One of the best ways to secure any server, is using something called a "firewall".
One of the most longstanding and popular firewalls is something called IPTABLES. IPTABLES is basically an evolved version of the old IPCHAINS firewall which was the standard firewall which nearly every *nux box ran for years.
Here are some of the main commands any firewall admin has to know.
# KEY FIREWALL COMMANDS using IPTABLES (not old ipchains)
To CLEAR OUT the /var/log/firewall and /var/log/syslog , run: etc/rc.d/rc.syslog stop
then run: mv /var/log/firewall /var/log/firewall-backup
then run: mv /var/log/syslog /var/log/syslog-backup
then run: /etc/rc.d/rc.syslog restart
then, inside of your /var/log directory, run: ls -ks Note: You do this to make sure that the new firewall and syslog files exist and are logging.