https://syscoding.com/tutorials/40/how-to-install-memcached-on-ubuntu-1604/

http://www.servermom.org/install-use-memcached-nginx-php-7-ubuntu-16-04/3670/

$ sudo apt-get update
$ sudo apt-get install memcached
$ sudo apt install php-memcached
$ service memcached restart
$ service php7.0-fpm restart