Cabinet Office
The Hypertext Transfer Protocol (HTTP) is relative to the TCP/IP set of protocols, which sets the rules for exchanging data on the World Wide Web. Its name implies that files can contain links to other files via additional transfer requests. A web server contains a program called an HTTP daemon that handles HTTP requests from web clients (browsers) which are either directly entered URLs or links from existing pages. The server processes this request from the browser and the appropriate file is returned.
The following is a selection of the common HTTP server status codes. Most of these will never be seen be an average web user. They are usually only noticeable when looking through server logs on a web server.
The numerical codes are standard; the reasons text attached to each can be manipulated by the Web manager.
They are broken into five categories, each designated by the first numerical value of the status code:
1xx - Informational
2xx - Success
3xx - Redirection
4xx - Client Error
5xx - Server Error
Each status code shows a transaction between the client web browser and the HTTP server and can be found listed against each individual GET request, the 200 status code is most common as it illustrates a successful request for a file.
200
OK
A file has been successfully requested from the server.
202
Request accepted for processing
301
Moved
May be followed by a redirection URL.
304
Not Modified
A file that has not been modified has been requested. This message shows the request to the server but the user will have accessed the information from a cache store, either from own PC or local caching service. Covers all file types.
400
Bad Request
Request was impossible or a syntax error occurred.
401
Unauthorised
Request should be re-attempted with a proper authorisation header.
403
Forbidden
A user has attempted to access a password-protected area of the service.
404
Not Found
This code means that the requested URL does not reside on the server. In modern browsers this may result in a specialised page being displayed directly by the web browser itself. Correctly administered systems should never server a 404-error page; instead, a general search page for the server should be served.
408
Request Timeout
This either means that the file could not be accessed correctly on the server or that the users connection has failed.
500
Internal Server Error
This is an exception error that could have resulted from HTTP server overload or a failed server script or program.