将近两个月没有登录过我的美国服务器SSH了，登录后心血来潮来了个yum update，发现yum源是国内大厂某某云的，我顿时就迷了，我一个美国服务器要啥自行车？直接用官方源不是更快更香吗？

于是我就开始着手还原yum到官网状态，下面记录一下操作步骤：

Centos6:

cd /etc/yum.repos.d/
rm -rf CentOS-*
rpm -Uvh --force http://mirror.centos.org/centos-6/6.10/os/x86_64/Packages/centos-release-6-10.el6.centos.12.3.x86_64.rpm
yum clean all
yum makecache
yum update -y

cd /etc/yum.repos.d/
rm -rf CentOS-*
rpm -Uvh --force http://mirror.centos.org/centos-7/7.7.1908/os/x86_64/Packages/centos-release-7-7.1908.0.el7.centos.x86_64.rpm
yum clean all
yum makecache
yum update -y

cd /etc/yum.repos.d/
rm -rf CentOS-*
rpm -Uvh --force http://mirror.centos.org/centos-8/8.1.1911/BaseOS/x86_64/os/Packages/centos-release-8.1-1.1911.0.8.el8.x86_64.rpm
yum clean all
yum makecache
yum update -y