A Simple Script to Kill Whatever is on a Port

Hey everyone,

If you're a developer, you've almost certainly run into this problem: you stop a development server, but the process doesn't exit cleanly. When you try to restart it, you get the dreaded Address already in use error because the old process is still squatting on the port.

The usual solution is a multi-step dance of using lsof or netstat to find the Process ID (PID) and then using kill to terminate it. It's a hassle. To solve this, I wrote a simple shell script that automates the whole process into a single command.

The kill-port Script

This script does exactly one thing: it finds and kills the process running on a given port. It's designed to be both fast and widely compatible.

GitHub Gist: kill-port.sh

#!/bin/bash

find_pids() {
    local port=$1

    if command -v ss &>/dev/null; then
        ss -lptn "sport = :$port" 2>/dev/null \
        | grep -oP 'pid=\K[0-9]+' \
        | sort -u           # one PID per line
    elif command -v lsof &>/dev/null; then
        lsof -t -i:"$port"
    else
        echo "Neither ss nor lsof found." >&2
        return 1
    fi
}

#— main —#
[ -z "$1" ] && { echo "Usage: $0 "; exit 1; }
PORT=$1

# Get PIDs as a space-separated list
PIDS=$(find_pids "$PORT" | tr '\n' ' ')

if [ -n "$PIDS" ]; then
    echo "Killing processes on port $PORT: $PIDS"
    # shellcheck disable=SC2086  # intentional word-splitting so each PID is separate
    kill -9 $PIDS
    echo "Process(es) killed."
else
    echo "No process found on port $PORT"
fi

How It Works

The script is designed to be efficient. It first checks if the modern ss (socket statistics) command is available, which is very fast for this kind of task. If ss isn't found, it gracefully falls back to using the more traditional lsof command, ensuring it works in a wide variety of environments.

This approach makes the script fast on modern Linux systems while remaining compatible with older ones. Once it finds the PID using either method, it uses kill -9 to terminate the process.

How to Use It

1. Save the code above to a file named kill-port in a directory that's in your PATH (like ~/.local/bin).
2. Make the script executable: chmod +x ~/.local/bin/kill-port
3. Now, anytime a process is stuck on a port, you can just run:

   kill-port 5000
   

It's a tiny utility, but it's one of those quality-of-life scripts that saves a little bit of time and a whole lot of annoyance.

As always,
Michael Garcia a.k.a. TheCrazyGM