```shell
#centos7修改yum源为阿里源
#1.查看yum源信息
yum repolist
#2.备份原先的yum源配置文件
cd /etc/yum.repos.d
mv CentOS-Base.repo CentOS-Base.repo.bak
#3.下载阿里源配置文件
wget -O CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
#4.更新缓存
yum clean all
yum makecache
#5.再次查看yum源信息
yum repolist
```