maintenance_nag

function maintenance_nag() {
	// Include an unmodified $wp_version.
	require ABSPATH . WPINC . '/version.php';
	global $upgrading;
	$nag = isset( $upgrading );
	if ( ! $nag ) {
		$failed = get_site_option( 'auto_core_update_failed' );
		/*
		 * If an update failed critically, we may have copied over version.php but not other files.
		 * In that case, if the installation claims we're running the version we attempted, nag.
		 * This is serious enough to err on the side of nagging.
		 *
		 * If we simply failed to update before we tried to copy any files, then assume things are
		 * OK if they are now running the latest.
		 *
		 * This flag is cleared whenever a successful update occurs using Core_Upgrader.
		 */
		$comparison = ! empty( $failed['critical'] ) ? '>=' : '>';
		if ( isset( $failed['attempted'] ) && version_compare( $failed['attempted'], $wp_version, $comparison ) ) {
			$nag = true;
		}
	}

	if ( ! $nag ) {
		return false;
	}

	if ( current_user_can( 'update_core' ) ) {
		$msg = sprintf(
			/* translators: %s: URL to WordPress Updates screen. */
			__( 'An automated WordPress update has failed to complete - <a href="%s">please attempt the update again now</a>.' ),
			'update-core.php'
		);
	} else {
		$msg = __( 'An automated WordPress update has failed to complete! Please notify the site administrator.' );
	}

	echo "<div class='update-nag notice notice-warning inline'>$msg</div>";
}