MongoDB运行正常，但现在它无法连接。当我运行mongo时，我收到了这条消息：
warm@ULTP-500:~$ mongo
MongoDB shell version v3.4.6
connecting to: mongodb://127.0.0.1:27017
2018-01-13T15:53:18.609+0530 W NETWORK [thread1] Failed to connect to
127.0.0.1:27017, in(checking socket for error after poll), reason:
Connection refused
2018-01-13T15:53:18.609+0530 E QUERY [thread1] Error: couldn't
connect to server 127.0.0.1:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:237:13
@(connect):1:6
exception: connect failed
我尝试重新启动mongod服务，但这没有帮助。你能指导我如何调试这个问题吗？