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DESCRIPTION

The date utility displays the date and time read from the kernel clock. When used to set the date and time, both the kernel clock and the hardware clock are updated.

Only the superuser may set the date, and if the system securelevel (see securelevel(7)) is greater than 1, the time may not be changed by more than 1 second.

The options are as follows:

-d dst

Set the kernel's value for daylight saving time. If dst is non-zero, future calls to gettimeofday(2) will return a non-zero for tz_dsttime.

-f

Use input_fmt as the format string to parse the new_date provided rather than using the default [[[[[cc]yy]mm]dd]HH]MM[.ss] format. Parsing is done using strptime(3).

-I[FMT]

Use ISO 8601 output format. FMT may be omitted, in which case the default is ‘date’. Valid FMT values are ‘date’, ‘hours’, ‘minutes’, and ‘seconds’. The date and time is formatted to the specified precision. When FMT is ‘hours’ (or the more precise ‘minutes’ or ‘seconds’), the ISO 8601 format includes the timezone.

-j

Do not try to set the date. This allows you to use the -f flag in addition to the + option to convert one date format to another.

-n

By default, if the timed(8) daemon is running, date sets the time on all of the machines in the local group. The -n option suppresses this behavior and causes the time to be set only on the current machine.

-R

Use RFC 2822 date and time output format. This is equivalent to using “%a, %d %b %Y %T %z” as output_fmt while LC_TIME is set to the “C” locale .

-r seconds

Print the date and time represented by seconds, where seconds is the number of seconds since the Epoch (00:00:00 UTC, January 1, 1970; see time(3)), and can be specified in decimal, octal, or hex.

-r filename

Print the date and time of the last modification of filename.

-t minutes_west

Set the system's value for minutes west of GMT. minutes_west specifies the number of minutes returned in tz_minuteswest by future calls to gettimeofday(2).

-u

Display or set the date in UTC (Coordinated Universal) time.

-v

Adjust (i.e., take the current date and display the result of the adjustment; not actually set the date) the second, minute, hour, month day, week day, month or year according to val. If 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.

When setting values (rather than adjusting them), seconds are in the range 0-59, minutes are in the range 0-59, hours are in the range 0-23, month days are in the range 1-31, week days are in the range 0-6 (Sun-Sat), months are in the range 1-12 (Jan-Dec) and years are in the range 80-38 or 1980-2038.

If val is numeric, one of either y, m, w, d, H, M or S must be used to specify which part of the date is to be adjusted.

The week day or month may be specified using a name rather than a number. If a name is used with the plus (or minus) sign, the date will be put forwards (or backwards) to the next (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.

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 honor daylight saving 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 -v +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 -v +3H will be necessary to reach October 29, 2:30.

When the date is adjusted to a specific value that does not actually exist (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 (for example October 29, 1:30 2000), the resulting timezone will be set so that the date matches the earlier of the two times.

It is not possible to adjust a date to an invalid absolute day, so using the switches -v 31d -v 12m will simply fail five months of the year. It is therefore usual to set the month before setting the day; using -v 12m -v 31d always works.

Adjusting the date by months is inherently ambiguous because a month is a unit of variable length depending on the current date. This kind of date adjustment is applied in the most intuitive way. First of all, date tries to preserve the day of the month. If it is impossible because the target month is shorter than the present one, the last day of the target month will be the result. For example, using -v +1m on May 31 will adjust the date to June 30, while using the same option on January 30 will result in the date adjusted to the last day of February. This approach is also believed to make the most sense for shell scripting. Nevertheless, be aware that going forth and back by the same number of months may take you to a different date.

Refer to the examples below for further details.

An operand with a leading plus (‘+’) 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 strftime(3) manual page, as well as any arbitrary text. A newline (‘\n’) character is always output after the characters specified by the format string. The format string for the default display is “+%+”.

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:

Everything but the minutes is optional.

Time changes for Daylight Saving Time, standard time, leap seconds, and leap years are handled automatically.

DATE: 1987-11-21
TIME: 13:36:16