ConfigServer Firewall, or CSF, is a common Linux security suite. Log in to your VPS as the root user and run the following commands to install CSF:

# rm -fv csf.tgz

# wget http://www.configserver.com/free/csf.tgz

# tar -xzf csf.tgz

# cd csf

# sh install.sh

If WHM/cPanel is installed on your server, you can configure CSF from WHM, otherwise edit the files in /etc/csf.

For more information, see: https://configserver.com/cp/csf.html