Identifying Duplicate Modules

Issue

Duplicate modules can create issues when installed on Drupal sites.  This article will help you to identify and troubleshoot these type of issues.

Resolution

To identify a fatal error caused by a duplicate module, review the logs files and the PHP errors log file in particular. For a failed page load, you can trace the error via the request_id to confirm the failed page load is related to the PHP fatal error in the PHP error log. The request_id is a unique ID attached to a request by the load balancer, which appears in several Acquia Cloud log files.  

Example error due to duplicate modules:

php-errors.log:[19-Dec-2017 23:28:36 Europe/Berlin] PHP Fatal error:  Cannot redeclare ctools_content_process() (previously declared in /mnt/www/html/sitename/docroot/sites/default/modules/contrib/ctools/includes/content.inc:18) in /mnt/www/html/sitename/docroot/sites/default/modules/updated/ctools/includes/content.inc on line 18 request_id="v-ebdc7366-53a3-11e7-b286-44008ac409b7"

To rectify the error, remove one of the modules from the codebase. The error message itself should contain the paths to the duplicate modules. Using the above error as an example, you can see the ctools module is located in both /sites/default/modules/contrib/ and /sites/default/modules/updated/directories:

/mnt/www/html/sitename/docroot/sites/default/modules/contrib/ctools/includes/content.inc
/mnt/www/html/sitename/docroot/sites/default/modules/updated/ctools/includes/content.inc

You may need to perform a database update and clear Drupal cache after removing the duplicate module from the codebase. As a best practice, it's advisable to take an on-demand database backup prior to making any configuration or code changes.  

More Information

About Acquia Cloud logging 
Errors in the PHP log 
Using HTTP request IDs