Questions about ports on macOS

How do I see which ports are in use on my Mac?

In the terminal, run lsof -nP -iTCP -sTCP:LISTEN to list every listening TCP port and the process behind each one.

If you'd rather not memorize flags, Portero shows all listening ports in a live table, with each process explained in plain words, its PID, address, and start time.

How do I kill a process running on a specific port?

In the terminal, find the PID with lsof -ti :3000 and pass it to kill. Add -9 only if the process ignores the first signal.

In Portero you just click Kill on the row, with a choice between a graceful stop (SIGTERM) and a force kill (SIGKILL). Select several rows to kill them all at once.

How do I fix the "address already in use" error?

That error means two processes are trying to use the same port. Usually it's an old dev server that never died, or two projects configured for the same port.

Portero detects these conflicts automatically, flags the port, and shows exactly which processes collide so you can stop the one you don't need.

How do I block a port on macOS?

macOS ships with the pf firewall, normally driven by pfctl and rule files in the terminal.

Portero writes the pf rules for you: pick a port, choose inbound or outbound blocking, and confirm with your administrator password. Rules live in a dedicated anchor, so no system files are modified.

Is Portero free?

Yes. Portero is free and open source, and runs on both Apple Silicon and Intel Macs.