1.把默认yum源备份(可选)
mv?/etc/yum.repos.d/CentOS-Base.repo?/etc/yum.repos.d/CentOS-Base.repo.bak
2.下载yum源repo文件
阿里云官方教程：http://mirrors.aliyun.com/help/centos
163官方教程：http://mirrors.163.com/.help/centos.html
CentOS5
阿里云：wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-5.repo
163：wget -O /etc/yum.repos.d/CentOS5-Base-163.repo http://mirrors.163.com/.help/CentOS5-Base-163.repo
CentOS6
阿里云：wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
163：wget -O /etc/yum.repos.d/CentOS6-Base-163.repo http://mirrors.163.com/.help/CentOS6-Base-163.repo
CentOS7
阿里云：wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
163:wget -O /etc/yum.repos.d/CentOS7-Base-163.repo http://mirrors.163.com/.help/CentOS7-Base-163.repo
3.清除缓存
yum clean all
yum makecache
