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AUTO_DLIGHT_SAV, Daylight Savings Time, DST?

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The Question is:

In the new features manual for 7.3 it mentions the new sysgen parameter
 AUTO_DLIGHT_SAV. The definition it gives is:
AUTO_DLIGHT_SAV is set to either 1 or 0. The default is 0.
If AUTO_DLIGHT_SAV is set to 1, OpenVMS automatically makes the change to and
 from daylight saving time.
Could you expand on how this takes place and if there are any other associated
 changes that might also need to be performed.
We currently use NTP and are looking for an automated way of changing time
 since now we have to execute the sys$examples:daylight_savings.com.
I checked in the FAQ but there was no mention of this new sysgen parameter.

The Answer is :

  A chapter on Time and Time-keeping exists within the OpenVMS System
  Manager's Manual, and the chapter includes a section on the automatic
  Daylight savings time (DST; AUTO_DLIGHT_SAV) mechanisms.  Please read
  and familiarize yourself with this information, as a start.
  When the DST switchover (if any) for the current timezone arrives,
  OpenVMS V7.3 and later -- when AUTO_DLIGHT_SAV is enabled -- will
  switch the system time forward or backward by the specified interval.
  The DST switchover does not drift the system time, as that is part of
  the definition of the change-over to or from DST.
  As of V7.3, OpenVMS has integrated the DTSS mechanisms into the base
  operating system.  As a result, OpenVMS, DECnet-Plus, the C run-time
  and other components and other layered products can now use a common
  timezone implementation.
  When the DST change occurs, applications that have requested notification
  of DST switchover will receive the associated event.  (For details on
  this DST notification, please see the system service reference manual
  documentation for the $set_system_event and the $clear_system_event
  services.)  Obviously, not all applications will have been recoded to
  request this notification.
  Applications that do not utilize the DST notification mechanisms may
  need to be restarted when the system time is altered -- this is why
  the AUTO_DLIGHT_SAV is disabled by default.  Changing the running system
  time forward or backward on-line -- as was stated back during the Y2K
  testing days -- has been known to perturb the operations of applications.
  Please ensure that you have the DST ECO (if any) and all mandatory ECO
  kits for the particular OpenVMS release of interest installed.  To find
  the mandatory ECO kits, please consider utilizing the available ECO
  search engine.  (The ECO search engine is referenced in the FAQ.)

answer written or last revised on ( 7-APR-2003 )

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