update.php

<?php

/**
 * @file
 * Administrative page for handling updates from one Drupal version to another.
 *
 * Point your browser to "http://www.example.com/core/update.php" and follow the
 * instructions.
 *
 * If you are not logged in using either the site maintenance account or an
 * account with the "Administer software updates" permission, you will need to
 * modify the access check statement inside your settings.php file. After
 * finishing the upgrade, be sure to open settings.php again, and change it
 * back to its original state!
 */

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

// Change the directory to the Drupal root.
chdir('..');

/**
 * Root directory of Drupal installation.
 */
define('DRUPAL_ROOT', getcwd());

// Exit early if running an incompatible PHP version to avoid fatal errors.
// The minimum version is specified explicitly, as DRUPAL_MINIMUM_PHP is not
// yet available. It is defined in bootstrap.inc, but it is not possible to
// load that file yet as it would cause a fatal error on older versions of PHP.
if (version_compare(PHP_VERSION, '5.3.3') < 0) {
  print 'Your PHP installation is too old. Drupal requires at least PHP 5.3.3. See the <a href="http://drupal.org/requirements">system requirements</a> page for more information.';
  exit;
}

/**
 * Global flag indicating that update.php is being run.
 *
 * When this flag is set, various operations do not take place, such as invoking
 * hook_init() and hook_exit(), css/js preprocessing, and translation.
 *
 * This constant is defined using define() instead of const so that PHP
 * versions older than 5.3 can display the proper PHP requirements instead of
 * causing a fatal error.
 */
define('MAINTENANCE_MODE', 'update');

function update_selection_page() {
  drupal_set_title('Drupal database update');
  $elements = drupal_get_form('update_script_selection_form');
  $output = drupal_render($elements);

  update_task_list('select');

  return $output;
}

function update_script_selection_form($form, &$form_state) {
  $count = 0;
  $incompatible_count = 0;
  $form['start'] = array(
    '#tree' => TRUE,
    '#type' => 'fieldset',
    '#collapsed' => TRUE,
    '#collapsible' => TRUE,
  );

  // Ensure system.module's updates appear first.
  $form['start']['system'] = array();