> ## Documentation Index > Fetch the complete documentation index at: https://help.freakhosting.com/llms.txt > Use this file to discover all available pages before exploring further. # How to Check Open Ports on Linux with ss and netstat > Check open ports on Linux with sudo ss -tulpn, which lists every listening TCP and UDP port with the program using it. Includes netstat, lsof and firewall checks. To check open ports on Linux, run `sudo ss -tulpn`. It lists every TCP and UDP port the server is listening on, the address it listens on and the program that owns it. To check one port, add a filter: `sudo ss -tlnp 'sport = :80'`. On older systems `sudo netstat -tulpn` gives the same list. A listening port is only reachable from outside if your firewall allows it. | Difficulty | Time | Works on | Needs | | - | - | - | - | | Beginner | 5 minutes | Ubuntu 22.04 / 24.04, Debian 12 / 13, AlmaLinux / Rocky 9 / 10 | sudo to see process names | ## Before you start * [Connect with SSH](https://help.freakhosting.com/portals/other/how-to-connect-to-a-linux-server-with-ssh.md). `ss` works for any user, but only shows which program owns a port when run with `sudo` (root can leave it out). * A **port** is a numbered door a program uses for network traffic: SSH uses 22, websites 80 and 443. A port is **listening** when a program waits for connections on it. ## How to list all listening ports with ss ```bash theme={null} sudo ss -tulpn ``` Example output: ```text theme={null} Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port Process udp UNCONN 0 0 127.0.0.54:53 0.0.0.0:* users:(("systemd-resolve",pid=512,fd=16)) tcp LISTEN 0 4096 0.0.0.0:22 0.0.0.0:* users:(("sshd",pid=901,fd=3)) tcp LISTEN 0 511 0.0.0.0:80 0.0.0.0:* users:(("nginx",pid=1204,fd=6)) tcp LISTEN 0 80 127.0.0.1:3306 0.0.0.0:* users:(("mariadbd",pid=1388,fd=22)) tcp LISTEN 0 4096 [::]:22 [::]:* users:(("sshd",pid=901,fd=4)) ``` | Option | Meaning | | - | - | | `-t` | TCP | | `-u` | UDP | | `-l` | Listening sockets only | | `-p` | Show the process | | `-n` | Show numbers, not service names (`22`, not `ssh`) | ### How to read the Local Address column | Local Address | Reachable from | | - | - | | `0.0.0.0:80` | Every IPv4 address on the server, so the internet (if the firewall allows it) | | `[::]:80` | Every IPv6 address (often IPv4 too) | | `203.0.113.10:80` | Only that one IP address | | `127.0.0.1:3306` or `[::1]:3306` | Only the server itself (localhost) | In the example, MariaDB on `127.0.0.1:3306` is safe: nothing outside can reach it. A database on `0.0.0.0` is reachable by anyone your firewall lets through. ## How to check one port ```bash theme={null} sudo ss -tlnp 'sport = :80' sudo ss -tulpn | grep ':25565' ``` If the command prints only the header line, nothing is listening on that port. ### Which program is using a port? ```bash theme={null} sudo lsof -i :80 -P -n ``` ```text theme={null} COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME nginx 1204 root 6u IPv4 58876 0t0 TCP *:80 (LISTEN) ``` Use this when a program fails with "Address already in use". Stop the other program, or move one of them to a different port. If you want to end it, see [kill a process](https://help.freakhosting.com/portals/other/how-to-kill-a-process-on-linux.md). ## How to use netstat (older systems) `netstat` is part of the older `net-tools` package, which may not be installed. The options are the same: > [tab] Ubuntu / Debian > > ```bash theme={null} > sudo apt install net-tools > sudo netstat -tulpn > ``` > [tab] AlmaLinux / Rocky > > ```bash theme={null} > sudo dnf install net-tools > sudo netstat -tulpn > ``` Prefer `ss`: it is installed everywhere (package `iproute2` / `iproute`) and is faster. ## How to see active connections ```bash theme={null} ss -tn state established ss -s ``` The first lists open TCP connections with the remote IP and port. `ss -s` prints totals, which helps when you suspect a flood of connections. ## Is a listening