Title: Fatal error: Cannot redeclare wp_cache_add() Last modified: December 16, 2022 --- # Fatal error: Cannot redeclare wp_cache_add() * Resolved [Razva](https://wordpress.org/support/users/razva/) * (@razva) * [3 years, 5 months ago](https://wordpress.org/support/topic/fatal-error-cannot-redeclare-wp_cache_add-3/) * Hey, * I’m getting this when trying to install your plugin: * ```wp-block-code Fatal error: Cannot redeclare wp_cache_add() (previously declared in /home/plantemania/public_html/wp-includes/cache.php:41) in /home/plantemania/public_html/wp-content/plugins/object-cache.php on line 19 ``` * Please note that I have manually uploaded `object-cache.php` to `wp-content` as recommended in the installation instructions. * I’ve also added `define( 'WP_CACHE_KEY_SALT', 'plantemania' );` in `wp-config. php`. * Yes, the PHP module is installed and the service is running: * ```wp-block-code plantemania@server:~$ php -m | grep memcache memcached plantemania@server:~$ systemctl status memcached ● memcached.service - memcached daemon Loaded: loaded (/lib/systemd/system/memcached.service; enabled; vendor preset: enabled) Active: active (running) since Fri 2022-12-16 08:58:34 EET; 32min ago Docs: man:memcached(1) Main PID: 1473014 (memcached) Tasks: 10 (limit: 4694) Memory: 29.6M CPU: 1.599s CGroup: /system.slice/memcached.service └─1473014 /usr/bin/memcached -m 64 -p 11211 -u memcache -l 127.0.0.1 -P /var/run/memcached/memcached.pid plantemania@server:~$ ``` * Any way to fix this? Thank you - This topic was modified 3 years, 5 months ago by [Razva](https://wordpress.org/support/users/razva/). Viewing 5 replies - 1 through 5 (of 5 total) * Plugin Contributor [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * (@aidvu) * [3 years, 5 months ago](https://wordpress.org/support/topic/fatal-error-cannot-redeclare-wp_cache_add-3/#post-16296083) * Hey, * ```wp-block-code plantemania@server:~$ php -m | grep memcachememcached ``` * So this isn’t the correct extension. It should return `memcache` not `memcacheD`. * As for the fatal: * ```wp-block-code Fatal error: Cannot redeclare wp_cache_add() (previously declared in /home/plantemania/public_html/wp-includes/cache.php:41) in /home/plantemania/public_html/wp-content/plugins/object-cache.php on line 19 ``` * Did you by chance also install the plugin? If yes, uninstall and just copy `object- cache.php` to `wp-content`. No idea what the `wp-content/plugins/object-cache. php` file is (notice the `/plugins`). * Thread Starter [Razva](https://wordpress.org/support/users/razva/) * (@razva) * [3 years, 5 months ago](https://wordpress.org/support/topic/fatal-error-cannot-redeclare-wp_cache_add-3/#post-16296885) * Hey, * I appreciate the fast reply. * As instructed I moved `object-cache.php` to from `wp-content/plugins` to `wp- content`. Here it is: * ```wp-block-code $ ls ~/public_html/wp-content/ index.php languages object-cache.php plugins smush-webp themes upgrade uploads ``` * Here’s the content’s of the `plugins` folder: * ```wp-block-code $ ls ~/public_html/wp-content/plugins/ contact-form-7 google-site-kit js_composer meta-box meta-box-tabs redux-framework sumodiscounts wordpress-seo envato-market index.php mailpoet meta-box-show-hide nt-agro-shortcodes revslider woocommerce wp-smushit ``` * The current result is `wp-admin` throwing `There has been a critical error on this website.` * I have uploaded a [simple PHP script](https://experienceleague.adobe.com/docs/commerce-operations/configuration-guide/storage/session-storage/memcache-ubuntu.html) to test if `memcache` is working and [it’s fully functional](https://plantemania.ro/memcachetest.php)( on the same page you can find a `phpinfo` that confirms that `memcache 3.2.0` is installed and fully functional). * Any hints on this? * Thank you! * **Later edit:** I can confirm that both W3 and LiteSpeedCache plugins can connect to the `memcache` server and enable the Object Cache function. - This reply was modified 3 years, 5 months ago by [Razva](https://wordpress.org/support/users/razva/). - This reply was modified 3 years, 5 months ago by [Razva](https://wordpress.org/support/users/razva/). * Plugin Contributor [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * (@aidvu) * [3 years, 5 months ago](https://wordpress.org/support/topic/fatal-error-cannot-redeclare-wp_cache_add-3/#post-16297628) * > The current result is `wp-admin` throwing `There has been a critical error > on this website.` * What does the PHP error log show for this now that you’ve moved the file? * > I have uploaded a [simple PHP script](https://experienceleague.adobe.com/docs/commerce-operations/configuration-guide/storage/session-storage/memcache-ubuntu.html) > to test if `memcache` is working and [it’s fully functional](https://plantemania.ro/memcachetest.php)( > on the same page you can find a `phpinfo` that confirms that `memcache 3.2.0` > is installed and fully functional). * This is what I’ve been trying to tell you. 🙂 * There are two PECL extensions for memcached backend: - memcache – [https://pecl.php.net/package/memcache](https://pecl.php.net/package/memcache)– the one this plugin uses - memcached – [https://pecl.php.net/package/memcached](https://pecl.php.net/package/memcached)– the one you have, but is not supported * Hope that helps. * Thread Starter [Razva](https://wordpress.org/support/users/razva/) * (@razva) * [3 years, 5 months ago](https://wordpress.org/support/topic/fatal-error-cannot-redeclare-wp_cache_add-3/#post-16298461) * Oh, ok, **sorry for my stupidity**! I’ve successfully installed `memcache`. * > For posterity, doing `apt install phpX-memcached` does not equal with `apt > install phpX-memcache`. * The `Critical error` is not being displayed after installing the correct PECL extension. * Thank you for your patience and support! * Plugin Contributor [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * (@aidvu) * [3 years, 5 months ago](https://wordpress.org/support/topic/fatal-error-cannot-redeclare-wp_cache_add-3/#post-16298573) * > Oh, ok, **sorry for my stupidity**! I’ve successfully installed `memcache`. * Don’t worry. 🙂 Glad it works now! * > Thank you for your patience and support! * <3 Viewing 5 replies - 1 through 5 (of 5 total) The topic ‘Fatal error: Cannot redeclare wp_cache_add()’ 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/) * 5 replies * 2 participants * Last reply from: [Andrija Vučinić](https://wordpress.org/support/users/aidvu/) * Last activity: [3 years, 5 months ago](https://wordpress.org/support/topic/fatal-error-cannot-redeclare-wp_cache_add-3/#post-16298573) * Status: resolved