Download a copy of Zend Guard Loader from here . By default PHP 5.4 is installed on debian wheezy so select the package Zend Guard Loader (Runtime for PHP 5.4).
Enter the directory where Zend Guard Loader is located and extract the downloaded package using the following command
#tar zxvf ZendGuardLoader-70429-PHP-5.4-linux-glibc23-x86_64.tar.gz
Now replace with the name of the file downloaded from zend.com
Create a directory where Zend Guard loader will be located
Move the Zend optimizer lib to a permanent location
# mv ZendGuardLoader-70429-PHP-5.4-linux-glibc23-x86_64/php-5.4.x/ZendGuardLoader.so /usr/local/lib/Zend/
The ZendGuardLoader.so may be located in a different location based on the package downloaded from zend.com.
Add these two lines to the bottom of your php.ini to enable Zend Guard Loader
add the following lines
zend_extension = /usr/local/lib/Zend/ZendGuardLoader.so
Save and exit the file
Restart apache2 server using the following command
service apache2 restart