From Fedora Project Wiki

The GNU C Library version 2.21


Switch glibc in Fedora 22 to glibc version 2.21.


Current status

  • Targeted release: Fedora 22
  • Last updated: 2015-01-21
  • Tracker bug: ???

Detailed Description

The GNU C Library version 2.21 will be released at the end of January 2015; we have started closely tracking the glibc 2.21 development code in Fedora Rawhide and are addressing any issues as they arise. Given the present schedule Fedora 22 will branch after GLIBC 2.21. Fedora 22 will be based on the stable GLIBC 2.21.

Benefit to Fedora

Stays up to date with latests security and bug fixes from glibc.


  • Proposal owners: Update glibc to 2.21 from tested upstream release.
  • Other developers: Aside from Carlos O'Donell <>, Siddhesh Poyarekar <>, Alexandre Oliva <>, Torvald Riegel <>, Martin Sebor <>, and Patsy Franklin <>, no other developers are required. These developers need to ensure that rawhide is stable and ready for the Fedora 22 branch. Given that glibc is backwards compatible and we have been testing the new glibc in rawhide it should make very little impact when updated.
  • Release engineering: In general coordination with release engineering is not required. A mass rebuild is not required.
  • Policies and guidelines: The policies and guidelines do not need to be updated.

Upgrade/compatibility impact

The library is backwards compatible with the version of glibc that was shipped in Fedora 21.

Some packaging changes are recommended here:

How To Test

The GNU C Library has its own testsuite, which is run during the package build and examined by the glibc developers before being uploaded. This test suite has 1000+ tests that run to verify the correct operation of the library. In the future we'll also be running the microbenchmark to look for performance regressions as well as behavioural ones.

User Experience

Users will see improved performance, many bugfixes and improvements to POSIX compliance, additional locales, etc. The glibc 2.21 NEWS update will include more details.


All packages do not need to be rebuilt.

We depend on another change proposal to fix unicode data issues in glibc. If the other proposal is not accepted then glibc's unicode data will remain flawed, but will not regress. The proposal is:

Contingency Plan

  • Contingency mechanism: Given that Rawhide has started tracking GLIBC 2.21, no show-stopper problems are expected. In the unlikely event a major problem were discovered, we could fall back to the older glibc 2.20 and release with that.
  • Contingency deadline: Beta freeze.
  • Blocks release? Upgrading glibc does block the release. We should not ship without a newer glibc, there will be gcc and language features that depend on glibc being upraded. Thus without the upgrade some features will be disabled or fall back to less optimal implementations.


The glibc manual contains the documentation for the release and doesn't need any more additional work.

Release Notes

The GNU C Library version 2.21 will be released at the end of January 2015. The current NEWS notes can be seen here as they are added:;a=blob;f=NEWS;hb=HEAD