网易163网络源地址：http://mirrors.163.com/ CentOS网络源地址：http://centos.ustc.edu.cn/centos/检查yum源是否安装
rpm -qa|grep yum卸载yum源
rpm -qa|grep yum|xargs rpm -e --nodeps
网站下载yum源-3个
系统中下载（版本会更新，用新版本即可）wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-cron-3.4.3-168.el7.centos.noarch.rpm wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm安装
rpm -ivh --force --nodeps *.rpm // 如果提示没有rpm工具 安装 apt install rpm验证是否安装
rpm -qa|grep yum
