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If you're not logged in as the root user, you can su to root to adjust your configuration. The file is called csf.conf, and it's saved to /etc/csf/csf.conf by default. To do this, type cd /etc/csf and press ↵ Enter. You can use any text editor you wish, such as vim or nano. To open csf.conf in vim, type vim csf.config and press ↵ Enter. TCP ports. Once you have the file open, you will see TCP_IN and TCP_OUT sections. The TCP_IN section lists open inbound TCP ports separated by commas. The ports are in numerical order to make things easy, but it's not required that the ports you stick to the order. You can add ports to the end of the sequence, just separate them with commas.  For example, let's say you want to open port 999, and the current open ports are 20, 21, 22, 25, 53, 80, 110, 143, 443, 465, 587, 993, 995. After adding port 999 to the list, it will look like this: 20, 21, 22, 25, 53, 80, 110, 143, 443, 465, 587, 993, 995, 999. To get into insertion/typing mode in vim, press the i key on the keyboard. Just as you did with the incoming port, add any outbound TCP ports you'd like to open to the TCP_OUT list. Follow these steps to save and exit the file:  Press the Esc key. Type :wq!. Press ↵ Enter. This restarts the firewall and opens the new ports. To deny a port, re-open the file, delete the port, save the file, and then re-start the firewall.

Summary:
Log in to your server. Go to directory that contains your CSF config file. Open csf.conf in a text editor. Add an incoming port to the TCP_IN list. Allow outgoing TCP to the TCP_OUT list. Save your changes and exit the file. Type service csf restart and press ↵ Enter.