Shutdown and startup

after creating my first user I stoped mongod server using db.shutdownserver , now i try to connect but getting following error.
how can we startup server

startup mongo server

[mongo@localhost init.d] service mongod start Error starting mongod. /var/run/mongodb/ exists. [mongo@localhost init.d]

[mongo@localhost init.d] ps -ef | grep -i mongod mongo 4514 4400 0 19:43 pts/0 00:00:00 grep -i mongod [mongo@localhost init.d]

error while connecting mongo

[mongo@localhost ~] mongo --username root --password root123 --authenticationDatabase admin MongoDB shell version v4.0.10 connecting to: mongodb:// 2019-06-06T19:33:37.185-0700 E QUERY [js] Error: couldn't connect to server, connection attempt failed: SocketException: Error connecting to :: caused by :: Connection refused : connect@src/mongo/shell/mongo.js:344:17 @(connect):2:6 exception: connect failed [mongo@localhost ~]

Responded in other thread
Please check