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FTP Internal Protocol Commands and Command Groups
(Page 2 of 2)
FTP Protocol Commands
Since the commands are based on the
Telnet specifications, they are just sent as plain text as specified
by Telnet's Network
Virtual Terminal (NVT) conventions. I
have provided below three tables that describe the FTP internal protocol
commands in the order that they appear in the FTP standard (RFC 959).
Table 225
covers FTP access control commands, Table 226
lists transfer parameter commands, and Table 227
service commands.
Table 225: FTP Access Control Commands
Command
Code
|
Command
|
Description
|
USER
|
User Name
|
Identifies the user attempting
to establish an FTP session.
|
PASS
|
Password
|
Specifies the
password for the user given previously by the USER command during
login authentication.
|
ACCT
|
Account
|
Specifies an account for an authenticated
user during the FTP session. Only used on systems that require this
to be separately identified; most select an account automatically based
on the name entered in the USER command.
|
CWD
|
Change
Working Directory
|
Allows the
user to specify a different directory for file transfer during an FTP
session.
|
CDUP
|
Change To
Parent Directory (Change Directory Up)
|
A special case of the CWD command
that goes to the directory one level up in the server's directory structure.
It is implemented separately to abstract out differences in directory
structures between file systems; the user can just use CDUP instead
of knowing the specific syntax for navigating up the directory tree
on the server.
|
SMNT
|
Structure
Mount
|
Allows the
user to mount a particular file system for access to different resources.
|
REIN
|
Reinitialize
|
Reinitializes the FTP session,
flushing all set parameters and user information. This returns the session
to the state when the control connection is just established. It is,
in essence, the opposite of the USER command. The next command
issued is often USER, to log in a different user.
|
QUIT
|
Logout
|
Terminates
the FTP session and closes the control connection.
Note that the naming of this command Logout was unfortunate;
the REIN command is really most similar to a conventional logout
command, as it terminates a logged-in user and allows another user to
log in. In contrast, the QUIT command shuts down the entire session.
|
Table 226: FTP Transfer Parameter Commands
Command
Code
|
Command
|
Description
|
PORT
|
Data Port
|
Used to tell the FTP server that
the client wants to accept an active data connection on a specific port
number.
|
PASV
|
Passive
|
Requests that
the FTP server allow the User-DTP to initiate passive data connections.
|
TYPE
|
Representation
Type
|
Specifies for the file to be
transferred the data type (ASCII, EBCDIC, Image or Local), and optionally
the format control (Non Print, Telnet or Carriage Control).
|
STRU
|
File
Structure
|
Specifies the
data structure for the file (File, Record or Page).
|
MODE
|
Transfer
Mode
|
Specifies the transmission mode
to be used (Stream, Block or Compressed).
|
Table 227: FTP Service Commands
Command
Code
|
Command
|
Description
|
RETR
|
Retrieve
|
Tells the server to send the
user a file.
|
STOR
|
Store
|
Sends a file
to the server.
|
STOU
|
Store Unique
|
Like STOR, but instructs the
server to make sure the file has a unique name in the current directory.
This is used to prevent overwriting a file that may already exist with
the same name. The server replies back with the name used for the file.
|
APPE
|
Append
(with Create)
|
Like STOR,
but if a file with the name specified already exists, the data being
sent is appended to it instead of replacing it.
|
ALLO
|
Allocate
|
An optional command used to reserve
storage on the server before a file is sent.
|
REST
|
Restart
|
Restarts a
file transfer at a particular server marker. Used only for Block
or Compressed transfer modes.
|
RNFR
|
Rename From
|
Specifies the old name of a file
to be renamed. See the RNTO command just below.
|
RNTO
|
Rename
To
|
Specifies the
new name of a file to be renamed. Used with the RNFR command.
|
ABOR
|
Abort
|
Tells the server to abort the
last FTP command and/or the current data transfer.
|
DELE
|
Delete
|
Deletes a specified
file on the server.
|
RMD
|
Remove Directory
|
Deletes a directory on the server.
|
MKD
|
Make
Directory
|
Creates a directory.
|
PWD
|
Print Working
Directory
|
Displays the current server working
directory for the FTP session; shows the user where they are
in the server's file system.
|
LIST
|
List
|
Requests a
list of the contents of the current directory from the server, including
both names and other information. Similar in concept to the DIR
command in DOS/Windows or the ls command in UNIX.
|
NLST
|
Name List
|
Like LIST, but returns
only the names in a directory.
|
SITE
|
Site
Parameters
|
Used to implement
site-specific functions.
|
SYST
|
System
|
Requests that the server send
to the client information about the server's operating system.
|
STAT
|
Status
|
Prompts the
server to send an indication of the status of a file or the transfer
currently in progress.
|
HELP
|
Help
|
Asks the server for any help
information that might be useful in allowing the user to determine how
the server should be used.
|
NOOP
|
No
Operation
|
Does nothing,
other than prompting the server to send an OK response to
verify that the control channel is alive.
|
Note: FTP commands are not case-sensitive, but have been shown in upper case for clarity.
|
FTP commands are all sent between
FTP protocol elements; they are not usually issued directly by users.
Instead, a special set of user
commands is employed for this purpose.
The FTP user interface implements the link between the user and the
User-FTP process, including the translation of user commands into FTP
protocol commands.
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Version 3.0 - Version Date: September 20, 2005
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