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UFW (Uncomplicated Firewall) is Ubuntu’s simpler command-line front end for host firewall rules. A safe baseline is to deny unsolicited incoming connections, allow outgoing connections, permit SSH before switching the firewall on, and then add only the services your machine must expose. Check the rule list before deleting anything, and use man ufw on the target system for the syntax supported by its installed version.
What UFW is and when to use it
UFW makes common IPv4 and IPv6 host-firewall tasks easier than writing equivalent rules directly for iptables. It is available by default in Ubuntu installations since Ubuntu 8.04 LTS, although it ships disabled. While inactive, rules can be stored without being enforced; enforcement starts only after sudo ufw enable.
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Inspect the current state before changing anything
Start by finding out whether UFW is active and what it will do. Nearly all administrative UFW commands require root privileges, so the examples use sudo.
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| Command | What it shows or does |
|---|---|
sudo ufw status |
Reports whether the firewall is active. |
sudo ufw status verbose |
Adds the default policies and logging level to the status output. |
sudo ufw status numbered |
Lists rules with numbers, which you need when deleting a rule by number. |
sudo ufw app list |
Shows application profiles installed on the system. |
An inactive status means UFW is not enforcing its rules. It does not necessarily mean that every previously entered rule has vanished; enable the firewall only after verifying that remote access and required services are allowed.
A safe first-time setup
For a typical Ubuntu server, enter the following sequence. The order matters: the SSH exception is created before activation so a remote session is not cut off by the new incoming default.
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sudo ufw default deny incoming
Set unsolicited inbound traffic to be denied by default.sudo ufw default allow outgoing
Permit outbound connections unless a more specific rule changes that behavior.sudo ufw allow OpenSSH
Allow the installed OpenSSH application profile. If that profile is unavailable, usesudo ufw allow sshor an explicit port rule such assudo ufw allow 22/tcp.sudo ufw enable
Turn enforcement on. Confirm the warning before proceeding.sudo ufw status verbose
Verify that the firewall is active, the defaults are correct, and the SSH rule is present.
If you administer the machine over SSH, never skip step 3. Enabling UFW with a deny-incoming policy and no matching SSH rule can terminate your remote access. For a new server, establish a second management path—such as a provider console or local terminal—before experimenting with rules that could affect your only connection.
Allowing services and ports
Allow a TCP or UDP port
Use an explicit port and protocol when you know exactly what should be reachable:
sudo ufw allow 22/tcpallows TCP port 22, commonly used for SSH.sudo ufw allow 53/udpallows UDP port 53, commonly used for DNS queries.
Specifying the protocol avoids opening the other transport unnecessarily. Add only ports for services that are actually listening and that clients need to reach.
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Allow a named service
For common services, UFW can use a service name instead of a numeric port:
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Named services depend on the service definitions available to UFW. If a name is rejected or does not map to the port you expect, use an explicit port/protocol rule and confirm the result with sudo ufw status.
Allow an application profile
Application profiles bundle a service name with its expected ports. List what is installed with sudo ufw app list, then use the displayed name. For example, sudo ufw allow OpenSSH permits the OpenSSH profile. Profile names are system-dependent, so copy the spelling shown by the command rather than assuming a profile exists.
Restrict an allowance by source address
A rule can be narrower than “any source on the internet.” To allow an entire subnet:
sudo ufw allow from 192.168.10.0/24
To allow one host to reach SSH:
sudo ufw allow from 192.168.1.7 port ssh
Source restrictions are useful for administration networks and private services. Make sure the source address or subnet is stable and is the address actually seen by the server; NAT or a proxy can make that different from the client’s local address.
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Denying, rejecting, and rate-limiting traffic
Deny a port
A specific deny rule can block a service even when the port might otherwise be reachable. The documented example is:
sudo ufw deny 3306/tcp
Use a deny rule when you want an explicit exception in the rule set. Remember that a default deny-incoming policy already blocks unsolicited inbound connections that have no allow rule.
Limit repeated SSH connections
sudo ufw limit 22/tcp applies UFW’s rate-limiting behavior to TCP port 22. It is intended to slow repeated SSH connection attempts, such as brute-force bursts, while still permitting normal access. It is not a replacement for strong authentication, timely updates, or account protections.
Reject instead of silently dropping
A reject action tells the sender that the traffic was refused rather than silently discarding it. Use the reject action when that response behavior is appropriate for the service and your troubleshooting needs. Because exact argument forms can vary with the installed UFW version and rule syntax, verify the command in man ufw before applying it to a production rule set.
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Delete by rule number
First display numbered rules:
sudo ufw status numbered
Then remove the unwanted entry by its displayed number:
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sudo ufw delete NUMBER
Replace NUMBER with the actual value. Re-run status numbered after each deletion if you are removing several entries, because the remaining rules can be renumbered.
