It depends.
If you have an external time source (or the hardware STP feature), this is 
probably automatic. Check your CLOCKxx members in SYS1.PARMLIB.

The other alternative is to manually issue a SET TZ  command at the appropriate 
time (either by automation or human).

For the record, all of the major subsystems (DB2, IMS, CICS, z/OS, Websphere, 
BMC..., Compuware... CA,,, ) I am aware of need no intervention to handle the 
time change.
The only remaining hurdle in most shops regarding time change is application 

For the Spring time change there is usually no issue, for the Fall time change, 
many shops go idle for 1 hour to prevent the possibility of duplicate time 
stamps (based on local time).


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf 
Of Charles Mills
Sent: Wednesday, February 21, 2018 6:46 PM
Subject: Two summer time change questions

First though, apologies for asking what perhaps has been covered before -- 
perhaps even asked by me. I am having no luck searching the archives. I search 
on CVTTZ and get no hits even though I have IBM-MAIN messages in my own Outlook 
that contain CVTTZ.

1. Humor a guy with almost no operations experience with the world's most 
newbie operations question. If you are a shop in North America, how will you 
"convert" your z/OS instances to summer time next month? Do you or does your 
console automation software have to enter a SET command, or does it happen 
automagically internally to z/OS on some pre-configured schedule? (I remember I 
had a P/390 back in the day and VM had an internal table that did the time 
change automagically but I recall I had to re-IPL OS/390 to pick up the change.)

2. When the above happens, will CVTTZ and CVTLDTO get updated on the fly? If I 
inspected them one second would I see an offset of, e.g., 8 hours (in TOD or 
"TOD-high word" format as appropriate) and if I inspected them a second later I 
would see 7 hours?


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