centos7 更新及切换yum 源

1.备份源

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

2.切换目录

cd /etc/yum.repos.d/

3.下载阿里源

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

4.清除缓存

yum clean all

5.生成新的缓存

yum makecache

6.更新系统

yum -y update