Проблемы, устанавливающие rdoc, irb, bluecloth, хронический на мягкой фетровой шляпе 12

Что означают эти ошибки?

[root@localhost config]# gem install bluecloth
Building native extensions.  This could take a while...
ERROR:  Error installing bluecloth:
    ERROR: Failed to build gem native extension.

/usr/bin/ruby extconf.rb
can't find header files for ruby.


Gem files will remain installed in /usr/lib64/ruby/gems/1.8/gems/bluecloth-2.0.7 for 
inspection.
Results logged to /usr/lib64/ruby/gems/1.8/gems/bluecloth-2.0.7/ext/gem_make.out
[root@localhost config]# 

И это

[root@localhost config]# gem install chronic
Successfully installed json_pure-1.4.3
Successfully installed rubyforge-2.0.4
Successfully installed hoe-2.6.0
Successfully installed chronic-0.2.3
4 gems installed
/usr/lib64/ruby/gems/1.8/gems/rdoc-2.5.8/lib/rdoc/ruby_lex.rb:67: warning: 
parenthesize argument(s) for future version
ERROR:  While executing gem ... (Gem::DocumentError)
    ERROR: RDoc documentation generator not installed: no such file to load -- irb/slex
[root@localhost config]# 

Я установил rdocs, использование "конфетки устанавливает рубин-rdocs". Но я не понимаю то, что означает эта ошибка