为什么ri对Rails一无所知？
$ ri link_to Nothing known about .link_to 实际上，似乎ri对Rails一无所知。 但是ri --list-doc-dirs显示包含Rails文件夹：
/usr/share/ri/1.8/system /usr/share/ri/1.8/site /root/.rdoc /usr/lib64/ruby/gems/1.8/doc/actionmailer-2.3.5/ri /usr/lib64/ruby/gems/1.8/doc/actionpack-2.3.5/ri /usr/lib64/ruby/gems/1.8/doc/activerecord-2.3.5/ri /usr/lib64/ruby/gems/1.8/doc/activeresource-2.3.5/ri /usr/lib64/ruby/gems/1.8/doc/activesupport-2.3.5/ri /usr/lib64/ruby/gems/1.8/doc/cgi_multipart_eof_fix-2.5.0/ri /usr/lib64/ruby/gems/1.8/doc/columnize-0.3.5/ri /usr/lib64/ruby/gems/1.8/doc/daemons-1.0.10/ri /usr/lib64/ruby/gems/1.8/doc/fastthread-1.0.1/ri /usr/lib64/ruby/gems/1.8/doc/gem_plugin-0.2.3/ri /usr/lib64/ruby/gems/1.8/doc/json-1.6.3/ri /usr/lib64/ruby/gems/1.8/doc/linecache-0.46/ri /usr/lib64/ruby/gems/1.8/doc/macaddr-1.0.0/ri /usr/lib64/ruby/gems/1.8/doc/mime-types-1.17.2/ri /usr/lib64/ruby/gems/1.8/doc/mongrel-1.1.5/ri /usr/lib64/ruby/gems/1.8/doc/mongrel_cluster-1.0.5/ri /usr/lib64/ruby/gems/1.8/doc/multipart-post-1.1.4/ri /usr/lib64/ruby/gems/1.8/doc/postgres-0.7.9.2008.01.28/ri /usr/lib64/ruby/gems/1.8/doc/rack-1.0.1/ri /usr/lib64/ruby/gems/1.8/doc/rake-0.8.7/ri /usr/lib64/ruby/gems/1.8/doc/rbx-require-relative-0.0.5/ri /usr/lib64/ruby/gems/1.8/doc/rdoc-3.12/ri /usr/lib64/ruby/gems/1.8/doc/rdoc-tags-1.2/ri /usr/lib64/ruby/gems/1.8/doc/rest-client-1.6.7/ri /usr/lib64/ruby/gems/1.8/doc/ruby-debug-0.10.4/ri /usr/lib64/ruby/gems/1.8/doc/ruby-debug-base-0.10.4/ri /usr/lib64/ruby/gems/1.8/doc/sqlite3-ruby-1.2.4/ri /usr/lib64/ruby/gems/1.8/doc/uuidtools-2.1.1/ri
它出什么问题了？
UPDATE
我在/usr/lib64/ruby/gems/1.8/doc/actionpack-2.3.5/ri/ActionView/Helpers/UrlHelper/的文件夹中找到了这些yaml文件：
button_to-i.yaml cdesc-UrlHelper.yaml current_page%3f-i.yaml link_to-i.yaml link_to_if-i.yaml link_to_unless-i.yaml link_to_unless_current-i.yaml mail_to-i.yaml url_for-i.yaml
但是在ri工作良好的另一个系统中，文件是*.ri ，而不是*.yaml 。
你试过跑步了吗：
gem rdoc rails
来自文档：
Summary: Generates RDoc for pre-installed gems Description: The rdoc command builds RDoc and RI documentation for installed gems. Use --overwrite to force rebuilding of documentation.
我发现安装ri文档的唯一可靠方法是这样（即它安装最新的Rails包括ri文档）：
sudo gem install rails --pre --ri