Immanuelbint Docs

Appearance

Using firewall-cmd for configuring Firewall in linux ​

The firewall-cmd command is used to configure and manage the firewalld service on Linux systems. It allows you to dynamically add, remove, and modify firewall rules without restarting the service.

Check Firewall status ​

bash
firewall-cmd --state

output:

running

Listing Active Zones ​

Show all available zones and the default one:

bash
firewall-cmd --get-active-zones

output:

public
  interfaces: eth0

Allowing Service ​

Permit HTTP service in the public zone:

bash
firewall-cmd --zone=public --add-service=http

To make it permanent after reboot, use param --permanent

bash
firewall-cmd --zone=public --add-service=http --permanent

Reload the firewall to apply permanent rules:

bash
firewall-cmd --reload

Allowing a Specific Port ​

Open port 5432/tcp temporarily:

bash
firewall-cmd --zone=public --add-port=5432/tcp

Make it permanent:

bash
firewall-cmd --zone=public --add-port=5432/tcp --permanent
firewall-cmd --reload

Blocking a Service ​

Remove SSH access from the public zone:

bash
firewall-cmd --zone=public --remove-service=ssh --permanent
firewall-cmd --reload

Listing All Rules ​

To see all active rules in the public zone:

bash
firewall-cmd --zone=public --list-all

output:

bash
public (active)
  target: default
  interfaces: eth0
  services: dhcpv6-client http https ssh
  ports: 5432/tcp
  masquerade: no
  forward-ports:
  icmp-blocks:
  rich rules:

Useful Flags

  • --permanent → makes changes persistent across reboots.
  • --reload → reloads configuration to apply permanent changes.
  • --list-all-zones → displays rules for every zone.
  • --runtime-to-permanent → copies current runtime config into permanent rules.

Additional Notes ​

  • firewall-cmd manages zones (trusted, public, internal, etc.), each with its own rules.
  • Good practice: test rules without --permanent first, then apply permanently after confirming.
  • Always keep a console session open when changing SSH rules, to avoid locking yourself out.