How to use the result of child_process spawn in a request (getting ENOENT)

I get an ENOENT when executing the js file containing the exact code below. And I don't know how to fix this.

Any explanation or advice is welcome but I would prefer a solution for the way I'm trying to do it. (Except if I'm doing something really stupid of course)

I have written this fake request function for testing purpose:

(function imaginaryRequest(req, res)
{
  getDiskInfo('/dev/simfs', info =>
  {
    console.log(info.ratio)
  })
}())

It is supposed to use the getDiskInfo function that uses child_process.spawn to get the df -Ph output and store it into an object.

/**
 * Get information on the disk space of the specified File system
 * @param {string} sysFile (ex: /dev/sda)
 * @param {function} callback
 * @return {object} df -Ph output stored into object
 */
function getDiskInfo(sysFile, callback) {

  const spawn = require('child_process').spawn
  const df_Ph = spawn("df -Ph | grep " + sysFile);

  df_Ph.stdout.on('data', data => {
    let info = data
      .split(' ')
      .filter(el => el != '')

    callback({
      maxSpace: info[1],
      used: info[2],
      unused: info[3],
      ratio: info[4],
    })
  })

  df_Ph.stderr.on('data', (data) => {
    console.log(`stderr: ${data}`);
  });

  df_Ph.on('close', (code) => {
    console.log(`child process exited with code ${code}`);
  });
}

And here is the error I get in the shell:

events.js:160
      throw er; // Unhandled 'error' event
      ^

Error: spawn df -Ph | grep /dev/simfs ENOENT
    at exports._errnoException (util.js:1022:11)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:193:32)
    at onErrorNT (internal/child_process.js:359:16)
    at _combinedTickCallback (internal/process/next_tick.js:74:11)
    at process._tickCallback (internal/process/next_tick.js:98:9)
    at Module.runMain (module.js:607:11)
    at run (bootstrap_node.js:420:7)
    at startup (bootstrap_node.js:139:9)
    at bootstrap_node.js:535:3

Thank you.

via Romain Vincent