FTP Commands

FTP commands sent across the control connection consist of simple text strings (and follow the Telnet protocol - see RFC 854). For example, to retrieve a file, the client sends "RETR filename" on the control connection to the FTP server. To transfer a file, the client sends "STOR filename".

The FTP server acknowledges each command with an FTP reply, which consists of a three digit number followed by human-readable text. The first digit indicates if the response is good, bad, or incomplete. If an error occurred, the second digit may be used to indicate what type of error occurred. Similarly, the third digit can indicate more details of the error.

The first digit is the most important, and the five possible values are described below:

Reply	Description
1yz	Positive Preliminary reply. The request action has been initiated, but another reply is to be expected before the client issues another command.
2yz	Positive Completion reply. The requested action has successfully completed, and the client may issue another command.
3yz	Positive Intermediate reply. The command has been accepted, but more information is required. The client should send another command in reply.
4yz	Transient Negative reply. The command failed, but it can be retried.
5yz	Permanent Negative Completion reply. The command failed, and should not be repeated.

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