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?
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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