You can use the time adjustment function of IBM® Navigator for i to adjust the system time, or use a time maintenance application to adjust the system time automatically.
Time adjustments are preferred over manually setting the time of day system value because a time adjustment speeds up or slows down time in small increments rather than making a single, instantaneous time change.
If you do not use the time adjustment function, you can manually change the system time using the time of day system value. For example, if you want to set the system time backward three minutes, you can manually change the time of day system value from 3:00:00 (HH:MM:SS) to 2:57:00. By doing this, the system time from 2:57:00 to 3:00:00 is repeated. This can cause problems for applications recording time.
To avoid these types of problems, you can use the time adjustment function to change the system time and time will not be skipped or repeated. Adjusting the clock means to incrementally speed up or slow down the clock so that time is gradually adjusted to the desired time value. Adjusting does not cause large jumps in time that can be experienced with setting the clock with the time of day system value. However, adjusting does take time to complete because it is not a single, instantaneous change to the clock. For example, adjusting the clock by 1 second can take 10 seconds of real time to complete.
The following figure shows the difference between manually setting the time of day system value and using the time adjustment function. The lines represent the progression forward in time. The section highlighted in blue shows the period of time that is either skipped or repeated (during manual changes), or continuous (during time adjustments).
The Manual Change figure shows that if you set the system time from 9:00 a.m. to 11:00 a.m., the two-hour interval from 9:00 a.m. to 11:00 a.m. is skipped. Also, if you set the time backward from 11:00 a.m. to 9:00 a.m., the system time repeats the time frame from 9:00 a.m. to 11:00 a.m.
The Time Adjustment figure shows that if you adjust the system time using the time adjustment function, the flow of time is neither skipped nor repeated. Time gradually speeds up or slows down until the appropriate time value is reached. The amount of time that an adjustment takes to complete depends on the length of the adjustment. A two-hour time adjustment, either negative or positive, is the maximum adjustment allowed. Time adjustment ensures that the system time flows continuously. Therefore, time adjustment is the suggested method for changing system time.
For more information about how to change the system time, either a manual time change or a time adjustment, see Updating system time.