So I thought I would share my joy with a quick guide, because it was great to see it actually work!

What do you need…



Requirements:

• WordPress Mu – if you dont know how to install it – check out Sarah Gooding’s great tutorial here
• Domain Mapping Plugin
• Access to the WordPress Mu install files on your hosting via FTP or File Manager (whatever,a s long as you can edit the code!)
• A hosting provider that is willing to make apache changes – critical to success – I had the privilege of working with RSAWEB on these projects but also confirmed with Serve Hosting that they can do it as well (although I havent tried it with them yet).

Just tell me how already!

• Install WordPress Mu
• Make sure Subdomains have been chosen as the blog option during install – needs wildcard DNS for this
• Download and extract the WordPress Domain Mapping Plugin
• Upload the sunrise.php file into your wp-content folder
• Upload the domain_mapping.php file into your wp-content/mu-plugins folder
• Now…edit your wp-config.php file in the document root of your site
• Find the line that says define( 'SUNRISE', 'on' ); and uncomment it – add it if it isnt in the file
• Dont forget to save your edited wp-config.php file
• Activate the Domain Mapping Plugin on the main WordPress Mu site backend
• Go to the Domain Mapping Plugin section in the main site backend
• Enter the IP for the main site in the Server IP Address field as example below
• 
• If you dont know how to get the IP – you can ping the domain by going into the command prompt (if you’re working in windows) and type “ping mydomain.com”
• Now go to the sub blog backend that you want to domain map
• Activate the Domain Mapping Plugin
• Go to the Domain Mapping Plugin section in the sub blog backend
• Enter the domain that you want to map to the sub blog in the Add new domain field until it appears under the Active domains on this blog
• 
• Now – you need to notify your hosting provider that they need to get Apache to catch the domain and point it at the same document root of the main site domain – ie the document root of your WordPress Mu install
• Usually this involves them doing one of 2 things – editing the vhost and/or editing the A records/CNAME records – they ‘should’ know what to do though
• Once the above has been done, all should be working great and you can view your sub blog at the new domain just like a regular WordPress site but on one code base!

Warning : Things can go pear shaped very quickly if you are not careful – the first time I did this I almost broke the entire install – not good if you are doing client work on a live site – don’t go editing database records; you can get it done that way but I don’t recommend it because your upgrading functionality becomes obsolete.