Tip of the Trade: Y2K Redux With DST

by Carla Schroder

Did the new Daylight Savings Time implementation date sneak up on you? Although not the same size and scope as Y2K, the time change must also be dealt with. Seeing if your Linux systems have been updated to reflect the new date is a quick check. As is updating them.

Are you ready for the changes Daylight Savings Time is bringing upon us? Did you budget enough time to rant at having to deal with it in the first place? You did? Good, once that's out of your system, you can get to work updating systems. True, it's not quite on the same scale as the same as the infamous and fun Y2K updates. But like Y2K, it would be nice not to have to hassle with it.

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Complaining aside, Linux is easy. You should get the necessary changes in your regular system updates. Run this command to check if they're there:

$ zdump -v /etc/localtime | grep 2007
/etc/localtime Sun Mar 11 09:59:59 2007 UTC = Sun Mar 11 01:59:59 2007 PST isdst=0 gmtoff=-28800
/etc/localtime Sun Mar 11 10:00:00 2007 UTC = Sun Mar 11 03:00:00 2007 PDT isdst=1 gmtoff=-25200
/etc/localtime Sun Nov 4 08:59:59 2007 UTC = Sun Nov 4 01:59:59 2007 PDT isdst=1 gmtoff=-25200
/etc/localtime Sun Nov 4 09:00:00 2007 UTC = Sun Nov 4 01:00:00 2007 PST isdst=0 gmtoff=-28800

If it shows April 1 instead of March 11, your system does not have the new time zone data. Linux system time relies on the tzdata file, so look for an updated version of this file. Before panicking, run your usual system updater commands first, such as yum update on Fedora- and Red-Hat-type systems, or apt-get update && apt-get upgrade on Debian and its offspring.

This command also shows the GMT offsets in seconds, which can be useful when you're configuring time-sensitive applications.

Applications that keep their own time zone databases are more trouble. Check the Web site of your particular flavor of Linux. For example, this page for Red Hat Enterprise Linux, is a good reference for other Linux distros as well. Again, your regular system updates should take care of this for you, but this page is helpful if you have to make manual corrections.

Admins of other operating systems, like the big commercial Unixes and Windows, have their work cut out for them. After checking that your Linux systems are OK, consider lending them a hand. Or just take a well-earned rest.

This article was originally published on Tuesday Mar 6th 2007
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