Quick WordPress Multisite (MU) Installation and Setup for Different Domains and Sites

WordPress Multisite (or Network) is 1 wordpress installation that enables hosting of multiple different websites and domain names.

WordPress Multisite uses the same wordpress base (including the themes and plugins), wordpress database, and wp-config.php configuration file – for all sites in the network.

To install and use WP MU (Multisite), you would:

1. Install WordPress on a base website and domain. This installation will provide for all your MU sites.
2. Activate (turn on) Multisite / Network:
   1. Edit wp-config.php
      define( 'WP_ALLOW_MULTISITE', true );
   2. Go to Tools > Network Setup, select to use: sub-domains, and provide the asked “network” details (primary: domain, title, mail address). Install.
   3. Make sure the displayed wp-config.php and .htaccess changes are made (and if not made automatically, make edits manually).
3. Install the “WordPress MU Domain Mapping” plugin to be able to use separate domain names for different sites (otherwise you’ll only be able to use sub-domains for sites, such as: site1.example.com, site2.example.com, site3.example.com).
4. In the website’s settings (or directly in the HTTP and SSL VirtualHost files), add your list of sub-domains and full-domains into theServerAlias field. Make sure redirects are turned off.
5. If hosting (i.e., not local dev), you’ll need to make sure that you have proper DNS set up for:
   • Each site’s domain name with a “CNAME” record resolving to the base (primary) domain name.
   • Wildcard (*) on the base (primary) domain’s host (sub-domains) with a “A” record resolving to the server’s IP address.
   • And of course the base domain name resolved to the server’s IP address.
6. Make sure to clear your Browser’s cookies and cache.

http://codex.wordpress.org/Create_A_Network