Linux firewall commands

Most modern Linux distribution use the following tools:

1. ufw – Used by Ubuntu and Debian based system to manage the firewall.
2. firewalld – Used by RHEL, CentOS and clones. It is a dynamic solution to manage the firewall.

Linux disable firewall command

Let us see how to stop and disable Firewalld on a CentOS or RHEL 7.x based system.

Is firewalld running on my system?

Run:
sudo firewall-cmd --state

Stop the the firewalld

Again, type:
sudo systemctl stop firewalld

Disable the FirewallD service at boot time

sudo systemctl disable firewalld
sudo systemctl mask --now firewalld

Verify that the FirewallD is gone

Simply type:
sudo systemctl status firewalld
Sample outputs:

* firewalld.service
   Loaded: masked (Reason: Unit firewalld.service is masked.)
   Active: inactive (dead)
 
Apr 09 13:54:23 nixcraft-nuc systemd[1]: Starting firewalld - dynamic firewall daemon...
Apr 09 13:54:24 nixcraft-nuc systemd[1]: Started firewalld - dynamic firewall daemon.
Apr 16 23:34:29 nixcraft-nuc systemd[1]: Stopping firewalld - dynamic firewall daemon...
Apr 16 23:34:29 nixcraft-nuc systemd[1]: Stopped firewalld - dynamic firewall daemon.

How do enable the firewalld again?
Simply run the following commands:

sudo systemctl unmask --now firewalld

sudo systemctl enable firewalld

sudo systemctl start firewalld

## verify that the firewalld started ##

sudo firewall-cmd --state
Linux disable ufw based firewall
ufw is easy to use app for managing a Linux firewall and aims to 
provide an easy to use interface for the user. It is the default on 
Ubuntu and can be installed on Debian, CentOS, and other Linux distros.
Is the ufw running?
The syntax is:

sudo ufw status
Stop the ufw on Linux
sudo ufw disable
Disable the ufw on Linux at boot time
sudo systemctl disable ufw
Verify that the ufw is gone
sudo ufw status

sudo systemctl status ufw


How do enable the ufw again?

Just issue the following two commands to enable the firewall and protect your box again:

sudo systemctl enable ufw

sudo ufw enable

## verify that ufw started ##

sudo ufw status

A note about older Linux distro

You need to use the service command and you must be a root user to run the following commands:

Stop the iptables service on Linux

service iptables stop

Disable the iptables service at boot time on Linux

# chkconfig iptables off