备份旧配置

各版本配置源复制在/etc/yum.repo.d/

更新缓存

备注

备份系统旧配置文件

mv /etc/yum.repos.d/CentOS-Base.repo 	
/etc/yum.repos.d/CentOS-Base.repo.backup

获取对应版本的CentOS-Base.repo到/etc/yum.repos.d/目录

各版本源配置列表
CentOS5

wget -O /etc/yum.repos.d/CentOS-Base.repo 	
http://mirrors.cloud.tencent.com/repo/centos5_base.repo

CentOS6

wget -O /etc/yum.repos.d/CentOS-Base.repo 	
http://mirrors.cloud.tencent.com/repo/centos6_base.repo

CentOS7

wget -O /etc/yum.repos.d/CentOS-Base.repo 	
http://mirrors.cloud.tencent.com/repo/centos7_base.repo

CentOS8

wget -O /etc/yum.repos.d/CentOS-Base.repo 	
http://mirrors.cloud.tencent.com/repo/centos8_base.repo

更新缓存

yum clean all
yum makecache

备注：

配置yum仓库
  # cd /etc/yum.repos.d 
  # mkdir  bak
  # mv C* bak
  # vi yum.repo
   [base]
   name=centos7
   baseurl=file:///media
   gpgcheck=0
   enabled=1

检查虚拟机的光驱是否是连接状态 
  # mount /dev/sr0 /media/       ---每一次重启之后，都要执行这条命令
  # yum clean all
  # yum makecache
  # yum install mlocate -y