How to check if the Time Zone database (often called tz or zoneinfo or tzdata ) has the right daylight savings or summer time (DST) change over dates?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux (RHEL) 4
  • Red Hat Enterprise Linux (RHEL) 5
  • Red Hat Enterprise Linux (RHEL) 6

Issue

  • How to check if the timezone data has the right daylight savings or summer time changeover dates?
  • How to check the offset and drift values for tzdata package?

Resolution

  • The timezone information, including changeover dates for daylight savings and summer time (DST), is included in the tzdata package.

  • The Time Zone Database contains code and data that represent the history of local time for many representative locations around the globe.

  • It is updated periodically to reflect changes made by political bodies to time zone boundaries, UTC offsets, and daylight-saving rules.

  • Check the version of the tzdata package which is installed on the machine, with the following command:

# rpm -q tzdata
tzdata-2009u-1.el5
  • This reports the year and revision of the files in use and it means that the installed timezone files date from 2009, and are at revision u.

  • To view the changeover dates for DST in a particular timezone:

# zdump -v /usr/share/zoneinfo/<Region>/<Timezone> | grep <year> 
  • This will give a list of the changeover dates such as the following:
# zdump -v /usr/share/zoneinfo/America/Los_Angeles | grep 2010
/usr/share/zoneinfo/America/Los_Angeles  Sun Mar 14 09:59:59 2010 UTC = Sun Mar 14 01:59:59 2010 PST isdst=0 gmtoff=-28800
/usr/share/zoneinfo/America/Los_Angeles  Sun Mar 14 10:00:00 2010 UTC = Sun Mar 14 03:00:00 2010 PDT isdst=1 gmtoff=-25200
/usr/share/zoneinfo/America/Los_Angeles  Sun Nov  7 08:59:59 2010 UTC = Sun Nov  7 01:59:59 2010 PDT isdst=1 gmtoff=-25200
/usr/share/zoneinfo/America/Los_Angeles  Sun Nov  7 09:00:00 2010 UTC = Sun Nov  7 01:00:00 2010 PST isdst=0 gmtoff=-28800
  • If there are any discrepancies between the changeover dates listed on the system and the expected changeover dates, update to the latest version of tzdata with:

  • For RHEL 4:

# up2date tzdata
  • For RHEL 5 and RHEL 6:
# yum -y update tzdata

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