How to kill a process on a port on ubuntu

You want to use backtick, not regular tick:

sudo kill -9 `sudo lsof -t -i:9001`

If that doesn't work, you could also use $() for command interpolation:

sudo kill -9 $(sudo lsof -t -i:9001)

you can use

fuser -n tcp -k 9001 

see more details in wikipedia