在Ubuntu 18.10上安装MongoDB之后，我想运行MongoDB时遇到问题。 这是错误：
MongoDB shell version v3.6.3
connecting to: mongodb://127.0.0.1:27017
2019-06-06T01:23:58.859+0430 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused
2019-06-06T01:23:58.941+0430 E QUERY [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:251:13
@(connect):1:6
exception: connect failed