Rails server says port already used, how to kill that process?

Question

I'm on a mac, doing:

rails server

I get:

2010-12-17 12:35:15] INFO  WEBrick 1.3.1
[2010-12-17 12:35:15] INFO  ruby 1.8.7 (2010-08-16) [i686-darwin10.4.0]
[2010-12-17 12:35:15] WARN  TCPServer Error: Address already in use - bind(2)
Exiting

I know I can start one on a new port, but I want to kill this process.

Answer 1

Assuming you're looking to kill whatever is on port 3000 (which is what webrick normally uses), type this in your terminal to find out the PID of the process:

$ lsof -wni tcp:3000

Then, use the number in the PID column to kill the process:

$ kill -9 PID