code: def _construct_mongos(self, logpath, port, configdb):
          
          extra = ''
  
          auth_param = ''
          if self.args['auth']:
              key_path = os.path.abspath(os.path.join(self.dir, 'keyfile'))
              auth_param = '--keyFile %s' % key_path
  
          if self.unknown_args:
              extra = self._filter_valid_arguments(self.unknown_args,
                                                   "mongos") + extra
  
          extra += ' ' + self._get_ssl_server_args()
  
          path = self.args['binarypath'] or ''
          if os.name == 'nt':
              newlogpath = logpath.replace('\\', '\\\\')
              command_str = ("start /b %s --logpath \"%s\" --port %i --configdb %s "
                             "%s %s " % (os.path.join(path, 'mongos'),
                                         newlogpath, port, configdb,
                                         auth_param, extra))
          else:
              command_str = ("%s --logpath \"%s\" --port %i --configdb %s %s %s "
                             "--fork" % (os.path.join(path, 'mongos'), logpath,
                                         port, configdb, auth_param, extra))
  
          # store parameters in startup_info
          self.startup_info[str(port)] = command_str
docs: Construct command line strings for a mongos process.