PortAtlas.
Registered port (1024–10000) Medium risk

Port 9090 PROMETHEUS

Quick answer

Port 9090 is most commonly used by Prometheus. The IANA registry lists TCP / UDP for this number.

Check and block Is it safe? Troubleshooting FAQ
TransportTCP / UDP
RiskMedium
Typical useMonitoring and metrics

What is port 9090 used for?

Port 9090 is most commonly used by Prometheus. Prometheus exposes its web UI and API on port 9090 by default; the IANA registry assigns the number to websm. It sits in the registered range, the block used by databases, application servers and developer tooling. Port conflicts here are common when several local services start at once.

Ports are the transport-layer address a service listens on. A client that wants to reach websm connects to port 9090. A TCP connection is refused when nothing is listening, while a UDP request simply goes unanswered. That is why a port conflict appears whenever two processes try to bind the same number.

Use the commands below to confirm whether port 9090 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.

Browse all Monitoring and metrics ports

Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [I_Hsing_Tsao].

Check and block port 9090

Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.

Check on Linux

sudo ss -tlpn 'sport = :9090' sudo ss -ulpn 'sport = :9090'

Check on Windows

Get-NetTCPConnection -LocalPort 9090 -State Listen -ErrorAction SilentlyContinue Get-NetUDPEndpoint -LocalPort 9090 -ErrorAction SilentlyContinue

Block with UFW

sudo ufw deny 9090/tcp sudo ufw deny 9090/udp

Block with iptables

sudo iptables -A INPUT -p tcp --dport 9090 -j DROP sudo iptables -A INPUT -p udp --dport 9090 -j DROP

These commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.

Is port 9090 safe to expose?

Medium

Metrics endpoints such as Prometheus can disclose internal topology, versions and traffic patterns. Restrict them to your monitoring network. Expose this port only when the service is actually needed. Keep it patched, prefer an encrypted alternative, and limit source addresses with a firewall allowlist.

Where port 9090 is usually used

Most traffic on port 9090 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.

Demo

Check Prometheus health

The health endpoint returns a short plain-text response when the server is ready.

curl -s http://127.0.0.1:9090/-/healthy

Common problems with port 9090

Connection refused or timed out

Refused usually means the host is reachable but nothing is listening on port 9090. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.

Port already in use

Find the process holding the port with sudo ss -tlpn 'sport = :9090' or sudo lsof -i :9090. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.

Firewall rule did not survive a reboot

UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.

The port is blocked but still reachable

A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.

Port 9090 at a glance

Port number9090
IANA service namewebsm
Commonly used byPrometheus
Transport protocolTCP / UDP
CategoryMonitoring and metrics
RangeRegistered port (1024–10000)
Risk levelMedium
Registered assignee[I_Hsing_Tsao]
Registry descriptionWebSM
SourceIANA Service Name and Transport Protocol Port Number Registry

Frequently asked questions

What is port 9090 used for?

Port 9090 (PROMETHEUS). The IANA registry lists TCP / UDP for this number. Prometheus exposes its web UI and API on port 9090 by default; the IANA registry assigns the number to websm.

How do I check if port 9090 is open?

On Linux run `sudo ss -tlpn 'sport = :9090'` and `sudo ss -ulpn 'sport = :9090'`. On Windows run `Get-NetTCPConnection -LocalPort 9090 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 9090 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 9090; empty output usually means nothing is bound to it.

How do I block port 9090?

With UFW run `sudo ufw deny 9090/tcp` and `sudo ufw deny 9090/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 9090 -j DROP` and `sudo iptables -A INPUT -p udp --dport 9090 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.

Is port 9090 safe to expose?

Metrics endpoints such as Prometheus can disclose internal topology, versions and traffic patterns. Restrict them to your monitoring network. Nevertheless, expose this port only when the service is actually needed. Keep it patched, prefer an encrypted alternative, and limit source addresses with a firewall allowlist.

See all Monitoring and metrics ports

Primary data: IANA Service Name and Transport Protocol Port Number Registry.

Last reviewed 2026-10-30 · Methodology · About · Privacy