官网安装步骤:https://docs.mongodb.com/manual/tutorial/install-mongodb-on-ubuntu/ (强烈推荐)
如看不懂请参考:https://www.jianshu.com/p/f0952b4118ec
但是在启动DB时,即 sudo service mongod start,会出现错误:Failed to start mongod.service: Unit mongod.service not found.
解决方法(链接:https://stackoverflow.com/questions/48092353/failed-to-start-mongod-service-unit-mongod-service-not-found):
命令行输入:sudo systemctl unmask mongodb
sudo service mongod start