Delete by repeating the original rule
You can also prefix the original rule with delete. For example, a rule created with sudo ufw allow 53/udp can be removed with:
sudo ufw delete allow 53/udp
Use the numbered method when duplicate-looking rules or complex source restrictions make it difficult to reproduce the original command exactly.
Reload versus reset
sudo ufw reloadreapplies the current rules.sudo ufw resetclears all UFW rules. Treat this as a destructive operation: record the intended policy first and be prepared to recreate required SSH and service allowances.
Logging and verification
Enable firewall logging with:
sudo ufw logging on
Other logging levels can be selected with sudo ufw logging LEVEL; replace LEVEL with a level supported by the installed UFW version. Use sudo ufw status verbose to see the current logging level. Logging can help diagnose a blocked connection, but high-volume services can produce substantial log output, so choose a level that your storage and monitoring can handle.
After any change, verify the effective rule list with sudo ufw status numbered or sudo ufw status verbose. Also check the service itself: a firewall allow rule does not start a daemon, and a listening daemon does not make a port reachable if UFW still blocks it.
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Common failure cases and recovery
“ufw enable” locked me out
The usual cause is activating UFW over SSH without an SSH allow rule. Use an out-of-band console or local terminal supplied by the machine or hosting environment, then inspect the rules and add the correct allowance—for example, sudo ufw allow OpenSSH or the actual SSH port/protocol rule. If you cannot obtain console access, the machine operator must provide a recovery path; repeated remote attempts will not bypass a host firewall.
The expected service is still unreachable
- Run
sudo ufw status verboseand confirm the rule is active, not merely stored while UFW is inactive. - Check that the rule uses the right protocol. A UDP allowance does not permit TCP traffic on the same number.
- Check the source restriction and address family. A rule limited to one host or subnet will not match a different source.
- Confirm the service is listening on the expected interface and port; UFW cannot make a stopped service listen.
- Use logging temporarily to identify blocked traffic, then return to an appropriate logging level.
A rule was deleted accidentally
Recreate it from the service requirement, then verify with sudo ufw status numbered. If many rules were removed or the policy is unclear, do not guess: reconstruct the intended baseline, ensure SSH is allowed, and only then enable or reload UFW.
Practical rule-design checklist
- Inventory services that must accept inbound connections before writing allow rules.
- Set
deny incomingandallow outgoingas the starting policy when that matches your server’s role. - Allow administrative access before enabling enforcement.
- Prefer a specific protocol, port, source host, or subnet over a broad allowance.
- Use application profiles only after checking their names with
sudo ufw app list. - Review numbered rules before deleting, and verify again afterward.
- Use
sudo ufw resetonly when you intentionally want to remove the complete UFW rule set. - Consult
man ufwon the actual machine for authoritative, version-specific syntax. The Ubuntu wiki identifies the ufw(8) manual as the reference for current commands.
UFW command quick reference
| Goal | Command |
|---|---|
| Check whether UFW is active | sudo ufw status |
| Show defaults and logging | sudo ufw status verbose |
| Show numbered rules | sudo ufw status numbered |
| Deny incoming by default | sudo ufw default deny incoming |
| Allow outgoing by default | sudo ufw default allow outgoing |
| Allow SSH profile | sudo ufw allow OpenSSH |
| Allow SSH service name | sudo ufw allow ssh |
| Allow a port/protocol | sudo ufw allow 22/tcp |
| Deny a port/protocol | sudo ufw deny 3306/tcp |
| Allow a source subnet | sudo ufw allow from 192.168.10.0/24 |
| Allow one source host to SSH | sudo ufw allow from 192.168.1.7 port ssh |
| Rate-limit SSH | sudo ufw limit 22/tcp |
| List profiles | sudo ufw app list |
| Enable logging | sudo ufw logging on |
| Enable enforcement | sudo ufw enable |
| Disable enforcement | sudo ufw disable |
| Reload rules | sudo ufw reload |
| Delete rule by number | sudo ufw delete NUMBER |
| Clear all UFW rules | sudo ufw reset |
Frequently Asked Questions
Is UFW enabled by default on Ubuntu?
No. UFW ships disabled, so rules are not enforced until you run sudo ufw enable.
Why should SSH be allowed before enabling UFW?
A deny-incoming policy can block the SSH connection you are using to administer the machine. Add an OpenSSH, ssh-service, or correct port/protocol allowance first.
How do I know which rule number to delete?
Run sudo ufw status numbered, identify the unwanted entry, and then run sudo ufw delete NUMBER.
Does an allow rule prove that a service is working?
No. UFW controls packet filtering; the service must also be running and listening on the expected interface, port, and protocol.
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The Bottom Line
Use UFW as a focused host-firewall layer: inspect first, deny unsolicited inbound traffic by default, allow SSH before activation, add narrowly scoped service rules, and verify numbered rules after every change. For syntax beyond these straightforward operations, the installed system’s ufw(8) manual is the authoritative reference.
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