Drupal - How to install drush 8 properly?

For Ubuntu

export PATH="$HOME/.composer/vendor/bin:$PATH"
source $HOME/.bashrc
composer global require drush/drush:8.x

composer require drush/drush:dev-master gave me Drush 8 three days ago when I ran this tutorial to setup different versions of Drush on my system http://www.jpstacey.info/blog/2014-04-07/switching-between-drush-major-versions

Multiple versions of Drush can be useful if a site is no longer in development and for example custom drush commands were created for a specific version of Drush.