Enabling/disabling linux firewall?.

To increase the security of the instance, you want to enable linux firewall. To check the current ports open in the firewall you can run

$sudo iptables -v -L

Additionally, you can check if firewall is enabled at boot time

$ chkconfig --list |grep iptables
iptables        0:off   1:off   2:on    3:on    4:on    5:on    6:off

To disable firewall at boot time you can run the below command:

$ sudo chkconfig iptables off

To confirm the runlevels (2,3,4,5), you can again run the below command:

$ chkconfig --list | grep iptables
iptables        0:off   1:off   2:off   3:off   4:off   5:off   6:off

To the save the current firewall rules to a file, you can run

$sudo iptables-save > $HOME/firewall.rules

To restore the firewall rules, you can run

$sudo iptables-restore < $HOME/firewall.rules

To temporarily stop the firewall you can run the below command (NOTE:- before you stop iptables make sure to run iptables-save command to save the rules to a file)

$sudo /etc/init.d/iptables stop

Once the firewall has stopped, you can list the rules and it will show up like

$ sudo iptables -v -L

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

To restart firewall, run

$sudo /etc/init.d/iptables start