date/date.1

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  32 .\"     @(#)date.1      8.3 (Berkeley) 4/28/95
  33 .\" $FreeBSD: src/bin/date/date.1,v 1.72 2005/02/13 22:25:09 ru Exp $
  34 .\"
  35 .Dd August 16, 2007
  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 ju
  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 Ar mm Oc Ar dd Oc Ar HH
  58 .Ar MM Oo Oo Ar cc Oc Ar yy Oc Op Ar .ss
  59 .Sm on
  60 .Nm
  61 .Op Fl jnu
  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
  68 When invoked without arguments, the
  69 .Nm
  70 utility displays the current date and time.
  71 Otherwise, depending on the options specified,
  72 .Nm
  73 will set the date and time or print it in a user-defined way.
  74 .Pp
  75 The
  76 .Nm
  77 utility displays the date and time read from the kernel clock.
  78 When used to set the date and time,
  79 both the kernel clock and the hardware clock are updated.
  80 .Pp
  81 Only the superuser may set the date,
  82 and if the system securelevel (see
  83 .Xr securelevel 8 )
  84 is greater than 1,
  85 the time may not be changed by more than 1 second.
  86 .Pp
  87 The options are as follows:
  88 .Bl -tag -width Ds
  89 .It Fl d Ar dst
  90 Set the kernel's value for daylight saving time.
  91 If
  92 .Ar dst
  93 is non-zero, future calls
  94 to
  95 .Xr gettimeofday 2
  96 will return a non-zero for
  97 .Fa tz_dsttime .
  98 .It Fl f
  99 Use
 100 .Ar input_fmt
 101 as the format string to parse the
 102 .Ar new_date
 103 provided rather than using the default
 104 .Sm off
 105 .Oo Oo Oo
 106 .Ar mm Oc
 107 .Ar dd Oc
 108 .Ar HH Oc
 109 .Ar MM
 110 .Oo Oo
 111 .Ar cc Oc
 112 .Ar yy Oc Oo
 113 .Ar .ss Oc
 114 .Sm on
 115 format.
 116 Parsing is done using
 117 .Xr strptime 3 .
 118 .It Fl j
 119 Do not try to set the date.
 120 This allows you to use the
 121 .Fl f
 122 flag in addition to the
 123 .Cm +
 124 option to convert one date format to another.
 125 .It Fl n
 126 By default, if the
 127 .Xr timed 8
 128 daemon is running,
 129 .Nm
 130 sets the time on all of the machines in the local group.
 131 The
 132 .Fl n
 133 option suppresses this behavior and causes the time to be set only on the
 134 current machine.
 135 .It Fl r Ar seconds
 136 Print the date and time represented by
 137 .Ar seconds ,
 138 where
 139 .Ar seconds
 140 is the number of seconds since the Epoch
 141 (00:00:00 UTC, January 1, 1970;
 142 see
 143 .Xr time 3 ) ,
 144 and can be specified in decimal, octal, or hex.
 145 .It Fl t Ar minutes_west
 146 Set the system's value for minutes west of
 147 .Tn GMT .
 148 .Ar minutes_west
 149 specifies the number of minutes returned in
 150 .Fa tz_minuteswest
 151 by future calls to
 152 .Xr gettimeofday 2 .
 153 .It Fl u
 154 Display or set the date in
 155 .Tn UTC
 156 (Coordinated Universal) time.
 157 .It Fl v
 158 Adjust (i.e., take the current date and display the result of the
 159 adjustment; not actually set the date) the second, minute, hour, month
 160 day, week day, month or year according to
 161 .Ar val .
 162 If
 163 .Ar val
 164 is preceded with a plus or minus sign,
 165 the date is adjusted forwards or backwards according to the remaining string,
 166 otherwise the relevant part of the date is set.
 167 The date can be adjusted as many times as required using these flags.
 168 Flags are processed in the order given.
 169 .Pp
 170 When setting values
 171 (rather than adjusting them),
 172 seconds are in the range 0-59, minutes are in the range 0-59, hours are
 173 in the range 0-23, month days are in the range 1-31, week days are in the
 174 range 0-6 (Sun-Sat),
 175 months are in the range 1-12 (Jan-Dec)
 176 and years are in the range 80-38 or 1980-2038.
 177 .Pp
 178 If
 179 .Ar val
 180 is numeric, one of either
 181 .Ar y ,
 182 .Ar m ,
 183 .Ar w ,
 184 .Ar d ,
 185 .Ar H ,
 186 .Ar M
 187 or
 188 .Ar S
 189 must be used to specify which part of the date is to be adjusted.
