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The Energy Policy Act of 2005 was passed by the United States Congress
on July 29, 2005 and signed into law on August 8, 2005.
This law extends Daylight Saving Time (DST) by four weeks, beginning in 2007
in the United States. Starting in March 2007, DST will begin on the second
Sunday in March and end on the first Sunday in November.
In addition to the U.S., Canada and Bermuda have decided to change their DST dates
in 2007 to follow the same time zone rules.
IBM has released updates to the z/OS operating systems to support
this change.
There are only three areas of the operating system that provide automated or
algorithmic changes to the local time based on the U.S. DST rules.
These are Language Environment, Distributed Computing Environment (DCE)
Base Services, and certain workstation tools within Resource Measurement Facility (RMF).
No other elements or features of the operating system are affected.
The following updates should be applied prior to March 11, 2007.
Other IBM and non-IBM products and applications that run on z/OS
may require updates and should be evaluated to determine the potential effect
of the DST change on the overall environment.
For IBM product information, visit the
IBM Daylight Saving Time alert page.
Language Environment changes
Language Environment
APAR PK24076
provides needed changes to the Time Zone (TZ)
environment variable.
PTFs for this APAR are available at various operating system releases including:
- z/OS V1.2 through z/OS V1.8
- z/OS.e V1.3 through z/OS.e V1.8
- OS/390 V2.10
The Language Environment element of z/OS provides support in the TZ and _TZ
environment variable that can be used by POSIX(ON) and POSIX(OFF) C/C++ applications,
respectively, to specify time zone information which may include rules for
Daylight Saving Time.
The default rules for Daylight Saving Time are based on U.S. rules, therefore
the z/OS C/C++ Run-Time Library needs to be updated to reflect the new rules.
The defaults are used only when TZ or _TZ specifies a daylight saving time zone
name that differs from the standard time zone name and the start and end dates
are omitted.
A full explanation of the TZ and _TZ environment variable and how time zone
information is processed by Language Environment is provided in the
z/OS XL C/C++ Programming Guide.
All applications that use TZ or _TZ that specifies a daylight saving time
zone name, but do not specify a DST rule, must be restarted after installing
this PTF in order for the new default rules to become effective.
For many, it may be simpler to re-IPL the system.
This allows every application that relies on the TZ (and _TZ) environment
variable to pick up the new DST rules.
Workaround:
If you do not have the opportunity to install this update or if you
are running on an out of support level of the operating system where a PTF is
not provided, you can get the same behavior of the extended DST by manually
changing the TZ or _TZ variable.
An example for the U.S. Central time zone follows:
TZ=CST6CDT,M3.2.0,M11.1.0
M3.2.0 means to observe DST starting in month 3 (March), week 2, and Day 0 (Sunday).
M11.1.0 means 1st Sunday in November and specifies when to end observing DST.
Possible locations where TZ or _TZ may be defined include the
Language Environment Installation Default Run-time Options
CSECTs (CEEDOPT, CEECOPT, CELQDOPT), the Language Environment
Region-Specific Options (CEEROPT), the Language Environment
PARMLIB member (CEEPRMxx), and, for the z/OS UNIX environment, in
/etc/profile, /etc/init.options, and /etc/rc.
In addition, the TZ and _TZ environment variable may be specified in individual
application configuration files.
In all cases where a change to TZ or _TZ is made, applications must be restarted.
Distributed Computing Environment (DCE) Base Services changes
DCE Base Services
APAR OA18692
provides needed changes to extend the
Daylight Saving Time for the U.S. and Canada.
PTFs for this APAR are available at various operating system releases including:
- z/OS V1.2 through z/OS V1.8
- z/OS.e V1.3 through z/OS.e V1.8
- OS/390 V2.10
Only DCE users that are NOT using the TZ environment variable (mentioned earlier)
for their DCE applications and/or DCE commands will need to install and apply this fix.
Resource Measurement Facility (RMF) tools changes
If you're using the following workstation tools:
- RMF Spreadsheet Reporter
- RMF Performance Monitoring (PM)
then you'll need to apply PTFs for the following APARs
for these z/OS releases:
After installing the respective PTFs, you'll need to download these tools from the
z/OS host server to the workstation where the tools execute.
Alternatively, instead of installing the PTFs, you can download the updated version
of the tools that contain the DST changes from the
RMF Web site.
Contact z/OS
Send us your questions and comments.
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