ERROR: RDoc documentation generator not installed!

i am installing rails on a new machine, and during each of my gem
installs, i am getting this:

1 gem installed
ERROR: While executing gem ... (Gem::DocumentError)
    ERROR: RDoc documentation generator not installed!

anyone have any ideas?

yum install ruby-docs

I just found this old thread searching for the same problem. For me,
the actual needed command was 'yum install ruby-rdoc'