我把它放到终端：
sudo gem install rails -V
我得到这个错误输出：
200 OK
GET http://rubygems.org/quick/Marshal.4.8/rack-1.4.2.gemspec.rz
302 Moved Temporarily
GET http://bb-m.rubygems.org/quick/Marshal.4.8/rack-1.4.2.gemspec.rz
200 OK
GET http://rubygems.org/quick/Marshal.4.8/rack-1.4.3.gemspec.rz
302 Moved Temporarily
GET http://rubygems.global.ssl.fastly.net/quick/Marshal.4.8/rack-1.4.3.gemspec.rz
200 OK
GET http://rubygems.org/quick/Marshal.4.8/rack-1.4.4.gemspec.rz
302 Moved Temporarily
GET http://rubygems.global.ssl.fastly.net/quick/Marshal.4.8/rack-1.4.4.gemspec.rz
200 OK
GET http://rubygems.org/quick/Marshal.4.8/rack-1.4.5.gemspec.rz
302 Moved Temporarily
...此时它最终说它无法安装导轨。