Cannot connect to MongoDB errno:61

I encountered similar problem. I have detailed the error trace and solution on this blog This is step by step process I did to solve this issue:

Step 1 - Installation ( Don't follow this step if you have already installed MongoDB ):

brew updatebrew install mongodb

Step 2 - Run Mongo Daemon:

mkdir -p /data/dbsudo mongod

Step 3 - Run Mongo Shell Interface:

mongo

In this sequence, I was able to run the mongo command without any error.

Yes, you would create /data/db at root. The MongoDB Documentation suggests the following command for creation on OS X mkdir -p /data/db.

Regarding your second question, also yes. Since the Mongo Daemon failed to start and isn't listening you get the connection error.

MongoDB defaults to /data/db for the data directory. You can override the default using the --dbpath option on the mongod command (also on the doc link above).

** WARNING: soft rlimits too low. Number of files is 256, should be at least 1000

you can add one line into your /etc/bashrc, the warning will disappear.

ulimit -S -n 1024

use chown -R {user} /data/db to change the owner of /data/db from root to yourself.Then you can start mongo shell just by mongo, no need to use sudo mongo.