Wordpress Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /wp-includes/wp-db.php:1570

Question

I am in big trouble. I installed a nulled version of woocommerce cart based shipping plugin and i found it not relevant according to my requiremnet and deleted that plugin from plugins area. After deleting that plugin my site went down. Its continuously showing me Fatal error:

Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /home/dev/public_html/new/wp-includes/wp-db.php:1570
Stack trace:
#0 /home/dev/public_html/new/wp-includes/wp-db.php(658): wpdb->db_connect()
#1 /home/dev/public_html/new/wp-includes/load.php(404): wpdb->__construct('dev_test', 'password', 'dev_test_ne...', 'localhost')
#2 /home/dev/public_html/new/wp-settings.php(107): require_wp_db()
#3 /home/dev/public_html/new/wp-config.php(82): require_once('/home/dev/p...')
#4 /home/dev/public_html/new/wp-load.php(37): require_once('/home/dev/p...')
#5 /home/dev/public_html/new/wp-blog-header.php(13): require_once('/home/dev/p...')
#6 /home/dev/public_html/new/index.php(17): require('/home/dev/p...')
#7 {main} thrown in /home/dev/public_html/new/wp-includes/wp-db.php on line 1570

I tried replacing all core files excluding wp-config.php and wp-content folder. Still I am getting the same error.

Also, i tried renameing plugins folder but the error is there.

Can you guys suggest me how i can get my site back.

Answer 1

I encountered this problem upgrading from PHP 5 to PHP 7 (on Windows). The problem was mysqli PHP extension was not enabled. If mysqli is not available Wordpress 5+ detects this and will instead attempt to connect to the database with deprecated mysql_connect() calls. This leads to a very misleading error message about mysql_connect() function not being available (since we don't want this function).

In php.ini make sure extension_dir is set (use full directory name) and mysqli extension is enabled

extension_dir = "C:\php-7.3.10\ext"
...
extension=mysqli

To double check what extensions are active you can run the following code

<pre>
<?php print_r(get_loaded_extensions()); ?>
</pre>