What is APC:
The Alternative PHP Cache (APC) is a free and open opcode cache for PHP. Its goal is to provide a free, open, and robust framework for caching and optimizing PHP intermediate code. Apart from caching opcode cache it provides a user cache for storing application data.
Installing APC on cPanel server :
Before installing APC on the server ensure eAccelerator is enabled on the server .
root@server [~]# php -m | grep eAccelerator
Now lets install APC on the server . Follow the following commands on the server :
root@mailspec [~]# cd /usr/local/src
root@mailspec [~]# wget http://pecl.php.net/get/APC-3.0.19.tgz
root@mailspec [~]# tar -xzf APC-3.0.19.tgz && cd APC-3.0.19
root@mailspec [~]# phpize && ./configure –enable-apc –enable-apc-mmap –with-apxs=/usr/local/apache/bin/apxs –with-php-config=/usr/local/bin/php-config && make && make install
This should now configure APC and install it in your extension directory.
root@mailspec [~]# cd /usr/local/lib/php/extensions/no-debug-non-zts-220XXXX
You can locate a file named apc.so in that directory.
You can now locate an entry for apc.so in the file /usr/local/lib/php.ini.
If you want to view APC interface via browser you can copy the file /usr/lib/php/apc.php into your sites documentroot path and access it via the browser. Ensure GD is installed on the server to view APC interface via the browser.

You can try accessing the URL:: http://domain.com/apc.com to view the interface
(replace the domain.com with your original domain name )
It will show you interface similar as follows :