APC is a cache system which stores compiled PHP code, also allows to store user data allowing the web server to serve a greater number of requests per second, it's a worth noting that a wrong configuration of it can slow the response process, so it is important to adjust the cache parameters until finding the proper performance.
The method described below requires the PEAR extension, to install PEAR on CentOS-5.6 follow the instructions from step 5 of the article: Upgrading to PHP 5.3. x on CentOS
# yum -y install gcc make php-devel pcre pcre-devel && pecl install apc
# echo "extension=apc.so">/etc/php.d/apc.ini
# service httpd graceful
$ php -i | grep apc Additional .ini files parsed => /etc/php.d/apc.ini, apc MMAP File Mask => /apc.shm.8Il1zO apc.cache_by_default => On => On ...
Create dir in the root of the web server
# mkdir /var/www/apc
Copy apc.php file
# cp -v /usr/share/pear/apc.php /var/www/apc/
# vim +42 /var/www/apc/apc.php
Create a VirtualHost
For more information on how to create a VirtualHost see article: Install and configure Apache HTTP server
The admin page only will be available to the IP1, 2 and 3
<VirtualHost *:80> Options FollowSymLinks -ExecCGI ServerName apc.midominio.com DirectoryIndex apc.php DocumentRoot /var/www/apc <Directory> Order Deny,Allow Deny from all Allow from IP1 Allow from IP2 Allow from IP3 </Directory> </VirtualHost>