Cannot redeclare civicrm_enable()

Question

I am trying to migrate a Drupal+CiviCRM from an old server to a new one.

I copied the files and database, updated civicrm.settings.php and settings.php, cleared the cache and made a drush up + drush updb, both ran fine.

As the new server uses PHP 7.0, I downloaded civicrm-4.7.31 drupal and l10n files to replace the version 4.4.19 that was used. However, I still have a white screen when going to the homepage.

In /var/log/nginx/error.log, I can find this error:

2018/04/30 17:54:16 [error] 20389#20389: *845 FastCGI sent in stderr:
"PHP message: PHP Fatal error:  Cannot redeclare civicrm_enable()
(previously declared in
<civicrm_root_path>/sites/all/modules/civicrm/drupal/civicrm.module:781)
in
<civicrm_root_path>/sites/all/modules/civicrm/drupal/civicrm.install
on line 40" while reading response header from upstream, client:
XXX.XXX.XXX.XXX, server: XXXX, request: "GET / HTTP/1.1", upstream:
"fastcgi://unix:/run/php/php7.0-fpm.sock:", host: "XXXX"

Edit: I already saw this post but that didn't help me fix my issue. I have only one copy of CiviCRM under my module directory. I tried the "drush vset civicrm_class_loader ''" command and now I have a new error message:

"2018/05/03 10:36:07 [error] 7010#7010: *2972 FastCGI sent in stderr:
"PHP message: PHP Fatal error: require_once(): Failed opening required
'CRM/Core/ClassLoader.php'
(include_path='.:<civicrm_old_root_path>/sites/all/modules/civicrm:<civicrm_old_root_path>/sites/all/modules/civicrm/packages:.:/usr/share/php')
> in <civicrm_root_path>/sites/default/civicrm.settings.php on line 280"
> while reading response header from upstream [...]"

With being the root path on the previous server, so it must be cached somewhere, but I cannot find where. This error disappears after a drush cc.

Answer 1

As answered by @davejenx here ("Cannot redeclare class CRM_Core_ClassLoader" in backup site) this could be your issue.

It sounds as though there is either a cached path to ClassLoader.php somewhere or there are two copies of the CiviCRM code under your modules directories. Various scenarios and solutions are discussed in this forum post: svn installation says "Cannot redeclare class CRM_Core_ClassLoader" Please post back here rather than on the forum, though.

If you're sure that there aren't multiple copies of CiviCRM under /home/mydomain/www/backup/ then the most likely fix is to clear the Drupal variable civicrm_class_loader, e.g. using drush:

drush vset civicrm_class_loader ''

There's a good chance the fatal error will prevent the use of drush. In that case, you can delete the row from Drupal's variable table where name = 'civicrm_class_loader'. It's possible the variables are cached in addition -- you may need to clear Drupal's cache tables manually. (A targeted approach -- in Drupal 6, anyway -- is to delete the row from Drupal's cache table where cid = 'variables'.)

Answer 2

I tried an intermediary update with the 4.6.36 with PHP 5 and, while I still have some update errors (I will open separate tickets if I cannot find the solution by myself), I do no longer have this one.