 190 .Pp
 191 The week day or month may be specified using a name rather than a
 192 number.
 193 If a name is used with the plus
 194 (or minus)
 195 sign, the date will be put forwards
 196 (or backwards)
 197 to the next
 198 (previous)
 199 date that matches the given week day or month.
 200 This will not adjust the date,
 201 if the given week day or month is the same as the current one.
 202 .Pp
 203 When a date is adjusted to a specific value or in units greater than hours,
 204 daylight savings time considerations are ignored.
 205 Adjustments in units of hours or less honor daylight saving time.
 206 So, assuming the current date is March 26, 0:30 and that the DST adjustment
 207 means that the clock goes forward at 01:00 to 02:00, using
 208 .Fl v No +1H
 209 will adjust the date to March 26, 2:30.
 210 Likewise, if the date is October 29, 0:30 and the DST adjustment means that
 211 the clock goes back at 02:00 to 01:00, using
 212 .Fl v No +3H
 213 will be necessary to reach October 29, 2:30.
 214 .Pp
 215 When the date is adjusted to a specific value that does not actually exist
 216 (for example March 26, 1:30 BST 2000 in the Europe/London timezone),
 217 the date will be silently adjusted forwards in units of one hour until it
 218 reaches a valid time.
 219 When the date is adjusted to a specific value that occurs twice
 220 (for example October 29, 1:30 2000),
 221 the resulting timezone will be set so that the date matches the earlier of
 222 the two times.
 223 .Pp
 224 Adjusting the date by months is inherently ambiguous because
 225 a month is a unit of variable length depending on the current date.
 226 This kind of date adjustment is applied in the most intuitive way.
 227 First of all,
 228 .Nm
 229 tries to preserve the day of the month.
 230 If it is impossible because the target month is shorter than the present one,
 231 the last day of the target month will be the result.
 232 For example, using
 233 .Fl v No +1m
 234 on May 31 will adjust the date to June 30, while using the same option
 235 on January 30 will result in the date adjusted to the last day of February.
 236 This approach is also believed to make the most sense for shell scripting.
 237 Nevertheless, be aware that going forth and back by the same number of
 238 months may take you to a different date.
 239 .Pp
 240 Refer to the examples below for further details.
 241 .El
 242 .Pp
 243 An operand with a leading plus
 244 .Pq Sq +
 245 sign signals a user-defined format string
 246 which specifies the format in which to display the date and time.
 247 The format string may contain any of the conversion specifications
 248 described in the
 249 .Xr strftime 3
 250 manual page, as well as any arbitrary text.
 251 A newline
 252 .Pq Ql \en
 253 character is always output after the characters specified by
 254 the format string.
 255 The format string for the default display is
 256 .Dq +%+ .
 257 .Pp
 258 If an operand does not have a leading plus sign, it is interpreted as
 259 a value for setting the system's notion of the current date and time.
 260 The canonical representation for setting the date and time is:
 261 .Pp
 262 .Bl -tag -width Ds -compact -offset indent
 263 .It Ar cc
 264 Century
 265 (either 19 or 20)
 266 prepended to the abbreviated year.
 267 .It Ar yy
 268 Year in abbreviated form
 269 (e.g., 89 for 1989, 06 for 2006).
 270 .It Ar mm
 271 Numeric month, a number from 1 to 12.
 272 .It Ar dd
 273 Day, a number from 1 to 31.
 274 .It Ar HH
 275 Hour, a number from 0 to 23.
 276 .It Ar MM
 277 Minutes, a number from 0 to 59.
 278 .It Ar ss
 279 Seconds, a number from 0 to 61
 280 (59 plus a maximum of two leap seconds).
 281 .El
 282 .Pp
 283 Everything but the minutes is optional.
 284 .Pp
 285 Time changes for Daylight Saving Time, standard time, leap seconds,
 286 and leap years are handled automatically.
 287 .Sh ENVIRONMENT
 288 The following environment variables affect the execution of
 289 .Nm :
 290 .Bl -tag -width Ds
 291 .It Ev TZ
 292 The timezone to use when displaying dates.
 293 The normal format is a pathname relative to
 294 .Pa /usr/share/zoneinfo .
 295 For example, the command
 296 .Dq TZ=America/Los_Angeles date
 297 displays the current time in California.
 298 See
 299 .Xr environ 7
 300 for more information.
