function _wpseo_activate() {
  require_once WPSEO_PATH . 'inc/wpseo-functions.php';
  require_once WPSEO_PATH . 'inc/class-wpseo-installation.php';

  wpseo_load_textdomain(); // Make sure we have our translations available for the defaults.

  new WPSEO_Installation();

  WPSEO_Options::get_instance();
  if ( ! is_multisite() ) {
    WPSEO_Options::initialize();
  }
  else {
    WPSEO_Options::maybe_set_multisite_defaults( true );
  }
  WPSEO_Options::ensure_options_exist();

  if ( is_multisite() && ms_is_switched() ) {
    delete_option( 'rewrite_rules' );
  }
  else {
    $wpseo_rewrite = new WPSEO_Rewrite();
    $wpseo_rewrite->schedule_flush();
  }

  // Reset tracking to be disabled by default.
  if ( ! WPSEO_Utils::is_yoast_seo_premium() ) {
    WPSEO_Options::set( 'tracking', false );
  }

  WPSEO_Options::set( 'indexing_reason', 'first_install' );

  do_action( 'wpseo_register_roles' );
  WPSEO_Role_Manager_Factory::get()->add();

  do_action( 'wpseo_register_capabilities' );
  WPSEO_Capability_Manager_Factory::get()->add();

  // Clear cache so the changes are obvious.
  WPSEO_Utils::clear_cache();

  // Schedule cronjob when it doesn't exists on activation.
  $wpseo_ryte = new WPSEO_Ryte();
  $wpseo_ryte->activate_hooks();

  do_action( 'wpseo_activate' );
}