Technical data

Setting System Time
6.5 Adjusting for Daylight Saving Time
If AUTO_DLIGHT_SAV is set to 1, an OpenVMS Alpha Version 7.3 (and later)
system automatically sets the time forward or back when local time changes
between daylight saving time and standard time.
If AUTO_DLIGHT_SAV is set to 0 (the default), OpenVMS does not automatically
change between daylight saving time and standard time.
The AUTO_DLIGHT_SAV parameter and the automatic changes between
daylight saving time and standard time are implemented only on OpenVMS
Alpha Version 7.3 and later.
For this to work correctly, you must set a time zone rule for your time zone.
See Section 6.2 for information about setting time zone rules on OpenVMS Alpha
Version 7.3 systems.
To enable or disable the automatic changing from standard time to daylight
saving time, you must modify AUTO_DLIGHT_SAV. See Chapter 15 for
information about modifying system parameters.
Note
Automatic changes between daylight saving time and standard time work
only on OpenVMS Alpha Version 7.3. Compaq recommends that you do
not enable automatic daylight saving time conversion on mixed-version or
mixed-architecture OpenVMS Clusters.
For details on manually adjusting for daylight saving time on OpenVMS Version
7.3 systems, see Section 6.5.2.
6.5.2 Manually Adjusting for Daylight Saving Time on OpenVMS Version 7.3
This section contains instructions for adjusting system time between standard
time and daylight saving time on OpenVMS Version 7.3 when DTSS is not in use.
Use these instruction for OpenVMS VAX Version 7.3 and for OpenVMS Alpha
Version 7.3 when automatic daylight saving time switching is disabled (system
parameter AUTO_DLIGHT_SAV is set to 0).
To adjust the local time to daylight saving time or standard time, invoke
command procedure SYS$EXAMPLES:DAYLIGHT_SAVINGS.COM to perform
both of the following tasks:
• Adjust the TDF
• Modify the local time by one hour forward or backward
DAYLIGHT_SAVINGS.COM allows you to perform either of the following actions:
• Make the changes immediately.
• Queue a batch job to make the changes at a future time. (This is the most
common use of this command procedure.)
DAYLIGHT_SAVINGS.COM creates a command procedure, DST$CHANGE.COM,
in the current directory. DST$CHANGE.COM can execute on the current node
only. To change the time for all nodes in an OpenVMS Cluster, DAYLIGHT_
SAVINGS.COM also creates command procedure DST$SYSMAN.COM that
executes DST$CHANGE.COM by executing a SYSMAN DO command. Note that
to change all nodes, you must run DAYLIGHT_SAVINGS.COM on a node that
has OpenVMS Alpha Version 7.3 installed.
6–14 Setting System Time