[svlug] revised timezone info posted Feb 26

[Sameer Verma]

Brian J. Tarricone wrote:
> On Thu, 01 Mar 2007 11:30:48 -0800 Rick Kwan wrote:
>
>   
>> I just updated my machine at work for the new Daylight Savings Time,
>> which starts March 11, and ran into a little surprise along the way.
>> Many web pages
>> say to grab the new timezone file via:
>>    wget ftp://elsie.nci.nih.gov/pub/tzdata2007b.tar.gz
>> That file no longer exists; it has been replaced by
>> 'tzdata2007c.tar.gz'. Internally, it looks like 'northamerica' was
>> updated on Feb. 26, 2007.
>>
>> There is an article at TechRepublic:
>>    http://articles.techrepublic.com.com/5100-10877_11-6163042.html
>> which shows the following example for Mountain Time after update.
>> --------
>> /etc/localtime  Sun Mar 11 08:59:59 2007 UTC = Sun Mar 11 02:59:59
>> 2007 MST isdst=0 gmtoff=-25200
>> /etc/localtime  Sun Mar 11 09:00:00 2007 UTC = Sun Mar 11 04:00:00
>> 2007 MDT isdst=1 gmtoff=-21600
>> /etc/localtime  Sun Nov  4 07:59:59 2007 UTC = Sun Nov  4 02:59:59
>> 2007 MDT isdst=1 gmtoff=-21600
>> /etc/localtime  Sun Nov  4 08:00:00 2007 UTC = Sun Nov  4 02:00:00
>> 2007 MST isdst=0 gmtoff=-25200
>> --------
>>
>> But when I execute the following command for Mountain Time
>>    /usr/sbin/zdump -v /usr/share/zoneinfo/MST7MDT | grep 2007
>> I get something different:
>> --------
>> /usr/share/zoneinfo/MST7MDT  Sun Mar 11 08:59:59 2007 UTC = Sun Mar 11 
>> 01:59:59 2007 MST isdst=0 gmtoff=-25200
>> /usr/share/zoneinfo/MST7MDT  Sun Mar 11 09:00:00 2007 UTC = Sun Mar 11 
>> 03:00:00 2007 MDT isdst=1 gmtoff=-21600
>> /usr/share/zoneinfo/MST7MDT  Sun Nov  4 07:59:59 2007 UTC = Sun Nov  4 
>> 01:59:59 2007 MDT isdst=1 gmtoff=-21600
>> /usr/share/zoneinfo/MST7MDT  Sun Nov  4 08:00:00 2007 UTC = Sun Nov  4 
>> 01:00:00 2007 MST isdst=0 gmtoff=-25200
>> --------
>> Note the assignments of UTC to MST.  The two sets of results
>> differ by an hour, but "gmtoff" is unchanged.
>>
>> I assume that Linux basically ignores local time, and runs all its time
>> services off of UTC.  If that's not true, then things might be really
>> interesting. :-)
>>
>> Anyone have better insight into this?
>>     
>
> The difference between the two isn't in the offset, it's in the time
> that the switch occurs.  The TechRepublic example has the time change
> wait until 3am, at which time your clock will jump forward to 4am
> (which I believe is incorrect).
>
>   
I can attest to this. It switches from 1:59:59 am to 3:00:00 am. I was 
awake, doing some work, so I actually saw it change that way :-)

Sameer
> The one you downloaded for your system will jump to 3am when your clock
> hits 2am.  My understanding is that this case is correct.  At least,
> according to Wikipedia[1], "the time is adjusted at 2 AM local time."
>
> For what it's worth, the PST8PDT zone info file on my system (Gentoo)
> seems to agree with yours (switching at 2am).
>
> 	-brian
>
> [1]http://en.wikipedia.org/wiki/Daylight_saving_time_around_the_world#United_States
>
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