You have probably already installed PHP on your system since you are reading this book. However, just in case you haven't, here are the simple steps to quickly install the latest PHP version (Phalcon is running on PHP version >= 5.3). I recommend you to use the Personal Package Archive (PPA) from Ondřej Surý (https://launchpad.net/~ondrej/+archive/ubuntu/php5) because it has the latest PHP version available on it:

$ sudo add-apt-repository ppa:ondrej/php5
$ sudo apt-get update

If you don't want to use this step, you can simply install PHP from the official repositories:

$ sudo apt-get install php

Apache will be installed by default with PHP. However, if you want Nginx instead of Apache, you must install PHP in a certain order.

The following command will automatically install PHP and Apache. If you don't need/want to use Apache, please skip using this command:

$ sudo apt-get install php5 php5-fpm

To avoid Apache installation, execute the following commands in the exact same order:

$ sudo apt-get install php5-common
$ sudo apt-get install php5-cgi
$ sudo apt-get install php5 php5-fpm

The php5-cgi package fulfills the dependencies that would otherwise be fulfilled by Apache.

To install the Nginx web server, we need to execute the following commands:

$ sudo add-apt-repository ppa:nginx/stable
$ sudo apt-get update
$ sudo apt-get install nginx

MySQL is probably the most widely spread RDBMS system with a market share that is greater than 50 percent. Since we are going to use it to develop our project, we need to install it by executing the following command:

$ sudo apt-get install mysql-server

Redis is an advanced key-value storage/cache system. We are going to use this mostly for our session and to cache objects to improve the speed of our application. Let's install it by executing the following commands:

$ sudo add-apt-repository ppa:chris-lea/redis-server
$ sudo apt-get update
$ sudo apt-get install redis-server
$ sudo apt-get install php5-redis

MongoDB is a document database (NoSQL database) system. We will use this to store data that is accessed frequently. Let's install it:

$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
$ echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | sudo tee /etc/apt/sources.list.d/mongodb.list
$ sudo apt-get update
$ sudo apt-get install -y mongodb-org
$ sudo service mongodb start
$ sudo apt-get install php5-mongo

Git is a distributed version control system that we will use to track changes to our application and much more. We will install Git by executing the following command:

$ sudo apt-get install git