Fix "Address Already in Use" / Port Already in Use

This error means another process is already listening on the port your server wants. Usually it's a previous instance that didn't shut down. Here's how to find and clear it, including the Docker- and panel-specific cases.

"Address already in use", "bind: EADDRINUSE" and "failed to bind to port" are the same problem: something already holds the port. The fix is always these three steps:

1. Find what's on the port: ss -tlnp | grep PORT (gives you a PID).
2. Confirm that PID really is your old server — not a system service.
3. Free it: kill PID (or kill -9 PID if it won't stop), then start your server.

Find what's using the port

On Linux, ss (or lsof) shows which process holds the port — say 25565:

ss -tlnp | grep 25565
# or
lsof -i :25565

You'll get a PID (process ID) of whatever is bound to it.

Free the port

If it's a stuck old instance of your server, stop it cleanly first; if it won't die, force it:

kill 12345        # graceful, by PID
kill -9 12345     # force, if it won't stop

Common real causes

• A previous server instance is still running (the usual cause).
• Two servers configured on the same port — change one.
• A crashed process left the port in a lingering TIME_WAIT state — wait a minute and retry.
• You're starting the server twice (e.g. a leftover screen/tmux session).

Or just change the port

If you genuinely want two servers, give the second one a different port in its config and update your firewall/forwarding to match.

Something already owns the port. Find the PID with ss/lsof, stop that process, then start your server.

Docker and panel-specific causes

• A Docker container maps a host port that's already used by another container or a bare-metal process — docker ps shows the mapping, and ss -tlnp shows the actual owner.
• On Pterodactyl/panel setups, this usually means the primary allocation (IP:port) is already assigned to another server. Free or reassign the allocation in the panel rather than hunting for a process — see fixing Pterodactyl server won't start.
• systemd socket activation can pre-bind a port before your service even starts, making it look "in use" by nothing obvious — check systemctl list-sockets.

How to prevent it

• Always stop a server cleanly (console command, not just closing the window) so it releases its port.
• Document which service owns which port on a shared box, especially with multiple game servers.
• Use a process manager or panel that tracks state, so you can't accidentally start the same server twice.