MongoDB shell version v3.4.2connecting to: mongodb://127.0.0.1:270172017-03-01T12:06:59.013+0800 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused2017-03-01T12:06:59.015+0800 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):1:6exception: connect failed