We often get an issue with our MEAN vagrant dev environments where a previously working server will fail to connect to the mongo db the next time a developer does
It appears if the vagrant server is abruptly shutdown (host power down for example), mongo does not gracefully disconnect and you get a corrupted mongo lock file. Until we work out a way to stop this happening our workaround is to simply kill the lock file and re start mongo...
Then on the vagrant server thats hosts mongo....
sudo rm /var/lib/mongodb/mongod.lock && sudo service mongodb restart