sudo yum install ntpdate
sudo ntpdate -d science
sudo yum install ntp ntp-doc
systemctl status ntpd.service
sudo systemctl enable ntpd.service
sudo systemctl start ntpd.service
netstat -an | grep 123
sudo journalctl -xn
sudo vi /etc/sysconfig/iptables
sudo service iptables restart
sudo iptables -L