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NAME

date — display or set date and time

SYNOPSIS

DESCRIPTION

When invoked without arguments, the date utility displays the current date and time. Otherwise, depending on the options specified, date will set the date and time or print it in a user-defined way.

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:

-f

Use input_fmt as the format string to parse the new_date provided rather than using the default [[[mm]dd]HH]MM[[cc]yy][.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. Note that any date or time components unspecified by the -f format string take their values from the current time.

-n

Obsolete flag, accepted and ignored for compatibility.

-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.

-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.

ENVIRONMENT

The following environment variables affect the execution of date:

TZ

The timezone to use when displaying dates. The normal format is a pathname relative to /usr/share/zoneinfo. For example, the command “TZ=America/Los_Angeles date” displays the current time in California. See environ(7) for more information.

FILES

/var/log/messages

record of the user setting the time

EXIT STATUS

The date 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.

EXAMPLES

The command:

will display:

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

In the Europe/London timezone, the command:

will display:

where it is currently Mon Aug 4 04:15:24 BST 1997.

The command:

will display the last day of February in the year 2000:

So will the command:

because there is no such date as the 30th of February.

The command:

will display the last Friday of the month:

where it is currently Mon Aug 4 04:31:11 BST 1997.

The command:

sets the date to “June 13, 1985, 4:27 PM”.

may be used on one machine to print out the date suitable for setting on another.

The command:

sets the time to 2:32 PM, without modifying the date.

The command

will display

Finally the command:

can be used to parse the output from date and express it in Epoch time.

DIAGNOSTICS

It is invalid to combine the -I flag with either -R or an output format (“+...”) operand. If this occurs, date prints: ‘multiple output formats specified’ and exits with an error status.

LEGACY SYNOPSIS

As above, except for the second line, which is:

date [-jnu] [[[[[cc]yy]mm]dd]HH]MM[.ss]

For more information about legacy mode, see compat(5).

SEE ALSO

locale(1), gettimeofday(2), getutxent(3), strftime(3), strptime(3)

R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX 4.3BSD.

STANDARDS

The date utility is expected to be compatible with IEEE Std 1003.2 (“POSIX.2”). The -d, -f, -I, -j, -r, -t, and -v options are all extensions to the standard.

The format selected by the -I flag is compatible with ISO 8601.

HISTORY

A date command appeared in Version 1 AT&T UNIX.

The -I flag was added in FreeBSD 12.0.