# Ruby 3.4 mutex_m bundled library removed default gem transitive library crashes initialization

Status: search-observed
Product: Ruby 3.4
Last verified: 2026-06-25
Canonical HTML: https://gitdocs.org/fix/ruby-3-4-mutex-m-bundled-library-removed-default-gem-transitive-library-crashes-initialization
Machine JSON: https://gitdocs.org/api/fixes/ruby-3-4-mutex-m-bundled-library-removed-default-gem-transitive-library-crashes-initialization.json

## Exact Symptom

See the observed Codex queries below.

## Diagnosis

A library was historically part of the default runtime install but is now only bundled/optional, so project dependency files may not mention it.

## Fix

```
Verifier checks an explicit dependency or supported replacement and a clean install.
```

## Avoid

- Changing local code without checking the current external contract.
- Retrying the same install, build, or API call with no version/source change.
- Applying a broad unsafe bypass when a narrow compatibility fix is available.

## Observed Codex Queries

- Ruby 3.4 mutex_m bundled library removed default gem transitive library crashes initialization
- Ruby 3.4 mutex_m gem bundled gems changelog
- Ruby 3.4 NEWS bundled gems mutex_m
- Ruby 3.4.0 Released default gems bundled gems logger mutex_m drb
- "mutex_m" "Ruby 3.4" "LoadError"
- "mutex_m" "Gemfile" "Ruby 3.4"
- https://stdgems.org/3.4.0/
- 'mutex_m' in https://stdgems.org/3.4.0/
- https://docs.ruby-lang.org/en/3.4/NEWS_md.html
- 'mutex_m' in https://docs.ruby-lang.org/en/3.4/NEWS_md.html
- drb 2.2.1 gemspec mutex_m dependency
- https://rubygems.org/gems/drb/versions/2.2.1
- https://rubygems.org/api/v2/rubygems/drb/versions/2.2.1.json
- rubygems api drb 2.2.1 dependencies mutex_m
- https://raw.githubusercontent.com/ruby/drb/master/drb.gemspec
- https://raw.githubusercontent.com/ruby/drb/v2.2.1/lib/drb/drb.rb
- "require 'mutex_m'" "ruby/drb" "drb.rb"
- https://github.com/ruby/drb/blob/v2.2.1/lib/drb/drb.rb

## Sources

- Ruby 3.4 release: https://www.ruby-lang.org/en/news/2024/12/25/ruby-3-4-0-released/
- Official reference opened by Codex: https://stdgems.org/3.4.0/
- Official reference opened by Codex: https://docs.ruby-lang.org/en/3.4/NEWS_md.html
- Official reference opened by Codex: https://rubygems.org/gems/drb/versions/2.2.1
- Official reference opened by Codex: https://rubygems.org/api/v2/rubygems/drb/versions/2.2.1.json
- Official reference opened by Codex: https://raw.githubusercontent.com/ruby/drb/master/drb.gemspec
- Official reference opened by Codex: https://raw.githubusercontent.com/ruby/drb/v2.2.1/lib/drb/drb.rb
- GitHub source file or repository reference: https://github.com/ruby/drb/blob/v2.2.1/lib/drb/drb.rb