Section 4. FILE TRANSFER FUNCTIONS


   The communication channel from the user-PI to the server-PI is
   established as a TCP connection from the user to the standard server
   port.  The user protocol interpreter is responsible for sending FTP
   commands and interpreting the replies received; the server-PI
   interprets commands, sends replies and directs its DTP to set up the
   data connection and transfer the data.  If the second party to the
   data transfer (the passive transfer process) is the user-DTP, then it
   is governed through the internal protocol of the user-FTP host; if it
   is a second server-DTP, then it is governed by its PI on command from
   the user-PI.  The FTP replies are discussed in the next section.  In
   the description of a few of the commands in this section, it is
   helpful to be explicit about the possible replies.

   4.1.  FTP COMMANDS

      4.1.1.  ACCESS CONTROL COMMANDS

         The following commands specify access control identifiers
         (command codes are shown in parentheses).

         USER NAME (USER)

            The argument field is a Telnet string identifying the user.
            The user identification is that which is required by the
            server for access to its file system.  This command will
            normally be the first command transmitted by the user after
            the control connections are made (some servers may require
            this).  Additional identification information in the form of
            a password and/or an account command may also be required by
            some servers.  Servers may allow a new USER command to be
            entered at any point in order to change the access control
            and/or accounting information.  This has the effect of
            flushing any user, password, and account information already
            supplied and beginning the login sequence again.  All
            transfer parameters are unchanged and any file transfer in
            progress is completed under the old access control
            parameters.







         PASSWORD (PASS)

            The argument field is a Telnet string specifying the user's
            password.  This command must be immediately preceded by the
            user name command, and, for some sites, completes the user's
            identification for access control.  Since password
            information is quite sensitive, it is desirable in general
            to "mask" it or suppress typeout.  It appears that the
            server has no foolproof way to achieve this.  It is
            therefore the responsibility of the user-FTP process to hide
            the sensitive password information.

         ACCOUNT (ACCT)

            The argument field is a Telnet string identifying the user's
            account.  The command is not necessarily related to the USER
            command, as some sites may require an account for login and
            others only for specific access, such as storing files.  In
            the latter case the command may arrive at any time.

            There are reply codes to differentiate these cases for the
            automation: when account information is required for login,
            the response to a successful PASSword command is reply code
            332.  On the other hand, if account information is NOT
            required for login, the reply to a successful PASSword
            command is 230; and if the account information is needed for
            a command issued later in the dialogue, the server should
            return a 332 or 532 reply depending on whether it stores
            (pending receipt of the ACCounT command) or discards the
            command, respectively.

         CHANGE WORKING DIRECTORY (CWD)

            This command allows the user to work with a different
            directory or dataset for file storage or retrieval without
            altering his login or accounting information.  Transfer
            parameters are similarly unchanged.  The argument is a
            pathname specifying a directory or other system dependent
            file group designator.

         CHANGE TO PARENT DIRECTORY (CDUP)

            This command is a special case of CWD, and is included to
            simplify the implementation of programs for transferring
            directory trees between operating systems having different





            syntaxes for naming the parent directory.  The reply codes
            shall be identical to the reply codes of CWD.  See
            Appendix II for further details.

         STRUCTURE MOUNT (SMNT)

            This command allows the user to mount a different file
            system data structure without altering his login or
            accounting information.  Transfer parameters are similarly
            unchanged.  The argument is a pathname specifying a
            directory or other system dependent file group designator.

         REINITIALIZE (REIN)

            This command terminates a USER, flushing all I/O and account
            information, except to allow any transfer in progress to be
            completed.  All parameters are reset to the default settings
            and the control connection is left open.  This is identical
            to the state in which a user finds himself immediately after
            the control connection is opened.  A USER command may be
            expected to follow.

         LOGOUT (QUIT)

            This command terminates a USER and if file transfer is not
            in progress, the server closes the control connection.  If
            file transfer is in progress, the connection will remain
            open for result response and the server will then close it.
            If the user-process is transferring files for several USERs
            but does not wish to close and then reopen connections for
            each, then the REIN command should be used instead of QUIT.

