$ mongo

MongoDB shell version v3.4.9

connecting to: mongodb://127.0.0.1:27017

2017-10-10T15:54:42.503+0800 W NETWORK  [thread1] Failed to connect to 127.0.0.1:27017 after 5000ms milliseconds, giving up.

2017-10-10T15:54:42.503+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):1:6

exception: connect failed