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Short answer: connect to the VPS, allow your SSH service first, add an inbound rule for the application port, enable UFW, and verify the resulting policy. For example, an application using TCP port 8080 can be opened with sudo ufw allow 8080/tcp. Do not run sudo ufw enable on a remote VPS until SSH is allowed, or the firewall can block your management session.
What UFW does—and what it does not do
UFW (Uncomplicated Firewall) is Ubuntu’s default firewall configuration tool. A new Ubuntu installation normally has UFW disabled, so adding a rule alone does not enforce a firewall policy until you enable it. UFW’s simple command syntax is designed for straightforward allow and deny rules; it is not a complete replacement for every advanced firewall, routing, or network-policy requirement.
An allow rule changes the firewall on the VPS itself. It does not start a web server, make an application bind to a socket, or change a hosting company’s network firewall. If a client still cannot connect after UFW shows an allow rule, check the service and any provider-level firewall, security group, or network ACL separately.
Before you change anything on a remote VPS
Keep an active SSH session
Leave your current SSH connection open while changing UFW. If a rule is wrong, that session may be your easiest way to correct it. Test a second connection in another terminal after the rules are in place before closing the first one.
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Identify the real SSH port
If SSH uses the standard TCP port 22, you can allow it with sudo ufw allow ssh or sudo ufw allow 22/tcp. If the SSH daemon listens on a custom port, replace 22 with that port. Allowing port 22 when SSH actually listens elsewhere does not protect your management connection.
Know the application protocol
TCP and UDP are separate protocols. A rule that names TCP does not open UDP on the same number. UFW accepts a port with an optional protocol; omitting the protocol allows both TCP and UDP, which is broader than many services need. Use an explicit protocol whenever the application documentation identifies one.
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1. Allow SSH before enabling UFW
For standard SSH, run one of these commands:
sudo ufw allow ssh
sudo ufw allow 22/tcpUse only one equivalent SSH rule unless you deliberately want both entries. For a custom SSH port, substitute the actual port number:
sudo ufw allow 2222/tcpThe number 2222 is an example; use the port configured by your SSH service.
2. Add the application rule
For an inbound TCP service on port 8080:
sudo ufw allow 8080/tcpFor a service that genuinely needs both protocols, omit the protocol:
sudo ufw allow 8080Use the actual listening port rather than the port exposed by a local development configuration or a container’s internal network unless they are the same endpoint seen by the VPS network.
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UFW can print the rules it would create without applying the change:
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sudo ufw --dry-run allow httpThe output lets you inspect the resulting rule before committing it. You can replace the service name with another supported service name or use the port-and-protocol form for a custom service.
4. Enable the firewall
sudo ufw enableEnabling UFW activates the policy and its rules. On a remote machine, perform this only after the correct SSH allow rule is present.
5. Inspect the active policy
sudo ufw status verbose
sudo ufw status numberedstatus verbose provides the policy’s expanded view. status numbered adds rule numbers, which are useful when you need to delete or reorder a particular entry. Confirm that the SSH rule and the intended application rule appear with the expected protocol.
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Common port-opening examples
| Purpose | Command | Protocol and exposure |
|---|---|---|
| Standard SSH | sudo ufw allow 22/tcp |
TCP; available from any source unless further restricted |
| SSH service by profile name | sudo ufw allow ssh |
Uses UFW’s SSH application profile |
| HTTP service | sudo ufw allow http |
Uses an available application profile; inspect profiles first if unsure |
| Custom web or API service | sudo ufw allow 8080/tcp |
TCP only on port 8080 |
| Both TCP and UDP on one number | sudo ufw allow 8080 |
Both protocols; use only when the service requires both |
The profile-based examples depend on a matching UFW application profile being installed. A raw port rule is more explicit for a custom service.
Restrict an administration port to trusted addresses
Opening SSH to every source is convenient but exposes the management service to the entire internet. If you have a stable office, VPN, or bastion address, restrict the rule to that source:
sudo ufw allow proto tcp from 203.0.113.10 to any port 22The address 203.0.113.10 is an example source address. Replace it with the public address from which you administer the VPS. A network can be expressed in CIDR notation:
sudo ufw allow proto tcp from 203.0.113.0/24 to any port 22A CIDR rule covers every address in that range, so choose the narrowest range that contains your legitimate administrators. Before tightening an existing rule, verify that your current connection originates from an address included by the new rule and keep the existing session open while testing.
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Use an application profile instead of a raw port
Some software installs a named UFW application profile. Profiles are stored under /etc/ufw/applications.d. Discover the profiles available on the VPS:
sudo ufw app listInspect a profile’s ports and description before allowing it:
sudo ufw app info NAMEReplace NAME with the exact profile name shown by app list, then allow that profile:
sudo ufw allow 'NAME'Profile names can contain spaces, which is why quoting the name is prudent. A profile is useful when the package maintainer defines the service’s ports for you; a raw rule such as sudo ufw allow 8080/tcp is clearer for a one-off or custom application.
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| Decision | Narrower choice | Broader choice | Why it matters |
|---|---|---|---|
| Protocol | Specify /tcp or /udp |
Omit the protocol | Omitting it permits both TCP and UDP on the port. |
| Source | One IP or a CIDR range | Any source | A source restriction reduces who can reach administration or private services. |
| Management method | Named application profile | Raw port rule | Profiles describe packaged services; raw rules suit custom ports. |
| Network layer | Host UFW rule | Provider firewall or ACL change | Both layers can affect reachability; changing UFW does not alter provider controls. |
| Address family | Check the displayed IPv4 and IPv6 entries | Assume one family covers both | Rules can be represented separately for IPv4 and IPv6, so inspect the actual status output. |
Most commands in this guide create inbound access to the VPS. If your design depends on a particular network interface, routed traffic, forwarding, or more complex policy, the simple UFW command interface may not express the requirement completely.
