Centos7系統更換yum源鏡像爲國內鏡像

cd /etc/yum.repos.d/
mv CentOS-Base.repo CentOS-Base.repo.bak
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo 
yum clean all
yum makecache
yum -y update