The SYST command
A SYST request asks for information about the server's operating system. The server accepts this request with code 215. Examples from five different servers:
215 UNIX Type: L8 215 UNIX Type: L8 Version: BSD-44 215 NetWare system type. 215 MACOS Dave's Server 215 AmigaOS
The STAT command
A STAT request asks for human-readable information about the server's status. The server normally accepts this request with code 211:
211- ftp.heaven.af.mil FTP server status:
Connected to heaven.af.mil (10.1.2.3)
Logged in anonymously
TYPE: ASCII, FORM: Nonprint; Structure:
File; transfer MODE: Stream
No data connection
211 End of status
The response format varies widely from server to server.
A STAT request may include a parameter. In this case it asks for information about a file identified by the parameter, similar to the information provided by LIST. The server normally accepts this request with code 211, 212, or 213, returning information in its response. A
Some servers may ignore STAT parameters. Some servers reject STAT parameters with code 504. Even when servers try to support STAT , the output is even more difficult to parse than the output of LIST.
The HELP command
A HELP request asks for human-readable information from the server. The server may accept this request with code 211 or 214, or reject it with code 502.
A HELP request may include a parameter. The meaning of the parameter is defined by the server. Some servers interpret the parameter as an FTP verb, and respond by briefly explaining the syntax of the verb:
> HELP RETR < 214 Syntax: RETR <sp> file-name > HELP FOO < 502 Unknown command FOO.
The HELP response is a good place for server implementors to declare the operating system type and the name of the server program.
The NOOP command
A NOOP request does nothing other than elicit a response from the server. NOOP parameters are prohibited. A typical server accepts NOOP (required code 200).