Executable version of the guide posted on the official MongoDB page (http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/) to install it on Ubuntu 14.04.

install_mongodb_on_ubuntu.sh

#!/bin/bash

# Install MongoDB on Ubuntu 14.04

# Executable version of the guide posted on the official MongoDB page:
# SOURCE: http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/

# On a c9.io ubuntu machine, refer instead to the support document "Setting Up MongoDB · Cloud9"
# SOURCE: https://docs.c9.io/docs/setting-up-mongodb

set -eox pipefail

# Create a log file of the script output
LOG_FILENAME="$(basename $0 .sh)_$(date +"%Y%m%d_%H%M%S").log"
exec >  >(tee -a ${LOG_FILENAME})
exec 2> >(tee -a ${LOG_FILENAME} >&2)


# 1 Import the public key used by the package management system.

# The Ubuntu package management tools (i.e. dpkg and apt) ensure package
# consistency and authenticity by requiring that distributors sign
# packages with GPG keys. Issue the following command to import the
# MongoDB public GPG Key:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10

# 2 Create a list file for MongoDB.

# Create the /etc/apt/sources.list.d/mongodb-org-3.0.list list file
# using the command appropriate for your version of Ubuntu:

# Ubuntu 12.04
#   echo "deb http://repo.mongodb.org/apt/ubuntu precise/mongodb-org/3.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.0.list

# Ubuntu 14.04
echo "deb http://repo.mongodb.org/apt/ubuntu trusty/mongodb-org/3.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.0.list

# 3 Reload local package database.

# Issue the following command to reload the local package database:

sudo apt-get update -y

# 4 Install the MongoDB packages.

# You can install either the latest stable version of MongoDB or a
# specific version of MongoDB.

# Install the latest stable version of MongoDB.
# Issue the following command:

sudo apt-get install -y mongodb-org

# Install a specific release of MongoDB.
# To install a specific release, you must specify each component
# package individually along with the version number, as in the
# following example:

#   sudo apt-get install -y mongodb-org=3.0.6 mongodb-org-server=3.0.6 mongodb-org-shell=3.0.6 mongodb-org-mongos=3.0.6 mongodb-org-tools=3.0.6

# If you only install mongodb-org=3.0.6 and do not include the component
# packages, the latest version of each MongoDB package will be installed
# regardless of what version you specified.

# Pin a specific version of MongoDB.

# Although you can specify any available version of MongoDB, apt-get
# will upgrade the packages when a newer version becomes available. To
# prevent unintended upgrades, pin the package. To pin the version of
# MongoDB at the currently installed version, issue the following
# command sequence:

#   echo "mongodb-org hold" | sudo dpkg --set-selections
#   echo "mongodb-org-server hold" | sudo dpkg --set-selections
#   echo "mongodb-org-shell hold" | sudo dpkg --set-selections
#   echo "mongodb-org-mongos hold" | sudo dpkg --set-selections
#   echo "mongodb-org-tools hold" | sudo dpkg --set-selections

# Versions of the MongoDB packages before 2.6 use a different repository
# location. Refer to the version of the documentation appropriate for
# your MongoDB version.

################################################################################

# Run MongoDB

# The MongoDB instance stores its data files in /var/lib/mongodb and its
# log files in /var/log/mongodb by default, and runs using the mongodb
# user account. You can specify alternate log and data file directories
# in /etc/mongod.conf. See systemLog.path and storage.dbPath for
# additional information.

# If you change the user that runs the MongoDB process, you must modify
# the access control rights to the /var/lib/mongodb and /var/log/mongodb
# directories to give this user access to these directories.

# 1 Start MongoDB.

# Issue the following command to start mongod:

sudo service mongod start

# 2 Verify that MongoDB has started successfully

# Verify that the mongod process has started successfully by checking
# the contents of the log file at /var/log/mongodb/mongod.log for a line
# reading

#   [initandlisten] waiting for connections on port <port>

# where <port> is the port configured in /etc/mongod.conf, 27017 by default.

# 3 Stop MongoDB.

# As needed, you can stop the mongod process by issuing the following
# command:

#   sudo service mongod stop

# 4 Restart MongoDB.

# Issue the following command to restart mongod:

#   sudo service mongod restart