Editing HTTP 404 (section)

==Overview==

When communicating via HTTP, a server is required to respond to a request, such as a [[web browser]] request for a [[web page]], with a numeric response code and an optional, mandatory, or disallowed (based upon the status code) message. In code 404, the first digit indicates a client error, such as a mistyped [[Uniform Resource Locator]] (URL). The following two digits indicate the specific error encountered. HTTP's use of three-digit codes is similar to the use of such codes in earlier protocols such as [[File Transfer Protocol|FTP]] and [[Network News Transfer Protocol|NNTP]]. At the HTTP level, a 404 response code is followed by a human-readable "reason phrase". The HTTP specification suggests the phrase "Not Found"<ref name="section-654" /> and many web servers by default issue an HTML page that includes both the 404 code and the "Not Found" phrase.

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 [[Domain Name System|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.