composer require drush drupal ubuntu server 16.04

noah@ubuntuServer:~/tmp $ composer require drush/drush:~8
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Nothing to install or update
Generating autoload files
noah@ubuntuServer:~/tmp $ drush
The program 'drush' is currently not installed. You can install it by typing:
sudo apt install drush
noah@ubuntuServer:~/tmp $