My OS is Ubuntu 10.04. I started WebRick by "rails s" command. But now a can't stop him. I try to stop him using this hotkeys Ctrl + C and Ctrl +Break...but nothin helping...
Since it worked for the asker, I'll add my comment here as an answer for others.
Try (in a new terminal window) doing ps ax | grep ruby
. You'll see the process that's running. Then do a kill -9 <process number>
.