Re: Daylight Savings Time and NTP

[Bruce Vining <bvining@xxxxxxxxxx>]

With V5R3 the SNTP client provided with i5/OS will, by default, adjust the
so called hardware/system clock (what QTIME uses).  In releases prior to
V5R3 the system provided SNTP client adjusted the software clock (not
QTIME).  The V5R3 Memo to Users does document how to continue to use the
software clock in V5R3 if that is desired.

Daylight saving time observance though is not tied to SNTP.  V5R3 also
introduces time zone (*TIMZON) objects where you can tell the system what
rules to follow for daylight saving time.  There are several *TIMZON
objects that for instance define the end of daylight savings time as being
at 2:00AM on the last Sunday of October.  This will cause QTIME to go from
02:00:00 to 01:00:01 (assuming granularity of a second) this coming Sunday
independent of whether or not you are using SNTP to synchronize your system
time with an external time source.  Incremental time adjustments really do
not apply here as the local govenment usually defines the change in time to
be instantaneous and not something to be done gradually through speeding up
or slowing down the clock.  QTIME will go backward one hour in this case
(and can cause problems for time sensitive applications).  On the other
hand applications written to use UTC time will not see the UTC time value
go backward.




                                                                           
             Wayne McAlpine                                                
             <wmcalpine@xxxxxx                                             
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                                       Re: Daylight Savings Time and NTP   
             10/28/2004 03:44                                              
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Does V5R3 support changing the hardware clock as well as the software
clock?  I bought a software package for about a hundred bucks that does
both.  Just wondering if I still need it.


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