Example for an automatically generated sitemap with jekyll.

sitemap.xml

---
# Remember to set production_url in your _config.yml file!
layout: nil
title : Sitemap
---
<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  {% for page in site.pages %}
    <url>
      <loc>{{site.production_url}}{{ page.url }}</loc>
    </url>
  {% endfor %}
  {% for post in site.posts %}
    <url>
      <loc>{{site.production_url}}{{ post.url }}/</loc>
    </url>
  {% endfor %}
</urlset>

It works correctly they but I also added the url to sitemap.xml, I've solved this in the following way.Thanks

{% for page in site.pages %}

    {% if page.url != '/sitemap.xml' %}
      <url>
        <loc>{{site.production_url}}{{ page.url }}</loc>
      </url>
    {% endif %}
{% endfor %}