            An unexpected close on the control connection will cause the
            server to take the effective action of an abort (ABOR) and a
            logout (QUIT).

      4.1.2.  TRANSFER PARAMETER COMMANDS

         All data transfer parameters have default values, and the
         commands specifying data transfer parameters are required only
         if the default parameter values are to be changed.  The default
         value is the last specified value, or if no value has been
         specified, the standard default value is as stated here.  This
         implies that the server must "remember" the applicable default
         values.  The commands may be in any order except that they must
         precede the FTP service request.  The following commands
         specify data transfer parameters:



         DATA PORT (PORT)

            The argument is a HOST-PORT specification for the data port
            to be used in data connection.  There are defaults for both
            the user and server data ports, and under normal
            circumstances this command and its reply are not needed.  If
            this command is used, the argument is the concatenation of a
            32-bit internet host address and a 16-bit TCP port address.
            This address information is broken into 8-bit fields and the
            value of each field is transmitted as a decimal number (in
            character string representation).  The fields are separated
            by commas.  A port command would be:

               PORT h1,h2,h3,h4,p1,p2

            where h1 is the high order 8 bits of the internet host
            address.

         PASSIVE (PASV)

            This command requests the server-DTP to "listen" on a data
            port (which is not its default data port) and to wait for a
            connection rather than initiate one upon receipt of a
            transfer command.  The response to this command includes the
            host and port address this server is listening on.

         REPRESENTATION TYPE (TYPE)

            The argument specifies the representation type as described
            in the Section on Data Representation and Storage.  Several
            types take a second parameter.  The first parameter is
            denoted by a single Telnet character, as is the second
            Format parameter for ASCII and EBCDIC; the second parameter
            for local byte is a decimal integer to indicate Bytesize.
            The parameters are separated by a <SP> (Space, ASCII code
            32).

            The following codes are assigned for type:

                         \    /
               A - ASCII |    | N - Non-print
                         |-><-| T - Telnet format effectors
               E - EBCDIC|    | C - Carriage Control (ASA)
                         /    \
               I - Image
               
               L <byte size> - Local byte Byte size



            The default representation type is ASCII Non-print.  If the
            Format parameter is changed, and later just the first
            argument is changed, Format then returns to the Non-print
            default.

         FILE STRUCTURE (STRU)

            The argument is a single Telnet character code specifying
            file structure described in the Section on Data
            Representation and Storage.

            The following codes are assigned for structure:

               F - File (no record structure)
               R - Record structure
               P - Page structure

            The default structure is File.

         TRANSFER MODE (MODE)

            The argument is a single Telnet character code specifying
            the data transfer modes described in the Section on
            Transmission Modes.

            The following codes are assigned for transfer modes:

               S - Stream
               B - Block
               C - Compressed

            The default transfer mode is Stream.

      4.1.3.  FTP SERVICE COMMANDS

         The FTP service commands define the file transfer or the file
         system function requested by the user.  The argument of an FTP
         service command will normally be a pathname.  The syntax of
         pathnames must conform to server site conventions (with
         standard defaults applicable), and the language conventions of
         the control connection.  The suggested default handling is to
         use the last specified device, directory or file name, or the
         standard default defined for local users.  The commands may be
         in any order except that a "rename from" command must be
         followed by a "rename to" command and the restart command must
         be followed by the interrupted service command (e.g., STOR or
         RETR).  The data, when transferred in response to FTP service



         commands, shall always be sent over the data connection, except
         for certain informative replies.  The following commands
         specify FTP service requests:

         RETRIEVE (RETR)

            This command causes the server-DTP to transfer a copy of the
            file, specified in the pathname, to the server- or user-DTP
            at the other end of the data connection.  The status and
            contents of the file at the server site shall be unaffected.

