$mongo

--------------
MongoDB shell version v3.4.10
connecting to: mongodb://127.0.0.1:27017
2018-01-17T20:21:16.583+0530 W NETWORK  [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused
2018-01-17T20:21:16.584+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

[1]: https://i.stack.imgur.com/WBYwE.png