The Zend Optimizer enables you to run Zend Guard encoded files.
1. Download a copy of Zend Optimizer / Guard from the location below and put it into /tmp
http://www.zend.com/en/products/guard/downloads
2. Extract
cd /tmp
tar zxvf ZendOptimizer-3.3.9-linux-glibc23-i386.tar.gz
Replace with your actual filename
3. Create a directory to contain Zend optimizer
mkdir /usr/local/lib/Zend
3. Move the Zend optimizer lib to a permanent location
mv ZendOptimizer-3.3.9-linux-glibc23-i386/data/5_2_x_comp/ZendOptimizer.so /usr/local/lib/Zend/
Your ZendOptimizer directory name may be different since it includes version numbers and platform. I'm using the 5_2_x_comp directory because I have PHP 5.2 installed.
4. Add reference to your php.ini file (pico /etc/php5/apache2/php.ini)
zend_extension = /usr/local/lib/Zend/ZendOptimizer.so
zend_optimizer.optimization_level = 15
5. Restart apache
/etc/init.d/apache2 restart