GNU bug report logs - #23008
Daylight Savings Time Bug in Date

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Sarah Corriher <sarah.c <at> healthwyze.org>
To: bug-coreutils <at> gnu.org
Subject: Daylight Savings Time Bug in Date
Date: Mon, 14 Mar 2016 01:24:40 -0400

[Message part 1 (text/plain, inline)]

We detected a bug in the date program, which correlates to the daylight 
savings time change. A day disappeared from the date program between 
12:00 AM and 1:00 AM on 3/14/16. The date program began working as 
expected immediately after 1:00 AM. Here is the bizarre output that I 
got for basic commands on 3/14/16:

   $ date -d -0days +%Y-%m-%d
   2016-03-14

   $ date -d -1days +%Y-%m-%d
   2016-03-12

Notice that I was unable to obtain the expected output of 2016-03-13 for 
the day prior. I was able to reproduce this using version 8.13 on 
Debian, and 8.21 on Mint.

-- 
Sarah C. Corriher
Co-author of "Defy Your Doctor and Be Healed"
336-528-4120
http://HealthWyze.org

We're Health Wyze. Have you told your friends about us?

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Message #12 received at 23008-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Sarah Corriher <sarah.c <at> healthwyze.org>, 23008-done <at> debbugs.gnu.org,
 GNU bug control <control <at> debbugs.gnu.org>
Subject: Re: bug#23008: Daylight Savings Time Bug in Date
Date: Mon, 14 Mar 2016 09:04:16 -0600

[Message part 1 (text/plain, inline)]

tag 23008 notabug
thanks

On 03/13/2016 11:24 PM, Sarah Corriher wrote:
> We detected a bug in the date program, which correlates to the daylight
> savings time change.

Thanks for the report.  However, this is not a bug, but a FAQ that gets
asked twice a year.  See:

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

> 
>    $ date -d -0days +%Y-%m-%d
>    2016-03-14
> 
>    $ date -d -1days +%Y-%m-%d
>    2016-03-12

When trying to add units of 24 hours (the -1days), only to then display
just a day and not an hour, it's best to start from noon rather than
from a time that might be impacted by daylight savings:

# date -d '12:00pm 2014-03-14 -1day' +%Y-%m-%d
2016-03-13

Otherwise, as you discovered, starting at midnight and going 24 hours
across a day with only 23 hours is likely to skip that day.

I'm closing this as not a bug, but feel free to reply with further
questions or comments.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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