So far I have seen four different DNS mapping instructions and I don't know which is correct since none of them work for me. It's hard to troubleshoot when I don't know if I have this part correct.

Under "Manage Sites" clicking "Save" produces this message:
"...please review that domains (domain.com/dir,http://www.domain.com/dir) are mapped to the directory (/var/www/base/joomroot)."

Under "Manage Sites" the mouseover tooltip for the site name produces this message:
"DNS MAPPING: /var/www/base/joomroot/multisites/dir"

In the Documentation, 3.2.4 How to configure Apache it says:
"DocumentRoot /var/www/html/php/MultiSites"

And finally, somewhere in my reading I saw this:
"/var/www/base/joomroot/dir" which I ruled out since I am not using symlinks.

Can someone tell me which is the correct DNS mapping scheme?

Thank you!

If you are configuring the apache files manually, you can reverse the problem.

See the tutorial video 0.b that is a technical document that teach a litte the DNS and how a HTTP Server is working.

Start to decide where you want to deploy your subdomain or domain and in which document root you want to assign your domain or subdomain.
This document root must be identical to the deployed directory.

In the documentation and in the screen, it is mentioned 2 paths because the concept of JMS Multisites consist in sharing the same directory than the master website.
So you can use the "master" directory or the deployed directory.
It is recommended to use the deployed directory that give more flexibility when you want to have specific images or specific templates directory. In this case, the symbolic links can be replaced by a physical directory as show in the tutorial video CP-05 and also explained in the tutorial video 0.b slide 30-35

Perhaps I should say my objective to help understand.

I have one company and three divisions. Each division needs their own website. However, I need all three to share users and one or two extensions. Otherwise, they each have their own templates, images, modules, etc.

- Master
- Slave 1
- Slave 2

Only thing they share is users.

So you just have to create a JMS Template that select the master website and define the replication rule.
In the tutorial video 0.d at moreless minute 0:20, it is shown how to replicate the master.
In the tutorial video 16, it is show how to share the users between slave1 and slave 1A.
www.jms2win.com/en/tutorial#jms12x-16

You just have to select in the "template site" field the <master DB> instead of the slave 1.

So in JMS Template,
- Provide a template name
- Provide a domain name (ie {site_url}/multisites/{site_id}
- Select the template <master DB> <---------- This is the parameter to modify in the video 16
- Define a new table prefix (ie. {site_id}_ )
- Deploy directory = {site_dir}
Go in the sharing panel and select "Joomla Users"
Perhaps you have to review the directory structure.

Once the JMS Template is create, you can use it in "manage site"