Call to undefined function mysqli_init()

The error "Call to undefined function mysqli_init()" indicates that the MySQLi extension is not properly installed or enabled in your PHP configuration. Here are steps to resolve this issue:

1. Install MySQLi Extension: Ensure that the MySQLi extension is installed on your Ubuntu server. You can install it using the package manager. For PHP 8.1, you might use:

   bashCopy code
   sudo apt-get install php8.1-mysqli
   

   Make sure to replace "8.1" with your PHP version.

2. Enable MySQLi Extension: Ensure that the MySQLi extension is enabled in your PHP configuration. Edit the php.ini file and uncomment or add the following line:

   iniCopy code
   extension=mysqli
   

   You can locate the php.ini file by running:

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   php -i | grep "php.ini"
   

   After making changes, restart your Apache server:

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   sudo service apache2 restart
   

3. Verify MySQLi Extension: Create a PHP file (e.g., phpinfo.php) with the following content:

   phpCopy code
   <?php
   phpinfo();
   

   Open this file in your web browser and look for the MySQLi section to confirm that the extension is loaded.

4. Check for Multiple PHP Versions: Sometimes, multiple PHP versions may be installed on a server. Ensure that you are configuring the correct PHP version by checking the Apache configuration or using the correct CLI version.

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   sudo a2dismod php7.4  # Disable previous PHP version (if applicable)
   sudo a2enmod php8.1   # Enable PHP 8.1 (replace with your PHP version)
   sudo service apache2 restart
   

5. Check Apache Error Logs: Review the Apache error logs for any specific error messages related to the PHP configuration or MySQLi extension. The logs are usually located in /var/log/apache2/error.log.

If the issue persists after following these steps, double-check your PHP and Apache configurations and ensure that the MySQLi extension is correctly installed and enabled for the PHP version you are using.