MongoDB: Failed to connect to 127.0.0.1:27017 reason: Connection refused

# mongo
MongoDB shell version v3.6.8
connecting to: mongodb://127.0.0.1:27017
2022-04-08T13:16:33.543-0700 W NETWORK  [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused
2022-04-08T13:16:33.544-0700 E QUERY    [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:257:13
@(connect):1:6
exception: connect failed

The most common reason for Connection refused error when running the mongo command is that your mongod server is not running.

Run the mongod command to start the mongoDB server and then try the mongo command,

# mongod
2022-04-08T13:15:56.482-0700 I CONTROL  [initandlisten] MongoDB starting : pid=5171 port=27017 dbpath=/data/db 64-bit host=b2391b608026
2022-04-08T13:15:56.482-0700 I CONTROL  [initandlisten] db version v3.6.8
2022-04-08T13:15:56.482-0700 I CONTROL  [initandlisten] git version: 8e540c0b6db93ce994cc548f000900bdc740f80a
2022-04-08T13:15:56.482-0700 I CONTROL  [initandlisten] OpenSSL version: OpenSSL 1.1.1f  31 Mar 2020
..
..
2022-04-08T13:36:31.974-0700 I FTDC     [initandlisten] Initializing full-time diagnostic data capture with directory '/data/db/diagnostic.data'
2022-04-08T13:36:31.975-0700 I NETWORK  [initandlisten] waiting for connections on port 27017

# mongo
MongoDB shell version v3.6.8
connecting to: mongodb://127.0.0.1:27017
Implicit session: session { "id" : UUID("0e4156ce-070c-49a5-8bb9-fd43aae91bb1") }
MongoDB server version: 3.6.8