To install mcrypt in Ubuntu/Debian, run the following command:
sudo apt-get install php-mcrypt
In CentOS like this:
sudo yum install php-mcrypt
After that, the mcrypt.ini file will appear in the PHP directory with the mcrypt.so extension, in my case it appeared /etc/php/7.0/mods-available/mcrypt.ini.
You can activate/deactivate the module like this:
sudo phpenmod mcrypt sudo phpdismod mcrypt
Restart Apache2 to apply the changes:
sudo service apache2 restart
Let’s see if mcrypt is activated:
php -i | grep -i mcrypt