Drush 9 can't find installed module, yields CommandNotFoundException

Question

On my newly installed Drupal 8.4.4 sandbox installation, I've installed Drush 9 and the Devel module:

composer require drush/drush:^9
composer require drupal/devel

After running these commands, I installed the Devel module using the Extend tab in Drupal.

Drush seems be be installed correctly:

www-data@39e134dc7690:~/html$ /var/www/html/vendor/bin/drush version
Drush version : 9.1.0

The Devel modules seems to be installed correctly:

www-data@39e134dc7690:~/html$ grep -r devel-container-service /var/www/html/modules/contrib/devel/
/var/www/html/modules/contrib/devel/src/Commands/DevelCommands.php:   * @aliases devel-container-services,dcs,devel-services
/var/www/html/modules/contrib/devel/drush/devel.drush8.inc:  $items['devel-container-services'] = array(

But Drush doesn't seem to find the devel module:

www-data@39e134dc7690:~/html$ /var/www/html/vendor/bin/drush devel-container-services
[Symfony\Component\Console\Exception\CommandNotFoundException]
Command "devel-container-services" is not defined.

Are there any path settings I need to tweak to get Drush to find the Devel module?

Answer 1

I looks like I simply had forgotten to enable (i.e install) the module in /admin/modules. I had just ran "composer require", but not actually enabled it.

Answer 2

I encountered this issue when attempting to port an older global Drush command. While following the porting instructions generated the necessary Drush code, the command was not discovered by drush because it wasn't part of an enabled module.

If this is your issue, either create a module_name.info.yml file manually, or run drush generate module, then enable the module in question. The drush command no longer threw a CommandNotFoundException.