code: def start_stress(self, stress_cmd):
          
          with open(os.devnull, 'w') as dev_null:
              try:
                  stress_proc = subprocess.Popen(stress_cmd, stdout=dev_null,
                                                 stderr=dev_null)
                  self.set_stress_process(psutil.Process(stress_proc.pid))
              except OSError:
                  logging.debug("Unable to start stress")
docs: Starts a new stress process with a given cmd