core-bundle/src/Resources/contao/classes/Maintenance.php
public function run()
	{
		$objTemplate = new BackendTemplate('be_maintenance_mode');
		$objTemplate->action = ampersand(Environment::get('request'));
		$objTemplate->headline = $GLOBALS['TL_LANG']['tl_maintenance']['maintenanceMode'];
		$objTemplate->isActive = $this->isActive();

		try
		{
			$driver = System::getContainer()->get('lexik_maintenance.driver.factory')->getDriver();
			$isLocked = $driver->isExists();
		}
		catch (\Exception $e)
		{
			return '';
		}

		// Toggle the maintenance mode
		if (Input::post('FORM_SUBMIT') == 'tl_maintenance_mode')
		{
			if ($isLocked)
			{
				$driver->unlock();
			}
			else
			{
				$driver->lock();
			}

			$this->reload();
		}

		if ($isLocked)
		{
			$objTemplate->class= 'tl_error';
			$objTemplate->explain = $GLOBALS['TL_LANG']['MSC']['maintenanceEnabled'];
			$objTemplate->submit = $GLOBALS['TL_LANG']['MSC']['disable'];
		}
		else
		{
			$objTemplate->class= 'tl_info';
			$objTemplate->submit = $GLOBALS['TL_LANG']['MSC']['enable'];
		}

		return $objTemplate->parse();
	}
public function run()
	{
		$objTemplate = new BackendTemplate('be_maintenance_mode');
		$objTemplate->action = ampersand(Environment::get('request'));
		$objTemplate->headline = $GLOBALS['TL_LANG']['tl_maintenance']['maintenanceMode'];
		$objTemplate->isActive = $this->isActive();

		try
		{
			$driver = System::getContainer()->get('lexik_maintenance.driver.factory')->getDriver();
			$isLocked = $driver->isExists();
		}
		catch (\Exception $e)
		{
			return '';
		}

		// Toggle the maintenance mode
		if (Input::post('FORM_SUBMIT') == 'tl_maintenance_mode')
		{
			if ($isLocked)
			{
				$driver->unlock();
			}
			else
			{
				$driver->lock();
			}

			$this->reload();
		}

		if ($isLocked)
		{
			$objTemplate->class= 'tl_error';
			$objTemplate->explain = $GLOBALS['TL_LANG']['MSC']['maintenanceEnabled'];
			$objTemplate->submit = $GLOBALS['TL_LANG']['MSC']['disable'];
		}
		else
		{
			$objTemplate->class= 'tl_info';
			$objTemplate->submit = $GLOBALS['TL_LANG']['MSC']['enable'];
		}

		return $objTemplate->parse();
	}
Generate the module

@return string