恢复到之前的 YUM 源，可以使用以下命令：
sudo cp /etc/yum.repos.d/CentOS-Base.repo.bak /etc/yum.repos.d/CentOS-Base.repo
sudo yum clean all
sudo yum makecache
sudo cp /etc/yum.repos.d/CentOS-Base.repo.bak /etc/yum.repos.d/CentOS-Base.repo
sudo yum clean all
sudo yum makecache