# rpm -q ruby rubygems
ruby-2.5.5-101.fc29.x86_64
rubygems-2.7.6.2-101.fc29.noarch
# which gem
/usr/bin/gem
# gem
/usr/share/ruby/yaml.rb:5: warning: It seems your ruby installation is missing psych (for YAML output).
To eliminate this warning, please install libyaml and reinstall your ruby.
Traceback (most recent call last):
	16: from /usr/bin/gem:21:in `<main>'
	15: from /usr/share/rubygems/rubygems/gem_runner.rb:44:in `run'
	14: from /usr/share/rubygems/rubygems/gem_runner.rb:79:in `do_configuration'
	13: from /usr/share/rubygems/rubygems/gem_runner.rb:79:in `new'
	12: from /usr/share/rubygems/rubygems/config_file.rb:202:in `initialize'
	11: from /usr/share/rubygems/rubygems/config_file.rb:349:in `load_file'
	10: from /usr/share/rubygems/rubygems.rb:709:in `load_yaml'
	 9: from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:59:in `require'
	 8: from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:59:in `require'
	 7: from /usr/share/ruby/yaml.rb:6:in `<top (required)>'
	 6: from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:59:in `require'
	 5: from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:59:in `require'
	 4: from /usr/local/share/gems/gems/psych-3.1.0/lib/psych.rb:13:in `<top (required)>'
	 3: from /usr/local/share/gems/gems/psych-3.1.0/lib/psych.rb:16:in `rescue in <top (required)>'
	 2: from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:39:in `require'
	 1: from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:135:in `rescue in require'
/usr/share/rubygems/rubygems/core_ext/kernel_require.rb:135:in `require': libruby.so.2.4: cannot open shared object file: No such file or directory - /usr/local/lib64/gems/ruby/psych-3.1.0/psych.so (LoadError)