gracias master!
Entré a
http://localhost/sf_sandbox/web/helloworld_dev.php/ y me sale esto:
Cita: Symfony Project Created
Congratulations! You have successfully created your symfony project.
Project setup successful
This project uses the symfony libraries. If you see no image in this page, you may need to configure your web server so that it gains access to the symfony_data/web/sf/ directory.
This is a temporary page
This page is part of the symfony default module. It will disappear as soon as you define a homepage route in your routing.yml.
What's next
Create your data model
Customize the layout of the generated templates
Learn more from the online documentation
De lo que entiendo que debo generar el routing.yml (eso despues de arreglar sfRootConfigHandler.class.php )