rm -f /etc/yum.repos.d/*
cat>/etc/yum.repos.d/centos.repo<<EOF
[AppStream]
name=AppStream
gpgcheck=0
enabled=1
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/8.4.2105/AppStream/x86_64/os/
[BaseOS]
name=BaseOS
gpgcheck=0
enabled=1
baseurl=https://mirrors.tuna.tsinghua.edu.cn/centos-vault/8.4.2105/BaseOS/x86_64/os/
EOF
systemctl stop firewalld&&systemctl disable firewalld && setenforce 0
sed -i 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/selinux/config
yum install -y vim net-tools bash-completion wget chrony
 sed -i s/2\.centos\.pool\.ntp\.org/ntp\.aliyun\.com/g /etc/chrony.conf
 systemctl enable chronyd --now && systemctl restart chronyd && sleep 3 && chronyc sources