[Bug 2003797] Please test proposed package

[Brian Murray]

Hello Benjamin, or anyone else affected,

Accepted tzdata into focal-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/tzdata/2023b-0ubuntu0.20.04.0 in a
few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
focal to verification-done-focal. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-focal. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

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https://bugs.launchpad.net/bugs/2003797

Title:
  Pre-1970 timestamps are knowingly wrong

Status in tzdata package in Ubuntu:
  Fix Released
Status in tzdata source package in Bionic:
  New
Status in tzdata source package in Focal:
  Fix Committed
Status in tzdata source package in Jammy:
  Fix Committed
Status in tzdata source package in Kinetic:
  Fix Committed

Bug description:
  [ Impact ]

  tzdata 2021b says in NEWS: "Merge more location-based Zones whose
  timestamps agree since 1970, as pre-1970 timestamps are out of scope.
  This is part of a process that has been ongoing since 2013.  This does
  not affect post-1970 timestamps, and timezone historians who build
  with 'make PACKRATDATA=backzone' should see no changes to pre-1970
  timestamps." tzdata 2022b finished that process: "Finish moving to
  'backzone' the location-based zones whose timestamps since 1970 are
  duplicates; adjust links accordingly. This change ordinarily affects
  only pre-1970 timestamps, and with the new PACKRATLIST option it does
  not affect any timestamps. In this round the affected zones are
  Antarctica/Vostok, Asia/Brunei, Asia/Kuala_Lumpur, Atlantic/Reykjavik,
  Europe/Amsterdam, Europe/Copenhagen, Europe/Luxembourg, Europe/Monaco,
  Europe/Oslo, Europe/Stockholm, Indian/Christmas, Indian/Cocos,
  Indian/Kerguelen, Indian/Mahe, Indian/Reunion, Pacific/Chuuk,
  Pacific/Funafuti, Pacific/Majuro, Pacific/Pohnpei, Pacific/Wake and
  Pacific/Wallis, and the affected links are Arctic/Longyearbyen,
  Atlantic/Jan_Mayen, Iceland, Pacific/Ponape, Pacific/Truk, and
  Pacific/Yap."

  The Debian/Ubuntu package builds tzdata with the default settings
  (PACKRATDATA unset) which merges zones whose timestamps agree since
  1970. This leads to timestamps before 1970 being knowingly wrong.
  Example: Europe/Oslo is a link to Europe/Berlin since they are
  identical since 1970, but they differed before 1965. Berlin observed
  no summertime between 1950 and 1980, but Oslo did in 1959 to 1965. So
  summer 1960 in Oslo should be UTC+2 compared to UTC+1 in Berlin:

  ```
  $ TZ=Europe/Oslo date -d "1960-07-01 10:00 Z"
  Fri Jul  1 12:00:00 CEST 1960
  $ TZ=Europe/Berlin date -d "1960-07-01 10:00 Z"
  Fri Jul  1 11:00:00 CET 1960
  ```

  There was a big debate upstream (see https://lwn.net/Articles/870478/
  or https://mm.icann.org/pipermail/tz/2021-May/030137.html). The
  Debian/Ubuntu package should ship timezones from backzone. Users that
  care about pre-1970 timestamps will be satisfied and users not caring
  will probably not care about the additional timezones.

  The install size will increase by around 20% and the amount of
  distinct (i.e. not symlinked) timezones will increase by 33%:

  ```
  $ grep ^Zone africa antarctica asia australasia etcetera europe factory northamerica southamerica | wc -l
  352
  $ grep ^Zone backzone | wc -l
  119
  ```

  [ Test plan ]

  The test case `test_pre_1970_timestamps` was added to the python
  autopkgtest for testing this change. So the test plan is to check that
  the autopkgtest succeeds.

  [ Where problems could occur ]

  Systems with incorrect timezone set may observe unexpected time shift.

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