Kill the process listening to a port
It's inevitable if you work on enough projects, or with flakey enough servers, that when you start a server there is already something running on that port.
Here's an easy way to kill the process listening on port 8000:
kill $(lsof -t -i:8000)
What's going on here?
lsof -t -i:8000 returns the process number listening to port 8000 and
kill $() kills the process.
You can also use lsof to get more details without killing the process by running: