Changes/AllowRemovalOfTzdata

Allow Removal of tzdata

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes process, proposals are publicly announced in order to receive community feedback. This proposal will only be implemented if approved by the Fedora Engineering Steering Committee.

Summary

Allow the removal of tzdata especially on containers in order to minimize size.

Owner

• Name: Patsy Griffin (Franklin)
• Email: patsy@redhat.com

Current status

• Targeted release: Fedora Linux 39
• Last updated: 2023-06-23
• [<will be assigned by the Wrangler> devel thread]
• FESCo issue: <will be assigned by the Wrangler>
• Tracker bug: <will be assigned by the Wrangler>
• Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

This change will allow the removal of tzdata. When tzdata is removed, the system will default to UTC. In order to reduce overhead, many container installations now remove the data associated with tzdata but cannot fuly remove the package due to dependencies by other packages. This results in confusion regarding the expected timezone info.

In order for this to work, we need packages that use tzdata at run time to switch from Require'ing tzdata to Recommend'ing tzdata. These packages should also gracefully handle instances where tzdata has been removed. For example, this would require recognizing that tzdata is not present and providing an appropriate error, such as recommending that the user install tzdata.

Feedback

In June of 2021, we proposed creating a new tzdata sub-package that would only provide the UTC timezone. As part of the discussion around this proposal, it was recommended that we completely remove tzdata. We appreciated this input and welcome additional feedback.

Benefit to Fedora

This change will allow tzdata to be removed from containers without leaving inconsistent package remnants.

Scope

• Proposal owners: No changes are needed to tzdata.

• Other developers: Some packages need to change their spec files from Requires: tzdata to Recommends: tzdata. It would be beneficial if all packages switched in this way, but it is not required. Supporting optional tzdata installation for as many workloads as possible allows those workloads to minimize their container image size.

List of packages which need to be changed:

• glibc (glibc-common)
• gcc (libstdc++)
• python3.XX (3.9, 3.10, 3.11, 3.12)

List of packages which would be beneficial to be changed:

• python3-dateutil
• python3-pytz
• libical

Upon acceptance of the change request we will file bugs to fix each of these packages for Fedora 39.

• Release engineering: No changes needed.

• Policies and guidelines: N/A (not needed for this Change)

• Trademark approval: N/A (not needed for this Change)

• Alignment with Community Initiatives:

Upgrade/compatibility impact

If tzdata is already installed, then it continues to be installed on the system.

Following the Fedora Weak Dependencies Policy dnf will treat the Recommends on tzdata as if it were a Requires and tzdata will always be installed in a default system (https://docs.fedoraproject.org/en-US/packaging-guidelines/WeakDependencies/)

However, the recommends will allow tzdata to be correctly uninstalled in a container build file rather than having to use ‘rm -rf’ to delete the zone files to recover space.

How To Test

Language runtimes were installed and A/B tests carried out with tzdata present and tzdata removed. The intent of these tests was to ensure that the system can use the language frameworks without tzdata present and that when the data was required that meaningful errors were presented to the user.

Packages tested were C (glibc), C++ (libstdc++), Python (Python 3.11), using their time and date APIs. This testing led to the correction of the libstdc++ implementation as noted here: https://gcc.gnu.org/cgit/gcc/commit/?id=4abd5bc600193e821fbc41995a0b8d9ea42b42c3

Developers can test this by installing Rawhide and uninstalling tzdata and verifying their package operates as expected.

If tzdata cannot be uninstalled then we recommend filling a bug against the package that Requires: tzdata and having a discussion with the maintainer to make tzdata optional e.g. Recommends: tzdata.

User Experience

The user can remove tzdata to minimize the container size.

With tzdata removed the system is UTC only.

Dependencies

Fixing glibc, gcc, and python3.xx at a minimum to make tzdata Recommends instead of Requires.

Contingency Plan

• Contingency mechanism: Back out the change. Don’t do it.
• Contingency deadline: Can be backed out at the last minute since we are only dealing with conversions from Requires to Recommends.
• Blocks release? No

Documentation

Document that the tzdata package may be removed if needed to reduce space on containers. With tzdata removed, the system will default to UTC.