apt-get install php-apc

apc
apc.shm_size=256M

cp /etc/php.d/apc.ini /home/rack && sed -i 's/^.*apc.shm_size=.*$/apc.shm_size=256M/' /etc/php.d/apc.ini && grep "apc.shm_size=" /etc/php.d/apc.ini

cp  /usr/share/doc/php*apc*/apc.php /var/www/

service httpd graceful && service httpd status

PHP5.5 -> If it has Zend OPcache it doesn’t need APC anymore

php -m

Look for this:

[Zend Modules]
Zend OPcache

GUI: https://github.com/amnuts/opcache-gui

wget https://raw.githubusercontent.com/amnuts/opcache-gui/master/index.php

/etc/php5/mods-available/opcache.ini or /etc/php5/fpm/conf.d/05-opcache.ini

opcache.memory_consumption=128
opcache.interned_strings_buffer=8
opcache.max_accelerated_files=4000
opcache.revalidate_freq=60
opcache.fast_shutdown=1
opcache.enable_cli=1