CICS and Daylight Savings Time

Time changes tonight, so it’s time to make sure that our CICS systems are in sync with the operating system clock when that occurs. The best way to accomplish this depends on the method that the operating system clock is set.

If your operating system clock is set as an offset from GMT, then all you will need to do for the operating system clock is to change the offset at the appropriate time. If you do so before midnight and you have AUTORESETTIME in your CICS SIT tables set to yes, you are done; at midnight, CICS’s will adjust their clocks. If you change the offset after midnight or do not have AUTORESETTIME set to yes (default is no), you will need to perform a CEMT PERFORM RESET for the CICS clocks to adjust.

If your operating system clock is set to the hardware clock and not to a GMT offset, then you are probably planning to perform a POR (power-on reset). If so, your CICS systems will have the correct time when they are brought up. You are probably having to let the system sit idle for an hour in the fall if you are performing a POR so that your applications do not encounter times that have already occured. If this is your standard mode of operation, you can make your life easier if you investigate having your operating system clock set as an offset from GMT time.

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2 responses to “CICS and Daylight Savings Time

  1. >If you do so before midnight and you have AUTORESETTIME in your CICS SIT tables set to yes, you are done; at midnight, CICS’s will adjust their clocks

    Well, but doesn’t that mean that from 2AM till midnight, you’re running with the wrong time in CICS? So it’s not “You are done”. I think.

  2. Zalman – Thanks for your comment. You have a good point. I did not mention that on the time change night, the hours between shortly before midnight and 2AM are not critical at our shop, so we actually set the GMT offset in z/OS before midnight, so the midnight adjustment done by AUTORESETTIME does the trick for us – otherwise, you are correct, the time would be off from 2AM until midnight.

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