mac环境中mongodb启动失败

rimideiMac-83:bin rimi$ ./mongo

MongoDB shell version v3.6.9

connecting to: mongodb://127.0.0.1:27017

2018-11-22T18:34:17.494+0800 W NETWORK  [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused

2018-11-22T18:34:17.499+0800 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

rimideiMac-83:~ rimi$ cd Documents   

rimideiMac-83:Documents rimi$ mkdir mongo

rimideiMac-83:Documents rimi$ cd mongo

rimideiMac-83:mongo rimi$ mkdir db

rimideiMac-83:bin rimi$ ./mongod --dbpath ~/Documents/mongo/db