1.删除/etc/yum.repos.d/所有文件
2.创建yum文件
cat /etc/yum.repos.d/centos.repo [Centos7] name=Centos7 baseurl=file:///mnt/ enabled=1 gpgcheck=0 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
3.挂载ios至/mnt
4.执行yum clean all