Node / Express: EADDRINUSE, Address already in use – Kill server

When working with Node.js and Express, encountering the “EADDRINUSE” error, which indicates that the address is already in use, is not uncommon. This issue arises when attempting to start a server on a port that is already occupied by another process. To resolve this, you need to identify the conflicting process and either terminate it or choose a different port for your Node.js application.

To find and kill the process using the port, you can use the terminal commands like lsof on Unix-based systems or netstat on Windows. For example, on Unix:

You can change the port your Node.js application listens on by modifying the server configuration. It’s crucial to handle port conflicts to ensure smooth development and deployment of your Express applications.

var server = require('connect').createServer();
//actions...
server.listen(3000);

What does EADDRINUSE mean?

“EADDRINUSE” is an error code in networking, particularly associated with server applications. It stands for “Error: Address Already in Use.” This error occurs when a program attempts to bind a socket to a particular address and port, but that combination is already in use by another process on the same machine.

In the context of Node.js and other server-side technologies, you might encounter this error when trying to start a server on a specific port, but another process or server is already using that port. Each port on a machine can only be used by one process at a time.

To resolve the “EADDRINUSE” error, you typically need to either stop the process using the conflicting port, choose a different port for your application, or restart your computer to free up the ports. It’s a common issue during development and server deployment, and understanding how to identify and manage port conflicts is crucial for smooth operation of server applications.

Error: listen EADDRINUSE: Address already in use

The “EADDRINUSE” error in Node.js indicates that the port you’re trying to use for your server is already in use by another process. This commonly happens when you attempt to start your Node.js application, but a previous instance of the server is still running or another application is using the same port.

To resolve this issue, you can take the following steps:

Identify the process using the port:
On Unix-based systems, you can use the following command in the terminal:

lsof -i :<port_number>

On Windows, you can use:

netstat -ano | findstr :<port_number>

Replace with the actual port number your Node.js application is trying to use.

Terminate the process:
Once you identify the process ID (PID) using the port, you can terminate it. On Unix-based systems:

kill -9 <process_id>

On Windows, you can use Task Manager to end the process associated with the port.

Change the port:
If terminating the process is not an option, or if you prefer to use a different port, you can modify your Node.js application to listen on a different port. Update the port number in your server configuration.

For example, if your server code looks like this:

const express = require('express');
const app = express();

const port = 3000; // Change this to your desired port

app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});

Change the port variable to a different number, and then restart your Node.js application.

Stop the process that runs on the specified port

To stop a process running on a specific port, you need to follow these general steps:

On Unix-based systems (Linux, macOS):

Identify the process using the port:

lsof -i :<port_number>

Find the Process ID (PID) and terminate it:

kill -9 <process_id>

On Windows:

Identify the process using the port:

netstat -ano | findstr :<port_number>

Find the Process ID (PID) in the last column of the output and terminate it:

taskkill /F /PID <process_id>

Replace with the actual port number you want to free up. If you don’t have lsof or netstat installed on your system, you may need to install them or use alternative commands specific to your system.

After terminating the process, you should be able to start your Node.js application on the specified port without encountering the “EADDRINUSE” error.

Restarting your computer

If you are unable to identify and stop the process using a specific port using the methods mentioned earlier, or if you find it cumbersome, restarting your computer is a straightforward solution. Restarting the computer will terminate all running processes and free up the ports.

Here are the general steps to restart your computer:

On Windows:

Click on the “Start” button.
Select “Power.”
Choose “Restart.”

On Unix-based systems (Linux, macOS):
Open a terminal.
Type sudo reboot and press Enter.
Enter your password if prompted.

After the computer restarts, all processes, including those using ports, will be terminated. You can then start your Node.js application without encountering the “EADDRINUSE” error on the specified port. Keep in mind that while this is a simple solution, it might not be the most convenient if you have other important processes running on your machine. In such cases, identifying and stopping the specific process using the port would be a more targeted approach.

Stop the process that runs on the port on Windows

Certainly! On Windows, you can use the netstat command along with Taskkill to identify and stop the process using a specific port. Here’s a step-by-step guide:

Identify and Stop the Process on Windows:
Open Command Prompt:

Press Win + R to open the Run dialog.
Type cmd and press Enter.
Identify the Process using the Port:

netstat -ano | findstr :<port_number>

Replace with the actual port number you want to free up.

Locate the Process ID (PID) in the last column of the output.

Terminate the Process:

taskkill /F /PID <process_id>

Replace with the PID you obtained from the previous step.

For example:

netstat -ano | findstr :3000
taskkill /F /PID 12345

This will forcefully terminate the process using the specified port. Afterward, you should be able to use the port for your Node.js application without encountering the “EADDRINUSE” error.

FAQs

Conclusion

The “EADDRINUSE” error in Node.js and Express, signaling that the address is already in use, is a common stumbling block during development and deployment. This error arises when attempting to start a server on a port that’s already occupied by another process. Resolving this issue involves identifying and terminating the conflicting process or opting for a different port. Both Unix-based and Windows systems offer commands like lsof and netstat to identify the process, and subsequent termination can be achieved using kill or taskkill commands. Restarting your computer is a simple but effective solution when the culprit is elusive.

To preemptively handle such conflicts, developers can adopt best practices, including judiciously choosing ports, dynamically setting them during development, and employing error-handling mechanisms in the code. Utilizing tools like cross-env for dynamic port assignment or libraries like get-port for programmatic availability checks can streamline the development process, ensuring smoother server operations. Understanding and adeptly managing port conflicts contribute to a seamless and efficient server deployment experience.