Kill Port: A Comprehensive Guide for Developers

When developing applications, you might encounter situations where a specific port is already in use, blocking you from starting your server or application. The utility kill-port is a handy tool to easily terminate processes running on specified ports. Here, we introduce kill-port and provide useful APIs with code snippets to give you a deep dive into managing ports effectively.

Installing kill-port

To get started with kill-port, you need to install it globally via npm:

npm install -g kill-port

Basic Usage

The basic usage of kill-port is straightforward; just specify the port you want to free up:

kill-port 3000

Specifying Multiple Ports

You can specify multiple ports at once to be killed by separating them with spaces:

kill-port 3000 4000 5000

Killing TCP and UDP Ports

If you need to kill both TCP and UDP ports, you can use the --tcp and --udp flags:

kill-port 3000 --tcp --udp

Using kill-port Programmatically

For more advanced usage, you can use kill-port programmatically in your Node.js scripts:

 const killPort = require('kill-port');
(async () => {
  try {
    await killPort(3000);
    console.log('Port 3000 killed successfully');
  } catch (err) {
    console.error('Error killing port:', err);
  }
})();

Example Application

Below is an example of using kill-port in a Node.js application. The application attempts to start a simple HTTP server on port 3000 and ensures the port is available before starting:

 const http = require('http'); const killPort = require('kill-port');
const startServer = () => {
  const server = http.createServer((req, res) => {
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Hello, World!\n');
  });

  server.listen(3000, '127.0.0.1', () => {
    console.log('Server is running at http://127.0.0.1:3000/');
  });
};
killPort(3000).then(() => {
  console.log('Port 3000 is now free, starting server...');
  startServer();
}).catch((err) => {
  console.error('Failed to kill port 3000:', err);
});

By using kill-port, you can ensure that the port required for your new server instance is free, thus preventing “port already in use” errors.

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