修改为阿里源:
sudo mkdir /etc/yum.repos.d/backup
sudo mv /etc/yum.repos.d/*.* /etc/yum.repos.d/backup
sudo wget -O /etc/yum.repos.d/CentOS7-Aliyun.repo http://mirrors.aliyun.com/repo/Centos-7.repo
sudo wget -O /etc/yum.repos.d/epel-7-Aliyun.repo http://mirrors.aliyun.com/repo/epel-7.repo
sudo yum clean all
sudo yum makecache