Linux: Find Listening Ports and Processes with ss
A web service is unreachable. Check whether anything listens on TCP 8080 and identify its process. Work through it yourself in the live host terminal below.
Symptom
A web service is unreachable. Check whether anything listens on TCP 8080 and identify its process.
Your mission
Inspect, recover, then verify
Format
Linux shell
Investigate before you configure.
Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.
Observe the symptom and link state.
Diagnose by comparing the protocol evidence.
Verify the expected device state and confirm the original symptom is resolved.
Console access: Linux
This workspace stacks for portrait phones. Rotate to landscape for the full split-screen console.
Need a hint?
Reveal the root cause when you're ready.
Try the investigation first, then use this as your escape hatch, not a dead end.
Lab debrief
Turn the session into a repeatable troubleshooting pattern.
Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.
The problem
The application should listen on all interfaces at TCP 8080, but clients get connection refused.
What you'll practice
- List listening TCP sockets
- Keep addresses and ports numeric
- Display process ownership
- Distinguish loopback-only from all-interface listeners
The topology
One Linux application server has enp0s3 at 10.20.30.50. A Python service initially binds only to loopback.
Commands to run yourself
The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.
sudo ss -lntpsudo ss -lntp '( sport = :8080 )'Topology diagram
Fact-checked references
The commands and behaviour in this lab were checked against these primary references.
Frequently asked
What does 127.0.0.1:8080 mean?
The listener accepts only local loopback connections. It is not reachable through the host's Ethernet address.
Does 0.0.0.0 guarantee remote access?
No. It means the socket listens on all local IPv4 addresses. Host and network firewalls can still block traffic.
Ready to run this lab yourself?
No setup, no image sourcing. Book a session or ask for a live demo.