I am running LAMP on Ubuntu 16.04.  I have a drupal 7 installation and I have installed drush 8.1.3 via composer.  It appears that my problem is that Drush 8.1.13 is not connecting to any db for my drupal site(s).  The output of `drush status` at the command prompt is: 

    drush status
    PHP executable         :  /usr/bin/php                                 
    PHP configuration      :  /etc/php/7.1/cli/php.ini                     
    PHP OS                 :  Linux                                        
    Drush script           :  /home/USER/vendor/drush/drush/drush.php 
    Drush version          :  8.1.13                                       
    Drush temp directory   :  /tmp                                         
    Drush configuration    :                                               
    Drush alias files      :   

and the result of `drush status` from inside a drupal installation is:

     drush status
     PHP executable         :  /usr/bin/php                                 
     PHP configuration      :  /etc/php/7.1/cli/php.ini                     
     PHP OS                 :  Linux                                        
     Drush script           :  /home/USER/vendor/drush/drush/drush.php 
     Drush version          :  8.1.13                                       
     Drush temp directory   :  /tmp                                         
     Drush configuration    :                                               
     Drush alias files      :                                       

Obviously, these results do NOT include any information about the db that is being used .  

If I execute `drush sql-connect`

    drush sql-cli
    Unable to load class Drush\Sql\Sql                                 [error]
    Drush\Sql\SqlException: Unable to find a matching SQL Class. Drush [error]
    cannot find your database connection details. in /home/user/vendor/drush/drush/commands/sql/sql.drush.inc:541

Also, I have edited my ~/.bashrc file, adding the 2 lines below:

    export PATH="$HOME/.composer/vendor/bin:$PATH"
    export PATH=/bin:/usr/local/bin:/usr/local/mysql/bin:$PATH

**EDIT:** The result of `drush cc all` is:

    No Drupal site found, only 'drush' cache was cleared. 

Anyone know how to connect drush to the db(s) for my local (LAMP) Drupal 7 installations?

thx