text: const exec = require('child_process').exec;
  const psTree = require('ps-tree');
  const utils = require('./utils');
  var hasPS = true;
  
  // discover if the OS has `ps`, and therefore can use psTree
  exec('ps', error => {
    module.exports.hasPS = hasPS = !error;
  });
  
  module.exports = function main(pid, callback) {
    if (typeof pid === 'number') {
      pid = pid.toString();
    }
  
    if (hasPS && !process.env.NO_PS) {
      return psTree(pid, callback);
    }
  
    utils
      .getStat()
      .then(utils.tree)
      .then(tree => utils.pidsForTree(tree, pid))
      .then(res => callback(null, res))
      .catch(error => callback(error));
  };
  
  module.exports.hasPS = hasPS;
  