path: root/bin/date/date.1

.\"	$OpenBSD: date.1,v 1.17 1998/12/15 01:20:18 aaron Exp $
.\"	$NetBSD: date.1,v 1.12 1996/03/12 04:32:37 phil Exp $
.\"
.\" Copyright (c) 1980, 1990, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Institute of Electrical and Electronics Engineers, Inc.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)date.1	8.3 (Berkeley) 4/28/95
.\"
.Dd April 28, 1995
.Dt DATE 1
.Os
.Sh NAME
.Nm date
.Nd display or set date and time
.Sh SYNOPSIS
.Nm date
.Op Fl d Ar dst
.Op Fl r Ar seconds
.Op Fl t Ar minutes_west
.Op Fl nu
.Op Cm + Ns Ar format
.Op [[[[[cc]yy]mm]dd]HH]MM[\&.SS]
.Sh DESCRIPTION
.Nm
displays the current date and time when invoked without arguments.
Providing arguments will format the date and time in a user-defined
way or set the date.
Only the superuser may set the date.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl d Ar dst
Set the kernel's value for daylight saving time.
If
.Ar dst
is non-zero, future calls
to
.Xr gettimeofday 2
will return a non-zero
.Ql tz_dsttime .
.It Fl n
The utility
.Xr timed 8
is used to synchronize the clocks on groups of machines.
By default, if
.Xr timed 8
is running,
.Nm
will set the time on all of the machines in the local group.
The
.Fl n
option stops
.Nm
from setting the time for other than the current machine.
.It Fl r Ar seconds
Print out (in specified format) the date and time represented by
.Ar seconds
from the Epoch.
.It Fl t Ar minutes_west
Set the kernel's value for minutes west of
.Tn GMT .
.Ar minutes_west
specifies the number of minutes returned in
.Ql tz_minuteswest  
by future calls to
.Xr gettimeofday 2 .
.It Fl u
Display or set the date in
.Tn UTC
(universal) time.
.El
.Pp
An operand with a leading plus sign
.Pq Sq +
signals a user-defined format
string which specifies the format in which to display the date and time.
The format string may contain any of the conversion specifications described
in the 
.Xr strftime 3
manual page, as well as any arbitrary text.
A <newline> character is always output after the characters specified by
the format string.
The format string for the default display is:
.Bd -literal -offset indent
.Dq %a %b %e %H:%M:%S %Z %Y
.Ed
.Pp
If an operand does not have a leading plus sign, it is interpreted as
a value for setting the system's notion of the current date and time.
The canonical representation for setting the date and time is:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ar yy
Year in abbreviated form (e.g. 89 for 1989, 06 for 2006).
The format
.Ar ccyymmddHHMM
is also permitted, for non-ambiguous years beyond 1999.
.It Ar mm
Numeric month, a number from 1 to 12.
.It Ar dd
Day, a number from 1 to 31.
.It Ar HH
Hour, a number from 0 to 23.
.It Ar MM
Minute, a number from 0 to 59.
.It Ar .SS
Second, a number from 0 to 61 (59 plus a maximum of two leap seconds).
.El
.Pp
Everything but the minute is optional.
.Pp
Time changes for daylight saving time, standard time, leap seconds,
and leap years are handled automatically.
.Sh EXAMPLES
The command:
.Bd -literal -offset indent
date "+DATE: %Y-%m-%d%nTIME: %H:%M:%S"
.Ed
.Pp
will display:
.Bd -literal -offset indent
DATE: 1987-11-21
TIME: 13:36:16
.Ed
.Pp
The command:
.Bd -literal -offset indent
date 8506131627
.Ed
.Pp
sets the date to
.Dq Li "June 13, 1985, 4:27 PM" .
.Pp
The command:
.Bd -literal -offset indent
date 1432
.Ed
.Pp
sets the time to
.Li "2:32 PM" ,
without modifying the date.
.Sh ENVIRONMENT
The following environment variables affect the execution of
.Nm date :
.Bl -tag -width TZ
.It Ev TZ
The timezone to use when displaying dates.
See
.Xr environ 7
for more information.
.El
.Sh FILES
.Bl -tag -width /var/log/messages -compact
.It Pa /var/log/wtmp
record of date resets and time changes
.It Pa /var/log/messages
record of the user setting the time
.El
.Sh SEE ALSO
.Xr gettimeofday 2 ,
.Xr strftime 3 ,
.Xr utmp 5 ,
.Xr timed 8
.Rs
.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
.%A R. Gusella
.%A S. Zatti
.Re
.Sh DIAGNOSTICS
Exit status is 0 on success, 1 if unable to set the date, and 2
if able to set the local date, but unable to set it globally.
.Pp
Occasionally, when
.Xr timed 8
synchronizes the time on many hosts, the setting of a new time value may
require more than a few seconds.
On these occasions,
.Nm
prints:
.Dq Network time being set .
The message
.Dq Communication error with timed
occurs when the communication
between
.Nm
and
.Xr timed 8
fails.
.Sh STANDARDS
The
.Nm
utility is expected to be compatible with
.St -p1003.2 .