Featured image: Time zone data (tzdata)

Daylight saving time transitions, a zone name change, and the removal of some obsolete files: These are some of the changes that occurred in the Time Zone Database (tzdata) package that provides Red Hat Enterprise Linux (RHEL) and applications with time zone information.

The GNU C Library (glibc) makes use of the tzdata package in order to make APIs such as strftime() work correctly, while applications such as /usr/bin/date make use of this information to print the local date. The tzdata package contains the data files documenting both current and historic transitions for various time zones around the world. This data represents changes required by local government bodies or by time zone boundary changes, as well as changes to UTC offsets and daylight saving time (DST).

In 2020, there were four upstream releases of the tzdata package:

  • Most changes related to daylight saving time (DST) start and end date transitions. These included Africa/Casablanca, Antarctica/Casey, Pacific/Fiji, Asia/Gaza and Asia/Hebron. Additionally, Canada's Yukon, represented by the America/Whitehorse and America/Dawson time zones, changed to use UTC-07 permanently.
  • There are rarely zone name changes but in 2020, the upstream project renamed America/Godthab to better reflect current usage in English, now America/Nuuk.
  • Some obsolete files were removed in 2020. These include pacificnew, systemv, and yearistype.sh. However, it was discovered that the removal of pacificnew could cause some applications to fail. An empty version of the pacificnew file was added in the rearguard data format version of tzdata to prevent these failures. For more information on the rearguard data format, see Time zone data (tzdata): 2018 data format changes and Red Hat Enterprise Linux.
  • There were also some changes to the version of zic provided by the upstream project. However, these do not impact Fedora or RHEL users as we use the version of zic provided by glibc.

In an effort to maintain the accuracy of the information provided by the time zone database, the upstream project frequently updates past timestamps as new information becomes available. In 2020, there were several corrections to past timestamps going back as far as 1891.

Occasionally, time zone changes are announced without a lot of lead time or with incomplete information. In these cases, we try to plan for different scenarios and rely on the upstream maintainers to make decisions based on their experience. Once an update is ready, we update our sources and our quality assurance, and release engineers help push the update out as quickly as possible.

The upstream time zone project releases updates on the iana.org website. You can also find information about subscribing to the tzdata email list and accessing the archives on this site. The email list includes discussions of proposed changes and corrections, release announcements, and time zone related news references.

For more information on Red Hat Enterprise Linux tzdata updates, see the Red Hat Enterprise Linux Timezone Data (tzdata) - Development Status Page.

Last updated: December 21, 2020