Change yum to Alibaba cloud source under centos7

1. Backup old configuration files

cd /etc/yum.repos.d
mv CentOS-Base.repo CentOS-Base.repo.bak

2. Download the files of Aliyuan

sudo wget -O CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

3. Update yum to rebuild the cache

yum clean all
yum makecache