报错：
rico@ubuntu:~$ mongo
MongoDB shell version: 3.2.17
connecting to: test
2017-11-16T23:48:59.362+0800 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: errno:111 Connection refused
2017-11-16T23:48:59.362+0800 E QUERY [thread1] Error: couldn’t connect to server 127.0.0.1:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:229:14
@(connect):1:6
exception: connect failed
解决方法：
sudo rm /var/lib/mongodb/mongod.lock
sudo mongod --repair --dbpath /var/lib/mongodb
sudo mongod --fork --logpath /var/lib/mongodb/mongodb.log --dbpath /var/lib/mongodb
sudo service mongodb start
报错：
rico@ubuntu:/var/lib/mongodb$ sudo service mongodb start
Failed to start mongodb.service: Unit mongodb.service is masked.
解决方法：
rico@ubuntu:/var/lib/mongodb$ sudo chown -R mongodb:mongodb /var/lib/mongodb
rico@ubuntu:/var/lib/mongodb$ sudo systemctl start mongod