更换centos的yum源为阿里源

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