Error fetching https://gems.ruby-china.org/: bad response Not Found 404 (https://gems.ruby-china.org/specs.4.8.gz)
https://gems.ruby-china.org/ 访问不了
域名改为
https://gems.ruby-china.com/
所以替换 ruby-china 提供镜像，正确的操作是：
$ sudo gem update --system
$ gem sources --remove https://rubygems.org/
$ gem sources --remove https://ruby.taobao.org/ //如果安装了淘宝的镜像
//等有反应之后再敲入以下命令
gem sources -a https://gems.ruby-china.com/
为了验证你的Ruby镜像是并且仅是ruby-china，可以用以下命令查看：
$ gem sources -l
*** CURRENT SOURCES ***
https://gems.ruby-china.com
Error fetching https://gems.ruby-china.org/: bad response Not Found 404 (https://gems.ruby-china.org/specs.4.8.gz)
原文地址：https://www.cnblogs.com/joyce306/p/9542777.html