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To open a port safely on a remote Linux VPS, allow your SSH connection first, add a UFW rule for the application’s port and protocol, enable UFW, and then inspect the active rules. For example, an inbound web service normally needs an explicit TCP rule for port 80 or 443, while a service on port 8080 needs its own rule. UFW changes the firewall on the VPS itself; it does not start an application, change the application’s listening address, or override a separate firewall at your VPS provider.
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The safe sequence on a remote VPS
Ubuntu identifies UFW as its default firewall configuration tool, and a fresh installation has it disabled. That disabled state is why enabling UFW over an existing SSH session requires care: if the SSH service is not allowed before activation, the firewall can block your next connection.
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Do these 3 things before closing this tab:
1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitches- Allow SSH before enabling anything. Use
sudo ufw allow sshwhen SSH uses the standard service definition, or use the explicit port rulesudo ufw allow 22/tcp. If the SSH daemon listens on another port, replace22with that port, for examplesudo ufw allow 2222/tcp. - Add the application rule. For a TCP service on port 8080, run
sudo ufw allow 8080/tcp. For ordinary web traffic, the equivalent explicit rules aresudo ufw allow 80/tcpandsudo ufw allow 443/tcp. - Enable UFW. Run
sudo ufw enableonly after the SSH rule and required application rules are present. Confirm the prompt if UFW asks for activation. - Inspect the result. Use the verbose and numbered status views described below to verify that the intended ports, protocols and address families are represented.
The simple UFW syntax takes a port and, optionally, a protocol. Writing 8080/tcp permits TCP traffic only. Omitting the protocol, as in sudo ufw allow 8080, permits both TCP and UDP, so specify the protocol whenever the service documentation identifies one.
Choose the narrowest rule that matches the service
A port number alone is not enough to describe exposure. Decide which transport protocol the application uses, whether clients can come from anywhere or only a known network, and whether a UFW application profile is preferable to a raw port rule.
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| Decision | Rule approach | When it fits |
|---|---|---|
| TCP only | sudo ufw allow PORT/tcp |
Web servers, SSH and other services that establish TCP connections. |
| UDP only | sudo ufw allow PORT/udp |
Applications whose documentation specifically requires UDP. |
| Both protocols | sudo ufw allow PORT |
Only when the application genuinely needs both TCP and UDP; omitting the protocol opens both. |
| Any source address | A normal allow rule |
Public services intended to accept clients from the internet. |
| One address or subnet | Add from ADDRESS or a CIDR network |
Administration ports and private services with a known source network. |
| Application profile | Allow a named profile discovered with ufw app list |
Software that ships a maintained UFW profile, rather than requiring a manually typed port. |
Use an explicit protocol instead of opening both transports by accident. A rule for TCP does not automatically permit UDP, and a UDP rule does not automatically permit TCP. Likewise, opening a port to every source is different from opening it only to an administrative workstation or corporate subnet.
Protect SSH from lockout
SSH is the recovery path for most remote VPS administration, so it should be the first service considered. The standard service rule is sudo ufw allow ssh; the explicit equivalent for the conventional SSH port is sudo ufw allow 22/tcp. If your SSH daemon is configured for a custom port, the rule must use that actual port. Allowing port 22 while the daemon listens on 2222 does not preserve access.
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sudo ufw allow proto tcp from 203.0.113.10 to any port 22The address in this example is a documentation address; substitute the real fixed source address you control. A CIDR network can be used when several trusted systems share a subnet, such as 203.0.113.0/24. This changes the rule from “TCP port 22 from anywhere” to “TCP port 22 from this address or network.” Ensure the source address is stable before relying on the restriction. If your SSH daemon uses a custom port, replace 22 in the restricted rule as well.
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When changing SSH ports, keep the existing working connection open while you add and verify the new rule. Start a separate test connection to the new port before removing any old rule. This staged approach gives you a way back if the daemon configuration and firewall rule do not match.
Open common web and application ports
HTTP and HTTPS
For a web server that accepts HTTP, allow TCP port 80 with sudo ufw allow 80/tcp. For HTTPS, allow TCP port 443 with sudo ufw allow 443/tcp. These rules only permit packets through UFW; the web server still has to be configured to listen on the corresponding port and address.
A custom TCP service
For an application listening on TCP port 8080, use sudo ufw allow 8080/tcp. Choose the actual port configured in the application rather than copying a commonly used example. If the service uses UDP, use sudo ufw allow 8080/udp instead. If its documentation requires both transports, use the protocol-omitted form and understand that it creates access for both.
