Site shows error: Your PHP installation appears to be missing the MySQL extension which is required by WordPress

Symptoms

• Site shows the following error:

  Your PHP installation appears to be missing the MySQL extension which is required by WordPress

• Plesk is installed on Cloudlinux

• The mysql extension is enabled in Plesk > Subscriptions  > example.com > PHP Selector > PHP 5.6

• Checking from SSH shows that mysql extension is enabled in PHP selector:

  # selectorctl --list-extensions --version=5.6 | grep mysql
  + mysql
  + mysqli
  - mysqlnd
  - nd_mysql
  - nd_mysqli
  - nd_pdo_mysql
  + pdo_mysql

• Checking directly the CloudLinux PHP 5.6 shows that mysql extension is not loaded:

  # /opt/alt/php56/usr/bin/php-cgi -m | grep mysql
  (Empty Output)

• The mysql library exists on the server:

  # ls -la  /opt/alt/php56/usr/lib64/php/modules | grep mysql
  lrwxrwxrwx 1 root root          36 Jul  5 13:55 mysql.so -> /opt/alt/php56/etc/mysql5.5/mysql.so

• MySQL PHP extension is enabled:

  # egrep -Ri mysql /opt/alt/php56/etc/php* | egrep ^extension
  /opt/alt/php56/etc/php.d.all/mysql.iniextension=mysql.so

• The following article did not help: Unable to install WordPress using WP Toolkit: Call to undefined function json_encode()

Cause

Cloudlinux PHP misconfiguration: Not all the alt-php required packages are installed

Resolution

Contact Cloudlinux Support to get support with PHP shipped by CloudLinux

Additional information

Why does phpinfo page show wrong information in CloudLinux when PHP Selector is used?