Title: Memcached activation error Last modified: November 11, 2022 --- # Memcached activation error * [etr316](https://wordpress.org/support/users/etr316/) * (@etr316) * [3 years, 7 months ago](https://wordpress.org/support/topic/memcached-activation-error/) * I down loaded the plugin memcached.4.0.0.zip, after a successful install it won’t activate, I receive an error. * Does anyone know what causes the following error? Fatal error: Cannot redeclare wp_cache_add() (previously declared in /home/hnshwagpa6rs/public_html/nsfwbuttons. com/wp-includes/cache.php:41) in /home/hnshwagpa6rs/public_html/nsfwbuttons.com/ wp-content/plugins/memcached/object-cache.php on line 19 * I am using the latest word press. 6.1 Viewing 11 replies - 1 through 11 (of 11 total) * Plugin Contributor [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * (@aidvu) * [3 years, 7 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16188957) * Hey! Did you take a look at [https://wordpress.org/plugins/memcached/#installation](https://wordpress.org/plugins/memcached/#installation)? * [tigmewp](https://wordpress.org/support/users/tigmewp/) * (@tigmewp) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16194873) * Hallo Memcached Object Cache Team * I experience the exact same error upon activation of your plugin: * > Plugin could not be activated because it triggered a fatal error. > Fatal error: > Cannot redeclare wp_cache_add() (previously declared in /usr/www/users/whalesdrdb/ > wp-includes/cache.php:41) in /usr/www/users/whalesdrdb/wp-content/plugins/memcached/ > object-cache.php on line 19 * I followed your installation guide, but the moment the **object-cache.php** file is copied into the **wp-content** folder as directed the whole site (back- and frontend) crashes. * The page caching plugin used is WP-Optimize 3.2.9 with the Vantage theme by SiteOrigin on WordPress 6.1 and the Memcached module has been enabled on my server. * Plugin Contributor [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * (@aidvu) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16195873) * > I followed your installation guide, but the moment the object-cache.php file > is copied into the wp-content folder as directed the whole site (back- and > frontend) crashes. * What errors do you see? What does “the whole site crashes” mean? * [tigmewp](https://wordpress.org/support/users/tigmewp/) * (@tigmewp) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16196032) * [@aidvu](https://wordpress.org/support/users/aidvu/), thank you for your reply. * > What does “the whole site crashes” mean? * The one where you get the white screen and the following error messages: * **BACKEND:** * > “The site is experiencing technical difficulties. Please check your site admin > email inbox for instructions.” * **FRONTEND:** * > “The site is experiencing technical difficulties.” * Plugin Contributor [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * (@aidvu) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16196046) * [@tigmewp](https://wordpress.org/support/users/tigmewp/) What’s in the PHP and web server logs? It’s fairly hard to figure anything without the logs. * In general, this plugin shouldn’t be installed. Just the object cache copied over the one in `wp-content/`. * [tigmewp](https://wordpress.org/support/users/tigmewp/) * (@tigmewp) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16196261) * There isn’t a file called object-cache.php in the wp-content folder and when I copy the **object-cache.php** file from your plugin folder into the **wp-content folder**, then the following error is displayed: * > `Fatal error: Uncaught Error: Class "Memcache" not found in /usr/www/users/ > website/wp-content/object-cache.php:849 Stack trace: #0 /usr/www/users/website/ > wp-content/object-cache.php(82): WP_Object_Cache->__construct() #1 /usr/www/ > users/website/wp-includes/load.php(730): wp_cache_init() #2 /usr/www/users/ > website/wp-settings.php(131): wp_start_object_cache() #3 /usr/www/users/website/ > wp-config.php(35): require_once('/usr/www/users/...') #4 /usr/www/users/website/ > wp-load.php(50): require_once('/usr/www/users/...') #5 /usr/www/users/website/ > wp-blog-header.php(13): require_once('/usr/www/users/...') #6 /usr/www/users/ > website/index.php(17): require('/usr/www/users/...') #7 {main} thrown in /usr/ > www/users/website/wp-content/object-cache.php on line 849` * Below is the full PHP error log on the server: * > `[14-Nov-2022 12:28:11 UTC] PHP Fatal error: Cannot redeclare wp_cache_add()( > previously declared in /usr/www/users/site/wp-includes/cache.php:41) in /usr/ > www/users/site/wp-content/plugins/memcached/object-cache.php on line 19 > [14- > Nov-2022 12:28:14 UTC] PHP Fatal error: Cannot redeclare wp_cache_add() (previously > declared in /usr/www/users/site/wp-includes/cache.php:41) in /usr/www/users/ > site/wp-content/plugins/memcached/object-cache.php on line 19 [14-Nov-2022 > 12:28:14 UTC] PHP Fatal error: Cannot redeclare wp_cache_add() (previously > declared in /usr/www/users/site/wp-includes/cache.php:41) in /usr/www/users/ > site/wp-content/plugins/memcached/object-cache.php on line 19 [14-Nov-2022 > 12:28:25 UTC] PHP Warning: Undefined variable $a_regionUrl in /usr/www/users/ > site/wp-content/themes/whalesandmore/includes/pods-custom-tourism-04-advertiser- > widget-template.php on