A multisite can have either subdirectory or a subdomain structure.
Subdirectories:
Main site: example.com
example.com/subsite
example.com/anothersubsite
Subdomains:
Main site: example.com
subdomain.example.com
anothersubdomain.example.com
Configuring Domains in Multisite
Whether you multisite installation uses subdirectories or subdomains, each of the subsites can be mapped with its own domain. You can define this domain in the subsite settings under Edit > Info > Site Address (URL).
You also need to remember to change the in the Siteurl and Home fields in the Settings tab.
If the subsites already have content and links, the address structure must be updated in the sites' database with search-replace command. You can use Seravo Plugin's features to run this command.
Subdomain Installations
If you are using a subdomain-based installation and mapping custom domains to sub-sites, you must add the following line to your wp-config.php file to ensure logins work correctly without errors:
define( 'COOKIE_DOMAIN', $_SERVER['HTTP_HOST'] ?? '' );
Mercator and Subdomain Installation
Note!
We do not recommend using Mercator, even if the plugin has been previously installed on network installations with a subdomain structure. Our customer service can assist you with the removal of Mercator. You can reach us by sending a message to [email protected].
If your multisite uses a subdomain structure and has Mercator installed, the plugin can be used to map sub-sites to separate domains. Once Mercator is installed, a new field called Aliases will appear in the All Sites menu.
In the picture below, in the leftmost column, URL must always show the main domain's (example.com) actual used subdomain (subsite.example.com), in order to, for the example, instance switcher cookies to function properly on subsites. The subdomain is defined from under the subdomain Edit > Info > Site Address (URL). In a subdomain multisite, accessing the subsite admin panel requires re-login.
Site Address (URL) setting should always show the subdomain.
The separate domain can be defined as an Alias, and must of course be marked as active. Alias works as alternative address to the subsite in addition with the subdomain.
Once a domain has been defined as an Alias for a subsite, it must also be configured as the subsite's Siteurl and Home (see the Settings-tab).
ATTN! It is recommended to have only one alias. If the intention is to direct several additional domains to a multisite subsite, it is recommended to use a nginx redirect instead.
Troubleshooting Common Issues
If you encounter issues after mapping domains, here are the solutions to the most common errors.
Error: "Cookies are blocked or not supported"
This is usually caused by a configuration mismatch. Ensure you have added the COOKIE_DOMAIN definition to your wp-config.php file as instructed above:
define( 'COOKIE_DOMAIN', $_SERVER['HTTP_HOST'] ?? '' );
Error: ERR_TOO_MANY_REDIRECTS
This typically occurs if there is a conflict between internal site settings and server-side redirections. Double-check that both the Site URL and Home URL in the network admin settings exactly match your primary domain.
Issue: Redirecting to wp-signup.php?new=...
If the domain redirects to the WordPress signup page, the network does not recognize it.
For primary sub-site domains: Verify the domain is correctly entered in the Site Address (URL) field.
For additional domains: If the domain is an alias, you must configure a redirect at the Nginx level. Without this, WordPress treats the traffic as a new site registration attempt.
I Wish to Make My WordPress a Multisite!
If you want to turn your site into a WordPress Network so that you can create a multisite, please contact Seravo's customer support.
Non-multisite WordPress
Are you looking for the instructions for how to configure a domain in a normal WordPress installation? See our instructions.