xref: /freebsd/bin/date/date.1 (revision 445ed7b40948c160f2f7d363d2d0ae1ffac4aabd)
1.\"-
2.\" Copyright (c) 1980, 1990, 1993
3.\"	The Regents of the University of California.  All rights reserved.
4.\"
5.\" This code is derived from software contributed to Berkeley by
6.\" the Institute of Electrical and Electronics Engineers, Inc.
7.\"
8.\" Redistribution and use in source and binary forms, with or without
9.\" modification, are permitted provided that the following conditions
10.\" are met:
11.\" 1. Redistributions of source code must retain the above copyright
12.\"    notice, this list of conditions and the following disclaimer.
13.\" 2. Redistributions in binary form must reproduce the above copyright
14.\"    notice, this list of conditions and the following disclaimer in the
15.\"    documentation and/or other materials provided with the distribution.
16.\" 4. Neither the name of the University nor the names of its contributors
17.\"    may be used to endorse or promote products derived from this software
18.\"    without specific prior written permission.
19.\"
20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30.\" SUCH DAMAGE.
31.\"
32.\"     @(#)date.1	8.3 (Berkeley) 4/28/95
33.\" $FreeBSD$
34.\"
35.Dd April 26, 2014
36.Dt DATE 1
37.Os
38.Sh NAME
39.Nm date
40.Nd display or set date and time
41.Sh SYNOPSIS
42.Nm
43.Op Fl jRu
44.Op Fl r Ar seconds
45.Oo
46.Fl v
47.Sm off
48.Op Cm + | -
49.Ar val Op Ar ymwdHMS
50.Sm on
51.Oc
52.Ar ...
53.Op Cm + Ns Ar output_fmt
54.Nm
55.Op Fl jnu
56.Sm off
57.Op Oo Oo Oo Oo Ar cc Oc Ar yy Oc Ar mm Oc Ar dd Oc Ar HH
58.Ar MM Op Ar .ss
59.Sm on
60.Nm
61.Op Fl jnRu
62.Fl f Ar input_fmt new_date
63.Op Cm + Ns Ar output_fmt
64.Nm
65.Op Fl d Ar dst
66.Op Fl t Ar minutes_west
67.Sh DESCRIPTION
68When invoked without arguments, the
69.Nm
70utility displays the current date and time.
71Otherwise, depending on the options specified,
72.Nm
73will set the date and time or print it in a user-defined way.
74.Pp
75The
76.Nm
77utility displays the date and time read from the kernel clock.
78When used to set the date and time,
79both the kernel clock and the hardware clock are updated.
80.Pp
81Only the superuser may set the date,
82and if the system securelevel (see
83.Xr securelevel 7 )
84is greater than 1,
85the time may not be changed by more than 1 second.
86.Pp
87The options are as follows:
88.Bl -tag -width Ds
89.It Fl d Ar dst
90Set the kernel's value for daylight saving time.
91If
92.Ar dst
93is non-zero, future calls
94to
95.Xr gettimeofday 2
96will return a non-zero for
97.Fa tz_dsttime .
98.It Fl f
99Use
100.Ar input_fmt
101as the format string to parse the
102.Ar new_date
103provided rather than using the default
104.Sm off
105.Oo Oo Oo Oo Oo
106.Ar cc Oc
107.Ar yy Oc
108.Ar mm Oc
109.Ar dd Oc
110.Ar HH
111.Oc Ar MM Op Ar .ss
112.Sm on
113format.
114Parsing is done using
115.Xr strptime 3 .
116.It Fl j
117Do not try to set the date.
118This allows you to use the
119.Fl f
120flag in addition to the
121.Cm +
122option to convert one date format to another.
123.It Fl n
124By default, if the
125.Xr timed 8
126daemon is running,
127.Nm
128sets the time on all of the machines in the local group.
129The
130.Fl n
131option suppresses this behavior and causes the time to be set only on the
132current machine.
133.It Fl R
134Use RFC 2822 date and time output format. This is equivalent to use
135.Dq Li %a, %d %b %Y \&%T %z
136as
137.Ar output_fmt
138while
139.Ev LC_TIME
140is set to the
141.Dq C
142locale .
143.It Fl r Ar seconds
144Print the date and time represented by
145.Ar seconds ,
146where
147.Ar seconds
148is the number of seconds since the Epoch
149(00:00:00 UTC, January 1, 1970;
150see
151.Xr time 3 ) ,
152and can be specified in decimal, octal, or hex.
153.It Fl t Ar minutes_west
154Set the system's value for minutes west of
155.Tn GMT .
