当我尝试mongo命令时，有人可以解释一下gitbash中显示的此错误消息的含义吗？ mongoDB已在系统上成功安装。我在一个单独的gitbash窗口中运行mongod来运行可执行文件以启动服务器：
MongoDB shell version v3.6.5
connecting to: mongodb://127.0.0.1:27017
2018-06-16T16:34:41.678+0530 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017 after 5000ms milliseconds, giving up.
2018-06-16T16:34:41.678+0530 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