更换yum源[亲测OK]

1.备份原来的文件
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
2.进入yum源配置文件夹
cd /etc/yum.repos.d/

3.下载163的yum源到/etc/yum.repos.d/
wget http://mirrors.163.com/.help/CentOS6-Base-163.repo

4.生成新缓存
yum makecache