Creating a detached child process in Node.js

10 Oct 2023

In Node.js, you can create child processes to run external commands or scripts. By default, child processes are attached to the parent process, which means they are terminated when the parent process is terminated. However, in some cases, you may want to create a detached child process that continues to run even after the parent process has exited.

Why Detached Child Processes are Useful

Detached child processes can be useful in various scenarios, such as:

Running background tasks or daemons that need to keep running even if the parent process is terminated.
Offloading heavy or time-consuming operations to separate processes to free up the main event loop.
Running scripts or commands that need to continue execution independently of the parent process.

Creating a Detached Child Process

To create a detached child process in Node.js, you can use the spawn function provided by the built-in child_process module. Here’s an example:

const { spawn } = require('child_process');

const child = spawn('node', ['myScript.js'], {
  detached: true,
  stdio: 'ignore'
});

// Detach the child process
child.unref();

In the above code:

We import the spawn function from the child_process module.
We use the spawn function to create a child process and pass the command and arguments as an array. In this example, we’re executing a Node.js script named myScript.js.
We set the detached option to true to detach the child process from the parent process.
We set the stdio option to 'ignore' to ignore the standard input/output/error streams of the child process.
We call the unref method on the child process object to detach it from the parent process. This allows the parent process to exit independently of the child process.

By creating a detached child process, it will continue running even if the parent process is terminated. Note that the detached child process becomes a leader of a new process group.

Conclusion

Creating a detached child process in Node.js allows you to run processes independently of the parent process. This can be useful for running background tasks, offloading heavy operations, or executing scripts that need to continue executing even if the parent process is terminated. Remember to use the spawn function from the child_process module and set the detached option to true to detach the child process from the parent process.