Address already in use (EADDRINUSE) — free the port

Address already in use — shown as EADDRINUSE in Node, bind() failed in nginx, or OSError: [Errno 98] in Python — means the port you want is already taken. Something is listening on it, and only one process can bind a port at a time. Find that process; then either stop it or use a different port.

Find what is holding the port

Replace 3000 with your port. This prints the process name and PID:

sudo ss -tlnp 'sport = :3000'
# or
sudo lsof -i :3000

Stop it — or realise it is what you meant to run

Very often it is a previous copy of your own app that did not exit cleanly. End it:

kill <PID>        # graceful
kill -9 <PID>     # only if it ignores the first

If it is a managed service you actually want, do not kill it — change your app’s port instead.

Use a different port

# Node
PORT=3001 node server.js

# generic: find a free one first
ss -tlnp | grep :30    # scan the 30xx range

The subtle case: TIME_WAIT after a restart

If you just stopped the app and an immediate restart still fails, the socket may be inTIME_WAIT — the kernel holds it briefly after close. Two fixes:

• Wait 30–60 seconds and start again.
• Enable address reuse in your app so restarts are instant. In Node, the default server already sets it; in custom C/Python sockets, set SO_REUSEADDR.

import socket
s = socket.socket()
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(("0.0.0.0", 3000))

Prevent it with a process manager

Zombie copies that hog ports usually come from starting apps by hand. Run them under systemd or a process manager so a restart cleanly replaces the old instance:

sudo systemctl restart your-app   # stops the old one first

Deploying several services on one box? A KVM VPS with a dedicated public IP lets you map ports cleanly instead of fighting over them.

Frequently asked