         STORE (STOR)

            This command causes the server-DTP to accept the data
            transferred via the data connection and to store the data as
            a file at the server site.  If the file specified in the
            pathname exists at the server site, then its contents shall
            be replaced by the data being transferred.  A new file is
            created at the server site if the file specified in the
            pathname does not already exist.

         STORE UNIQUE (STOU)

            This command behaves like STOR except that the resultant
            file is to be created in the current directory under a name
            unique to that directory.  The 250 Transfer Started response
            must include the name generated.

         APPEND (with create) (APPE)

            This command causes the server-DTP to accept the data
            transferred via the data connection and to store the data in
            a file at the server site.  If the file specified in the
            pathname exists at the server site, then the data shall be
            appended to that file; otherwise the file specified in the
            pathname shall be created at the server site.

         ALLOCATE (ALLO)

            This command may be required by some servers to reserve
            sufficient storage to accommodate the new file to be
            transferred.  The argument shall be a decimal integer
            representing the number of bytes (using the logical byte
            size) of storage to be reserved for the file.  For files
            sent with record or page structure a maximum record or page
            size (in logical bytes) might also be necessary; this is
            indicated by a decimal integer in a second argument field of



            the command.  This second argument is optional, but when
            present should be separated from the first by the three
            Telnet characters <SP> R <SP>.  This command shall be
            followed by a STORe or APPEnd command.  The ALLO command
            should be treated as a NOOP (no operation) by those servers
            which do not require that the maximum size of the file be
            declared beforehand, and those servers interested in only
            the maximum record or page size should accept a dummy value
            in the first argument and ignore it.

         RESTART (REST)

            The argument field represents the server marker at which
            file transfer is to be restarted.  This command does not
            cause file transfer but skips over the file to the specified
            data checkpoint.  This command shall be immediately followed
            by the appropriate FTP service command which shall cause
            file transfer to resume.

         RENAME FROM (RNFR)

            This command specifies the old pathname of the file which is
            to be renamed.  This command must be immediately followed by
            a "rename to" command specifying the new file pathname.

         RENAME TO (RNTO)

            This command specifies the new pathname of the file
            specified in the immediately preceding "rename from"
            command.  Together the two commands cause a file to be
            renamed.

         ABORT (ABOR)

            This command tells the server to abort the previous FTP
            service command and any associated transfer of data.  The
            abort command may require "special action", as discussed in
            the Section on FTP Commands, to force recognition by the
            server.  No action is to be taken if the previous command
            has been completed (including data transfer).  The control
            connection is not to be closed by the server, but the data
            connection must be closed.

            There are two cases for the server upon receipt of this
            command: (1) the FTP service command was already completed,
            or (2) the FTP service command is still in progress.




               In the first case, the server closes the data connection
               (if it is open) and responds with a 226 reply, indicating
               that the abort command was successfully processed.

               In the second case, the server aborts the FTP service in
               progress and closes the data connection, returning a 426
               reply to indicate that the service request terminated
               abnormally.  The server then sends a 226 reply,
               indicating that the abort command was successfully
               processed.

         DELETE (DELE)

            This command causes the file specified in the pathname to be
            deleted at the server site.  If an extra level of protection
            is desired (such as the query, "Do you really wish to
            delete?"), it should be provided by the user-FTP process.

         REMOVE DIRECTORY (RMD)

            This command causes the directory specified in the pathname
            to be removed as a directory (if the pathname is absolute)
            or as a subdirectory of the current working directory (if
            the pathname is relative).  See Appendix II.

         MAKE DIRECTORY (MKD)

            This command causes the directory specified in the pathname
            to be created as a directory (if the pathname is absolute)
            or as a subdirectory of the current working directory (if
            the pathname is relative).  See Appendix II.

         PRINT WORKING DIRECTORY (PWD)

            This command causes the name of the current working
            directory to be returned in the reply.  See Appendix II.

