I don't understand, I want show some vars during my dev. I work on windows and Linux.
On windows, When I use print_r for show $form or $form_state (from the hook form_alter). There isn't any problem, when the page is loaded, I can see the content of theses vars.
But on linux, when I use print_r, I see the RAM (via top/htop) rise continuously until 4Go and my OS freeze x) The page I request is never loaded.
I don't understand because I don't think have a special configuration. My configuration is recent.
On Linux (Mint)
php -v : 5.6.14 apache2 -v : 2.4.10 (Raspbian)
Activate the sub-extend drupal Kint from the devel package :)