I previously had Drush working on my VPS, but for some reason since a server update Drush can no longer be located.
If I do 'which drush' the output is '/root/.composer/vendor/bin/drush' which matches what is in my .bash_profile:
My drush installation is actually at /opt/drush-8.x/vendor/drush/drush
This may seem like an obvious answer, but when I tried editing .bash_profile to what made sense to me, something got broken (couldn't use any commands) and my hosts had to restore my old .bash_profile for me. I may just have made a typo then, but wanted someone to confirm exactly what my .bash_profile should say before I try again!