mongoDB遇到的一个小问题

报错信息如下，百度了好多也没有解决：
exception 'MongoConnectionException' with message 'Failed to connect to: localhost:27017: Previous connection attempts failed, server blacklisted' in /var/www/web/application/libraries/Mdb.php:57 Stack trace: #0 /var/www/web/application/libraries/Mdb.php(57): MongoClient->__construct('mongodb://jnexp...') #1 /var/www/web/system/core/Loader.php(1109): Mdb->__construct() #2 /var/www/web/system/core/Loader.php(985): CI_Loader->_ci_init_class('Mdb', '', NULL, NULL) #3 /var/www/web/system/core/Loader.php(216): CI_Loader->_ci_load_class('mdb', NULL, NULL) #4 /var/www/web/application/models/record_operate.php(14): CI_Loader->library('mdb') #5 /var/www/web/system/core/Loader.php(303): Record_operate->__construct() #6 /var/www/web/system/core/Controller.php(71): CI_Loader->model('record_operate') #7 /var/www/web/application/controllers/mng_login.php(12): CI_Controller->__construct() #8 /var/www/web/system/core/CodeIgniter.php(316): Mng_login->__construct() #9 /var/www/web/index.php(225): require_once('/var/www/web/sy...') #10 {main}