Every time I’m working with a new install of MediaWiki I have to hunt down this same information. I don’t think I’ve even installed or customized that many MediaWiki instances. The time between setting up each new wiki has allowed me to forget what the answer is and searching for this fix is really hard since lots of people are talking about the wiki Main Page in other contexts.
What you need to search for is “mainpage” on the mediawiki.org site; “mainpage” is variable key name that’s used to retrieve the value which is used for your wiki main or index page. Once you start searching for that instead of “custom Main Page” or something similar you’ll end up at the Media Wiki Help FAQ, perhaps you should just go there first every time…
Here’s the answer »
Going to your MediaWiki:Mainpage as a user with sysop privileges lets you change the index page your wiki will show. Now hopefully I’ll be able to search my own blog and find this answer next time, or more likely I will forget I even wrote this.