         LIST (LIST)

            This command causes a list to be sent from the server to the
            passive DTP.  If the pathname specifies a directory or other
            group of files, the server should transfer a list of files
            in the specified directory.  If the pathname specifies a
            file then the server should send current information on the
            file.  A null argument implies the user's current working or
            default directory.  The data transfer is over the data
            connection in type ASCII or type EBCDIC.  (The user must



            ensure that the TYPE is appropriately ASCII or EBCDIC).
            Since the information on a file may vary widely from system
            to system, this information may be hard to use automatically
            in a program, but may be quite useful to a human user.

         NAME LIST (NLST)

            This command causes a directory listing to be sent from
            server to user site.  The pathname should specify a
            directory or other system-specific file group descriptor; a
            null argument implies the current directory.  The server
            will return a stream of names of files and no other
            information.  The data will be transferred in ASCII or
            EBCDIC type over the data connection as valid pathname
            strings separated by <CRLF> or <NL>.  (Again the user must
            ensure that the TYPE is correct.)  This command is intended
            to return information that can be used by a program to
            further process the files automatically.  For example, in
            the implementation of a "multiple get" function.

         SITE PARAMETERS (SITE)

            This command is used by the server to provide services
            specific to his system that are essential to file transfer
            but not sufficiently universal to be included as commands in
            the protocol.  The nature of these services and the
            specification of their syntax can be stated in a reply to
            the HELP SITE command.

         SYSTEM (SYST)

            This command is used to find out the type of operating
            system at the server.  The reply shall have as its first
            word one of the system names listed in the current version
            of the Assigned Numbers document [4].

         STATUS (STAT)

            This command shall cause a status response to be sent over
            the control connection in the form of a reply.  The command
            may be sent during a file transfer (along with the Telnet IP
            and Synch signals--see the Section on FTP Commands) in which
            case the server will respond with the status of the
            operation in progress, or it may be sent between file
            transfers.  In the latter case, the command may have an
            argument field.  If the argument is a pathname, the command
            is analogous to the "list" command except that data shall be



            transferred over the control connection.  If a partial
            pathname is given, the server may respond with a list of
            file names or attributes associated with that specification.
            If no argument is given, the server should return general
            status information about the server FTP process.  This
            should include current values of all transfer parameters and
            the status of connections.

         HELP (HELP)

            This command shall cause the server to send helpful
            information regarding its implementation status over the
            control connection to the user.  The command may take an
            argument (e.g., any command name) and return more specific
            information as a response.  The reply is type 211 or 214.
            It is suggested that HELP be allowed before entering a USER
            command. The server may use this reply to specify
            site-dependent parameters, e.g., in response to HELP SITE.

         NOOP (NOOP)

            This command does not affect any parameters or previously
            entered commands. It specifies no action other than that the
            server send an OK reply.

   The File Transfer Protocol follows the specifications of the Telnet
   protocol for all communications over the control connection.  Since
   the language used for Telnet communication may be a negotiated
   option, all references in the next two sections will be to the
   "Telnet language" and the corresponding "Telnet end-of-line code".
   Currently, one may take these to mean NVT-ASCII and <CRLF>.  No other
   specifications of the Telnet protocol will be cited.

   FTP commands are "Telnet strings" terminated by the "Telnet end of
   line code".  The command codes themselves are alphabetic characters
   terminated by the character <SP> (Space) if parameters follow and
   Telnet-EOL otherwise.  The command codes and the semantics of
   commands are described in this section; the detailed syntax of
   commands is specified in the Section on Commands, the reply sequences
   are discussed in the Section on Sequencing of Commands and Replies,
   and scenarios illustrating the use of commands are provided in the
   Section on Typical FTP Scenarios.

