Cannot map to SiteID 1

Mapping a domain to the main site is not supported because it interferes with site lookup in some cases.

jsghagan, What are you wanting to do?

If you have created another site on your multi-site, and you want to map a domain name to it, you put the Site ID of the “another” site into the domain mapping screen, not the ID of the main site.

Is domain mapping working for any sites? You may not have the plugin files in the correct places…

This may help, though forgive me for just guessing:
https://lcblog.lernerconsult.com/2012-wordpress-3-multi-site-domain-mapping/
(updated enough so still works with WordPress 4.3)

@lernerconsulting We have a number of sites on the multisite instance and this tool works well for each of those. We want to change the name of the primary domain however, and the easiest way to do that is by a mapping. Otherwise, we’ll need to go through the db of each instance (there are almost 40) and change linkages. Obviously more risky and time consuming. Know what I mean?

@RonRennick – Any workaround that you would recommend? As you can see from my post above, it would be a reasonable big and risky job to change the primary domain name otherwise.

Thanks in advance.

We want to change the name of the primary domain however, and the easiest way to do that is by a mapping. Otherwise, we’ll need to go through the db of each instance (there are almost 40) and change linkages.

Assuming the plugin allowed it, mapping a domain to the main site would not change the URLs of or in the other 30+ sites.

@jsghagan – I am wondering still what you need to do this for. Do you need to retire olddomain.com and replace it with newdomain.com? You can change the domain that WordPress runs on. (You can’t map the domain for Site 1; you can completely replace the domain.) Changing that would be related to the process for moving WordPress single-site to a different domain name, except needs to check for olddomain.com in the additional tables for multi-site. Moving multi-site from development server to production server would require the identical process, if this is what you want.

I’ve never documented the steps for this. Somewhere I have notes which search/replace plugin I used. It would have to know about WordPress “serialized data” and multi-site tables.

Step 1, obviously, is Backup Your Data!
Step 2, backup again, to a different file name.
Step 3, I’ve heard prayer is always good.
Step 4, would you let us know what works, if this is even what you’re looking for?