GNU bug report logs - #16606
date command throws error when DST is turned on

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From: "Lakshmi Ramamurthi -X (lramamur - HCL TECHNOLOGIES LIMITED at Cisco)"
 <lramamur <at> cisco.com>
To: Bob Proulx <bob <at> proulx.com>
Cc: "16606 <at> debbugs.gnu.org" <16606 <at> debbugs.gnu.org>
Subject: bug#16606: date command throws error when DST is turned on
Date: Fri, 31 Jan 2014 07:56:35 +0000

Thanks a lot for your quick reply.

-Lakshmi

-----Original Message-----
From: Bob Proulx [mailto:bob <at> proulx.com] 
Sent: Friday, January 31, 2014 12:47 PM
To: Lakshmi Ramamurthi -X (lramamur - HCL TECHNOLOGIES LIMITED at Cisco)
Cc: 16606 <at> debbugs.gnu.org
Subject: Re: bug#16606: date command throws error when DST is turned on

tag 16606 +notabug
close 16606
thanks

Lakshmi Ramamurthi -X (lramamur - HCL TECHNOLOGIES LIMITED at Cisco) wrote:
> The date command throws error when the DST is turned on.
> 
> # date +%s -d "2013/11/20"
> 1384912800
> # date +%s -d "2013/10/20"
> date: invalid date `2013/10/20'
>
> 1 sec after Oct 19 23:59:59 2013 becomes Oct 20 01:00:00 2013 As there 
> is no 0th hour on Oct 20, it shows invalid date.

You are completely correct that there is no midnight in your timezone and therefore the date you are requesting *in your timezone* does not exist and therefore it is an invalid date.  The date command is working correctly in reporting it as an invalid date.  I will emphasize that this is timezone specific behavior.

> Are there any options to fix this problems ?
> Has there been a patch posted for this.

The option to fix this is the -u option to select UTC.  No patches are needed.

The best choice is to work with dates in the UTC timezone which avoids all DST issues since UTC never changes and never skips seconds.  The second best choice is to work with times around noon which avoids DST time changes that usually happen at night.  These hints are discussed in the FAQ entry in more detail.

You didn't say what specific timezone you were concerned with so I will pick one at random for an example.

  $ env TZ=America/Sao_Paulo date -R -d "2013/10/20"
  date: invalid date ‘2013/10/20’

That date at midnight does not exist in that timezone.

  $ env TZ=America/Sao_Paulo date -R -d "2013/10/20 12:00"
  Sun, 20 Oct 2013 12:00:00 -0200

Using 12:00 noon avoids the skipped interval.

  $ date -u -R -d "2013/10/20"
  Sun, 20 Oct 2013 00:00:00 +0000

Using UTC avoids the problem because UTC doesn't skip intervals for DST.  I also didn't show setting a default timezone (TZ) because that is also not matter when using UTC.  It is just simpler all around.

Please see the FAQ entry where this is explained in detail.

  http://www.gnu.org/software/coreutils/faq/coreutils-faq.html#The-date-command-is-not-working-right_002e

Bob

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