A 404 error is often returned when pages have been moved or deleted. In the first case, it is better to employ URL mapping or URL redirection by returning a 301 Moved Permanently response, which can be configured in most server configuration files, or through URL rewriting; in the second case, a 410 Gone should be returned. Because these two options require special server configuration, most websites do not make use of them.
404 errors should not be confused with DNS errors, which appear when the given URL refers to a server name that does not exist. A 404 error indicates that the server itself was found, but that the server was not able to retrieve the requested page.
Web servers can typically be configured to display a customised 404 error page, including a more natural description, the parent site's branding, and sometimes a site map, a search form or 404 page widget. The protocol level phrase, which is hidden from the user, is rarely customized.
Many organizations use 404 error pages as an opportunity to inject humor into what may otherwise be a serious website.
While many websites send additional information in a 404 error message—such as a link to the homepage of a website or a search box—some also endeavor to find the correct web page the user wanted. Extensions are available for some popular content management systems (CMSs) to do this.
Here are some things you can do:
Use a Web site analysis tool such as Web Trends or Weblog to identify links that result in 404s, then fix the links.
If you change the Uniform Resource Locator ( URL ) for a page on your site, retain the old URL as a redirect file, putting a message on it and inserting a META element with a REFRESH to change to the new URL in a specified number of seconds.
You can create the page contents for a 404 status code page and substitute it for the 404 page that the browser usually provides. This will allow you to personalize the message and encourage the user to send a note to the Webmaster so that the situation can be fixed.