   FTP commands may be partitioned as those specifying access-control
   identifiers, data transfer parameters, or FTP service requests.
   Certain commands (such as ABOR, STAT, QUIT) may be sent over the
   control connection while a data transfer is in progress.  Some



   servers may not be able to monitor the control and data connections
   simultaneously, in which case some special action will be necessary
   to get the server's attention.  The following ordered format is
   tentatively recommended:

      1. User system inserts the Telnet "Interrupt Process" (IP) signal
      in the Telnet stream.

      2. User system sends the Telnet "Synch" signal.

      3. User system inserts the command (e.g., ABOR) in the Telnet
      stream.

      4. Server PI, after receiving "IP", scans the Telnet stream for
      EXACTLY ONE FTP command.

   (For other servers this may not be necessary but the actions listed
   above should have no unusual effect.)

   4.2.  FTP REPLIES

      Replies to File Transfer Protocol commands are devised to ensure
      the synchronization of requests and actions in the process of file
      transfer, and to guarantee that the user process always knows the
      state of the Server.  Every command must generate at least one
      reply, although there may be more than one; in the latter case,
      the multiple replies must be easily distinguished.  In addition,
      some commands occur in sequential groups, such as USER, PASS and
      ACCT, or RNFR and RNTO.  The replies show the existence of an
      intermediate state if all preceding commands have been successful.
      A failure at any point in the sequence necessitates the repetition
      of the entire sequence from the beginning.

         The details of the command-reply sequence are made explicit in
         a set of state diagrams below.

      An FTP reply consists of a three digit number (transmitted as
      three alphanumeric characters) followed by some text.  The number
      is intended for use by automata to determine what state to enter
      next; the text is intended for the human user.  It is intended
      that the three digits contain enough encoded information that the
      user-process (the User-PI) will not need to examine the text and
      may either discard it or pass it on to the user, as appropriate.
      In particular, the text may be server-dependent, so there are
      likely to be varying texts for each reply code.

      A reply is defined to contain the 3-digit code, followed by Space



      <SP>, followed by one line of text (where some maximum line length
      has been specified), and terminated by the Telnet end-of-line
      code.  There will be cases however, where the text is longer than
      a single line.  In these cases the complete text must be bracketed
      so the User-process knows when it may stop reading the reply (i.e.
      stop processing input on the control connection) and go do other
      things.  This requires a special format on the first line to
      indicate that more than one line is coming, and another on the
      last line to designate it as the last.  At least one of these must
      contain the appropriate reply code to indicate the state of the
      transaction.  To satisfy all factions, it was decided that both
      the first and last line codes should be the same.

         Thus the format for multi-line replies is that the first line
         will begin with the exact required reply code, followed
         immediately by a Hyphen, "-" (also known as Minus), followed by
         text.  The last line will begin with the same code, followed
         immediately by Space <SP>, optionally some text, and the Telnet
         end-of-line code.

            For example:
                                123-First line
                                Second line
                                  234 A line beginning with numbers
                                123 The last line

         The user-process then simply needs to search for the second
         occurrence of the same reply code, followed by <SP> (Space), at
         the beginning of a line, and ignore all intermediary lines.  If
         an intermediary line begins with a 3-digit number, the Server
         must pad the front  to avoid confusion.

            This scheme allows standard system routines to be used for
            reply information (such as for the STAT reply), with
            "artificial" first and last lines tacked on.  In rare cases
            where these routines are able to generate three digits and a
            Space at the beginning of any line, the beginning of each
            text line should be offset by some neutral text, like Space.

         This scheme assumes that multi-line replies may not be nested.

      The three digits of the reply each have a special significance.
      This is intended to allow a range of very simple to very
      sophisticated responses by the user-process.  The first digit
      denotes whether the response is good, bad or incomplete.
      (Referring to the state diagram), an unsophisticated user-process
      will be able to determine its next action (proceed as planned,



      redo, retrench, etc.) by simply examining this first digit.  A
      user-process that wants to know approximately what kind of error
      occurred (e.g. file system error, command syntax error) may
      examine the second digit, reserving the third digit for the finest
      gradation of information (e.g., RNTO command without a preceding
      RNFR).

