At Agaric, we perform a lot of Drupal upgrades. These very often involve transitioning away from older versions of PHP. Even when your hosting service provides multiple versions of PHP, you can still run into issues activating the appropriate one for each site: whether that's within the web server, at the command line, or via drush (or other tools). In this blog post, we'll be providing remedies for all of these cases. Most content applies to any PHP application.