code: def start(self, payload):
          
          # Start specific processes, if `keys` is given in the payload
          if payload.get('keys'):
              succeeded = []
              failed = []
              for key in payload.get('keys'):
                  success = self.process_handler.start_process(key)
                  if success:
                      succeeded.append(str(key))
                  else:
                      failed.append(str(key))
  
              message = ''
              if len(succeeded) > 0:
                  message += 'Started processes: {}.'.format(', '.join(succeeded))
                  status = 'success'
              if len(failed) > 0:
                  message += '\nNo paused, queued or stashed process for keys: {}'.format(', '.join(failed))
                  status = 'error'
  
              answer = {'message': message.strip(), 'status': status}
  
          # Start a all processes and the daemon
          else:
              self.process_handler.start_all()
              if self.paused:
                  self.paused = False
                  answer = {'message': 'Daemon and all processes started.',
                            'status': 'success'}
              else:
                  answer = {'message': 'Daemon already running, starting all processes.',
                            'status': 'success'}
          return answer
docs: Start the daemon and all processes or only specific processes.