Could not find a valid gem ‘redis’ (>= 0) in any repository

错误：

[root@Cache conf]# yum install ruby rubygems  
[root@Cache conf]# gem install redis
WARNING:  RubyGems 1.2+ index not found for:
RubyGems will revert to legacy indexes degrading performance.
Updating metadata for 1 gems from http://rubygems.org/
.
complete
ERROR:  Could not find a valid gem 'redis' (>= 0) in any repository

解决：这个是由于没有安装rubygems-devel

[root@Cache conf]# yum install rubygems-devel