我刚刚重新安装到旧版本的Mongo，但无法使其连接。我已经在线尝试了一些解决方案，但是似乎没有任何效果。这是错误：
MongoDB shell version v3.4.17
connecting to: mongodb://127.0.0.1:27017
2018-10-22T23:27:58.010-0700 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused
2018-10-22T23:27:58.010-0700 E QUERY [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:240:13
@(connect):1:6
exception: connect failed
任何输入都会很棒。