Can a relative sitemap url be used in a robots.txt?

In robots.txt can I write the following relative URL for the sitemap file?

sitemap: /sitemap.ashx

Or do I have to use the complete (absolute) URL for the sitemap file, like:

sitemap: http://subdomain.domain.com/sitemap.ashx

Why I wonder:

• I own a new blog service, www.domain.com, that allow users to blog on accountname.domain.com.
• I use wildcards, so all subdomains (accounts) point to: "blog.domain.com".

In blog.domain.com I put the robots.txt to let search engines find the sitemap. But, due to the wildcards, all user account share the same robots.txt file.Thats why I can't use the second alternative. And for now I can't use url rewrite for txt files. (I guess that later versions of IIS can handle this?)

Solution 1:

According to the official documentation on sitemaps.org it needs to be a full URL:

You can specify the location of the Sitemap using a robots.txt file. To do this, simply add the following line including the full URL to the sitemap:

Sitemap: http://www.example.com/sitemap.xml

Solution 2:

Google crawlers are not smart enough, they can't crawl relative URLs, that's why it's always recommended to use absolute URL's for better crawlability and indexability.

Therefore, you can not use this variation

> sitemap: /sitemap.xml

Recommended syntax is

Sitemap: https://www.yourdomain.com/sitemap.xml

Note:

• Don't forgot to capitalise the first letter in "sitemap"
• Don't forgot to put space after "Sitemap:"