修改centos源为阿里云源

1.备份源文件

sudo  mkdir /opt/centos-yum.bak sudo  mv /etc/yum.repos.d/* /opt/centos-yum.bak/

2.查看centos 版本号

cat /etc/redhat-release

3.在阿里云镜像库找到符合自己centos版本的镜像源（以下操作都是在sudo 下进行的）

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

4.

 yum clean all yum makecache