我的教授告诉我使用linux来安装nodejs，expressjs和mongoDB。我从终端安装了mongodb，但是当我尝试执行命令“mongo”时，我得到了这个：
MongoDB shell version: 2.6.10
connecting to: test
2018-01-20T11:58:05.602-0500 warning: Failed to connect to
127.0.0.1:27017, reason: errno:111 Connection refused
2018-01-20T11:57:05.603-0500 Error: couldn't connect to server
127.0.0.1:27017 (127.0.0.1), connection attempt failed at
src/mongo/shell/mongo.js:146
exception: connect failed