cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak

sed -i 's|mirrorlist=http://mirrorlist.centos.org.*|#&|' /etc/yum.repos.d/CentOS-Base.repo
sed -i 's|#baseurl=http://mirror.centos.org/centos/$releasever|baseurl=http://vault.centos.org/7.9.2009|' /etc/yum.repos.d/CentOS-Base.repo