javascriptnode.jsprocessfork

How to tell if child Node.js Process was from fork() or not?


I have a small application that could be executed by a fork or directly by a developer, and I would for it to get configured slightly differently depending on how it was started.

I know that I could always pass in arguments to to signal that it was a fork, but I was just curious if there was a way to tell if I could somehow know in the child process if it came from a fork(). I looked around in process but didn't find anything telling.


Solution

  • You can check if process.send exists in your application. When it was started using fork() it will exist.

    if (process.send === undefined) { 
      console.log('started directly');
    } else {
      console.log('started from fork()');
    }
    

    Personally, I would probably set an environment variable in the parent and check for that in the child:

    // parent.js
    child_process.fork('./child', { env : { FORK : 1 } });
    
    // child.js
    if (process.env.FORK) {
      console.log('started from fork()');
    }