Profiles supplied by an application
Some software installs a UFW application profile. Discover available profiles with:
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sudo ufw app listInspect a profile’s ports and description with:
sudo ufw app info NAMEAfter confirming the profile is the one you need, allow it by profile name. Profiles are stored in /etc/ufw/applications.d. A profile can be easier to audit than a raw port because its name describes the service, but inspect it first so you know which ports and protocols it represents.
Preview a rule before applying it
UFW can show the resulting rules without changing the firewall. For an HTTP profile, for example, run:
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sudo ufw --dry-run allow httpThe dry-run output lets you review what UFW would add before committing the change. Use this when you are uncertain about a profile, protocol, or address restriction. It is especially useful on a production VPS where an incorrectly broad rule can expose an administration service.
Verify the active policy and rule order
After enabling UFW, inspect the policy with:
sudo ufw status verboseThis view is useful for confirming whether UFW is active and for seeing the expanded policy information. To obtain rule numbers for later deletion or reordering, run:
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sudo ufw status numberedRead the output as an inventory, not merely as a confirmation that a command succeeded. Check that SSH uses the daemon’s real port, that each application has the required protocol, and that a source restriction has not accidentally been omitted. If both IPv4 and IPv6 are in use, check that the displayed rules cover the address families your clients use.
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Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Delete or correct a rule safely
To remove a rule by repeating its original definition after delete, use the same syntax that created it. For the earlier example:
sudo ufw delete allow 8080/tcpYou can also delete a rule by the number shown in sudo ufw status numbered. Review the numbered list immediately before deletion because adding or removing rules changes the numbers. The UFW manual warns that deleting a generic rule by number can affect only the specified IPv4 or IPv6 rule. Deleting by the original rule text removes both address-family versions where applicable, so text-based deletion is preferable when you intend to remove both.
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Do not remove the only SSH rule until a replacement has been tested from a second session. If you discover that an application rule is too broad, add the narrower replacement, verify it, and then remove the broad rule.
Why an allowed port can still be unreachable
An UFW allow rule changes the host firewall; it does not make a process listen. Diagnose the failure in layers rather than adding increasingly broad rules.
| Symptom or situation | What to check | Likely correction |
|---|---|---|
| UFW shows the rule, but no connection succeeds | Confirm the application is running and bound to the expected port. | Start or reconfigure the service; the firewall cannot create a listener. |
| The service works locally but not from outside | Check the address to which the application is bound. | Configure it to listen on the VPS address or the intended interface, not only a local loopback address. |
| One client network works and another does not | Compare the source restriction and the client’s address. | Adjust the allowed IP or CIDR only if that exposure is intended. |
| UFW appears correct, but every external client is blocked | Inspect the VPS provider’s firewall, security group or network ACL. | Permit the same port and protocol at that separate network layer. |
| TCP connects but the application still fails | Check whether the application also requires UDP or additional ports. | Add only the documented companion protocol or port, rather than opening both by default. |
| SSH was lost after activation | Check whether the rule matches the daemon’s actual port and source address. | Use the VPS provider’s console or recovery access to restore the correct SSH rule, then test a new session before closing the old one. |
The provider-layer check is essential for VPS deployments. A provider firewall, security group or network ACL is outside UFW, so a packet can be accepted by the Linux host firewall and still be discarded before it reaches the server. Conversely, changing a provider rule cannot fix an application that is not listening locally.
Understand UFW’s scope and advanced-policy limits
Ubuntu’s documentation describes UFW as an easy interface for simple rules and states: “ufw is not intended to provide complete firewall functionality via its command interface, but instead provides an easy way to add or remove simple rules.” That scope matters when you need complex routing, sophisticated interface-specific policy, forwarding behavior or a larger rule-management system.
For ordinary inbound service access, a port, protocol and optional source restriction are usually the relevant dimensions. Direction and interface become important in more advanced designs, but the basic allow examples here should not be treated as a complete expression of every possible network policy. If your design depends on forwarding or intricate interface conditions, plan the full firewall architecture instead of assuming that a single port command is sufficient.
Quick Recap
A practical deployment checklist
- Identify the application’s real listening port and whether it uses TCP, UDP or both.
- Identify the SSH daemon’s actual port before enabling UFW.
- Add the SSH allow rule first; restrict it to a trusted IP or CIDR when practical.
- Add the application rule with an explicit protocol unless both transports are required.
- Use
ufw app listandufw app info NAMEwhen a maintained profile exists. - Use
ufw --dry-runto preview an unfamiliar rule. - Enable UFW only after the management path is covered.
- Review
ufw status verboseandufw status numbered. - Keep an existing SSH session open while testing any new or replacement SSH rule.
- If external clients still fail, verify the service binding and the VPS provider’s separate firewall controls.
- Remove obsolete rules by their original text when you need both IPv4 and IPv6 variants removed.
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