mongod won't start.
If you've tried
sudo service mongod start and it says it started but didn't, or maybe gives you a cryptic error.. consider removing the lock file at
/edx/var/mongo/mongodb/mongod.lock and try again.
No locks available.
So, when running some tests, I got the error "No locks available". This post suggests NFS. The actual fix appears to be to restart rpcbind
sudo service rpcbind restart which hung my vagrant VM. When it restarted, I got the error below, but things seemed to work as I wanted and I'm slowly backing away.