These are status reports from the server and indicate the response to the last command received from the client.
Status response lines begin with a 3 digit numeric code which is sufficient to distinguish all responses. Some of these may herald the subsequent transmission of text.
The first digit of the response broadly indicates the success, failure, or progress of the previous command.
1xx - Informative message
2xx - Command ok
3xx - Command ok so far, send the rest of it.
4xx - Command was correct, but couldn't be performed for
some reason.
5xx - Command unimplemented, or incorrect, or a serious
program error occurred.
The next digit in the code indicates the function response category.
x0x - Connection, setup, and miscellaneous messages
x1x - Newsgroup selection
x2x - Article selection
x3x - Distribution functions
x4x - Posting
x8x - Nonstandard (private implementation) extensions
x9x - Debugging output
The exact response codes that should be expected from each command are detailed in the description of that command. In addition, below is listed a general set of response codes that may be received at any time.
Certain status responses contain parameters such as numbers and names. The number and type of such parameters is fixed for each response code to simplify interpretation of the response.
Parameters are separated from the numeric response code and from each other by a single space. All numeric parameters are decimal, and may have leading zeros. All string parameters begin after the separating space, and end before the following separating space or the CR-LF pair at the end of the line. (String parameters may not, therefore, contain spaces.) All text, if any, in the response which is not a parameter of the response must follow and be separated from the last parameter by a space. Also, note that the text following a response number may vary in different implementations of the server. The 3-digit numeric code should be used to determine what response was sent.
Response codes not specified in this standard may be used for any installation-specific additional commands also not specified. These should be chosen to fit the pattern of x8x specified above. (Note that debugging is provided for explicitly in the x9x response codes.) The use of unspecified response codes for standard commands is prohibited.
We have provided a response pattern x9x for debugging. Since much debugging output may be classed as "informative messages", we would expect, therefore, that responses 190 through 199 would be used for various debugging outputs. There is no requirement in this specification for debugging output, but if such is provided over the connected stream, it must use these response codes. If appropriate to a specific implementation, other x9x codes may be used for debugging. (An example might be to use e.g., 290 to acknowledge a remote debugging request.)