|Academic Computing and Communications Center|
UIC ACCC: 2007 Daylight Savings Time Change
Last updated 2007-01-31
|Daylight Savings Time|
In 2005, the United States Congress passed the Energy Policy Act of 2005, which, among other things, changed the dates that Daylight Savings Time would begin and end in the United States, starting in 2007. Canada and Bermuda have followed suit.
Previously in the U.S., Daylight Savings Time began on the first Sunday in April and ended on the last Sunday in October. Starting in 2007, Daylight Savings Time in the U.S. will
Many other parts of the world have their own change dates for Daylight Savings Time, such as Europe, which begins later and ends earlier (the last Sunday in March and the last Sunday in October, respectively), Mexico, which will continue to observe the old U.S. change dates, and the Southern Hemisphere where the seasons are opposite ours.
Also, there have always been some areas of the U.S. and Canada which did not observe Daylight Savings Time, and some of those areas continue not to, such as Arizona, Hawaii, and Saskatchewan. Indiana previously did not observe Daylight Savings Time, but now observes it.
The information in this page applies only to the U.S., Canada, and other parts of the world that are following the new dates in the U.S. Energy Policy Act of 2005.
|-- The Daylight Savings Time Problem|
The Daylight Savings Time problem is that, during the extended periods of three weeks in the spring and one week in the fall, the clocks on many systems that normally change to and from Daylight Savings Time automatically will continue to operate on Standard Time, even though Daylight Time is actually in effect. Uncorrected systems in Indiana will encounter problems for the entire summer. Clocks on uncorrected systems will not be synchronized with clocks on systems that have been fixed.
We have until the second Sunday in March, March 11, 2007, to fix this problem.
General Information about Daylight Savings Time and the 2007 Changes
|1. Basic Operating Systems|
|2. ACCC Applications & Middleware|
None of the application software listed below can possibly function correctly, unless you first update the Daylight Time rules in the underlying operating system above.
Information for ACCC and UIC applications are below; for a more complete list, see
2.1. UICalendarThe Oracle Calendar software on the UICalendar server has been updated to observe the new Daylight Savings Time change dates, so everything you enter now will be fine.
Important: However, events that you entered earlier that are scheduled to occur in the extended times of March 11, 2007 to April 1, 2007 or October 28, 2007 to November 4, 2007, may or may not be wrong by one hour.
See Daylight Savings Time Problem: UICalendar for important information about what you need to do to correct this.
If you are using Microsoft Outlook with UICal, you should not run the Microsoft Outlook Timezone Update Tool!. See below. The Microsoft Office Outlook Connector does not, itself, contain any Daylight Time issues, although it is connecting between two things which do.
2.2. Microsoft OutlookYou need to make sure that the underlying operating system is updated for the change, and then you need to update Outlook itself. Calendar events created during the extended periods of Daylight Time may appear at the wrong time. Microsoft has provided a tool to fix these problems - but do not run it if you use Oracle Connector for Outlook and UICalendar. It is OK to use the tool if you run Outlook "stand-alone" on your PC. If you run Outlook against an Exchange server, contact your Exchange Sysadmins.
However, Microsoft advises that users "should minimize the time lag between applying updates to operating systems and running the Time Zone Data Update Tool." This means that you should wait before updating Windows until you have the Outlook Time Zone Update Tool downloaded, installed, and ready to run.
2.3. Novell Netware (ACCC Server Services)OES/NetWare servers in affected United States and Canada time zones should be updated with DSTShift.nlm, a Novell provided utility. TID 3397648 - Daylight Savings Time Adjustment Tool for Netware Servers
The Novell Client gets its time from the Novell Netware Server and then synchronizes the time setting on your computer with the Netware Server. Therefore, if your client computer's operating system is not patched or upgraded as specified in this document, the result could be confusion and unintended time changes when your Novell Client connects to the Novell Server and synchronizes.
Novell Netware can also run as a Java application. It uses Sun Java. See the section on Java. Also see 3980430: Daylight Saving Time (DST) defaults changing in 2007 and the impact on the NetWare Java Runtime Environment (JRE)
2.4. Blackboard Learning System
Blackboard depends on the underlying operating system and on Sun Java. Blackboard suggests running the Sun Java Updater Tool, listed above under Java Applications.
2.5. Tivoli Storage Manager (ADSM)Though there are no Daylight Savings Time dependencies in the TSM server or client programs per se, you must insure that your own client computer's operating system is updated or patched. Failure to do that will result in session failure due to unsynchronized clocks between client and server, or time-warp errors attempting to back up files created in the future, or restore recently backed-up files which might have been backed up in the future. We have found that TSM is tolerant of a client system clock being a few minutes off, but a whole hour is too much.
|3. General Considerations|
|-- Automatic schedulers - Unix cron, Windows Scheduled Tasks facility, etc.|
The cron facility in all Unix systems (Mac OS X, Linux, AIX, Solaris, HPUX, ...)
schedules processes to be performed at specified times.
A similar function is provided by the Scheduled Tasks facility in
the Windows Control Panel.
The fundamental problem here is that the input data to these schedulers is
specified in Local Time, so there is no way to avoid Daylight Time
In general, you should avoid starting critical once-a-day processes at any time between 1:00AM and 3:00AM. It may be hard to tell which approach is used on which system. Obviously though, events which are scheduled at a frequency of hourly or shorter, will not be affected by this consideration -- they will run at their expected frequency before, during, and after the time changes.
|-- Multi-Boot Systems|
Which system owns the hardware clock? (Probably both.)
