$ sudo apt-get install php5-dev libpcre3-dev gcc make php5-mysql git-core autoconf
Clone the framework repo onto your system.
$ git clone git://github.com/phalcon/cphalcon.git
Compile extension.
$ cd cphalcon/build
$ sudo ./install
Add extension to PHP and enable phalcon
$ sudo echo 'extension=phalcon.so' | sudo tee -a /etc/php5/mods-available/phalcon.ini
$ sudo php5enmod phalcon
Restart Apache2
$ sudo service apache2 restart