Free network socket with the specified port by killing the occupied process(es).

free_port.sh

#!/bin/bash

# Usage: free_port.sh <PORT> [PROTOCOL]
#   PROTOCOL: tcp | udp | (anything lsof -i:PORT would accept, e.g. "rpc", "icmp", etc.)
#   If PROTOCOL is omitted, all protocols on that port will be targeted.

if [ -z "$1" ]; then
  echo "Usage: $0 <PORT> [PROTOCOL]"
  exit 1
fi

PORT=$1
PROTO=$2

# build the -i filter: either ":PORT" (all protocols) or "PROTO:PORT"
if [ -n "$PROTO" ]; then
  FILTER="${PROTO}:${PORT}"
else
  FILTER=":${PORT}"
fi

pids=$(lsof -i "$FILTER" -t)

if [ -n "$pids" ]; then
  echo "Killing process(es) using port $PORT${PROTO:+/$PROTO}:"
  echo "$pids"
  echo "$pids" | xargs kill -9
else
  echo "No process is using port $PORT${PROTO:+/$PROTO}"
fi