Install CSF firewall on Ubuntu Server

First, install libwww-perl package needed for CSF firewall

apt -y install libwww-perl

Install CSF with

cd /usr/local/src
wget https://download.configserver.com/csf.tgz
tar -xzf csf.tgz
cd csf
sh install.sh

Change following settings in csf.conf file

/bin/sed -i "s/RESTRICT_SYSLOG\s*=.*$/RESTRICT_SYSLOG = \"3\"/g" /etc/csf/csf.conf
/bin/sed -i "s/SYSLOG_CHECK\s*=.*$/SYSLOG_CHECK = \"3600\"/g" /etc/csf/csf.conf
/bin/sed -i "s/TESTING = \"1\"/TESTING = \"0\"/g" /etc/csf/csf.conf

If you need GUI enabled, edit file

vi /etc/csf/csf.conf

Modify following settings

UI = "1"
UI_PORT = "8282"
UI_USER = "username"
UI_PASS = "password"
UI_ALLOW = "0"