In order block IP address/es from CSF Firewall at command line one need to execute below mentioned commands:
1) Login into the server via shell access.
2) Go to the path of APF firewall. It should be:
3) Edit the file csf.deny.
4) Add the IP address in the list and save the file to block the IP address.
Once the IP address added one need to restart the Firewall…To Restart Firewall one need to execute below mentioned command: