Henge Consulting LLC

March 8, 2007 - Daylight savings time is aproaching.

This Sunday (March 11) is the day to set your clocks forward for daylight savings, clocks should skip from 1:59:59 to 3:00:00.

Most computers if kept up to date with the latest patches for the OS will automatically update at the correct time. If you are running an older UNIX/Linux system here is a few steps you can follow to make sure that your system will know the correct time.

Use zdump to figure out if your system is up to date with the following command:

$ zdump -v /etc/localtime MST7MDT | grep 2007

Replace MST7MDT with your time zone so for eastern it would be EST5EDT. The output will look something like this.

--(root@henge)-(pts)-(07:31pm:03/08/07)--
--(~/downloads/tzdata2007)> zdump -v /etc/localtime MST7MDT | grep 2007
/etc/localtime  Sun Mar 11 08:59:59 2007 UTC = Sun Mar 11 01:59:59 2007 MST isdst=0 gmtoff=-25200
/etc/localtime  Sun Mar 11 09:00:00 2007 UTC = Sun Mar 11 03:00:00 2007 MDT isdst=1 gmtoff=-21600
/etc/localtime  Sun Nov  4 07:59:59 2007 UTC = Sun Nov  4 01:59:59 2007 MDT isdst=1 gmtoff=-21600
/etc/localtime  Sun Nov  4 08:00:00 2007 UTC = Sun Nov  4 01:00:00 2007 MST isdst=0 gmtoff=-25200
MST7MDT         Sun Mar 11 08:59:59 2007 UTC = Sun Mar 11 01:59:59 2007 MST isdst=0 gmtoff=-25200
MST7MDT         Sun Mar 11 09:00:00 2007 UTC = Sun Mar 11 03:00:00 2007 MDT isdst=1 gmtoff=-21600
MST7MDT         Sun Nov  4 07:59:59 2007 UTC = Sun Nov  4 01:59:59 2007 MDT isdst=1 gmtoff=-21600
MST7MDT         Sun Nov  4 08:00:00 2007 UTC = Sun Nov  4 01:00:00 2007 MST isdst=0 gmtoff=-25200

If you see "Sun Apr 1" instead of "Sun Mar 11" on any of those lines than you need to update the system. If you see the same dates as above then you are good to go, if not read on.

Make a directory and download the updated zonedata from ftp://elsie.nci.nih.gov/pub/.

$ mkdir tzdata
$ cd tzdata
$ wget ftp://elsie.nci.nih.gov/pub/tzdata2007c.tar.gz

Unzip the archive.

$ tar zxvf tzdata2007c.tar.gz

Switch to root and prepare the files.

# zic -d zoneinfo northamerica
# cd zoneinfo
# cp -r * /usr/share/zoneinfo/

If your system is older your zoneinfo directory may be located at /usr/lib/zoneinfo.

Now make sure that everything is setup right.

# zdump -v /etc/localtime MST7MDT | grep 2007

If your /etc/localtime lines do not match make sure you link it to the right file.

# rm /etc/localtime
# ln -s /usr/share/zoneinfo/MST7MDT /etc/localtime

Everything should be good to go until the government changes it's mind again about how time in this country works.

--Hunter