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Operating Systems Linux How does Linux handle DST ( daylight saving time)? Post 302922090 by jim mcnamara on Wednesday 22nd of October 2014 10:11:38 AM
Old 10-22-2014
No. Linux uses epoch time - the number of seconds since Jan 1, 1970. Look at the very top right of the pages here on UNIX.com. Look for UNIX time. Currently it is 1413986703 seconds.

There is something called the C runtime library - all of the commands in UNIX use that library. Because people use differing locale settings (alphabetic characters, names for months, different ways od doing daylight savings times etc.) the guys who put this together decided to use some library calls to change the UNIX epoch seconds into human readable time, including changes from standard to daylight time.

ctime() and strftime() are part of that library. The date command uses the library and provides a command line interface for times and dates.

So if you are in a country with no daylight/standard time change, then date knows about it through your locale and timezone settings.
Type
Code:
echo "TZ is $TZ, locale is `locale`"

at the command line to see your settings.
 

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Template::Plugin::Date(3)				User Contributed Perl Documentation				 Template::Plugin::Date(3)

NAME
Template::Plugin::Date - Plugin to generate formatted date strings SYNOPSIS
[% USE date %] # use current time and default format [% date.format %] # specify time as seconds since epoch # or as a 'h:m:s d-m-y' or 'y-m-d h:m:s' string [% date.format(960973980) %] [% date.format('4:20:36 21/12/2000') %] [% date.format('2000/12/21 4:20:36') %] # specify format [% date.format(mytime, '%H:%M:%S') %] # specify locale [% date.format(date.now, '%a %d %b %y', 'en_GB') %] # named parameters [% date.format(mytime, format = '%H:%M:%S') %] [% date.format(locale = 'en_GB') %] [% date.format(time = date.now, format = '%H:%M:%S', locale = 'en_GB) %] # specify default format to plugin [% USE date(format = '%H:%M:%S', locale = 'de_DE') %] [% date.format %] ... DESCRIPTION
The "Date" plugin provides an easy way to generate formatted time and date strings by delegating to the "POSIX" "strftime()" routine. The plugin can be loaded via the familiar USE directive. [% USE date %] This creates a plugin object with the default name of '"date"'. An alternate name can be specified as such: [% USE myname = date %] The plugin provides the "format()" method which accepts a time value, a format string and a locale name. All of these parameters are optional with the current system time, default format ('"%H:%M:%S %d-%b-%Y"') and current locale being used respectively, if undefined. Default values for the time, format and/or locale may be specified as named parameters in the "USE" directive. [% USE date(format = '%a %d-%b-%Y', locale = 'fr_FR') %] When called without any parameters, the "format()" method returns a string representing the current system time, formatted by "strftime()" according to the default format and for the default locale (which may not be the current one, if locale is set in the "USE" directive). [% date.format %] The plugin allows a time/date to be specified as seconds since the epoch, as is returned by "time()". File last modified: [% date.format(filemod_time) %] The time/date can also be specified as a string of the form "h:m:s d/m/y" or "y/m/d h:m:s". Any of the characters : / - or space may be used to delimit fields. [% USE day = date(format => '%A', locale => 'en_GB') %] [% day.format('4:20:00 9-13-2000') %] Output: Tuesday A format string can also be passed to the "format()" method, and a locale specification may follow that. [% date.format(filemod, '%d-%b-%Y') %] [% date.format(filemod, '%d-%b-%Y', 'en_GB') %] A fourth parameter allows you to force output in GMT, in the case of seconds-since-the-epoch input: [% date.format(filemod, '%d-%b-%Y', 'en_GB', 1) %] Note that in this case, if the local time is not GMT, then also specifying '%Z' (time zone) in the format parameter will lead to an extremely misleading result. Any or all of these parameters may be named. Positional parameters should always be in the order "($time, $format, $locale)". [% date.format(format => '%H:%M:%S') %] [% date.format(time => filemod, format => '%H:%M:%S') %] [% date.format(mytime, format => '%H:%M:%S') %] [% date.format(mytime, format => '%H:%M:%S', locale => 'fr_FR') %] [% date.format(mytime, format => '%H:%M:%S', gmt => 1) %] ...etc... The "now()" method returns the current system time in seconds since the epoch. [% date.format(date.now, '%A') %] The "calc()" method can be used to create an interface to the "Date::Calc" module (if installed on your system). [% calc = date.calc %] [% calc.Monday_of_Week(22, 2001).join('/') %] The "manip()" method can be used to create an interface to the "Date::Manip" module (if installed on your system). [% manip = date.manip %] [% manip.UnixDate("Noon Yesterday","%Y %b %d %H:%M") %] AUTHORS
Thierry-Michel Barral wrote the original plugin. Andy Wardley provided some minor fixups/enhancements, a test script and documentation. Mark D. Mills cloned "Date::Manip" from the "Date::Calc" sub-plugin. COPYRIGHT
Copyright (C) 2000-2007 Thierry-Michel Barral, Andy Wardley. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. SEE ALSO
Template::Plugin, POSIX perl v5.16.3 2012-01-13 Template::Plugin::Date(3)
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