WordPress at a glance
function is not described

site_admin_notice() WP 3.0.0

Displays an admin notice to upgrade all sites after a core upgrade.

  • Global. Int. $wp_db_version The version number of the database.
  • Global. String. $pagenow

No Hooks.

Return

false. False if the current user is not a super admin.

Usage

site_admin_notice();

Code of site admin notice: wp-admin/includes/ms.php WP 5.2.2

<?php
function site_admin_notice() {
	global $wp_db_version, $pagenow;

	if ( ! current_user_can( 'upgrade_network' ) ) {
		return false;
	}

	if ( 'upgrade.php' == $pagenow ) {
		return;
	}

	if ( get_site_option( 'wpmu_upgrade_site' ) != $wp_db_version ) {
		echo "<div class='update-nag'>" . sprintf( __( 'Thank you for Updating! Please visit the <a href="%s">Upgrade Network</a> page to update all your sites.' ), esc_url( network_admin_url( 'upgrade.php' ) ) ) . '</div>';
	}
}