CentOS的yum源更换为阿里云的源3步走

1.备份你的原镜像文件

	mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2.下载新的CentOS-Base.repo 到/etc/yum.repos.d/

	#CentOS 5
	wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo
	#CentOS 6
	wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
	#CentOS 7
	wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

3.运行yum makecache生成缓存