I came across an interesting challenge while working on my current project; which is a migration from a classic HTML-based website to SharePoint 2010 For Internet Sites, Enterprise.  Custom error pages…

Out of the box, SharePoint likes to give the user a useless 404 error like this:

While there is out-of-the-box support for custom error pages in SharePoint 2010, it’s not completely obvious how you set the custom error pages for a web application.  First of all, SharePoint includes an sps404.html page in the /_layouts/{language} folder which by default includes an STSNavigate reference to handle the redirect.  That’s all well and good, but I want my own!

Here’s how I got what I wanted:

Copy the sps404.html page and rename it to sps404custom.html – leave the new file in the same location.  Open the file in your favorite HTML editor and look for the STSNavigate line – change the link to an appropriate page, example /Pages/Page-Not-Found.aspx.

This would replace the OOTB 404 behavior with an automatic redirect to a Publishing page under the root Pages library of my web application.  Cool!

Now I just have to create a page at /Pages/Page-Not-Found.aspx and add some text.  The page will inherit whatever branding elements I’ve applied to the rest of my site, leaving the user with a much cleaner and consistent experience.  Once I’ve done those two things, there’s a little PowerShell that must be done to actually set the custom 404 page:

$WebApp = Get-SPWebApplication http://url
$WebApp.FileNotFoundPage = "sps404custom.html"
$WebApp.Update() 

Once that’s done, try going to a bogus page in your site and you should be taken to your custom 404 page!