The switch to daylight savings time

[Andy Piziali]

Israel, thank you for the detailed explanation of how UNIX systems typically
track the date, time, and daylight savings time (DST).  I have a related
question because my system failed to change to DST last weekend.

I am running IBM Xenix 1.0, a Microsoft Xenix 3.0 derivative, and noticed that
the kernel didn't switch to DST.  I expected the "date" program to report "CDT"
because my TZ environment variable has the value "CST6CDT."  A little bit of
investigation revealed that the kernal had been built with a "master" file
whose "daylight" entry was zero, indicating DST was not to be used.

I rebuilt the kernel with "daylight DSTFLAG 1" in the /usr/sys/conf/master file
and "date" still doesn't report "CDT."  I verified that the kernel's dstflag
is now set using the ftime(2) system call.

My question is: are the two dates which delimit the period of the year DST is
in effect hard coded into the kernel and could these dates have differed from
the current dates at the time this Xenix was written?  I believe the kernel was
last altered in 1983 or 1984.  What else should I look at to find out why Xenix
is not enabling DST?
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