Posix-Fork

posix-fork is a node.js module providing functionality of 2 UNIX system calls: fork() and daemon().

In order to install do npm install posix-fork. After that require('posix-fork') will return you an object with 3 methods: fork(), daemon() and getpid():

Getpid

getpid() is for getting current process' id. It is needed because process.pid will refer to parent's PID after fork() or daemon().

Fork

fork() creates a copy of the process you called it from (man fork for more). Both child and master will continue running the code below the invocation of fork(). However in master process the function returns child's PID and in child it returns 0. The following example will spawn 100 child processes:

var posix = require('posix-fork'),
    childPid = true,
    children = 0

for (var children = 0; childPid && children < 100; children++) {
  if (childPid = posix.fork()) // we're in master
    console.log('spawned one more child!')
  else                         // we're in child
    console.log('I am a child #%s', children)
}

Daemon

daemon() will fork and immediately exit from master process, thus detaching the program from the controlling terminal (or other process). It accepts two arguments: chdir and close. If chdir is trueish then daemon() will change process' working directory to /, otherwise working dir will be left unchanged. If close is trueish then standard input and standard output will be redirected to /dev/null, otherwise no changes will be made to these file descriptors. If daemon() succeeds it returns 0, if an error occurs it returns -1. The code below daemon() function invocation will run in child only. Warning: process.pid will report incorrect process id after daemon(), so use posix.getpid(). Read man daemon for more.

var posix = require('posix-fork')

if (posix.daemon())
  throw 'Could not daemonize'
else
  console.log('my pid is %s', posix.getpid())