Manual Pages  — DATE

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 input_fmt
	Use input_fmt as the format string to parse the new_date provided rather than using the default [[[[[cc ]yy ]mm ]dd ]HH]MM [amp;. file ...]format. Parsing is done using strptime(3).
-I [FMT]
	Use ISO/IEC output format. FMT may be omitted, in which case the default is date. Valid FMT values are date, hours, minutes, seconds, and ns (for nanoseconds). The date and time is formatted to the specified precision. When FMT is hours (or the more precise minutes, seconds, or ns ), the ISO/IEC 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 amp;%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. By default date displays the time in the time zone described by /etc/localtime or the TZ environment variable.
-z output_zone
	Just before printing the time, change to the specified timezone; see the description of TZ below. This can be used with -j to easily convert time specifications from one zone to another.
-v [+|-]val [y|m|w|d|H|M|S]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 by a plus or minus sign, the date is adjusted forward or backward 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 a limited range depending on the platform. On i386, years are in the range 69-38 representing 1969-2038. On every other platform, years 0-68 are accepted and represent 2000-2068, and 69-99 are accepted and represent 1969-1999. In both cases, years between 100 and 1900 (both included) are accepted and interpreted as relative to 1900 of the Gregorian calendar with a limit of 138 on i386 and a much higher limit on every other platform. Years starting at 1901 are also accepted, and are interpreted as absolute years. 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 forward 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 and ‘’ for nanoseconds, 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:

cc	Century (either 19 or 20) prepended to the abbreviated year.
yy	Year in abbreviated form (e.g., 89 for 1989, 06 for 2006).
mm	Numeric month, a number from 1 to 12.
dd	Day, a number from 1 to 31.
HH	Hour, a number from 0 to 23.
MM	Minutes, a number from 0 to 59.
file ...
	Seconds, a number from 0 to 60 (59 plus a potential leap second).

Everything but the minutes is optional.

date understands the time zone definitions from the IANA Time Zone Database, tzdata, located in /usr/share/zoneinfo. Time changes for Daylight Saving Time, standard time, leap seconds and leap years are handled automatically.

There are two ways to specify the time zone:

If the file or symlink /etc/localtime exists, it is interpreted as a time zone definition file, usually in the directory hierarchy /usr/share/zoneinfo, which contains the time zone definitions from tzdata.

If the environment variable TZ is set, its value is interpreted as the name of a time zone definition file, either an absolute path or a relative path to a time zone definition in /usr/share/zoneinfo. The TZ variable overrides /etc/localtime.

If the time zone definition file is invalid, date silently reverts to UTC.

Previous versions of date included the -d (set daylight saving time flag) and -t (set negative time zone offset) options, but these details are now handled automatically by tzdata. Modern offsets are positive for time zones ahead of UTC and negative for time zones behind UTC, but like the obsolete -t option, the tzdata files in the subdirectory /usr/share/zoneinfo/Etc still use an older convention where times ahead of UTC are considered negative.

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

Time Zone Database,