HTTP response codes

Knowledge of HTTP return codes (responses) is very important for the system administrator.

You probably already know that the HTTP protocol returns certain HTTP response codes, which are HTTP connection status codes.

Surely, the code 404 - Not Found is familiar to everyone, because all Internet users without exception face it. Error 404 is the most common because some links of web resources point to missing pages. Sometimes all errors from the 400 ... 415 range are regarded as a 404 error.

The HTTP 200 response code is a normal completion code for the operation; you cannot see it when you get the page.

A total of 5 categories of HTTP response codes are defined. Each of these categories may contain 100 return codes.

Range codes 100 ... 199 are informational. With their help, various information related to the request is returned.

The range 200 ... 299 is the range of successful operations. Codes belonging to this range, report on the successful completion of an operation. Codes reporting that the requested file is empty (no content) and reporting that the request has been accepted also belong to this range.

The range of response codes 300 ... 399 are redirect codes.

Range codes 400 ... 499 are customer errors. For example, a user may request a non-existent document. The "Forbidden" and "Unauthorized" errors also belong to this range. Both the first and second report that the client does not have access to a specific resource. In the first case, access is simply denied, and in the second case, the client is not authorized.

Response codes 500 ... 599 are server error codes. These errors occur when an internal server error or if it is not configured correctly. In the second case, the server simply cannot correctly return the response to the request. This type of error occurs normally when an error is made by a script (script) located on the server.

Some script interpreters, such as PHP, never make such an error. If there are errors in the PHP script, the PHP interpreter will simply return the error message to the client. From the server side, this will look like a normal response to the client (browser). For example, unlike the PHP interpreter, Perl returns an error message to the HTTP protocol.

Now we list the main HTTP return codes:

HTTP return code table

Of course, this is not a complete list of HTTP response codes, but the above list of basic return codes is enough.