1.进入到yum的源目录下

cd /etc/yum.repos.d/

2.将原来的CentOS-Base.repo进行备份

mv CentOS-Base.repo CentOS-Base.repo_back

3.下载阿里源
http://mirrors.aliyun.com/repo/Centos-7.repo 到/etc/yum.repos.d/目录下

4.改变名字

mv Centos-7.repo CentOS-Base.repo

5.生成缓存

yum makecache

6.更新

yum -y update