         There are five values for the first digit of the reply code:

            1yz   Positive Preliminary reply

               The requested action is being initiated; expect another
               reply before proceeding with a new command.  (The
               user-process sending another command before the
               completion reply would be in violation of protocol; but
               server-FTP processes should queue any commands that
               arrive while a preceding command is in progress.)  This
               type of reply can be used to indicate that the command
               was accepted and the user-process may now pay attention
               to the data connections, for implementations where
               simultaneous monitoring is difficult.  The server-FTP
               process may send at most, one 1yz reply per command.

            2yz   Positive Completion reply

               The requested action has been successfully completed.  A
               new request may be initiated.

            3yz   Positive Intermediate reply

               The command has been accepted, but the requested action
               is being held in abeyance, pending receipt of further
               information.  The user should send another command
               specifying this information.  This reply is used in
               command sequence groups.

            4yz   Transient Negative Completion reply

               The command was not accepted and the requested action did
               not take place, but the error condition is temporary and
               the action may be requested again.  The user should
               return to the beginning of the command sequence, if any.
               It is difficult to assign a meaning to "transient",
               particularly when two distinct sites (Server- and
               User-processes) have to agree on the interpretation.
               Each reply in the 4yz category might have a slightly
               different time value, but the intent is that the



               user-process is encouraged to try again.  A rule of thumb
               in determining if a reply fits into the 4yz or the 5yz
               (Permanent Negative) category is that replies are 4yz if
               the commands can be repeated without any change in
               command form or in properties of the User or Server
               (e.g., the command is spelled the same with the same
               arguments used; the user does not change his file access
               or user name; the server does not put up a new
               implementation.)

            5yz   Permanent Negative Completion reply

               The command was not accepted and the requested action did
               not take place.  The User-process is discouraged from
               repeating the exact request (in the same sequence).  Even
               some "permanent" error conditions can be corrected, so
               the human user may want to direct his User-process to
               reinitiate the command sequence by direct action at some
               point in the future (e.g., after the spelling has been
               changed, or the user has altered his directory status.)

         The following function groupings are encoded in the second
         digit:

            x0z   Syntax - These replies refer to syntax errors,
                  syntactically correct commands that don't fit any
                  functional category, unimplemented or superfluous
                  commands.

            x1z   Information -  These are replies to requests for
                  information, such as status or help.

            x2z   Connections - Replies referring to the control and
                  data connections.

            x3z   Authentication and accounting - Replies for the login
                  process and accounting procedures.

            x4z   Unspecified as yet.

            x5z   File system - These replies indicate the status of the
                  Server file system vis-a-vis the requested transfer or
                  other file system action.

         The third digit gives a finer gradation of meaning in each of
         the function categories, specified by the second digit.  The
         list of replies below will illustrate this.  Note that the text



         associated with each reply is recommended, rather than
         mandatory, and may even change according to the command with
         which it is associated.  The reply codes, on the other hand,
         must strictly follow the specifications in the last section;
         that is, Server implementations should not invent new codes for
         situations that are only slightly different from the ones
         described here, but rather should adapt codes already defined.

            A command such as TYPE or ALLO whose successful execution
            does not offer the user-process any new information will
            cause a 200 reply to be returned.  If the command is not
            implemented by a particular Server-FTP process because it
            has no relevance to that computer system, for example ALLO
            at a TOPS20 site, a Positive Completion reply is still
            desired so that the simple User-process knows it can proceed
            with its course of action.  A 202 reply is used in this case
            with, for example, the reply text:  "No storage allocation
            necessary."  If, on the other hand, the command requests a
            non-site-specific action and is unimplemented, the response
            is 502.  A refinement of that is the 504 reply for a command
            that is implemented, but that requests an unimplemented
            parameter.

      4.2.1  Reply Codes by Function Groups

         200 Command okay.
         500 Syntax error, command unrecognized.
             This may include errors such as command line too long.
         501 Syntax error in parameters or arguments.
         202 Command not implemented, superfluous at this site.
         502 Command not implemented.
         503 Bad sequence of commands.
         504 Command not implemented for that parameter.
          
