156.Ar minutes_west
157specifies the number of minutes returned in
158.Fa tz_minuteswest
159by future calls to
160.Xr gettimeofday 2 .
161.It Fl u
162Display or set the date in
163.Tn UTC
164(Coordinated Universal) time.
165.It Fl v
166Adjust (i.e., take the current date and display the result of the
167adjustment; not actually set the date) the second, minute, hour, month
168day, week day, month or year according to
169.Ar val .
170If
171.Ar val
172is preceded with a plus or minus sign,
173the date is adjusted forwards or backwards according to the remaining string,
174otherwise the relevant part of the date is set.
175The date can be adjusted as many times as required using these flags.
176Flags are processed in the order given.
177.Pp
178When setting values
179(rather than adjusting them),
180seconds are in the range 0-59, minutes are in the range 0-59, hours are
181in the range 0-23, month days are in the range 1-31, week days are in the
182range 0-6 (Sun-Sat),
183months are in the range 1-12 (Jan-Dec)
184and years are in the range 80-38 or 1980-2038.
185.Pp
186If
187.Ar val
188is numeric, one of either
189.Ar y ,
190.Ar m ,
191.Ar w ,
192.Ar d ,
193.Ar H ,
194.Ar M
195or
196.Ar S
197must be used to specify which part of the date is to be adjusted.
198.Pp
199The week day or month may be specified using a name rather than a
200number.
201If a name is used with the plus
202(or minus)
203sign, the date will be put forwards
204(or backwards)
205to the next
206(previous)
207date that matches the given week day or month.
208This will not adjust the date,
209if the given week day or month is the same as the current one.
210.Pp
211When a date is adjusted to a specific value or in units greater than hours,
212daylight savings time considerations are ignored.
213Adjustments in units of hours or less honor daylight saving time.
214So, assuming the current date is March 26, 0:30 and that the DST adjustment
215means that the clock goes forward at 01:00 to 02:00, using
216.Fl v No +1H
217will adjust the date to March 26, 2:30.
218Likewise, if the date is October 29, 0:30 and the DST adjustment means that
219the clock goes back at 02:00 to 01:00, using
220.Fl v No +3H
221will be necessary to reach October 29, 2:30.
222.Pp
223When the date is adjusted to a specific value that does not actually exist
224(for example March 26, 1:30 BST 2000 in the Europe/London timezone),
225the date will be silently adjusted forwards in units of one hour until it
226reaches a valid time.
227When the date is adjusted to a specific value that occurs twice
228(for example October 29, 1:30 2000),
229the resulting timezone will be set so that the date matches the earlier of
230the two times.
231.Pp
232It is not possible to adjust a date to an invalid absolute day, so using
233the switches
234.Fl v No 31d Fl v No 12m
235will simply fail five months of the year.
236It is therefore usual to set the month before setting the day; using
237.Fl v No 12m Fl v No 31d
238always works.
239.Pp
240Adjusting the date by months is inherently ambiguous because
241a month is a unit of variable length depending on the current date.
242This kind of date adjustment is applied in the most intuitive way.
243First of all,
244.Nm
245tries to preserve the day of the month.
246If it is impossible because the target month is shorter than the present one,
247the last day of the target month will be the result.
248For example, using
249.Fl v No +1m
250on May 31 will adjust the date to June 30, while using the same option
251on January 30 will result in the date adjusted to the last day of February.
252This approach is also believed to make the most sense for shell scripting.
253Nevertheless, be aware that going forth and back by the same number of
254months may take you to a different date.
255.Pp
256Refer to the examples below for further details.
257.El
258.Pp
259An operand with a leading plus
260.Pq Sq +
261sign signals a user-defined format string
262which specifies the format in which to display the date and time.
263The format string may contain any of the conversion specifications
264described in the
265.Xr strftime 3
266manual page, as well as any arbitrary text.
267A newline
268.Pq Ql \en
269character is always output after the characters specified by
270the format string.
271The format string for the default display is
272.Dq +%+ .
273.Pp
274If an operand does not have a leading plus sign, it is interpreted as
275a value for setting the system's notion of the current date and time.
276The canonical representation for setting the date and time is:
277.Pp
278.Bl -tag -width Ds -compact -offset indent
279.It Ar cc
280Century
281(either 19 or 20)
282prepended to the abbreviated year.
283.It Ar yy
284Year in abbreviated form
285(e.g., 89 for 1989, 06 for 2006).
286.It Ar mm
287Numeric month, a number from 1 to 12.
288.It Ar dd
289Day, a number from 1 to 31.
