Address already in use (port already bound)

1. About the error
2. Why do I see this error
3. Solution
4. Find what's using the port
5. Stop it or kill it
6. Or use a different port
7. Crashed process, port still held

#About the error

Starting a server fails with one of these:

bind() to 0.0.0.0:80 failed (98: Address already in use)   # nginx
Error: listen EADDRINUSE: address already in use :::3000    # Node
[ERROR] Can't start server: Bind on TCP/IP port: Address already in use  # MySQL

Only one process can listen on a given port at a time. The bind fails because something already holds it.

#Why do I see this error

• The service is already running (you started it twice).
• A previous instance crashed but didn't release the port yet.
• A different program is using that port (Apache holding 80 when you start nginx, another dev server on 3000).
• A php artisan serve or Vite process from an earlier session is still alive.

#Solution

#Find what's using the port

ss (or lsof) shows the process holding the port. For port 80:

sudo ss -tlnp | grep ':80'
# or
sudo lsof -i :80

The output includes the PID and program name, exactly what's holding it.

#Stop it or kill it

If it's a service you control, stop it properly:

sudo systemctl stop apache2     # e.g. Apache squatting on port 80

If it's a stray process that won't go away, kill it by PID:

kill <pid>
# if it ignores that:
kill -9 <pid>

To kill whatever is on a port in one step:

sudo fuser -k 80/tcp

#Or use a different port

If you actually want both running, change the port of the one you're starting. For artisan serve:

php artisan serve --port=8001

#Crashed process, port still held

A port can stay in TIME_WAIT briefly after a crash. Wait a few seconds and retry, or confirm with ss that nothing still owns it before restarting.