 301 .El
 302 .Sh FILES
 303 .Bl -tag -width /var/log/messages -compact
 304 .It Pa /var/log/messages
 305 record of the user setting the time
 306 .El
 307 .Sh EXIT STATUS
 308 The
 309 .Nm
 310 utility exits 0 on success, 1 if unable to set the date, and 2
 311 if able to set the local date, but unable to set it globally.
 312 .Sh EXAMPLES
 313 The command:
 314 .Pp
 315 .Dl "date ""+DATE: %Y-%m-%d%nTIME: %H:%M:%S"""
 316 .Pp
 317 will display:
 318 .Bd -literal -offset indent
 319 DATE: 1987-11-21
 320 TIME: 13:36:16
 321 .Ed
 322 .Pp
 323 In the Europe/London timezone, the command:
 324 .Pp
 325 .Dl "date -v1m -v+1y"
 326 .Pp
 327 will display:
 328 .Pp
 329 .Dl "Sun Jan  4 04:15:24 GMT 1998"
 330 .Pp
 331 where it is currently
 332 .Li "Mon Aug  4 04:15:24 BST 1997" .
 333 .Pp
 334 The command:
 335 .Pp
 336 .Dl "date -v1d -v3m -v0y -v-1d"
 337 .Pp
 338 will display the last day of February in the year 2000:
 339 .Pp
 340 .Dl "Tue Feb 29 03:18:00 GMT 2000"
 341 .Pp
 342 So will do the command:
 343 .Pp
 344 .Dl "date -v30d -v3m -v0y -v-1m"
 345 .Pp
 346 because there is no such date as the 30th of February.
 347 .Pp
 348 The command:
 349 .Pp
 350 .Dl "date -v1d -v+1m -v-1d -v-fri"
 351 .Pp
 352 will display the last Friday of the month:
 353 .Pp
 354 .Dl "Fri Aug 29 04:31:11 BST 1997"
 355 .Pp
 356 where it is currently
 357 .Li "Mon Aug  4 04:31:11 BST 1997" .
 358 .Pp
 359 The command:
 360 .Pp
 361 .Dl "date 0613162785"
 362 .Pp
 363 sets the date to
 364 .Dq Li "June 13, 1985, 4:27 PM" .
 365 .Pp
 366 .Dl "date ""+%m%d%H%M%Y.%S"""
 367 .Pp
 368 may be used on one machine to print out the date
 369 suitable for setting on another.
 370 .Pp
 371 The command:
 372 .Pp
 373 .Dl "date 1432"
 374 .Pp
 375 sets the time to
 376 .Li "2:32 PM" ,
 377 without modifying the date.
 378 .Pp
 379 Finally the command:
 380 .Pp
 381 .Dl "date -j -f ""%a %b %d %T %Z %Y"" ""`date`"" ""+%s"""
 382 .Pp
 383 can be used to parse the output from
 384 .Nm
 385 and express it in Epoch time.
 386 .Sh DIAGNOSTICS
 387 Occasionally, when
 388 .Xr timed 8
 389 synchronizes the time on many hosts, the setting of a new time value may
 390 require more than a few seconds.
 391 On these occasions,
 392 .Nm
 393 prints:
 394 .Ql Network time being set .
 395 The message
 396 .Ql Communication error with timed
 397 occurs when the communication
 398 between
 399 .Nm
 400 and
 401 .Xr timed 8
 402 fails.
 403 .Sh LEGACY SYNOPSIS
 404 As above, except for the second line, which is:
 405 .Pp
 406 .Nm
 407 .Op Fl jnu
 408 .Sm off
 409 .Op Oo Oo Oo Oo Ar cc Oc Ar yy Oc Ar mm Oc Ar dd Oc Ar HH
 410 .Ar MM Op Ar .ss
 411 .Sm on
 412 .Sh LEGACY DIAGNOSTICS
 413 When invoked in legacy mode, the following exit values are returned:
 414 .Bl -tag -width X -compact
 415 .It 0
 416 The date was written successfully
 417 .It 1
 418 Unable to set the date
 419 .It 2
 420 Able to set the local date, but unable to set it globally
 421 .El
 422 .Pp
 423 For more information about legacy mode, see
 424 .Xr compat 5 .
 425 .Sh SEE ALSO
 426 .Xr gettimeofday 2 ,
 427 .Xr strftime 3 ,
 428 .Xr strptime 3 ,
 429 .Xr utmpx 5 ,
 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
 437 The
 438 .Nm
 439 utility is expected to be compatible with
 440 .St -p1003.2 .
 441 .Sh HISTORY
 442 A
 443 .Nm
 444 command appeared in
 445 .At v1 .