Daylight Savings time

[Walter Scanlan <wscanlan@xxxxxxxxxx>]

Just a friendly reminder.


Title  *        Managing System Time changes 

Abstract        This document describes how to Manage system time changes 
due to Daylight Savings Time on OS/400 V5R3 and V5R2. 

   Cause           Domino on iSeries cannot manage a system time change 
while active

Content/Solution 
ALERT: ANY change in system time while a DOMINO server is active will 
impact Server performance. The larger the time change the larger the 
impact on performance.  DOMINO should be ended for any manual change to 
QTIME. 
 
Concerns for SNTP
        Each partition does have its own separate QTIME and QUTCOFFSET 
values.  For Daylight Savings Time, the system values must be updated for 
each partition.
        SNTP does not update QTIME.  SNTP updates a separate clock used by 
POSIX APIs.  There is no need to turn off SNTP when QTIME is changed for 
Daylight Savings Time.
 
        OS/400 V5R2 
        No native support for Daylight savings time.  When moving into or 
out of DST the system value QTIME  and  QUTCOFFSET must be altered by the 
system operator.
        QTIME holds the current time value of the OS/400.
            As DST ends QTIME would up updated from 2:00  to 1:00 
 
        Another consideration for changing the system time to reflect 
daylight savings time is that of the system value Coordinated universal 
time offset - QUTCOFFSET.  Greenwich Mean Time does not observe daylight 
savings time so the QUTCOFFSET value must be altered to reflect the 
difference in time caused by switching to daylight savings time.  The 
following table shows the appropriate values to use for this system value 
in the four time zones in continental USA:
 
 
 

Eastern Time Zone
Central Time Zone
Mountain Time Zone 
Pacific Time Zone
Daylight Savings Time
-4.00
-5.00
-6.00
-7.00
Standard Time
-5.00
-6.00
-7.00
-8.00

        As DST ends QUTCOFFSET would be updated by adding 1 hour to the 
existing value (see chart above).
 
 
        OS/400 V5R3
              Can use the same solution as V5R2 but also has this 
alternate option.
        Time maintenance application.
                This application will slow or speed the clock so no "time 
change" is required.  The system clock is either sped up or slowed to 
complete the desired time change. This tool is used on systems with 
applications which cannot permit duplicate time stamps which might occur 
by altering the system time. While Domino is not one of these applications 
the system Domino is hosted on might have one of this time sensitive 
applications requiring the use of this tool.
 
        This application relies on a new OS/400 system value QTIMZON
        If this application is used the Time is not CHANGED  the QTIME 
system clock is either slowed or sped to meet the time change. 
 
        Time maintenance application 
        Identifies the software to use to adjust the system clock to keep 
it synchronized with an external time source. This system value does not 
enforce the software specified, it only identifies the software to use. 
This value should be maintained by time adjustment software and is 
intended as an aid to prevent having multiple time adjustment applications 
conflict with each other. There are no checks performed by the system to 
verify this value or that software is or is not performing time 
adjustments. IBM time adjustment offerings will use identifiers that start 
with QIBM such as 'QIBM_OS400_SNTP'. Other software suppliers should 
follow a similar naming convention of company name and product name. 
        Time adjustment software should check this system value prior to 
starting. If this system value has an identifier for other time adjustment 
software, then the software being started should notify the user of this 
potential conflict and confirm that this time adjustment software should 
be started. When there is not an identifier associated with this system 
value, the software should update this system value to identify that it is 
now responsible for adjusting the system clock. Time adjustment software 
should check this system value again prior to ending. This system value 
should be set to the value None only if the current value identifies this 
time adjustment software that is ending. 
        Possible values are the following: 
        None
Indicates that time adjustment software has not been identified. 
        identifier
Identifies the software that will be used to adjust the system clock. 
        For more information about the SNTP client time maintenance 
application that IBM supplies with the system, see the iSeries information 
center.
 
Topic   Administration

Walter Scanlan 
Senior Software Engineer
Domino & Workplace for iSeries
507-286-6088
wscanlan@xxxxxxxxxx