How do I disable the firewall in Ubuntu Linux server edition? How do I turn off the firewall in Ubuntu Linux version 12.04 or 14.04 LTS server?
The latest version of Ubuntu comes with a program called ufw. It is used for managing a Linux firewall and aims to provide an easy to use interface for the user.

A Note About ufw

As I said earlier, the latest version of Ubuntu comes with ufw (now it is the default firewall configuration tool for Ubuntu). It is developed to ease iptables firewall configuration, ufw provides a user friendly way to create an IPv4 or IPv6 host-based firewall.

List ufw firewall rules, enter:

$ sudo ufw status verbose
Sample outputs:

Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing), deny (routed)
New profiles: skip
 
To                         Action      From
--                         ------      ----
71.81.22.14 80/tcp        ALLOW IN    Anywhere
71.81.22.15 80/tcp        ALLOW IN    Anywhere

To disable ufw based firewall, enter:

$ sudo ufw disable

List current firewall rules and stop firewall (old method)

You can type the following command to see if firewall is active or not (open a terminal or ssh session and type the following command):
$ sudo iptables -L -n
Sample outputs:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:53 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:53 
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0           udp dpt:67 
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0           tcp dpt:67 
 
Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  0.0.0.0/0            192.168.122.0/24    state RELATED,ESTABLISHED 
ACCEPT     all  --  192.168.122.0/24     0.0.0.0/0           
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable 
REJECT     all  --  0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable 
 
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

You can save existing firewall rules as follows:
$ sudo iptables-save > firewall.rules
Finally, type the following commands to stop firewall and flush all the rules:
$ sudo iptables -X
$ sudo iptables -t nat -F
$ sudo iptables -t nat -X
$ sudo iptables -t mangle -F
$ sudo iptables -t mangle -X
$ sudo iptables -P INPUT ACCEPT
$ sudo iptables -P FORWARD ACCEPT
$ sudo iptables -P OUTPUT ACCEPT

A note about GUI tools for Ubuntu desktop systems

You can also use GUI tool to enable or disable Firewall under Ubuntu Linux desktop edition by visiting System > Administration > Firewall configuration option:

Fig.01: Disabling Firewall In Ubuntu Linux

Simply unselect “Enabled” option to turn off the firewall.