Enable OPCache on Ubuntu: Alternative to APC Cache

If you are using PHP 5.5, it is not supported by APC Cache. For reference, see PHP Bug #65731

PHP 5.5 comes with it's own opcode cache which can be enabled with the following steps:

1. Enable opcache in php.ini

sudo nano /etc/php5/apache2/php.ini

Look for the line:

;opcache.enable=0

And replace with:

opcache.enable=1

2. Enable the php mod

sudo php5enmod opcache
sudo service apache2 restart

If you are using PHP lower than 5.5, then you can still use APC.
Just run this line in the terminal to install APC.

sudo apt-get install php-apc