你没有告诉你是如何安装 rbenv 的，但我认为它是按用户安装的(这是默认的).在这种情况下，您应该在不使用 sudo 的情况下安装 gem.当您执行 sudo gem install rails 时，它安装在系统 ruby​​ 中，而不是 rbenv 选择的一个.

You didn't tell how you installed rbenv, but I think it is per-user installation (which is default). In this case you should install gems without using sudo. When you did sudo gem install rails, it was installed in system ruby, not rbenv's selected one.

解决方案 - 在没有 sudo 的情况下安装 rails:

Solution - install rails without sudo:

rbenv global 2.1.0
gem install rails
rbenv rehash