port actually open to the internet? A port in `ss` is listening on the server. Whether the internet can reach it also depends on your firewall: > [tab] Ubuntu / Debian (ufw) > > ```bash theme={null} > sudo ufw status verbose > ``` > [tab] AlmaLinux / Rocky (firewalld) > > ```bash theme={null} > sudo firewall-cmd --list-all > ``` On a VPS, rules you set in the [FREAKHOSTING Firewall panel](https://help.freakhosting.com/portals/firewall/firewall-panel-overview.md) also apply. To test from outside, see [check if a port is open from outside](https://help.freakhosting.com/portals/other/how-to-check-if-a-port-is-open-from-outside.md). > [!WARNING] > > When you open a port, add the rule for the new port before removing an old one, and never remove the rule for your SSH port while connected. If a firewall change locks you out of a VPS, use the [VNC console](https://help.freakhosting.com/portals/vps-panel/how-to-enable-and-use-vnc-console-access.md). Don't open database ports (3306, 5432, 6379, 27017) to the whole internet; allow only the IP addresses that need them. ## How to check it worked Start a test listener and look for it: ```bash theme={null} python3 -m http.server 8080 & sudo ss -tlnp 'sport = :8080' kill %1 ``` You see a `LISTEN` line on `0.0.0.0:8080` owned by `python3`. After `kill %1` it is gone. ## Frequently asked questions ### What is the difference between ss and netstat? Both list sockets. `ss` is the modern tool from `iproute2`, installed by default and faster on busy servers. `netstat` comes from the older `net-tools` package. The options `-tulpn` work in both. ### Why don't I see the process name? Run the command with `sudo`. Without root rights, `ss` and `netstat` hide process names for other users' programs. ### How do I find which ports are open from the outside? Run a scan from another machine you own, for example `nmap -Pn 203.0.113.10`, or use the steps in [check if a port is open from outside](https://help.freakhosting.com/portals/other/how-to-check-if-a-port-is-open-from-outside.md). Only scan servers you are responsible for. ### Why does port 53 show on 127.0.0.53 or 127.0.0.54? That is `systemd-resolved`, the local DNS cache on Ubuntu. It only listens on the loopback address, so it isn't reachable from outside. ## Related guides > [card] [VPS and dedicated server guides](https://help.freakhosting.com/portals/other/vps-and-dedicated-server-guides.md) > > Every server guide in one place. > [card] [Check if a port is open from outside](https://help.freakhosting.com/portals/other/how-to-check-if-a-port-is-open-from-outside.md) > > Test from the internet. > [card] [Set up a firewall with UFW](https://help.freakhosting.com/portals/other/how-to-set-up-a-firewall-with-ufw.md) > > Open and close ports on Ubuntu. > [card] [Set up a firewall with firewalld](https://help.freakhosting.com/portals/other/how-to-set-up-a-firewall-with-firewalld.md) > > Open and close ports on AlmaLinux. > [card] [Kill a process](https://help.freakhosting.com/portals/other/how-to-kill-a-process-on-linux.md) > > Free a port that is in use. *** > [!NOTE] > > **Checked against the [ss(8) manual from iproute2](https://man7.org/linux/man-pages/man8/ss.8.html)** on 4 November 2026; `ss`, `netstat` and `lsof` tested on Ubuntu 24.04 LTS. Commands can differ on other distributions or releases. > [!NOTE] > > ### Need Extra Help? > > If you encounter any issues, our support team is ready to assist: > > * **Live Chat:** Quick assistance via our website. > * **Support Ticket:** [Open a Ticket](https://freakhosting.com/clientarea/submitticket.php) > * **Discord:** [Join our Community](https://discord.gg/freakhosting) > * **Email:** [support@freakhosting.com](mailto:support@freakhosting.com) > [!TIP] > > ### Save on Your Hosting > > Ready to upgrade your hosting? Use code **KB20** at checkout for **20% off** your first order! *** **Last Updated:** November 2026 This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.