         110 Restart marker reply.
             In this case, the text is exact and not left to the
             particular implementation; it must read:
                  MARK yyyy = mmmm
             Where yyyy is User-process data stream marker, and mmmm
             server's equivalent marker (note the spaces between markers
             and "=").
         211 System status, or system help reply.
         212 Directory status.
         213 File status.
         214 Help message.
             On how to use the server or the meaning of a particular
             non-standard command.  This reply is useful only to the
             human user.
         215 NAME system type.
             Where NAME is an official system name from the list in the
             Assigned Numbers document.
          
         120 Service ready in nnn minutes.
         220 Service ready for new user.
         221 Service closing control connection.
             Logged out if appropriate.
         421 Service not available, closing control connection.
             This may be a reply to any command if the service knows it
             must shut down.
         125 Data connection already open; transfer starting.
         225 Data connection open; no transfer in progress.
         425 Can't open data connection.
         226 Closing data connection.
             Requested file action successful (for example, file
             transfer or file abort).
         426 Connection closed; transfer aborted.
         227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
          
         230 User logged in, proceed.
         530 Not logged in.
         331 User name okay, need password.
         332 Need account for login.
         532 Need account for storing files.
          










         150 File status okay; about to open data connection.
         250 Requested file action okay, completed.
         257 "PATHNAME" created.
         350 Requested file action pending further information.
         450 Requested file action not taken.
             File unavailable (e.g., file busy).
         550 Requested action not taken.
             File unavailable (e.g., file not found, no access).
         451 Requested action aborted. Local error in processing.
         551 Requested action aborted. Page type unknown.
         452 Requested action not taken.
             Insufficient storage space in system.
         552 Requested file action aborted.
             Exceeded storage allocation (for current directory or
             dataset).
         553 Requested action not taken.
             File name not allowed.
         

      4.2.2 Numeric  Order List of Reply Codes

         110 Restart marker reply.
             In this case, the text is exact and not left to the
             particular implementation; it must read:
                  MARK yyyy = mmmm
             Where yyyy is User-process data stream marker, and mmmm
             server's equivalent marker (note the spaces between markers
             and "=").
         120 Service ready in nnn minutes.
         125 Data connection already open; transfer starting.
         150 File status okay; about to open data connection.
          


















         200 Command okay.
         202 Command not implemented, superfluous at this site.
         211 System status, or system help reply.
         212 Directory status.
         213 File status.
         214 Help message.
             On how to use the server or the meaning of a particular
             non-standard command.  This reply is useful only to the
             human user.
         215 NAME system type.
             Where NAME is an official system name from the list in the
             Assigned Numbers document.
         220 Service ready for new user.
         221 Service closing control connection.
             Logged out if appropriate.
         225 Data connection open; no transfer in progress.
         226 Closing data connection.
             Requested file action successful (for example, file
             transfer or file abort).
         227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
         230 User logged in, proceed.
         250 Requested file action okay, completed.
         257 "PATHNAME" created.
          
         331 User name okay, need password.
         332 Need account for login.
         350 Requested file action pending further information.
          
         421 Service not available, closing control connection.
             This may be a reply to any command if the service knows it
             must shut down.
         425 Can't open data connection.
         426 Connection closed; transfer aborted.
         450 Requested file action not taken.
             File unavailable (e.g., file busy).
         451 Requested action aborted: local error in processing.
         452 Requested action not taken.
             Insufficient storage space in system.
          











         500 Syntax error, command unrecognized.
             This may include errors such as command line too long.
         501 Syntax error in parameters or arguments.
         502 Command not implemented.
         503 Bad sequence of commands.
         504 Command not implemented for that parameter.
         530 Not logged in.
         532 Need account for storing files.
         550 Requested action not taken.
             File unavailable (e.g., file not found, no access).
         551 Requested action aborted: page type unknown.
         552 Requested file action aborted.
             Exceeded storage allocation (for current directory or
             dataset).
         553 Requested action not taken.
             File name not allowed.