Enable WordPress Multisite

WordPress Multisite lets you manage a network of sites from a single installation. The sites share the core and the catalogue of plugins and themes, but keep their own content and settings. Users belong to the network and can have different roles on several sites; they are not fully independent user bases. It is not the right option if each website needs full isolation, different versions or administrators able to install code.

Before enabling it

• Make a full backup of files and database and test restoring it.
• Update WordPress, plugins and themes, and temporarily deactivate plugins while the network is being created.
• Choose between sites in subdirectories, such as ejemplo.com/sitio, or in subdomains, such as sitio.ejemplo.com.
• For automatic subdomain sign-ups you will need wildcard DNS and every one of those hosts must load the WordPress directory. Manually added domains must also point to that installation through DNS and document root.
• Confirm that WordPress uses HTTPS and that WordPress Address and Site Address are correct before converting it.

Enable the network configuration

1. Edit wp-config.php and add this line before the comment telling you to stop editing:

define( 'WP_ALLOW_MULTISITE', true );

2. Go back to the dashboard and open Tools > Network Setup.
3. Choose subdomains or subdirectories, enter the network title and email and click Install.
4. WordPress will show two blocks generated specifically for your installation. Copy the first into wp-config.php and replace the WordPress rules inside .htaccess with the second. Do not copy rules from another tutorial: they change depending on the path, the type of network and when Multisite was enabled.
5. Log in again and open My Sites > Network Admin to create and configure the sites.

The official Create a network documentation details the restrictions and the steps for each mode. Keep the earlier backup until you have checked access, permalinks, uploads, email and certificates for every domain.

Domains, certificates and permissions

Wildcard DNS does not automatically create a wildcard certificate. Check that every name used resolves to the installation and has valid HTTPS. For different domains, also set up their root and the corresponding mapping in the network.

You will not always be free to choose subdomains or subdirectories: the age, paths and configuration of the installation play a part. Follow the restrictions the wizard shows rather than forcing constants copied from another network.

Review who has super admin permissions and which plugins can be activated per site or network-wide. A fault in a shared component can affect several websites; test updates and backups with that scope in mind.

Validate the network and recover

Create a test site and check the URL, access, media, emails and the permissions of a user without network privileges. Review the existing sites and make sure an account cannot see features it should not have.

Do not revert the conversion by just removing WP_ALLOW_MULTISITE: once the network is installed there will be other settings and SQL changes. To go back to the earlier point, use the consistent backup of files and database, taking into account any content created since then.