ufw Command in Linux: Uncomplicated Firewall Reference

If your server is open to the public network, it needs a firewall. On Ubuntu and Debian, the easiest way to set one up is with ufw. This tool sits on top of iptables (or nftables on newer systems) and replaces complex rules with simple, easy-to-read commands.

This guide walks through the ufw command, from enabling the firewall and setting default policies to writing rules for ports, services, and specific addresses.

ufw Syntax #

The general form of the command is:

sudo ufw [OPTIONS] COMMAND [ARGS]

• OPTIONS - Flags such as --dry-run to preview what a rule would do.
• COMMAND - The action, for example enable, allow, deny, delete, or status.
• ARGS - The rule body, such as a port number, a service name, or a full rule specification.

ufw changes firewall rules, so almost every invocation needs sudo.

Checking the Firewall Status #

Before you touch the rules, check whether the firewall is running and what is already in place:

sudo ufw status

If ufw is inactive, you will see:

Status: inactive

This confirms that ufw is installed but not currently enforcing any firewall rules.

Once active, the same command lists the rules:

Status: active

To                         Action      From
--                         ------      ----
22/tcp                     ALLOW       Anywhere
80/tcp                     ALLOW       Anywhere
22/tcp (v6)                ALLOW       Anywhere (v6)
80/tcp (v6)                ALLOW       Anywhere (v6)

For a numbered view that is easier to reference when deleting rules, use:

sudo ufw status numbered

And for a more detailed output that shows default policies and logging level:

sudo ufw status verbose

Enabling and Disabling the Firewall #

The first time you enable ufw, make sure you have already allowed SSH. Enabling the firewall over an SSH session without an allow ssh rule will lock you out of the server.

Allow SSH first:

sudo ufw allow ssh

Then turn the firewall on:

sudo ufw enable

Firewall is active and enabled on system startup

At this point, ufw starts enforcing the rules immediately and will come back automatically after a reboot.

To stop the firewall and clear it from the startup sequence:

sudo ufw disable

A disabled ufw keeps the rules you defined. When you re-enable it, the same rules come back.

Default Policies #

Default policies decide what happens to traffic that does not match any rule. The usual hardening is to deny incoming traffic and allow outgoing traffic:

sudo ufw default deny incoming
sudo ufw default allow outgoing

After running these two commands, you only need to open the specific inbound ports your server should expose. Outbound traffic still flows freely, which is what most servers need.

You can also set the default for forwarded traffic, which matters if the host acts as a router or runs containers:

sudo ufw default deny routed

Allowing Connections #

The allow command is the one you will use most often. It accepts a service name, a port, a protocol, or a full rule.

Allow a Service by Name #

ufw reads /etc/services and understands common service names:

sudo ufw allow ssh
sudo ufw allow http
sudo ufw allow https

Each command opens the matching port (22, 80, and 443) for both TCP and UDP where applicable.

Allow a Specific Port #

To open a port directly, pass the port number:

sudo ufw allow 8080

By default, this opens the port for both TCP and UDP. To limit it to one protocol, add /tcp or /udp:

sudo ufw allow 8080/tcp
sudo ufw allow 53/udp

Allow a Port Range #

Port ranges require an explicit protocol:

sudo ufw allow 6000:6007/tcp
sudo ufw allow 6000:6007/udp

The colon separates the start and the end of the range, both inclusive.

Allow Traffic From a Specific Address #

To accept connections from a single IP address, use from:

sudo ufw allow from 203.0.113.25

To restrict that to a single service, add to any port:

sudo ufw allow from 203.0.113.25 to any port 22

Allow Traffic From a Subnet #

CIDR notation works the same way for whole networks:

sudo ufw allow from 192.168.1.0/24 to any port 3306

This is a common pattern for databases: the port stays closed to the internet and is only reachable from your internal network.

Allow Traffic on a Specific Interface #

To tie a rule to a network interface, add on INTERFACE:

sudo ufw allow in on eth1 to any port 3306

The in keyword applies the rule to inbound traffic on eth1. Use out for outbound traffic.

Denying Connections #

The deny command is the mirror of allow and takes the same arguments:

sudo ufw deny 23
sudo ufw deny from 198.51.100.77

When the default incoming policy is already deny, you usually do not need to write explicit deny rules for closed ports. Explicit denies are useful when you want to block a specific address while keeping a port open to everyone else.

To log the denied packets instead of silently dropping them, use reject:

sudo ufw reject 23

A reject sends an ICMP message back to the sender, while a deny drops the packet with no response.

Rate Limiting SSH #

ufw can throttle repeated connections from the same IP, which is handy for SSH brute-force protection:

sudo ufw limit ssh

The limit rule denies a connection if the source address attempts six or more connections in 30 seconds. This is a quick way to slow down password-guessing bots without installing a full intrusion-prevention tool.

