title: how to enable xpack.security.enabled?
body: <p>I have installed Elasticsearch 7, on Ubuntu. I believe X-Pack is installed by default, but I need to enable it.</p>
  
  <p>In which file should I set this setting?</p>
  
  <p>My cluster settings are in: <code>/etc/elasticsearch/elasticsearch.yml</code> and <code>/etc/default/elasticsearch</code>, but I cannot see <code>xpack.security.enabled</code> in either of files...</p>