/usr/lib/ruby/1.8/rdoc/ is in libruby1.8 1.8.7.352-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/1.8/rdoc/code_objects.rb
/usr/lib/ruby/1.8/rdoc/diagram.rb
/usr/lib/ruby/1.8/rdoc/dot/
/usr/lib/ruby/1.8/rdoc/dot/dot.rb
/usr/lib/ruby/1.8/rdoc/generators/
/usr/lib/ruby/1.8/rdoc/generators/chm_generator.rb
/usr/lib/ruby/1.8/rdoc/generators/html_generator.rb
/usr/lib/ruby/1.8/rdoc/generators/ri_generator.rb
/usr/lib/ruby/1.8/rdoc/generators/template/
/usr/lib/ruby/1.8/rdoc/generators/template/chm/
/usr/lib/ruby/1.8/rdoc/generators/template/chm/chm.rb
/usr/lib/ruby/1.8/rdoc/generators/template/html/
/usr/lib/ruby/1.8/rdoc/generators/template/html/hefss.rb
/usr/lib/ruby/1.8/rdoc/generators/template/html/html.rb
/usr/lib/ruby/1.8/rdoc/generators/template/html/kilmer.rb
/usr/lib/ruby/1.8/rdoc/generators/template/html/old_html.rb
/usr/lib/ruby/1.8/rdoc/generators/template/html/one_page_html.rb
/usr/lib/ruby/1.8/rdoc/generators/template/xml/
/usr/lib/ruby/1.8/rdoc/generators/template/xml/rdf.rb
/usr/lib/ruby/1.8/rdoc/generators/template/xml/xml.rb
/usr/lib/ruby/1.8/rdoc/generators/xml_generator.rb
/usr/lib/ruby/1.8/rdoc/markup/
/usr/lib/ruby/1.8/rdoc/markup/sample/
/usr/lib/ruby/1.8/rdoc/markup/sample/rdoc2latex.rb
/usr/lib/ruby/1.8/rdoc/markup/sample/sample.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/
/usr/lib/ruby/1.8/rdoc/markup/simple_markup.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/fragments.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/inline.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/lines.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/preprocess.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/to_flow.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/to_html.rb
/usr/lib/ruby/1.8/rdoc/markup/simple_markup/to_latex.rb
/usr/lib/ruby/1.8/rdoc/markup/test/
/usr/lib/ruby/1.8/rdoc/markup/test/AllTests.rb
/usr/lib/ruby/1.8/rdoc/markup/test/TestInline.rb
/usr/lib/ruby/1.8/rdoc/markup/test/TestParse.rb
/usr/lib/ruby/1.8/rdoc/options.rb
/usr/lib/ruby/1.8/rdoc/parsers/
/usr/lib/ruby/1.8/rdoc/parsers/parse_c.rb
/usr/lib/ruby/1.8/rdoc/parsers/parse_f95.rb
/usr/lib/ruby/1.8/rdoc/parsers/parse_rb.rb
/usr/lib/ruby/1.8/rdoc/parsers/parse_simple.rb
/usr/lib/ruby/1.8/rdoc/parsers/parserfactory.rb
/usr/lib/ruby/1.8/rdoc/rdoc.rb
/usr/lib/ruby/1.8/rdoc/ri/
/usr/lib/ruby/1.8/rdoc/ri/ri_cache.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_descriptions.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_display.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_driver.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_formatter.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_options.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_paths.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_reader.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_util.rb
/usr/lib/ruby/1.8/rdoc/ri/ri_writer.rb
/usr/lib/ruby/1.8/rdoc/template.rb
/usr/lib/ruby/1.8/rdoc/tokenstream.rb
/usr/lib/ruby/1.8/rdoc/usage.rb