Drush was unable to query from the database

  drupal-7, drupal-8, drush, php, symfony

I am trying to migrate from drupal 7 to drupal 8 using drush at ubuntu localhost. My drush version is 10.3.5 and

When i am trying to install a module using drush en migrate_upgrade inside my /var/www/drupal8 folder i get the following message Command pm:enable was not found. Drush was unable to query the database. As a result, m any commands are unavailable. Re-run your command with --debug to see relevant log mess ages. and when i use –debug

In Application.php line 239:[SymfonyComponentConsoleExceptionCommandNotFoundException]

Exception trace: at /root/.composer/vendor/drush/drush/src/Application.php:239 DrushApplication->bootstrapAndFind() at /root/.composer/vendor/drush/drush/src/Application.php:192 DrushApplication->find() at /var/www/drupal8/vendor/symfony/console/Application.php:236 SymfonyComponentConsoleApplication->doRun() at /var/www/drupal8/vendor/symfony/console/Application.php:148 SymfonyComponentConsoleApplication->run() at /root/.composer/vendor/drush/drush/src/Runtime/Runtime.php:118 DrushRuntimeRuntime->doRun() at /root/.composer/vendor/drush/drush/src/Runtime/Runtime.php:49 DrushRuntimeRuntime->run() at /root/.composer/vendor/drush/drush/drush.php:72 require() at /root/.composer/vendor/drush/drush/drush:4

Source: Symfony Questions