19. In HTTP 1.0, the meaning of status code 401 is (?); If a prompt for "file not found" is returned, the header function is available with the statement (?). Write out HTTP common status codes and meanings, at least 5. [Perfect Topic]

Status 401 represents an unauthorized, header ("Location:www.xxx.php");

100-199 is used to specify certain actions that the client should be corresponding.

200-299 is used to indicate a successful request.

300-399 is used for files that have been moved and is often included in the locator header information to specify the new address information.

400-499 is used to indicate client-side errors.

500-599 is used to support server errors.

Success 2XX successfully processed the requested status code.

200 the server has successfully processed the request and provided the requested Web page.

204 The server successfully processed the request, but did not return any content.

REDIRECT 3xx use redirects in each request no more than 5 times.

301 The requested page has been permanently moved to a new location. When URLs change, use 301 code. The new URL is saved in the Search engine index.

302 The requested Web page is temporarily moved to a new location. The original URL is saved in the Search engine index.

304 If the page has not been updated since the requestor last requested it, use 304 code to tell the search engine robot that it saves bandwidth and overhead.

Client Error 4xx indicates a possible error in the request and prevents the server from processing.

400 the server does not understand the syntax of the request.

403 The server denied the request.

404 the server could not find the requested Web page. Pages that do not exist on the server often return this code.

410 after the requested resource is permanently deleted, the server returns this response. This code is similar to the 404 (not Found) code, but is sometimes used to replace the 404 code in cases where the resource existed before and now does not exist. If the resource has been permanently deleted, you should use 301 to specify a new location for the resource.

Server error 5xx indicates that an internal error occurred while the server was processing the request. These errors may be the error of the server itself, not the request.

500 the server encountered an error and could not complete the request.

503 servers are not currently available (due to overloading or downtime maintenance). Typically, this is only a temporary state.

19. In HTTP 1.0, the meaning of status code 401 is (?); If a prompt for "file not found" is returned, the header function is available with the statement (?). Write out HTTP common status codes and meanings, at least 5. [Perfect Topic]