System: HTTP Server Status Codes
A lot of people get confused when they start looking at raw log files. This is probably because they were never designed to be read by humans. The page focuses on one component of the log file - the Status Code.
Status Codes
The codes can be broken up into: successful response (codes beginning in 2), a redirection (codes beginning in 3), an error caused by the client (codes beginning in 4), or an error in the server (codes beginning in 5).
The specific meanings of the most commonly encountered codes are presented below:
- 200 - OK
- indicates a successful request resulting in a file being returned.
- 206 - Partial Content
- indicates that a file was only partially downloaded. The download could have been interrupted by someone leaving the page before it's fully loaded (in the case of embedded images) or cancelling a download (in the case of PDF, MP3 and similar file types).
- 301 - Moved Permanently
- the server has indicated that the requested file is now located at a new address. Search engines should update their index by removing the old address and replacing it (PR intact) with the new one.
- 302 - Found
- the user has been redirected, but as it's not a Permanent redirect no further action needs to be taken. This could be as simple as the server adding a / to the end of the request, or the result of a header command in PHP.
- 304 - Not Modified
- an intelligent user agent (browser) has made a request for a file which is already present in it's cache. A 304 indicates that the cached version has the same timestamp as the 'live' version of the file so they don't need to download it. If the 'live' file was newer then the response would instead be a 200.
- 400 - Bad Request
- the server couldn't make sense of the request.
- 401 - Unauthorised (password required)
- an attempt has been made to access a directory or file that requires authentication (username and password). Subsequent requests would normally contain a username and password, resulting in either a 200 (user has been authenticated) or 401 (authentication failed).
- 403 - Forbidden
- the server has blocked access to a directory or file. This typically applies to requests that would otherwise result in a directory listing being displayed.
- 404 - Not Found
- the requested file does not exist on the server. This normally indicates a broken link (internal or external).
- 408 - Request Timeout
- the client/server connection process was so slow that the server decided to 'hang up'.
- 410 - Gone
- the server has indicated that the requested file used to exist but has now been permanently removed. Search engines should remove the address from their index
- 414 - Request-URI Too Long
- the request was too long. This normally indicates an attempt to compromise the server using a buffer overflow exploit.
For more on log file formats and analysing them using command-line tools, refer to the article Analyzing Apache Log Files.
References
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- Page Last Modified: 23 November 2009