ソースから ruby 1.9.3 をインストールし、rubygems 1.3.6 もソースからダウンロードしました。マニュアルを見て、tarball を untar して入力しました。ruby setup.rb
これが出力として得られるものです。
/usr/local/lib/ruby/1.9.1/rubygems.rb:206:in `try_activate': undefined method
`find_by_path' for Gem::Specification:Class (NoMethodError)
from /usr/local/lib/ruby/1.9.1/rubygems/custom_require.rb:59:in `rescue in require'
from /usr/local/lib/ruby/1.9.1/rubygems/custom_require.rb:35:in `require'
from /root/rubygems-1.3.6/lib/rubygems/config_file.rb:50:in `<class:ConfigFile>'
from /root/rubygems-1.3.6/lib/rubygems/config_file.rb:28:in `<top (required)>'
from /usr/local/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from /usr/local/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from /root/rubygems-1.3.6/lib/rubygems/gem_runner.rb:8:in `<top (required)>'
from /usr/local/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from /usr/local/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from setup.rb:25:in `<main>'
これはCentOS 5で行われます