Viewing the current status of firewalld
The firewall service, firewalld, is installed on the system by default. Use the firewalld CLI interface to check that the service is running.
$ sudo firewall-cmd --stateFor more information about the service status, use the systemctl command
$ sudo systemctl status firewalldfirewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor pr Active: active (running) since Mon 2017-12-18 16:05:15 CET; 50min ago Docs: man:firewalld(1) Main PID: 705 (firewalld) Tasks: 2 (limit: 4915) CGroup: /system.slice/firewalld.service └─705 /usr/bin/python3 -Es /usr/sbin/firewalld --nofork --nopidFurthermore, it is important to know how firewalld is set up and which rules are in force before you try to edit the settings. To display the firewall settings, see Viewing current firewalld settings
Viewing current firewalld settings
Viewing allowed services using GUI
To view the list of services using the graphical firewall-config tool, press the Super key to enter the Activities Overview, type firewall, and press Enter. The firewall-config tool appears. You can now view the list of services under the Services tab.
Alternatively, to start the graphical firewall configuration tool using the command-line, enter the following command:
$ firewall-config
The Firewall Configuration window opens. Note that this command can be run as a normal user, but you are prompted for an administrator password occasionally.
Viewing firewalld settings using CLI
With the CLI client, it is possible to get different views of the current firewall settings. The --list-all option shows a complete overview of the firewalld settings.
firewalld uses zones to manage the traffic. If a zone is not specified by the --zone option, the command is effective in the default zone assigned to the active network interface and connection.
To list all the relevant information for the default zone:
$ firewall-cmd --list-allpublic target: default icmp-block-inversion: no interfaces: sources: services: ssh dhcpv6-client ports: protocols: masquerade: no forward-ports: source-ports: icmp-blocks: rich rules:
To specify the zone for which to display the settings, add the ~]# firewall-cmd --list-all --zone=homehome target: default icmp-block-inversion: no interfaces: sources: services: ssh mdns samba-client dhcpv6-client... [output truncated] |
To see the settings for particular information, such as services or ports, use a specific option. See the firewalld manual pages or get a list of the options using the command help:
$ firewall-cmd --helpUsage: firewall-cmd [OPTIONS...]General Options -h, --help Prints a short help text and exists -V, --version Print the version string of firewalld -q, --quiet Do not print status messagesStatus Options --state Return and print firewalld state --reload Reload firewall and keep state information... [output truncated]
For example, to see which services are allowed in the current zone:
$ firewall-cmd --list-servicessamba-client ssh dhcpv6-client
Listing the settings for a certain subpart using the CLI tool can sometimes be difficult to interpret. For example, you allow the SSH service and firewalld opens the necessary port (22) for the service. Later, if you list the allowed services, the list shows the SSH service, but if you list open ports, it does not show any. Therefore, it is recommended to use the --list-all option to make sure you receive a complete information.
Runtime and permanent settings
Any changes made while firewalld is running will be lost when firewalld is restarted. When firewalld is restarted, the settings revert to their permanent values.
These changes are said to be made in runtime mode.
To make the changes persistent across reboots, apply them again using the --permanent option. Alternatively, to make changes persistent while firewalld is running, use the --runtime-to-permanent firewall-cmd option.
If you make changes while firewalld is running using only the --permanent option, they do not become effective until firewalld is restarted. However, restarting firewalld briefly stops the networking traffic, causing disruption to your system.
Changing settings in runtime and permanent configuration using CLI
Using the CLI, you can only modify either runtime or permanent mode. To modify the firewall settings in permanent mode, use the --permanent option with the firewall-cmd command.
$ sudo firewall-cmd --permanent <other options>
Without this option, the command modifies runtime mode.To change settings in both modes, you can use two methods:
Change runtime settings and then make them permanent as follows:
Change the runtime settings:
firewall-cmd <other options>Use
--runtime-to-permanentto make the changes permanent.firewall-cmd --runtime-to-permanent
Set permanent settings and reload the settings into runtime mode:
Make the changes in permanent mode:
firewall-cmd --permanent <other options>Reload the settings:
firewall-cmd --reload
The first method allows you to test the settings before you apply them to permanent mode.
It is possible that an incorrect setting will result in a user locking themselves out of a machine. To prevent this, use the For example, to add the SSH service for 15 minutes use this command: $ sudo firewall-cmd --add-service=ssh --timeout 15m The SSH service will be available until access is removed after 15 minutes. |
Controlling ports using firewalld
What are ports?
Ports are logical devices that enable an operating system to receive and distinguish network traffic and forward it accordingly to system services. These are usually represented by a daemon that listens on the port, that is it waits for any traffic coming to this port.
Normally, system services listen on standard ports that are reserved for them. The httpd daemon, for example, listens on port 80. However, system administrators may configure daemons to listen on different ports to enhance security.
Opening a port
Through open ports, the system is accessible from the outside, which represents a security risk. Generally, keep ports closed and only open them if they are required for certain services.
Opening a port using the command line
Get a list of allowed ports in the current zone:
$ firewall-cmd --list-ports
Add a port to the allowed ports to open it for incoming traffic:
$ sudo firewall-cmd --add-port=port-number/port-type
Make the new settings persistent:
$ sudo firewall-cmd --runtime-to-permanent
The port types are either tcp, udp, sctp, or dccp. The type must match the type of network communication.
Closing a port
When an open port is no longer needed, close that port in firewalld. It is highly recommended to close all unnecessary ports as soon as they are not used because leaving a port open represents a security risk.
Closing a port using the command line
To close a port, remove it from the list of allowed ports:
List all allowed ports:
$ firewall-cmd --list-ports
This command will only give you a list of ports that have been opened as ports. You will not be able to see any open ports that have been opened as a service. Therefore, you should consider using the --list-all option instead of --list-ports.
Remove the port from the allowed ports to close it for the incoming traffic:
$ sudo firewall-cmd --remove-port=port-number/port-type
Make the new settings persistent:
$ sudo firewall-cmd --runtime-to-permanent