Deleting Rules #

There are two common ways to remove a rule. The first is to repeat the rule with delete in front:

sudo ufw delete allow 8080/tcp

The second is to delete by rule number:

sudo ufw status numbered

     To                         Action      From
     --                         ------      ----
[ 1] 22/tcp                     ALLOW IN    Anywhere
[ 2] 80/tcp                     ALLOW IN    Anywhere
[ 3] 8080/tcp                   ALLOW IN    Anywhere

sudo ufw delete 3

ufw asks for confirmation before removing the rule. Keep in mind that after a deletion, the numbering shifts for the remaining rules, so always check the numbered status again before deleting another rule.

For a deeper walkthrough, see how to list and delete UFW firewall rules .

Application Profiles #

Services that come with their own ufw profile can be referenced by name. List them with:

sudo ufw app list

Available applications:
  Nginx Full
  Nginx HTTP
  Nginx HTTPS
  OpenSSH

To open the ports that a profile covers, pass its name to allow:

sudo ufw allow 'Nginx Full'

Quote profile names that contain spaces. To see what ports a profile includes, use:

sudo ufw app info 'Nginx Full'

Dry Run #

Before you commit to a change, you can preview the iptables rules ufw would add with --dry-run:

sudo ufw --dry-run allow 8080/tcp

No rule is created. The output shows the exact lines ufw would write, which is useful when you are writing rules over SSH and want to double-check them first.

Logging #

ufw can log packets that match rules, which helps when troubleshooting. The log level can be adjusted:

sudo ufw logging on
sudo ufw logging medium

Valid levels are off, low, medium, high, and full. ufw logs through the kernel log facility, so the exact destination depends on your system logging setup. On many Ubuntu systems with rsyslog, you will see entries in /var/log/ufw.log, and you can often inspect them with journalctl as well.

Reset the Firewall #

To clear every rule and set ufw back to its fresh state, run:

sudo ufw reset

IPv6 Support #

On most modern systems, ufw can manage IPv6 rules as well as IPv4 rules. Check the setting in /etc/default/ufw:

IPV6=yes

When IPV6=yes, generic rules such as sudo ufw allow 22/tcp are created for both IPv4 and IPv6. Rules that include an explicit address stay specific to that address family. In the status output, the IPv6 rules appear with (v6) next to them.

Quick Reference #

For a printable quick reference, see the ufw cheatsheet .

Troubleshooting #

ufw: command not found
Install the ufw package with sudo apt install ufw on Ubuntu or Debian. On Fedora, RHEL, and derivatives, firewalld is the default and ufw is rarely used.

Locked out after enabling the firewall over SSH
The default deny policy blocked your SSH session. You will need console access to the server. Once in, run sudo ufw allow ssh and sudo ufw reload to restore access. The usual safeguard is to allow SSH before the first enable.

Rule added but traffic still blocked
Confirm the rule is in the right direction (inbound vs outbound) and on the right interface. Check with sudo ufw status verbose. If Docker is running, it writes its own iptables rules that can bypass ufw.

Changes do not take effect
After manual edits to /etc/ufw/ files, reload the firewall with sudo ufw reload. Commands issued through ufw apply immediately and do not need a reload.

FAQ #

Is ufw the same as iptables?
No. ufw is a front end that generates iptables (or nftables) rules for you. The kernel still enforces the rules through its packet filter, but you do not need to edit the raw tables yourself.

Does ufw start automatically after reboot?
Yes, once you run sudo ufw enable, the service is registered with systemd and starts on boot. You can confirm with systemctl status ufw.

How do I allow a port for a single IP address?
Use the from and to any port form: sudo ufw allow from 203.0.113.25 to any port 22. This keeps the port closed to the rest of the internet and only opens it for that one address.

What is the difference between deny and reject?
deny drops the packet without any reply. reject sends an ICMP message back to the sender telling them the connection was refused. Reject is slightly friendlier to well-behaved clients but makes the server more visible to scans.

How do I undo everything and start over?
Run sudo ufw reset. It disables the firewall and removes every rule. Remember to re-add the SSH rule before re-enabling, especially on a remote server.

Conclusion #

ufw keeps firewall management readable: allow what you need, deny what you do not, and lean on the default policies to cover the rest. If you want step-by-step instructions for setting it up on a new server, see how to set up a firewall with UFW on Ubuntu 24.04 .

About the authors

Dejan Panovski

Dejan Panovski is the founder of Linuxize, an RHCSA-certified Linux system administrator and DevOps engineer based in Skopje, Macedonia. Author of 800+ Linux tutorials with 20+ years of experience turning complex Linux tasks into clear, reliable guides.

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