Port 9090 (Prometheus, Cockpit)
Port 9090 is the default of Prometheus (its web UI and API) and of Cockpit, the web console for Linux servers. IANA registers the number for WebSM.
- Service
- Prometheus, Cockpit
- Protocol
- TCP
- IANA registry
- Assigned to a different service: websm (WebSM), TCP/UDP. The use described here is not registered.
- Commonly used by
Check if a port is open on your IP
We only check the address you are visiting from, one TCP port at a time. You cannot enter someone else’s address: this is not a port scanner.
Is it safe to open port 9090?
Prometheus has no login by default and shows everything it collects; Cockpit gives a shell to whoever signs in. Keep 9090 on a private network or behind a VPN.
“Port 9090 is already in use”: how to fix it
The error means another program is already listening on port 9090. Find its process ID (PID), then stop that program or start yours on a different port.
Windows (Command Prompt or PowerShell as administrator)
netstat -ano | findstr :9090taskkill /PID <PID> /FmacOS
lsof -nP -iTCP:9090 -sTCP:LISTENkill <PID>Linux
sudo ss -ltnp | grep :9090sudo lsof -i :9090sudo kill <PID>Replace <PID> with the number from the last column (Windows) or the PID column (macOS, Linux).
Why a port can look closed when your server is running
Most home networks sit behind a router doing NAT: the router owns the public address, and your computer has a private one such as 192.168.1.10. A connection from the internet reaches the router and stops there unless you add a port forwarding rule to your computer.
Many mobile and some home providers go further and use carrier-grade NAT (CGNAT): several customers share one public address, and your router itself gets an address from 100.64.0.0/10. Then no rule on your side can open a port; ask the provider for a public IP or use a tunnel or VPN service.
Even with forwarding in place, the firewall on the computer (Windows Defender Firewall, ufw, firewalld) must allow the port, and the program must listen on all interfaces (0.0.0.0), not only on 127.0.0.1.
UDP cannot be checked this way: a UDP service usually stays silent to packets it does not understand, so “no answer” means nothing. This check uses TCP only.
Frequently asked questions
What is port 9090 used for?
Port 9090 is the default of Prometheus (its web UI and API) and of Cockpit, the web console for Linux servers. IANA registers the number for WebSM.
Is port 9090 TCP or UDP?
Port 9090 uses TCP. This use is not registered with IANA.
Is it safe to open port 9090?
Prometheus has no login by default and shows everything it collects; Cockpit gives a shell to whoever signs in. Keep 9090 on a private network or behind a VPN.
How do I free port 9090 if it is already in use?
Find the process: on Windows run netstat -ano | findstr :9090 and stop it with taskkill /PID <pid> /F; on macOS or Linux run lsof -i :9090 and stop it with kill <pid>.