On my system (Debian 8.3) I was using Drush 9.0-dev (I know, you should never use a dev version in production but I did this before I knew any better). To make a long story short I tried to change my drush version to the latest (at this time 8.1.13). I researched what I needed to do to make this change but nothing worked. I ended up having to remove (rename the syslink) and then installed the version I wanted with composer.
Over the last couple of weeks I have started playing with Drupal 8. So far it's been a pleasant experience (surprisingly) though originally I had issues with getting it installed. I tried using drush dl but it would not work (when used it would only download the latest version of Drupal 7). Turns out Drush 6 (the version I was currently at) does not support Drupal 8. Inorder to run Drush with Drupal 8 we have to upgrade Drush to version 7.