I have just installed XML Sitemap on a EC2 drupal 8 instance. I am seeing the following error message in the admin report status page:
XML sitemap cache directory Not found or not writable The directory public://xmlsitemap was not found or is not writable by the server. See http://drupal.org/node/34025 for more information. 
The provided link is broken. I have done some reading and created a /xmlsitemap directory in /var/www/html (which is the root of my drupal installation). I chmod it to give rwx access to everyone (a+).
But, the issue remains. I cannot generate the cache files.
How can I solve this issue?