freebsd-skq/bin/date/date.1

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.\"     @(#)date.1	8.3 (Berkeley) 4/28/95
.\" $FreeBSD$
.\"
.Dd November 17, 1993
.Dt DATE 1
.Os
.Sh NAME
.Nm date
.Nd display or set date and time
.Sh SYNOPSIS
.Nm date
.Op Fl jnu
.Op Fl d Ar dst
.Op Fl r Ar seconds
.Op Fl t Ar minutes_west
.Oo
.Fl v
.Op +|- Ns
.No val Ns Op ymwdHMS
.Oc Ns ...
.Oo Fl f No " "
.Ar fmt date No |
.Oo Oo Oo Oo Oo "\&cc" Ns
.Oc "\&yy" Oc "\&mm" Oc "\&dd" Oc "\&HH" Ns
.Oc
.No "\&MM" Ns Op "\&.ss"
.Oc
.Op Cm + Ns Ar format
.Sh DESCRIPTION
.Nm Date
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
Set the kernel's value for daylight savings time.
If
.Ar dst
is non-zero, future calls
to
.Xr gettimeofday 2
will return a non-zero
.Ql tz_dsttime  .
.It Fl f
Use
.Ar fmt
as the format string to parse the date provided rather than using
the default
.\" .Ar [[[[[cc]yy]mm]dd]HH]MM[.ss]
.Xo
.Oo Oo Oo Oo Oo "\&cc" Ns
.Oc "\&yy" Oc "\&mm" Oc "\&dd" Oc "\&HH" Ns
.Oc
.No "\&MM" Ns Op "\&.ss" Xc
format.  Parsing is done using
.Xr strptime 3 .
.It Fl j
Do not try to set the date.  This allows you to use the
.Fl f
flag in addition to the
.Cm +
option to convert one date format to another.
.It Fl n
The utility
.Xr timed 8
is used to synchronize the clocks on groups of machines.
By default, if
.Xr timed
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
Print out the date and time that is
.Ar seconds
from the Epoch
.Po
00:00:00 UTC, January 1, 1970;
see
.Xr time 3
.Pc .
.It Fl t
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
.Pq universal
time.
.It Fl v
Adjust the second, minute, hour, month day, week day, month or year according to
.Ar val .  
If
.Ar val
is preceded with a plus or minus sign, the date is adjusted forwards
or backwards according to the remaining string, otherwise the relevant
part of the date is set.  The date can be adjusted as many times as
required using these flags.  Flags are processed in the order given.
.Pp
When setting values
.Pq rather than adjusting them ,
seconds are in the range 0-59, minutes are in the range 0-59, hours are
in the range 1-12, month days are in the range 1-31, week days are in the
range 0-6
.Pq Sun-Sat ,
months are in the range 1-12
.Pq Jan-Dec
and years are in the range 80-38 or 1980-2038.
.Pp
If
.Ar val
is numeric, one of either
.Ar y ,
.Ar m ,
.Ar w ,
.Ar d ,
.Ar H ,
.Ar M
or
.Ar S
must be used to specify which part of the date is to be adjusted.
.Pp
The week day or month may be specified using a name rather than a
number.  If a name is used with the plus
.Pq or minus
sign, the date will be put forwards
.Pq or backwards
to the next
.Pq previous
date that matches the given week day or month.  This will not adjust the date
if the given week day or month is the same as the current one.
.Pp
When a date is adjusted to a specific value or in units greater than hours,
daylight savings time considerations are ignored.
Adjustments in units of hours or less honour daylight savings time.
So, assuming the current date is March 26, 0:30 and that the DST adjustment
means that the clock goes forward at 01:00 to 02:00, using
.Fl v No +1H
will adjust the date to March 26, 2:30.
Likewise, if the date is October 29, 0:30 and the DST adjustment means that
the clock goes back at 02:00 to 01:00, using
.Fl v No +3H
will be necessary to reach October 29, 2:30.
.Pp
When the date is adjusted to a specific value that doesn't actually exist
.Pq for example March 26, 1:30 BST 2000 in the Europe/London timezone ,
the date will be silently adjusted forwards in units of one hour until it
reaches a valid time.
When the date is adjusted to a specific value that occurs twice
.Pq for example October 29, 1:30 2000 ,
the resulting timezone will be set so that the date matches the earlier of
the two times.
.Pp
Refer to the examples below for further details.
.El
.Pp
An operand with a leading plus
.Pq Dq \&+
sign 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
.Dq +%+ .
.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 cc
Century
.Pq either 19 or 20
prepended to the abbreviated year.
.It Ar yy
Year in abbreviated form
.Pq e.g. 89 for 1989, 06 for 2006 .
.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
Minutes, a number from 0 to 59.
.It Ar .ss
Seconds, a number from 0 to 61
.Pq 59 plus a maximum of two leap seconds .
.El
.Pp
Everything but the minutes is optional.
.Pp
Time changes for Daylight Saving and Standard time and leap seconds
and 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
In the Europe/London timezone, the command:
.Bd -literal -offset indent
date -v1m -v+1y
.Ed
.Pp
will display:
.Bd -literal -offset indent
Sun Jan  4 04:15:24 GMT 1998
.Ed
.Pp
where it is currently Mon Aug  4 04:15:24 BST 1997.
.Pp
The command:
.Bd -literal -offset indent
date -v1d -v3m -v0y -v-1d
.Ed
.Pp
will display the last day of February in the year 2000:
.Bd -literal -offset indent
Tue Feb 29 03:18:00 GMT 2000
.Ed
.Pp
The command:
.Bd -literal -offset indent
date -v1d -v+1m -v-1d -v-fri
.Ed
.Pp
will display the last Friday of the month:
.Bd -literal -offset indent
Fri Aug 29 04:31:11 BST 1997
.Ed
.Pp
where it is currently Mon Aug  4 04:31:11 BST 1997.
.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 execution of
.Nm
is affected by the following environment variables:
.Bl -tag -width Ds
.It Ev TZ
The timezone to use when displaying dates.
The normal format is a pathname relative to
.Pa /usr/share/zoneinfo .
For example, the command
.Dq TZ=America/Los_Angeles date
displays the current time in California.
See
.Xr environ 7
for more information.
.El
.Sh FILES
.Bl -tag -width /var/log/messages -compact
.It Pa /var/log/wtmp
a record of date resets and time changes
.It Pa /var/log/messages
a record of the user setting the time
.El
.Sh SEE ALSO
.Xr gettimeofday 2 ,
.Xr strftime 3 ,
.Xr strptime 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
The
.Nm
utility exits 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
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:
.Ql Network time being set .
The message
.Ql Communication error with timed
occurs when the communication
between
.Nm
and
.Xr timed
fails.
.Sh STANDARDS
The
.Nm
command is expected to be compatible with
.St -p1003.2 .
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .