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Document Information
| Document Number: | 443097604 |
| Functional Area: | Operating System |
| Subfunctional Area: | Programming |
| Sub-Subfunctional Area: | PASE (Portable Application Solutions Environment) |
| OS/400 Release: | V5R2M0; V5R3M0; V5R3M5; V5R4M0 |
| Product: | 400-33 PRIVAT ADR SP (5722SS1PA) 400-33 PRIVAT ADR SP (5769SS1PA) |
| Product Release: | N/A |
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Document Title
i5/OS PASE Programs Explicitly Setting TZ and Upcoming Changes to Daylight Savings Time in the United States
Document Description
Beginning in 2007, Daylight Savings Time will begin on the second Sunday in March and end on the first Sunday in November in the United States.
Programs using the IBM® i5/OS® PASE runtime determine their time zone based on the TZ environment variable. Since V5R3, i5/OS automatically sets the i5/OS PASE TZ environment variable based on the QTIMZON system value. If you are not explicitly specifying an i5/OS PASE time zone with the TZ or PASE_TZ environment variables, the rest of this document does not apply to you.
If you are explicitly specifying the i5/OS PASE time zone using the TZ or PASE_TZ environment variable, you might need to modify that value to reflect the new Daylight Savings Time start and end dates within the United States. Examples for the four most common US time zones follow:
| Time Zone | TZ Environment Variable Setting |
| Eastern US | TZ=EST5EDT,M3.2.0,M11.1.0 |
| Central US | TZ=CST6CDT,M3.2.0,M11.1.0 |
| Mountain US | TZ=MST7MDT,M3.2.0,M11.1.0 |
| Pacific US | TZ=PST8PDT,M3.2.0,M11.1.0 |
In the TZ environment variable examples above, the first three characters represent the name of the time zone when not observing Daylight Savings Time, such as EST for Eastern Standard Time. The first numeral to appear reflects the number of hours behind Coordinated Universal Time (UTC); for example, EST is 5 hours behind UTC. The next three characters represent the name of the time zone when observing Daylight Savings Time, such as EDT for Eastern Daylight Time. Following the time zone names is a comma-separated rule for when the location begins and ends observance of Daylight Savings Time:
| o | M3.2.0 means to begin observing Daylight Savings Time starting in month 3 (March), week 2, and Day 0 (Sunday), which is the second Sunday in March. |
| o | M11.1.0 means to end observing Daylight Savings Time on the first Sunday in November. Because no time is specified, the default is 02:00:00 for the time change. |
These examples correspond to the new US rules for 2007 and beyond. After it is updated, the TZ (or PASE_TZ) environment variable will not need to be adjusted again (unless a new law changes the rules again). Locations outside the US might need to set the rule to a different month or week number to reflect their own local Daylight Savings Time observances.
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