centOS7更新yum源
1.备份原来的yum源
sudo cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
2. 设置阿里云的yum源
sudo wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
3.添加EPEL源
sudo wget -P /etc/yum.repos.d/ http://mirrors.aliyun.com/repo/epel-7.repo
4.清理缓存,生成新的缓存,执行yum更新
sudo yum clean all;yum makecache;yum update