~/railsdoc$ rails mybook
/usr/local/ruby/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in require': cannot load such file -- active_support (LoadError)
from /usr/local/ruby/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in
require'
from /usr/lib/ruby/vendor_ruby/railties/lib/rails_generator.rb:30:in <top (required)>'
from /usr/local/ruby/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in
require'
from /usr/local/ruby/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in require'
from /usr/lib/ruby/vendor_ruby/railties/bin/rails:16:in