It could be combination of $PATH and Permission issue.

Try following steps given below:

Update your $PATH variable to point to your MongoDB bin file. In my case brew install MongoDB to this folder:

/usr/local/Cellar/mongodb/2.4.6/

In order to update your $PATH variable, do following:

$ sudo vi /etc/paths

Then, press ‘i’ to insert text in Vi and append the your MongoDB path to the end of the ‘paths’ file and restart the terminal.

/usr/local/Cellar/mongodb/2.4.6/bin

Use ‘Esc : w q’ to save and exit from Vi editor.

Use echo to display your path variable:

$ echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/Cellar/mongodb/2.4.6/bin

Now try to check the Mongo version, if you get following, then you are on the right track!

$ mongo --version
MongoDB shell version: 2.4.6

Now we need to create the database directory. I used the default ‘/data/db’ location suggested in MongoDB docs. I also created a log directory to avoid any permission issues while Mongo tries to create any logs. Change ownership and that will do the job.

$ sudo mkdir /data/db
$ sudo mkdir /data/log
$ whoami
username
$ chown -R username /data

Now, we will create a default config file for MongoDB to be provided for the first time we run ‘mongod’ command. Now, I will also like to point out that ‘mongod’ will start a service, which will listen for incoming data connections. This is similar having ‘$service mysqld start’ executed.Let’s go ahead and create the config file. Please keep in mind that I have created very basic config file. However, you can add many other variables to configure MongoDB. This is the first time I am playing with MongoDB, so I just know as much as I read on MongoDB docs!I created ‘mongodb.conf’.

$ sudo vi /etc/mongodb.conf

Add following:

fork = true
port = 27017
quiet = true
dbpath = /data/db
logpath = /data/log/mongod.log
logappend = true
journal = true

Please note that the default port for MongoDB server is 27017. Use your own path for dbpath and logpath you created in Step – 5. Don’t forget to close and save the conf file.

Now we are all set to start our MongoDB service. Open two instances of Terminal.In Terminal 1, type in:

$ sudo mongod -f /etc/mongodb.conf
about to fork child process, waiting until server is ready for connections.
forked process: 3516
all output going to: /data/log/mongod.log
child process started successfully, parent exiting

If you get above message, then know that you have successfully started your Mongod service.

Now, to connect to it, in Terminal 2 type following:

$mongo test
MongoDB shell version: 2.4.6
connecting to: test
Server has startup warnings:
Tue Sep 3 16:55:43.527 [initandlisten]
Tue Sep 3 16:55:43.527 [initandlisten] ** WARNING: soft rlimits too low. Number of files is 256, should be at least 1000
>

Ignore the warnings, but you are successfully connected to the ‘test’ database! Cool!

That’s all. I applied this solution, when I tried to install copy of MongoDB on my Mac for the first time. See if this help you too.

For detailed post you can go here – http://arcanebytes.com/2013/09/03/mongodb-installation-on-mac-os-x/#comment-1036112094.

I hope it helps!

Cheers,
Chinmay