Inspect, remove, and reorder rules
List numbered rules before editing
sudo ufw status numberedNumbered output is the safest starting point when several similar rules exist. Record the exact rule text as well as its number; numbers can change after an earlier rule is deleted.
Delete by repeating the original definition
To remove the example TCP rule, repeat its original definition after delete:
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sudo ufw delete allow 8080/tcpDeleting by the original rule text is useful when you know exactly what was added. For a rule displayed in numbered output, UFW also supports deletion by number. The manual warns that deleting a generic rule by number can affect only the specified IPv4 or IPv6 entry; deleting by the original rule text removes both where applicable. After any deletion, run sudo ufw status numbered again and verify the remaining policy.
Reordering considerations
When rules overlap, the order shown by UFW can matter. Use numbered status output to understand the current order before changing it, and make one change at a time. If the policy has grown beyond simple service allows, document the intended source, protocol, and destination for every rule before editing.
Verify that the service—not just UFW—is ready
An allow rule only tells the host firewall to permit matching traffic. The application must also be running and listening on the expected port and address. Check the application’s own configuration and service status, then inspect the VPS’s listening sockets with an appropriate socket-inspection tool. For example, on a system with the standard ss utility, you can inspect listening TCP sockets with:
sudo ss -lntpLook for the expected port and confirm that the process is bound to an address reachable by the client. A service bound only to a loopback address such as 127.0.0.1 is local to the VPS even when UFW allows the port. Conversely, a service listening on the wrong port will not receive connections to the port you opened.
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UFW is still disabled
Run sudo ufw status verbose. If it reports that UFW is inactive, the rules are not enforcing a host firewall policy yet. Confirm the SSH rule first, then enable UFW with sudo ufw enable.
The wrong protocol was opened
Check whether the client uses TCP or UDP and compare that with sudo ufw status numbered. A TCP rule does not allow UDP traffic, and vice versa. If the service requires both, use a rule without a protocol or create explicit rules for each protocol according to the service’s requirements.
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The service is not listening
Use the application’s service status and a socket inspection tool to verify that a process is bound to the expected port. Restart or reconfigure the application only after confirming its documented listening address and port. UFW cannot create a listener for a stopped service.
The service is bound only to localhost
If socket inspection shows a loopback-only address, change the application’s bind address according to its documentation, then retest. Opening UFW does not make a loopback-bound process externally reachable.
A provider-level firewall is blocking traffic
When UFW is active, the rule is correct, and the service is listening, inspect the VPS provider’s firewall, security group, and network ACL. These controls can deny traffic before it reaches the operating system, so changing UFW alone cannot resolve that block.
SSH access was lost after enabling UFW
Use an existing SSH session, an out-of-band console, or the provider’s recovery console if available. Add an allow rule for the actual SSH port, then inspect status. If SSH uses a custom port, adding a rule for port 22 will not restore access to that service.
An old or duplicate rule is confusing the policy
Run sudo ufw status numbered, identify duplicate or obsolete entries, and remove them using the original definition or the displayed number. Recheck both the protocol and the source restriction after every edit.
Practical patterns for common deployments
Public web service on ports 80 and 443
Allow the web service’s TCP ports using installed profiles when available, or explicit TCP rules when the service is custom. Confirm that the web server is listening on the public interface and that the provider’s network firewall permits the same ports. Do not assume that an HTTP profile automatically opens every port used by a reverse proxy or application server.
Private API on port 8080
If only another server should call the API, use a source-restricted TCP rule instead of sudo ufw allow 8080/tcp from anywhere. The source should be the caller’s stable public IP or an appropriate CIDR range. Verify both ends: the API listener must be reachable on its intended address, and the caller must be permitted by any provider-level controls.
Administrative service on a custom SSH port
Determine the configured SSH port, allow that TCP port before enabling UFW, and test a second connection using the same port. Once confirmed, remove any unnecessary broad SSH rule. A nonstandard port is not a substitute for source restrictions, strong authentication, or other SSH hardening; it only changes which port the daemon uses.
Operational checklist
- Keep the current remote session open.
- Confirm the actual SSH port and allow it before enabling UFW.
- Identify whether the application needs TCP, UDP, or both.
- Use the narrowest source IP or CIDR range practical for administrative services.
- Preview a sensitive change with
sudo ufw --dry-runwhen appropriate. - Add the application rule or inspect and allow its UFW profile.
- Enable UFW only after management access is covered.
- Check both
sudo ufw status verboseandsudo ufw status numbered. - Verify that the application is running and listening on the expected address and port.
- Test from an external client and inspect provider firewalls, security groups, and ACLs if it still fails.
- Record the original rule text before deleting or changing entries.
Where UFW stops being the right abstraction
UFW is intentionally convenient for adding and removing simple rules. Ubuntu describes its scope this way: “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.” If you need intricate forwarding, routed-network policy, interface-specific designs, stateful exceptions, or a large rule set, plan the policy at the appropriate firewall layer rather than forcing it into a single simple allow command. For ordinary VPS service exposure, however, the disciplined sequence—protect SSH, allow the required protocol and port, enable, inspect, and validate the listener and provider network—prevents the most common lockouts and false diagnoses.
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