skip book previous and next navigation links
go up to top of book: HP OpenVMS System Manager's Manual, Volume 1:... HP OpenVMS System Manager's Manual, Volume 1:...
go to beginning of chapter: Setting System Time Setting System Time
 
go to next page: Setting Time Zone Information on OpenVMS Alpha Version 7.3 and Later and on OpenVMS I64 SystemsSetting Time Zone Information on OpenVMS Alpha Version 7.3 and...
end of book navigation links

Setting Correct Time Zone Information on Your System  



Beginning with OpenVMS Version 7.0, Compaq C RTL implements its default date/time support for programs compiled with HP C Version 5.2 and later using a model based on Coordinated Universal Time (UTC), an international standard for measuring time of day.
NoteEven if you do not use the HP C RTL directly, you must set correct time zone information on your system because other system utilities written in the HP C language might require it.

Distributed Time Synchronization Service (DTSS)  

Your system may be using Distributed Time Synchronization Service (DTSS). DTSS is provided as an option with DECnet-Plus and the Distributed Computing Environment (DCE). If you are using DTSS, you must not use the procedures described in this chapter. Instead, use the procedures supplied with DTSS to set time zone information.

Understanding Time-Setting Concepts  

Understanding some time concepts will help you see the importance of setting correct time zone information on your system.

Coordinated Universal Time  

Coordinated Universal Time (UTC) is similar in most respects to Greenwich Mean Time (GMT). Under the UTC time standard, zero hours occurs when the Greenwich Meridian is at midnight. Unlike local time, which can go backward and forward depending on daylight saving time, UTC always increases.

Local times can be up to 12 hours behind Greenwich Mean Time or 13 hours ahead of it.

Because UTC is independent of time zones, you can use UTC around the world; for example, it is 2:00 UTC at the same moment in Paris as it is in Tokyo. You can examine data that is time-stamped with UTC values in Paris and Tokyo without performing complicated conversions to deal with local time zones.

Time Zones  

Time zones for geographical areas that share the same local time also share the same rule or rules for seasonal changes between standard time and daylight saving time.

Daylight Saving Time and Standard Time  

Typically, you make seasonal changes to the local system time (for example, for daylight saving time and standard time). You usually adjust the local time one hour forward or backward.

Time Differential Factor  

One of the steps in setting the correct time on your system is to calculate a time differential factor (TDF) for your time zone.

The TDF associates each local time zone with UTC; it is the difference between your local system time and UTC. When your system time changes to reflect a local time change between standard time and daylight saving time, the TDF must also change to compensate for the new local system time. The TDF changes in the same direction as the local time; that is, if you add an hour to the local time, you must also add an hour to the TDF. Note, however, that the UTC does not change.

The TDF value is expressed in signed (+ or -) hh:mm format. The Americas have negative TDFs, while Europe, Africa, Asia, and Australia have positive TDFs.

OpenVMS procedures calculate the normal TDFs for standard and daylight saving time (if any) for your time zone. These are presented as the default for your TDF setting. HP recommends that you accept this default.

You can also use the map in Time Differential Factor Map to determine the TDF for your time zone. If you prefer, you can use the tables in Appendix B in the HP OpenVMS System Manager's Manual to determine the standard or daylight saving time TDF for your time zone.

To use the map to determine the TDF of your time zone, follow these steps:

  1. Find your location on the map and notice the time zone band at that location.
  2. Follow the time zone band to the top of the map and note the TDF that corresponds to your time zone. For example, the TDF for California is -8:00; the TDF for Italy is +1:00.

Some time zones do not have full-hour TDFs. In these cases, find the specific value on the map itself. For example, if you live in Adelaide, Australia, your TDF is +9:30.

In a time zone with daylight saving time, the TDF for daylight saving time is typically +1:00 from the standard time. For example, if the standard time TDF is +2:00, the daylight saving time TDF is +3:00; if the standard time TDF is -7:00, the daylight saving time TDF is -6:00. 

Figure 1  Time Differential Factor Map  
Time Differential Factor Map


NoteTime zone rules are under control of each country and are subject to change for political and other reasons. Printed maps are almost inevitably out-of-date. For up-to-date information, see the following web location:
  http://aa.usno.navy.mil/AA/faq/docs/world_tzones.HTML

Time Zone Rules  

A time zone rule is used to define the short name (usually three letters) for the time zone, the daylight saving time and standard time TDFs, and the rule for determining when changes are made between daylight saving time and standard time. The format of the time zone rules are defined in the HP C Run-Time Library Reference Manual for OpenVMS Systems .

Setting Time Zone Information  

How you set the time zone information on your system depends on the following:


NoteIf you are using the Distributed Time Synchronization Service (DTSS), use the procedures supplied with DTSS to set time zone information. See Distributed Time Synchronization Service (DTSS).

If DTSS is not in use, use the following table to determine how to set time zone information

OpenVMS Version Architecture See
7.3 and later
Alpha
Setting Time Zone Information on OpenVMS Alpha Version 7.3 and Later and on OpenVMS I64 Systems
7.3 and later
VAX
Setting Time Zone Information on OpenVMS VAX Systems
7.2 and earlier
VAX or Alpha
Setting Time Zone Information on OpenVMS VAX Systems
All
OpenVMS Cluster Environment
Setting Time in an OpenVMS Cluster Environment


 
go to next page: Setting Time Zone Information on OpenVMS Alpha Version 7.3 and Later and on OpenVMS I64 SystemsSetting Time Zone Information on OpenVMS Alpha Version 7.3 and...