1.首先进入yum文件夹
cd /etc/yum.repos.d
2.删除已有的yum源
rm -rf *
3.下载yum源(阿里腾讯二选一)
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.cloud.tencent.com/repo/centos7_base.repo #腾讯
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo #阿里
4.清除yum缓存
yum clean all
5.更新缓存
yum makecache
6.更新(可选)
yum -y update