How to set custom master page as default master page with site definition in Moss and WSS 3.0?

Changing a default master page for our custom need is not at all good idea and creating a custom master page and use it as default master page is a headache.

Here is the way to create and use your custom master page with site definition.

Go to “C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\GLOBAL” where you can find default master page (default.master).

Copy that default.master and pest it with customdefault.master or your own custom name.
(Note: while copying default.master please take care that you must not have already modified It. Use a fresh copy)

Put your custom master page at same location as default.master.

Now go to “12\TEMPLATE\GLOBAL\XML” open “ONET.xml”

At the last you will find module tag which provision “default.master” same way add your entry for custom.master.

<Modules>
<Module Name="DefaultMasterPage" List="116" Url="_catalogs/masterpage" RootWebOnly="FALSE">
<File Url=" customdefault.master" Type="GhostableInLibrary" IgnoreIfAlreadyExists="TRUE" />
<File Url="default.master" Type="GhostableInLibrary" IgnoreIfAlreadyExists="TRUE" />
</Module>
</Modules>

This code will automatically put your custom masterpage into the masterpage gallery when a new site is created.

Now open your onet.xml file from 12/template/SiteTemplates
Change the default masterpage to the new one.
Find <Configuration> tag
Add MasterUrl attribute like MasterUrl=”_catalogs/masterpage/customdefault.master” and if you already have this tag change it with your custom master page.

So it will look like

<Configuration ID="0" Name="YOUR NAME" MasterUrl="_catalogs/masterpage/customdefault.master">

Now the new site created with this definition have this master page as default master page. Click here for more info.

What about already existing site?

For that you need to put master page manually and change master page url for each wab
Here is the code snippet (only for setting master page url of the web):
Note: use this snippet carefully. If you run this snippet and you do not have Master page in Master page gallery for that web you will get master or page not found error.

SPSite spsite = new SPSite("Your site name");
foreach (SPWeb Myweb in spsite.AllWebs)
{
string masterurl = Myweb.ServerRelativeUrl;
if (!masterurl.EndsWith(@"/"))
masterurl = masterurl + @"/";
Myweb.MasterUrl = masterurl + "_catalogs/masterpage/customdefault.master";
Myweb.Update();
}

This kind of snippet you will find in Inside WSS 3.0 book