Access denied on hello world custom module Drupal 8 installed in Debian VPS server.
Some installed themes do not work, some do.
When tried to creat a simple 'Hello World' module,as described in a beginners book for drupal, installing of the module was fine; but when trying to open :              www.my***site.com/hello/world i got "Access denied" message.
After installing drupal i treated permissions using this and its comments through the command : chown -R www-data:www-data drupal/ 

The hello World module creation:
in drupal/module created custom/ and contrib/ folder as well as custom/hello_world/. Within hello_world/ created three files hello_world.info.yml, hello_worl.module, hello_world.routing.ymland hello_world/src/Controller/HelloWorldController.php

hello_world.info.yml

name: Hello World
type: module
description: 'A basic Drupal 8 Hello World Module.'
package: Custom Modules
version: 1.0
core: 8.x


hello_world.routing.yml

hello_world_settings:
  path: '/hello/world'
defaults:
  _controller: '\Drupal\hello_world\Controller\HelloWorldController::
myCallbackMethod'
  _title: 'Hello World'
requirements:
  _permission: 'access content'


hello_world/src/Controller/HelloWorldController.php

&lt;?php
/**
* @file
* Contains \Drupal\hello_world\HelloWorldController.
*/
namespace Drupal\hello_world\Controller;
/**
 * Provides route responses for the hello world page example.
 */
class HelloWorldController {
  /**
  * Returns a simple hello world page.
  *
  * @return array
  * A very simple renderable array is returned.
  */
  public function myCallbackMethod() {
    $element = array(
      '#markup' =&gt; '&lt;p&gt;&lt;b&gt;Saying Hello World in Drupal 8 is cool!&lt;/b&gt;&lt;/p&gt;',
    );
    return $element;
  }
}


upon  opening www.my****website.com/admin/hello/world i got Access Denied. Looking further into My**website.com/admin/reports/dblog/event/***5 i got just that it is an Access Denied and Warning in the security field.
Can anyone please explain what is going on?
The issue is with the indentation of the hello_world.routing.yml file. Simply change the indentation of it to:

hello_world_settings:
  path: '/hello/world'
  defaults:
    _controller: '\Drupal\hello_world\Controller\HelloWorldController::myCallbackMethod'
    _title: 'Hello World'
  requirements:
    _permission: 'access content'


And the Access denied issue should be solved. The indentation of YAML file is  important, in Drupal 8. It should be as follow:


path, defaults, and requirements should be indented by 2 spaces
_controller, _title, and _permission should be indented by 4 spaces