glibc, Linux: about the time zone transition values in the localt ime file

Tue Feb 1 21:14:01 UTC 2005

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!
Yuming 
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