Server Response Codes

Monday Feb 9th 1998 by Joe Burns

What exactly does that 404 error mean? What about that 412 error and that pesky 501 error? Here are the answers to all your server error questions.

...use these to jump around or read it all

[Headers] [The Server Response Codes]

     Ah, the dreaded error message. There you were surfing along just fine when all of a sudden you get that horrible white screen with the big number up in the corner.

     Most of you know the 404 error. (See So, You Want A 404 Error Page, Huh? ) That means the server can't find the page you're looking for. I hate that one. It always seems to pop up when I'm using a search engine trying to find a specific topic. Just when I find a page that looks perfect - boom. 404 Error. Ugh!

     What you may not know is that there are errors other than the 404. Oh, yeah. There's a whole run of fun little error message that can plague you into submission. As a surfer, you're probably most familiar with the 400 and 500 level errors. Those are the most common ones to pop up in a browser window.

     The 404, and all of its numeric partners, are what are known as Server Response Codes (SRC). Their created when the server itself sends back a message that all it OK, or that all has gone wrong. Most of these you'll never see because they act silently. That means, the response is given that all is OK and the process continues without your ever seeing the response given. Those SRC's are numbers found mostly within 100 through 399. Then there are those that you get to see. Those you find mostly within the 400 to 599 range.

     In the descriptions below, I'm going to say that the "header" was the reason for the error again and again. So what's a header?


     A header is text that is used to transfer information between clients and servers. You will never see the headers unless you get deeper into programming on the server itself. They're created by the machines that move information around on the Web. There are basically four types of headers:

  • General - This is information related to the client, the server or the protocol (like http or ftp)

  • Entity - This is information about the actual data being tranferred.

  • Request - This sets standards regarding acceptable formats and parameters.

  • Response - This contains information about the server sending the response.
     Every time a server is contacted by a user, a "handshake" occurs. This is where the two machines "talk" to each other and make sure they can connect and then create the transfer you are asking for. These headers are used to provide all the information requred to have a successful handshake.

     The codes below are created as a result of that handshake.

The Server Response Codes

Here's how it all breaks down:

SRC's provide confirmation that a request was received and is being processed. (silent)
100 This is good. The request was completed and the process can move along.
101 Request to switch protocols (like from HTTP to FTP) was accepted.
SRC's report that requests were performed sucessfully. (silent)
200 It simply means all is OK. What the client requested is available
201 This means a new address was successfully created through a CGI or posting form data.
202 The client's request was accepted, although not yet acted upon.
203 The accepted information in the entity header is not from the original server, but from a third party.
204 There is no content in the requested click. Let's say you click on an image map section not attached to a page. This allows the server to just sit there waiting for another click rather than throwing an error.
205 This allows the server to reset the content returned by a CGI.
206 Only partial content is being returned for some reason.
300-399 Request was not performed, a redirection is occuring.(usually silent)
300 The requested address refers to more than one entity. Depending on how the server is configured, you get an error or a choice of which page you want.
301 Page has been moved permanently, and the new URL is available. You should be sent there by the server.
302 Page has been moved temporarily, and the new URL is available. You should be sent there by the server.
303 This is a "see other" SRC. Data is somewhere else and the GET method is used to retreive it.
304 This is a "Not Modified" SRC. If the header in the request asks "If Modified Since", this will return how long it's been since the page was updated.
305 This tells the server the requested document must be accessed by using the proxy in the Location header (ie. ftp, http.)
400-499 Request is incomplete for some reason.
400 There is a syntax error in the request. It is denied.
401 The header in your request did not contain the correct authorization codes. You don't get to see what you requested.
402 Payment is required. Don't worry about this one. It's not in use yet.
403 You are forbidden to see the document you requested. It can also mean that the server doesn't have the ability to show you what you want to see.
404 Document not found. The page you want is not on the server nor has it ever been on the server. Most likely you have misspelled the title or used an incorrect capitalization pattern in the URL.
405 The method you are using to access the file is not allowed.
406 The page you are requesting exists but you cannot see it because your own system doesn't understand the format the page is configured for.
407 The request must be authorized before it can take place.
408 The request timed out. For some reason the server took too much time processing your request. Net congestion is the most likely reason.
409 Conflict. Too many people wanted the same file at the same time. It glutted the server. Try again.
410 The page use to be there, but now it's gone.
411 Your request is missing a Content-Length header.
412 The page you requested has some sort of pre-condition set up. That means that If something is a certain way, you can have the page. If you get a 412, that condition was not met. Oops.
413 Too big. What you requested is just too big to process.
414 The URL you entered is too long. Really. Too long.
415 The page is an unsupported media type, like a proprietary file made specifically for a certain program..
500-599 Errors have occured in the server itself.
501 What you requested of the server cannot be done by the server. Stop doing that you!
502 Your server has received errors from the server you are trying to reach. This is better known as the "Bad Gateway" error.
503 The format or service you are requesting is temporarily unavailable.
504 The gateway as timed out. This is a lot like the 408 error except the time-out occured specifically at the gateway of the server.
505 The HTTP protocol you are asking for is not supported.


[Headers] [The Server Response Codes]


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