我正在使用 Ubuntu 12.04 LTS。我在 ubuntu 上安装了 rails，然后运行jekyll --server. 但结果如下：
lo@lo-Rev-1-0:~/lf2013.github.com$ jekyll --server /usr/lib/ruby/1.9.1/rubygems/dependency.rb:247:in
to_specs': Could not find jekyll (>= 0) amongst [actionmailer-3.2.13, actionpack-3.2.13, activemodel-3.2.13, activerecord-3.2.13, activeresource-3.2.13, activesupport-3.2.13, arel-3.0.2, builder-3.0.4, bundler-1.3.4, bundler-1.3.4, coffee-rails-3.2.2, coffee-script-2.2.0, coffee-script-source-1.6.1, erubis-2.7.0, execjs-1.4.0, hike-1.2.1, i18n-0.6.1, journey-1.0.4, jquery-rails-2.2.1, json-1.7.7, mail-2.5.3, mime-types-1.21, multi_json-1.7.1, polyglot-0.3.3, rack-1.4.5, rack-cache-1.2, rack-ssl-1.3.3, rack-test-0.6.2, rails-3.2.13, railties-3.2.13, rake-10.0.3, rdoc-3.12.2, rubygems-bundler-1.1.1, rvm-1.11.3.6, sass-3.2.7, sass-rails-3.2.6, sprockets-2.2.2, sqlite3-1.3.7, thor-0.17.0, tilt-1.3.6, treetop-1.4.12, tzinfo-0.3.37, uglifier-1.3.0] (Gem::LoadError) from /usr/lib/ruby/1.9.1/rubygems/dependency.rb:256:into_spec' 来自 /usr/lib/ ruby/1.9.1/rubygems.rb:1210:ingem' from /usr/local/bin/jekyll:18:in'
现在我不知道该怎么做，因为我对 Ruby 知之甚少。