Mongodb start error with security.authorization enabled - macos

Question

I am getting an error attempting to start mongo with authorization enabled via the security.authorization configuration parameter (see http://docs.mongodb.org/manual/reference/configuration-options/#security.authorization)
On running mongod I get
Error parsing INI config file: unknown option security.authorization
try 'mongod --help' for more information
Any idea?
Thanks
Supporting data:
Mongo version 2.6.0 (installed via homebrew)
OSX Mavericks 10.9.2
start command:
mongod -f /usr/local/etc/mongod.conf
mongod.conf file (works fine if I comment out security.authorization):
# Store data in /usr/local/var/mongodb instead of the default /data/db
dbpath = /usr/local/var/mongodb
# Append logs to /usr/local/var/log/mongodb/mongo.log
logpath = /usr/local/var/log/mongodb/mongo.log
logappend = true
# Only accept local connections
bind_ip = 127.0.0.1
# auth
security.authorization = enabled
#security.authenticationMechanisms = MONGODB-CR #error occurs with or without this
No entry is made in the mongo.log file when this occurs

Answer 1

Note: I would have written this as a comment, however I do not have the points yet.
Just wondering whether what you are trying to achieve is authentication instead? If this is the case, all you need to set in mongodb.conf is:
# auth
auth = true # true or false. Whether or not authentication is required.
-- UPDATED:
Some other steps that are important:
Configure the db location: Set in mongodb.conf as (you already have this, but should check the directory and permissions exist):
# Store data in /usr/local/var/mongodb instead of the default /data/db
dbpath = /usr/local/var/mongodb
# Append logs to /usr/local/var/log/mongodb/mongo.log
logpath = /usr/local/var/log/mongodb/mongo.log
logappend = true
Dont forget to make sure the above /usr/local/var/mongodb directory and /usr/local/var/log/mongodb/ directory exist. The installer that you used may not have made them.
Create an Operating System user for mongodb: (If one has not already been created - this is how on linux, not sure for osx) - as root:
adduser --system --no-create-home --disabled-login --disabled-password --group mongodb
Add permissions to folders if they are not already set:
chown mongodb:mongodb -R /usr/local/var/mongodb
To setup database user authorization / privileges:
See the command reference here: http://docs.mongodb.org/manual/reference/command/#database-commands

Answer 2

MongoDB server config file format changed from version 2.6 and still old format works.
http://docs.mongodb.org/manual/reference/configuration-options/
Changed in version 2.6: MongoDB introduces a YAML-based configuration file format. The 2.4 configuration file format remains for backward compatibility.
The error is due to the reason your config file is using old format and adding parameter security.authorization = enabled using new format.You can fix the problem by
using old format settings mentioned at http://docs.mongodb.org/v2.4/reference/configuration-options
auth = true
or by converting conf file to new YAML format.