CentOS基礎包安裝或更新
安裝wget，yum install -y wget
更新yum源更舞，參見CentOS更新yum源為阿里云
Step1: 若本機未安裝
wget，則yum install wget -y
Step2: 備份/etc/yum.repos.d/CentOS-Base.repo
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
Step3: 進入yum源配置文件所在文件夾
cd /etc/yum.repos.d/
Step4: 下載aliyun的yum源配置文件宇葱，放入/etc/yum.repos.d/下刊头，并更改名稱為CentOS-Base.repo
wget http://mirrors.aliyun.com/repo/Centos-7.repo
mv Centos-7.repo CentOS-Base.repo
Step5: 運行yum makecache生成緩存
yum makecache
Step6: 更新yum，yum -y update
