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TIME: 13:36:16
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.Ed
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.Pp
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In the Europe/London timezone, the command:
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.Pp
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.Dl "date -v1m -v+1y"
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.Pp
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will display:
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.Pp
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.Dl "Sun Jan 4 04:15:24 GMT 1998"
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.Pp
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where it is currently
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.Li "Mon Aug 4 04:15:24 BST 1997" .
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.Pp
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The command:
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.Pp
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.Dl "date -v1d -v3m -v0y -v-1d"
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.Pp
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will display the last day of February in the year 2000:
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.Pp
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.Dl "Tue Feb 29 03:18:00 GMT 2000"
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.Pp
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So will do the command:
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.Pp
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.Dl "date -v30d -v3m -v0y -v-1m"
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.Pp
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because there is no such date as the 30th of February.
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.Pp
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The command:
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.Pp
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.Dl "date -v1d -v+1m -v-1d -v-fri"
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.Pp
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will display the last Friday of the month:
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.Pp
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.Dl "Fri Aug 29 04:31:11 BST 1997"
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.Pp
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where it is currently
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.Li "Mon Aug 4 04:31:11 BST 1997" .
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.Pp
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The command:
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.Pp
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.Dl "date 8506131627"
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.Pp
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sets the date to
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.Dq Li "June 13, 1985, 4:27 PM" .
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.Pp
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.Dl "date ""+%Y%m%d%H%M.%S"""
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.Pp
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may be used on one machine to print out the date
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suitable for setting on another.
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.Qq ( Li "+%m%d%H%M%Y.%S"
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for use on
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.Tn Linux . )
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.Pp
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The command:
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.Pp
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.Dl "date 1432"
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.Pp
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sets the time to
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.Li "2:32 PM" ,
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without modifying the date.
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.Pp
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Finally the command:
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.Pp
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.Dl "date -j -f ""%a %b %d %T %Z %Y"" ""`date`"" ""+%s"""
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.Pp
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can be used to parse the output from
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.Nm
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and express it in Epoch time.
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.Sh DIAGNOSTICS
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Occasionally, when
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.Xr timed 8
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synchronizes the time on many hosts, the setting of a new time value may
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require more than a few seconds.
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On these occasions,
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.Nm
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prints:
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.Ql Network time being set .
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The message
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.Ql Communication error with timed
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occurs when the communication
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between
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.Nm
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and
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.Xr timed 8
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fails.
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.Sh SEE ALSO
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.Xr locale 1 ,
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.Xr gettimeofday 2 ,
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.Xr strftime 3 ,
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.Xr strptime 3 ,
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.Xr utmp 5 ,
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.Xr timed 8
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.Rs
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.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
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.%A R. Gusella
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.%A S. Zatti
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.Re
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.Sh STANDARDS
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The
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.Nm
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utility is expected to be compatible with
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.St -p1003.2 .
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The
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.Fl d ,
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.Fl f ,
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.Fl j ,
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.Fl n ,
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.Fl r ,
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.Fl t ,
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and
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.Fl v
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options are all extensions to the standard.
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.Sh HISTORY
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A
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.Nm
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command appeared in
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.At v1 .
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