Preventing DST time problems?

Posted on 2006-04-15
Last Modified: 2010-04-13
I am running on a dual-boot system running Window2000/Solaris 10....The
last Daylight Savings Time change that we had this month just made my
clocks change erratically...I would like to ask, if whats the best Time
settings for both operating systems (windows and solaris) in order to
prevent drastic erratic time changes during DST changes??

Here are my current clock or time settings:

1. RTC or the Hardware Clock is set to UTC..(The BIOS is set to UTC)

2. Solaris DISPLAYED Time or TZ is set to TZ=UTC....and ZONE INFO is
set to UTC also...

3. Windows, is set to show local time zone....but, were it says under
the Time Zone properties, I have the "Adjust clock to DST
Automatically" UNCHECKED at the moment.

Now, #1 and in #2 I do want to leave were its at, in other words, I
want Solaris to keep its time in TZ=UTC and also the "Zone Info as UTC
also. Thats fine.

Now, in order to prevent problems or erratic time changes during the
DST changes, what should I do under Windows?? In other words, should I
leave the settings above were its at...Or, I do need to change some
things around to prevent possible issues during DST changes in a
dual-boot Windows/UNIX system?

Thanks in advance for the help!
Question by:slajoh01
    LVL 12

    Accepted Solution

    The BIOS time should normally be configured for the correct time in your timezone. If your local time is 14:43 (2:43 pm) then the BIOS clock should be set to that time. Then the timezone in the OS should be set to your local TZ (which is the case here for Windows but not for Solaris? Is that right?).

    In Windows, it's quite easy to configure NTP time synchronization. Then the adjustment for DST doesn't even apply: the time gets corrected every time the W32Time service checks its NTP servers. But it needs the correct time zone information to interpret the time.

    A good list of public NTP servers is at
    For example, I am in Europe. Then I would use the following command to sync time on a Windows box:

    net time /

    and just make sure that the Windows Time service is running and started automatically.
    I don't know anything about Solaris, but I'm sure it offers you the same kind of network time synchronization.

    On the other hand: Windows Time is maybe what's causing the erratic behaviour. The different time zones between both OS's and the fact that they both try to correct DST in different TZ can be quite confusing to an otherwise unintelligable piece of hardware ;-)

    Author Comment

    actually the time service is disabled because I dont want it to take up memory resources..
    LVL 12

    Expert Comment

    I've tried determining the W32Time memory footprint with Process Explorer, and memory use is negligible (I think less than 100K).

    I still don't really see what you mean by erratic... when does the issue occur, and what issue exactly?
    LVL 2

    Assisted Solution

    It all depends which operating system will be running when the clocks change.  If the one that will be running (or first booted from after the change if PC is off at the change) has automatic DST adjustment, and the other does not have automatic DST adjustment, you should be OK

    I you do not know wich OS you will be running at the DST change (or first boot from after the change), then there is no right answer.

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