In Magento 1.x, I had to create a PHP workbench script in order to be able to create an admin user from shell or terminal (http://www.magetricks.com/tricks/programmatically-create-new-magento-administrator" ). Thankfully, Magento 2's newly introduce CLI (command-line interface) allows you to do this without writing any code. Here is an example of how I would execute this command to create a new administrator.
// Head over to the webroot for your Magento 2 instance e.g. /var/www/html or maybe /var/www/magento2 // Execute admin:user:create with the appropriate arguments as demonstrated below php bin/magento admin:user:create --admin-user="John" --admin-password="password" --admin-email="firstname.lastname@example.org" --admin-firstname="John" --admin-lastname="Hancock" // bin/magento is a PHP executable file that allows you to issue any number of commands. See: http://devdocs.magento.com/guides/v2.0/install-gde/install/cli/install-cli.html // You can also setup a PATH command in your bash profile that allow you to execute Magento CLI commands from any directory and not just bin