Re: Network Time Protocol (NTP) client support question

-----Original Message-----
From: IBM Mainframe Discussion List On Behalf Of Paul Gilmartin

On Tue, 17 Jun 2008 12:57:39 -0700, Edward Jaffe wrote:

Paul Gilmartin wrote:
On Tue, 17 Jun 2008 08:27:18 -0700, Edward Jaffe wrote:

Keep in mind that the TOD clock represents GMT (or UTC).
Local time
is calculated by adjusting GMT by CVTLDTO and CVTLSO. If the TOD
drifts by a second or more, you can fix local time with a
compensating adjustment to the time zone offset. See SET
TIMEZONE= command.

Gaaaaaah! Since Good Practice dictates that critical
timestamps be
kept in UTC (or GMT) your suggestion more conceals the problem of
drift than fixes it.

The whole point of using UTC (or GMT) time stamps is to avoid issues
when the time zone offset is changed. For these logging
applications,
local time is irrelevant.

You seem to be saying that for those logging applications the
time stamp is a somewhat arbitrary parameter, increasing
monotonically, but whose offset and drift from true GMT don't
diminish its value.

A point of using UTC time stamps is correlating logs from the
z (e.g.) with logs from other systems in the enterprise,
possibly in different time zones. If the OP's requirement
includes agreement between UTC on the z and UTC on the other
systems, fudging the local time offset fails to satisfy it.

(I have long wondered whether correct UTC could be obtained
by fudging CVTLSO. I have not heard of this being done.)

How will this affect the time reported by z/OS Unix programs which
use time() to get UTC and strftime() to get civil time? How will
this affect Java applications?

I don't know how z/OS UNIX programs compute local time. If
they use a
technique that does not rely on CVTLDTO and CVTLSO, they are already
out-of-sync with the rest of the system.

POSIX defines UTC as primitive, and defines a relationship
from UTC to any other TZ (which can be chosen by the
individual user.) If the offset from UTC to any of those
zones is different from the POSIX specification, (perhaps by
an arbitrary value in CVTLDTO), "the system" is out of sync
with the rest of the industry.

What industry-wide standard specifies reliance on CVTLDTO and CVTLSO?

I have the possibly mistaken impression that time references provided by
the US government's "official time" sources already include the
adjustments for leap seconds. If that's true, then of what use is
CVTLSO?

-jc-

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