290.It Ar HH
291Hour, a number from 0 to 23.
292.It Ar MM
293Minutes, a number from 0 to 59.
294.It Ar ss
295Seconds, a number from 0 to 61
296(59 plus a maximum of two leap seconds).
297.El
298.Pp
299Everything but the minutes is optional.
300.Pp
301Time changes for Daylight Saving Time, standard time, leap seconds,
302and leap years are handled automatically.
303.Sh ENVIRONMENT
304The following environment variables affect the execution of
305.Nm :
306.Bl -tag -width Ds
307.It Ev TZ
308The timezone to use when displaying dates.
309The normal format is a pathname relative to
310.Pa /usr/share/zoneinfo .
311For example, the command
312.Dq TZ=America/Los_Angeles date
313displays the current time in California.
314See
315.Xr environ 7
316for more information.
317.El
318.Sh FILES
319.Bl -tag -width /var/log/messages -compact
320.It Pa /var/log/utx.log
321record of date resets and time changes
322.It Pa /var/log/messages
323record of the user setting the time
324.El
325.Sh EXIT STATUS
326The
327.Nm
328utility exits 0 on success, 1 if unable to set the date, and 2
329if able to set the local date, but unable to set it globally.
330.Sh EXAMPLES
331The command:
332.Pp
333.Dl "date ""+DATE: %Y-%m-%d%nTIME: %H:%M:%S"""
334.Pp
335will display:
336.Bd -literal -offset indent
337DATE: 1987-11-21
338TIME: 13:36:16
339.Ed
340.Pp
341In the Europe/London timezone, the command:
342.Pp
343.Dl "date -v1m -v+1y"
344.Pp
345will display:
346.Pp
347.Dl "Sun Jan  4 04:15:24 GMT 1998"
348.Pp
349where it is currently
350.Li "Mon Aug  4 04:15:24 BST 1997" .
351.Pp
352The command:
353.Pp
354.Dl "date -v1d -v3m -v0y -v-1d"
355.Pp
356will display the last day of February in the year 2000:
357.Pp
358.Dl "Tue Feb 29 03:18:00 GMT 2000"
359.Pp
360So will the command:
361.Pp
362.Dl "date -v3m -v30d -v0y -v-1m"
363.Pp
364because there is no such date as the 30th of February.
365.Pp
366The command:
367.Pp
368.Dl "date -v1d -v+1m -v-1d -v-fri"
369.Pp
370will display the last Friday of the month:
371.Pp
372.Dl "Fri Aug 29 04:31:11 BST 1997"
373.Pp
374where it is currently
375.Li "Mon Aug  4 04:31:11 BST 1997" .
376.Pp
377The command:
378.Pp
379.Dl "date 8506131627"
380.Pp
381sets the date to
382.Dq Li "June 13, 1985, 4:27 PM" .
383.Pp
384.Dl "date ""+%Y%m%d%H%M.%S"""
385.Pp
386may be used on one machine to print out the date
387suitable for setting on another.
388.Qq ( Li "+%m%d%H%M%Y.%S"
389for use on
390.Tn Linux . )
391.Pp
392The command:
393.Pp
394.Dl "date 1432"
395.Pp
396sets the time to
397.Li "2:32 PM" ,
398without modifying the date.
399.Pp
400Finally the command:
401.Pp
402.Dl "date -j -f ""%a %b %d %T %Z %Y"" ""`date`"" ""+%s"""
403.Pp
404can be used to parse the output from
405.Nm
406and express it in Epoch time.
407.Sh DIAGNOSTICS
408Occasionally, when
409.Xr timed 8
410synchronizes the time on many hosts, the setting of a new time value may
411require more than a few seconds.
412On these occasions,
413.Nm
414prints:
415.Ql Network time being set .
416The message
417.Ql Communication error with timed
418occurs when the communication
419between
420.Nm
421and
422.Xr timed 8
423fails.
424.Sh SEE ALSO
425.Xr locale 1 ,
426.Xr gettimeofday 2 ,
427.Xr getutxent 3 ,
428.Xr strftime 3 ,
429.Xr strptime 3 ,
430.Xr timed 8
431.Rs
432.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
433.%A R. Gusella
434.%A S. Zatti
435.Re
436.Sh STANDARDS
437The
438.Nm
439utility is expected to be compatible with
440.St -p1003.2 .
441The
442.Fl d , f , j , n , r , t ,
443and
444.Fl v
445options are all extensions to the standard.
446.Sh HISTORY
447A
448.Nm
449command appeared in
450.At v1 .
451