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The tzdata transition to 'vanguard' format


As of tzdata-2018e, the upstream will now default to using the 'vanguard' data format including negative DST offsets. As a fall-back, the 'rearguard' data format is still available on F28, F27 and F26.


  • Name: Patsy Franklin
  • Email:
  • Release notes owner:
  • Release notes ticket:

Current status

Detailed Description

tzdata-2018e defaults to the 'vanguard' data format. This format includes the POSIX compliant implementations of negative DST offsets which have been an issue for both Java and ICU parsers. We plan to transition to this default format in F29.

Benefit to Fedora

Transitioning to the tzdata 'vanguard' format will ensure that we are current on all format changes and improvements.


  • Proposal owners: Implement the proposal.
  • Other developers: Developers need to ensure that their packages are able to correctly parse and/or build with the new tzdata 'vanguard' format.
  • Release engineering: The tzdata maintainer will ensure that the package builds and passes all tests on F29.
    RelEng ticket: #7510
  • Policies and guidelines: The policies and guidelines do not need to be updated.
  • Trademark approval: Not needed for this change

Upgrade/compatibility impact

There are no upgrade issues as long as packages that parse tzdata data files are updated to work with the 'vanguard' data format changes.

Some packaging changes required, see: No packaging changes needed.

How To Test

The tzdata package will be tested to confirm that time zone changes are accurate and current.

User Experience

Users will see updated time zone transitions. Users who dump data with zdump will now see negative DST offsets where applicable.


All packages do not need to be rebuilt.

Contingency Plan

  • Contingency mechanism: If necessary we can revert to the 'rearguard' data format.
  • Contingency deadline: Upstream ABI freeze deadline of 2018-08-01.
  • Blocks release? tzdata-2018e implements a time zone change for North Korea that took place on May 5,2018. If we don't update to tzdata-2018e clocks will not be correct.


No documentation changes are needed at this time.

Release Notes

Rebase to tzdata-2018e

  • North Korea changed from UTC+8:30 to UTC+9 on May 5, 2018.
  • In this update, the upstream project now defaults to using the "vanguard" data implementation which includes negative DST offsets.