1. 报错：TypeError: db.db.collection is not a function。
参考链接：https://blog.csdn.net/bifjhh_sk/article/details/79383296
2. 启动mongo报错。
错误：
root@ubuntu:~$ mongo
MongoDB shell version v4.0.8
connecting to: mongodb://127.0.0.1:27017/?gssapiServiceName=mongodb
2019-06-14T11:19:43.729+0800 E QUERY [js] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed: SocketException: Error connecting to 127.0.0.1:27017 :: caused by :: Connection refused :
connect@src/mongo/shell/mongo.js:343:13
@(connect):2:6
exception: connect failed
解决方法：
（1）删除.lock文件
sudo rm /var/lib/mongodb/mongod.lock（2）修复mongodb
mongod -repair（3）启动mongodb服务
sudo service mongod start（4）测试
mongo
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