[Bug 2007611] Re: Undocumented date format (via date_fmt) change from Bionic to Focal, then reverted again from Focal to Jammy

[Dimitri John Ledkov]

Also note that this unfortunate instability affects SQL databases quite
badly. Some of them from time to time (postgresql?) generated indexes
based on the sorting of the glibc locale ordering which is unstable
across lts releases. This has caused production issues in the past -
where one server is upgraded to a newer LTS series in a pool and
returning different results. Thus things like database indexes should be
rebuild upon upgrade, and a cluster should operate ideally on the same
locale.

C.UTF-8 locale has always been provided by Ubuntu and it is now
upstream, and it is more stable in its formating than en_US. Ideally one
should typically use C.UTF-8 locale for most things.

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https://bugs.launchpad.net/bugs/2007611

Title:
  Undocumented date format (via date_fmt) change from Bionic to Focal,
  then reverted again from Focal to Jammy

Status in glibc package in Ubuntu:
  Opinion

Bug description:
  It seems like the output of `date` has changed between Bionic, Focal
  and Jammy, resulting from the lack of, inclusion of and subsequent
  removal of the `date_fmt` line in the `/usr/share/i18n/locales/en_US`
  file included in the glibc package.

  Since this change is not reflected in the ChangeLog for those
  respective releases, I'm wondering what the motivator for that change
  was, and if we can be consistent in the format of that file in those
  versions of the package.

  https://changelogs.ubuntu.com/changelogs/pool/main/g/glibc/glibc_2.37-0ubuntu1/changelog

  ubuntu at date-bionic-repro:~$ date
  Thu Feb 16 20:34:21 UTC 2023

  ubuntu at date-focal-repro:~$ date
  Thu 16 Feb 2023 08:34:21 PM UTC

  ubuntu at date-jammy-repro:~$ date
  Thu Feb 16 08:34:21 PM UTC 2023

  In each of these versions, we see:

  Bionic:
  =====================
  $ grep ^date_fmt /usr/share/i18n/locales/en_US; echo $?
  1

  Focal:
  =====================
  $ grep ^date_fmt /usr/share/i18n/locales/en_US; echo $?
  date_fmt "%a %d %b %Y %r %Z"
  0

  Jammy: 
  =====================
  $ grep ^date_fmt /usr/share/i18n/locales/en_US; echo $?
  date_fmt "%a %b %e %r %Z %Y"
  0

  Can we please ensure consistency in the `date_fmt` for these 3
  releases, so it doesn't change 3 different ways when upgrading through
  releases?

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