line 161 [14-Nov-2022 12:28:25 UTC] PHP Warning: foreach() > argument must be of type array|object, null given in /usr/www/users/site/wp- > content/themes/whalesandmore/includes/pods-custom-tourism-04-advertiser-widget- > template.php on line 161 [14-Nov-2022 12:29:03 UTC] PHP Fatal error: Uncaught > Error: Class “Memcache” not found in /usr/www/users/site/wp-content/object- > cache.php:849 Stack trace: #0 /usr/www/users/site/wp-content/object-cache.php( > 82): WP_Object_Cache->__construct() #1 /usr/www/users/site/wp-includes/load. > php(730): wp_cache_init() #2 /usr/www/users/site/wp-settings.php(131): wp_start_object_cache()# > 3 /usr/www/users/site/wp-config.php(35): require_once(‘/usr/www/users/…’) # > 4 /usr/www/users/site/wp-load.php(50): require_once(‘/usr/www/users/…’) #5 / > usr/www/users/site/wp-blog-header.php(13): require_once(‘/usr/www/users/…’)# > 6 /usr/www/users/site/index.php(17): require(‘/usr/www/users/…’) #7 {main} > thrown in /usr/www/users/site/wp-content/object-cache.php on line 849 [14-Nov- > 2022 12:29:14 UTC] PHP Fatal error: Uncaught Error: Class “Memcache” not found > in /usr/www/users/site/wp-content/object-cache.php:849 Stack trace: #0 /usr/ > www/users/site/wp-content/object-cache.php(82): WP_Object_Cache->__construct()# > 1 /usr/www/users/site/wp-includes/load.php(730): wp_cache_init() #2 /usr/www/ > users/site/wp-settings.php(131): wp_start_object_cache() #3 /usr/www/users/ > site/wp-config.php(35): require_once(‘/usr/www/users/…’) #4 /usr/www/users/ > site/wp-load.php(50): require_once(‘/usr/www/users/…’) #5 /usr/www/users/site/ > wp-admin/admin-ajax.php(22): require_once(‘/usr/www/users/…’) #6 {main} thrown > in /usr/www/users/site/wp-content/object-cache.php on line 849` * I hope this helps? * Plugin Contributor [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * (@aidvu) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16196954) * > Fatal error: Uncaught Error: Class “Memcache” not found * Ok, this makes more sense. There are 2 PHP extensions for the `memcached` backend. * – [https://pecl.php.net/package/memcache](https://pecl.php.net/package/memcache)( supported) – [https://pecl.php.net/package/memcached](https://pecl.php.net/package/memcached)( not supported) * That is what the message is about. * [tigmewp](https://wordpress.org/support/users/tigmewp/) * (@tigmewp) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16198849) * Hallo [@aidvu](https://wordpress.org/support/users/aidvu/) * Thank you for your time and efforts, but I am now abandoning this project. It requires more knowledge than I currently possess. * After following your installation instructions as well as the steps in [@ufukart](https://wordpress.org/support/users/ufukart/)’ s 5 star review it still is not working. * Kind regards, Mariska * [Vincèn](https://wordpress.org/support/users/vincen/) * (@vincen) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16211492) * Same issue here, gave up on this plugin as installation explanations are sorry to say very confusing and not clear at all * [paul](https://wordpress.org/support/users/paul/) * (@paul) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16215585) * `Fatal error: Cannot redeclare wp_cache_add() (previously declared in /usr/local/ www/wordpress/wp-content/object-cache.php:60) in /usr/local/www/wordpress/wp- content/plugins/memcached/object-cache.php on line 19` * Same error here. Can’t say I like the Site Health screen telling me I need an object cache when none of the ones I have tried are detected or install cleanly. Can that test be disabled? * [tigmewp](https://wordpress.org/support/users/tigmewp/) * (@tigmewp) * [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16218016) * [@paul](https://wordpress.org/support/users/paul/) * If you have Memcached enabled on your hosting server, then you can try Powered Cache ([https://wordpress.org/plugins/powered-cache/](https://wordpress.org/plugins/powered-cache/)). The free version of this caching plugin automatically detects and connects to your server’s Memcached module. * If you cannot enable the Memcached module on your hosting server, then you can try Docket Cache ([https://wordpress.org/plugins/docket-cache/](https://wordpress.org/plugins/docket-cache/)). The plugin stores persistent Object Cache as PHP code. * Hope this helps. - This reply was modified 3 years, 6 months ago by [tigmewp](https://wordpress.org/support/users/tigmewp/). Viewing 11 replies - 1 through 11 (of 11 total) The topic ‘Memcached activation error’ is closed to new replies. * ![](https://s.w.org/plugins/geopattern-icon/memcached.svg) * [Memcached Object Cache](https://wordpress.org/plugins/memcached/) * [Frequently Asked Questions](https://wordpress.org/plugins/memcached/#faq) * [Support Threads](https://wordpress.org/support/plugin/memcached/) * [Active Topics](https://wordpress.org/support/plugin/memcached/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/memcached/unresolved/) * [Reviews](https://wordpress.org/support/plugin/memcached/reviews/) ## Tags * [fatal error](https://wordpress.org/support/topic-tag/fatal-error/) * 11 replies * 5 participants * Last reply from: [tigmewp](https://wordpress.org/support/users/tigmewp/) * Last activity: [3 years, 6 months ago](https://wordpress.org/support/topic/memcached-activation-error/#post-16218016) * Status: not resolved