I've recently upgraded to Drush 8, from Drush 6.2 (That was installed using pear).
Drush on cPanel runs fine as root, but when I try to run it as a regular user in a valid Drupal directory I get the error:
Command pm-refresh needs a higher bootstrap level to run - you will need to invoke drush from a more functional Drupal environment to run[error]
Or for just trying to clear cache using drush cc all:
No Drupal site found, only 'drush' cache was cleared
And when I add --debug to the end of a command I get a mysql error with drush:
Access denied for user 'username'@'localhost'