What does it do with it?
When does it change it?
If you have a dual-boot, multi-boot, or virtual machine arrangement on your computer that allows you to run multiple operating systems, you've got to make sure they are not interfering with one another regarding your computer's hardware clock.
A very basic problem is that Windows (all versions, from DOS to Vista) operates with the hardware clock set to local time, while Unix (all versions, including Linux and Mac OS X) operates with the hardware clock set to UTC (Greenwich) time.
The other basic problem is that when any Windows system changes to or from Daylight Time, it resets the hardware clock to the new local time. If you then boot a second Windows system on the same computer, it will change the hardware clock again, for a total of a two hour change. If the second system is Unix, it will get very confused.
One simple solution to this is to run all systems on UTC. See Moving to Greenwich below.
The more realistic solution is to have your most frequently-used
If you are mixing Windows and Unix, such as running Windows and Mac OS X on an
|-- Time Interval Calculations|
What is the exact length of time between 12:00 Noon Local Time
on March 1 and 12:00 Noon Local Time on March 15?
That will vary by one hour, depending on the year.
What is the exact length of time between 12:00 Noon Local Time on March 1, 2006 and 12:00 Noon Local Time on April 10, 2007? That will vary by one hour, depending on which part of Indiana you are in. In a few parts of Indiana such as Evansville, offsetting errors may accidentally yield a correct answer.
If exact time intervals are important to you, such as in a lab experiment that counts the frequency of certain events over some period of time, then you should seriously consider using the UTC (GMT) time zone throughout. Otherwise you may find yourself trying to figure out why those cells completely stopped dividing for one hour at 2:00AM on March 11, 2007. See the section on Moving to Greenwich below.
|-- If All Else Fails, Move to Greenwich, England|
Greenwich (pronounced "GREN-itch")
is a pleasant, leafy, suburb of London, that overlooks the
Thames River as it makes its way from London to the sea.
Greenwich is home to the Royal Observatory, which first standardized
the global measurement of time in the 18th Century.
As ships passed by on their way out to sea, they would synchronize their
clocks to the time at the Royal Observatory.
This was crucial to navigation, because calculating the time difference
between solar noon at Greenwich, and solar noon anywhere else on earth,
was the first reliable method of determining your longitude, and thereby
your exact position on earth.
The Prime Meridian, 0 degrees longitude, runs through the Royal
Observatory building, and solar time on the Prime Meridian, originally
called Greenwich Mean Time (GMT) but now called Coordinated Universal
Time (UTC), remains the standard today for worldwide time-keeping.
If the system you have cannot easily be fixed to observe the new change dates for Daylight Savings Time, you could always set that system to run all year on UTC/GMT. Many organizations, especially those with worldwide operations, operate all their computing systems on UTC. This completely avoids the issues of Daylight Savings Time or the latest changes to the dates it is observed.
When doing so, some systems (Windows, Mac) force you to select a time zone as it is observed in a particular location. In that case, do not select London or any other location in Europe, because all of Europe observes Daylight Savings Time. On these systems, select a western African location, such as Monrovia Liberia, because these places do not use Daylight Time. They observe UTC all year round.
When setting your clock on a system configured to operate on UTC, remember to set the correct date also. During the evening in Chicago, it is tomorrow in the UTC time zone, so set the correct UTC date too. The www.time.gov time service has a UTC option you can select, to display the current time and date in the UTC time zone.
Alternatively, many systems can be configured to be switched manually between Standard Time and Daylight Time. For instance, the page on Windows contains instructions that are generally applicable to any Windows system. Instructions for manually switching Mac OS X are in the page on Macs.
|-- What time is it in Indiana?|
In 2005 and before, time zone and daylight time observance differed
from one county in Indiana
to the next, and the question, "What time is it?"
was complicated to answer, requiring reference to both a map and a
calendar. Brochures were available at locations such as toll road plazas
explaining it all.
In a major simplification,
|-- What time is it right now?|
The Official U.S. Time
Clever java-powered web site from the U.S. Government
displays the current time to within a tiny fraction of a second, by
measuring and compensating for network delay.
This public service is cooperatively provided by the two time agencies
of the United States: a Department of Commerce agency, the National
Institute of Standards and Technology (NIST), and its military
counterpart, the U. S. Naval Observatory (USNO). Readings from the
clocks of these agencies contribute to world time, called Coordinated
Universal Time (UTC). The time maintained by both agencies should
never differ by more than 0.000 0001 seconds from UTC.
On that page, click the link "About this service" for a page of more information, including links to programs to automatically set your computer's clock to the correct time.
|-- Automatically setting your clock with NTP|
The Internet Network Time service, or NTP, is a way to automatically
synchronize your computer's
clock with the correct time standard maintained by the government.
It is widely used.
For instance, Macintosh computers have it configured by default.
When your computer asks a handy NTP server what time it is, the answer is always in the UTC (Greenwich) time zone. Your computer then translates that into Local Time.
The problem is, that if your computer does not have the correct time zone calculations, it will be set to the wrong time.
|-- Is it Daylight "Savings" or "Saving"?|
I mention this only to deflect some of the inevitable flames that will be
directed my way for using it both ways.
Both grammatical forms are in common usage, and are therefore both correct.
There has been an especially animated discussion on
Author: Roger Deschner firstname.lastname@example.org
Did you know that Time Zones were invented here in Chicago, by the railroads?
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