2007 Daylight Savings Time Changes for Unix

In 2005, the United States congress passed the Energy Policy Act of 2005, which among other things extended the duration of Daylight Savings Time in United States, starting in 2007. Canada and Bermuda have followed suit.

The problem is that, during the extended periods of three weeks in the spring and one week in the fall, many clocks on systems which automatically to change to and from Daylight Savings Time will continue to operate on Standard Time, even though Daylight Time is actually in effect. These uncorrected systems will not be synchronized with other systems which have been fixed.

This page tells you how to correct that, so that the automatic Daylight Time changes take place on the correct date.

We have until March 11, 2007 to fix this problem in the U.S. and Canada.

• Daylight Saving Time updates to Linux operating systems for year 2007 IBM web page that covers patches for Red Hat Linux, Novel SUSE Linux, and changes to JAVA that affect both. Lots of good links.
• Red Hat Linux Daylight Savings Time Changes Note that this web page contains links dealing with problems in both IBM Java and Sun Java.
• U.S. Daylight Saving Time (DST) default dates changing in 2007 and its impact on Novell SUSE Linux Enterprise products
• Linux can also be updated by following the instructions "How to build the Unix Zoneinfo Time Zone Files Manually" contained in 2007 DST Changes and Impacts on Computers
• You can also fix Linux by overriding the setting of the TZ environment variable:
  TZ=CST6CDT,M3.2.0,M11.1.0
  This should be regarded as a temporary measure until you can load updated Zoneinfo data files.

1. Apply correcting APARs from IBM for the latest supported versions
2. Modify the TZ variable in the /etc/environment file.

Note that all of the patches mentioned in this section can be applied at once to AIX by updating to level 5300-05-05.

The TZ variable method might be preferable where you do not want to change or update anything else; you just want to fix the Daylight Time change dates. Setting the TZ environment variable should be regarded as a temporary measure until more permanent patches can be installed. Both methods are described on these IBM web pages:

• AIX O/S updated to support 2007 Daylight Saving Time change
• IBM AIX: Managing the Time Zone Variable

AIX also contains time zone information in directory /usr/share/lib/zoneinfo which is used only by the zdump command. This information is not used by any other parts of the system itself, though it is used by the MySQL database system, and possibly other application programs. The following IBM APARs address these Unix Zoneinfo data files to insure that the zdump command will return correct output:

• APAR IY91662 for AIX 5.3. This will provide fileset bos.rte.date.5.3.0.51. This APAR is also included in level 5300-05-05.
• APAR IY91985 for AIX 5.2. This will provide fileset bos.rte.date.5.2.0.41.
• The zdump command and the /usr/share/lib/zoneinfo data did not exist in AIX prior to 5.2.

Be sure not to ignore the additional issues in IBM Java, described here:
Changes to Daylight Saving Time will affect IBM Java and AIX

There are four issues highlighted in that article:

1. Unix Timezone data needs to be updated. If solaris patches cannot be installed, you can also temporarily set the TZ environment variable: TZ=CST6CDT,M3.2.0,M11.1.0
2. Some Sun mid-range servers require firmware patches to correct the system controller.
   Sun Alert ID: 102617 - Required Server Firmware for Timezone Changes Due to U.S. Energy Policy Act of 2005
3. Patches to the Rogue Wave Tools.h++ library that is included with Sun C++ are at Sun Alert 102754
4. Java issues, described at Overview and Mitigation of the USA2007DST Issue for the Java SE platform and Solaris OS

The notes under 3. General Considerations on the introduction page. Various information there applies to Unix.