FW: glibc, Linux: about the time zone transition values in the lo calt ime file

Olson, Arthur David (NIH/NCI) olsona at dc37a.nci.nih.gov
Thu Feb 3 13:57:18 UTC 2005

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From: Fei Yuming-CYF001 [mailto:Yuming.Fei at motorola.com] 
Sent: Tuesday, February 01, 2005 4:14 PM
To: 'tz at elsie.nci.nih.gov'
Subject: glibc, Linux: about the time zone transition values in the localt
ime file

Dear Sir:
On Linux systems, it seems that the transitions stored in the localtime file
are not the current time to start the transition, but the new local current
time right after the transition.
For example, I have the glibc-2.2.5 library on my Linux 2.4.20 system, my
timezone is set to US/Central and my current time is in CST. The
/etc/localtime (or /usr/share/zoneinfo/US/Central) shows that in 2005, the
time to transfer into DST is 1112515200 seconds, i.e. Sun Apr 3 03:00:00
2005. (This can be got, e.g., by breaking into the
glibc-2.2.5/time/tzfile.c's __tzfile_read() function, and printing out the
transitions values, i.e. transitions[169] == 1112515200).
However, as we know, the transition to DST is Apr 3 02:00:00 --> Apr 3
03:00:00.  The time after the transition (i.e. 03:00:00) instead of the
current time to start the transition (ie.. 02:00:00) has been stored in the
localtime file. Could you please let me know what the reason it is to do so
(i.e. why not storing 02:00:00)?
I will highly appreciate your help!
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