Some proxy servers generate a 404 error when a 500-range error code would be more correct. There are also "soft 3XX" errors where content is returned with a status 200 but comes from a redirected page, such as when missing pages are redirected to the domain root/home page. This can also be done on purpose to force some browsers (like Internet Explorer) to display a customized 404 error message rather than replacing what is served with a browser-specific "friendly" error message (in Internet Explorer, this behavior is triggered when a 404 is served and the received HTML is shorter than a certain length, and can be manually disabled by the user). ) rather than a relative path (/error.html). htaccess file) is specified as an absolute path (e.g. Soft 404s can occur as a result of configuration errors when using certain HTTP server software, for example with the Apache software, when an Error Document 404 (specified in a. Some search engines, like Yahoo and Google, use automated processes to detect soft 404s. Soft 404s are problematic for automated methods of discovering whether a link is broken. The term "soft 404" was introduced in 2004 by Ziv Bar-Yossef et al. Some websites report a "not found" error by returning a standard web page with a "200 OK" response code, falsely reporting that the page loaded properly this is known as a soft 404. A 404 error indicates that the server itself was found, but that the server was not able to retrieve the requested page. Because these two options require special server configuration, most websites do not make use of them.Ĥ04 errors should not be confused with DNS errors, which appear when the given URL refers to a server name that does not exist. 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. The HTTP specification suggests the phrase "Not Found" and many web servers by default issue an HTML page that includes both the 404 code and the "Not Found" phrase.Ī 404 error is often returned when pages have been moved or deleted. At the HTTP level, a 404 response code is followed by a human-readable "reason phrase". HTTP's use of three-digit codes is similar to the use of such codes in earlier protocols such as FTP and NNTP. The following two digits indicate the specific error encountered. In code 404, the first digit indicates a client error, such as a mistyped Uniform Resource Locator (URL). 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.
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