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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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Time(3pm)						  LogReport's Lire Documentation						 Time(3pm)

NAME
Lire::Time - parses and prints date in formats common to many log files. SYNOPSIS
use Lire::Time qw/ syslog2cal /; my @ltime = localtime; while ( <LOGFILE> ) { #... my $time = syslog2cal( $m, $d, $t, @ltime ); } DESCRIPTION
This module supplies many functions to parse dates in formats that you are likely to encounter in log files. It also offers many functions to format epoch time in useful format. NOTE ABOUT FUNCTION EXPORT Altough all documented functions are exported by default to the caller namespace, you should explicitely import the functions you require since exporting by default isn't recommanded by the perl modules guidelines. DATE PARSING FUNCTIONS
This module includes several functions that convert between a more human readable date format and UNIX epoch time. All parsing functions will return the number of seconds since Jan 1 1970 00:00:00 UTC and will die() when passed invalid arguments. date2cal() my $time = date2cal( $year, $month, $day, $time, [$timezone] ); my $time = date2cal( "2001 Mar 20 09:32:29 +0100" ); This function will convert a date in the date(1) default output format to UNIX epoch time. The function accepts either the date in a string or splitted on whitespace. If the timezone component is omitted, the local timezone is assumed (usually based on the value of the TZ environment variable). syslog2cal() my $time = syslog2cal( $month, $day, $time, $local_tm_ref ); my $time = syslog2cal( "Mar 11 13:21:00", $local_tm_ref ); This function will convert a date in the syslog default output format to UNIX epoch time. The function accepts either the date in a string or splitted on whitespace. Since the syslog format doesn't contain timezone information, the local timezone is assumed (usually determined by the TZ environment variable). The last argument is a reference to an array returned by localtime(). my $local_tm_ref = [localtime()]; It is used to determine the year. clf2cal() my $time = clf2cal( "[18/Mar/2001:15:59:30 +0100]" ); This function will convert a date as found in Common Log Format to UNIX epoch time. DATE FORMATING FUNCTIONS
This module includes some functions to convert date in UNIX epoch time to some more human readable output. All functions will die() when passed invalid arguments. cal2rfc() print cal2rfc( $time ); This function will convert a date in UNIX epoch time to the RFC822 format (used in email, for example). A RFC822 date looks like Wed, 30 May 2001 12:45:13 +0000 The timezone offset specification will correspond to the local timezone (usually determined by the TZ environment variable). cal2ymdhms() print cal2ymdhms( $time ); This function converts a date in UNIX epoch time to a string of the form: YYYYMMDDHHMMSS This representation will correspond the time in the local timezone (usually determined by the TZ environment variable.) getMonthName() print getMonthName( 0 ); # Gives 'Jan' This function takes as parameter a number (0-11) representing the month (as returned by localtime() for example) and will return the English abbreviated name of that month ( Jan, Feb, etc. ). AUTHOR
Joost van Baal <joostvb@logreport.org> VERSION
$Id: Time.pm,v 1.10 2006/07/23 13:16:30 vanbaal Exp $ COPYRIGHT
Copyright (C) 2000-2002 Stichting LogReport Foundation LogReport@LogReport.org This file is part of Lire. Lire is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program (see COPYING); if not, check with http://www.gnu.org/copyleft/gpl.html. Lire 2.1.1 2006-07-23 Time(3pm)
All times are GMT -4. The time now is 05:01 AM.
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