怎样更新centos6 yum源

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
cd /etc/yum.repos.d/
wget http://mirrors.163.com/.help/CentOS6-Base-163.repo
curl -o /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo
yum clean all
yum makecache
yum install -y vim wget bash-completion tree lrzsz nmap nc htop #shell快捷帮助 #其他常用软件
yum install -y net-tools  setuptool