Set up MySQL
$ sudo yum install mysql-server
$ sudo apt-get install php5-mysql mysql-server mysql-client
Note for CentOS 7
As of version 7 CentOS no longer includes MySQL in its repos. If you are using CentOS 7 you will need to install MySQL following these instructions here, or you can use MariaDB instead of MySQL. You will still need the mysql-client.
You need to create a database, and a DreamFactory user in your MySQL instance. On a fresh install, this is quite simple:
$ mysql -u root mysql> create database dreamfactory; mysql> grant all privileges on dreamfactory.* to 'dsp_user'@'localhost' identified by 'dsp_user'; mysql> quit