How To Harden PHP5 With Suhosin on Linux

Suhosin is an advanced protection system for PHP installations. It was designed to protect servers and users from known and unknown flaws in PHP applications and the PHP core.

Suhosin comes in two independent parts, that can be used separately or in combination. The first part is a small patch against the PHP core, that implements a few low-level protections against bufferoverflows or format string vulnerabilities and the second part is a powerful PHP extension that implements all the other protections.

Installation
OpenSuSe user can install Suhosin using "1-click" installer - here

After successful installation check the entries in your /etc/php5/conf.d/suhosin.ini configuration file to suite your requirement.

Restart apache using following command:

# /etc/init.d/apache restart

Make sure Suhosin is working, type following command:

php -v
PHP 5.3.1 (cli) (built: Feb 15 2010 17:27:14)
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2009 Zend Technologies
    with XCache v1.3.0, Copyright (c) 2005-2009, by mOo
    with Suhosin v0.9.29, Copyright (c) 2007, by SektionEins GmbH

Check Suhosin project for more detail