#cd /etc/yum.repos.d/
#wget http://mirrors.163.com/.help/CentOS-Base-163.repo
3.修改repo文件
在所有mirrorlist前面加上#,把所有$releasever替换成5,保存
#sed -i '/mirrorlist/d' CentOS-Base-163.repo
#sed -i 's/\$releasever/5/' CentOS-Base-163.repo
4.清理并重新生成yum缓存
#yum clean metadata
#yum makecache