mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
yum makecache
centos7 更换yum源为阿里云
原文：http://www.cnblogs.com/topcoder/p/6363637.html
