Sometimes while installing WordPress plugins, you might come across a message to install / enable Mcrypt extension for PHP.
Mcrypt is an interface which supports a wide range of block algorithims. It support Algorithims like DES, TripleDES, GOST, OFB etc.
Note : The Mcrypt extension relies on the 'libmcrypt' extension, which is not maintained since 2007. So some people consider installing the extension useless. None the less some WordPress plugins do require this extension to be installed and enabled.
Step 1 : Download and isntall the mcrypt extension
apt-get install php5-mcrypt
Step 2 : Create a symlink for Mcrypt to mods-available
ln -s /etc/php5/conf.d/mcrypt.ini /etc/php5/mods-available/mcrypt.ini
If you are running PHP-FPM your path might be like
ln -s /etc/php5/fpm/conf.d/mcrypt.ini /etc/php5/mods-available/mcrypt.ini
If you get an error message like:
ln: failed to create symbolic link ‘/etc/php5/mods-available/mcrypt.ini’: File exists
This means that the extension is already installed on your server and you just need to enable it by skipping to the next step.
Step 3 : Enable Mcrypt extension
Step 4 Restart PHP and Nginx
service php5-fpm restart service nginx restart