File Transfer Protocol
- See file transfer protocol (disambiguation) and FTP (disambiguation) for alternative meanings.
The File Transfer Protocol (FTP) is a software standard for transferring computer files between machines with widely different operating systems. It belongs to the application layer of the Internet protocol suite.
FTP is an 8-bit client-server protocol, capable of handling any type of file without further processing, such as MIME or Uuencode. However, FTP has extremely high latency; that is, the time between beginning the request and starting to receive the required data can be quite long, and a sometimes-lengthy login procedure is required.
Overview FTP is commonly run on two ports, 20 and 21. Port 20 is a data stream which transfers the data between the client and the server. Port 21 is the control stream and is the port where commands are passed to the ftp server. While data is being transferred via the data stream, the control stream sits idle. This can cause problems with large data transfers through firewalls which time out sessions after lengthy periods of idleness. While the file may well be successfully transferred, the control session can be disconnected by the firewall, causing an error to be generated. The objectives of FTP are: - To promote sharing of files (computer programs and/or data).
- To encourage indirect or implicit use of remote computers.
- To shield a user from variations in file storage systems among different hostss.
- To transfer data reliably and efficiently.
Disadvantages are: - Passwords and file contents are sent in clear text, which can be intercepted by eavesdroppers.
- Multiple TCP/IP connections are used, one for the control connection, and one for each download, upload, or directory listing. Firewall software needs additional logic to account for these connections.
- It is hard to filter active mode FTP traffic on the client side by using a firewall, since the client must open an arbitrary port in order to receive the connection. This problem is largely resolved by using passive mode FTP.
- It is possible to abuse the protocol's built-in proxy features to tell a server to send data to an arbitrary port of a third computer.
FTP, though usable directly by a user at a terminal, is designed mainly for use by FTP client programs. Many sites that run FTP servers enable so-called "anonymous ftp". Under this arrangement, users do not need an account on the server. By default, the account name for the anonymous access is 'anonymous'. This account does not need a password. Although users are commonly asked to send their email addresses as their passwords for authentication, usually there is trivial or no verification, depending on the FTP server and its configuration.
FTP and web browsers Most recent web browsers and file managers can connect to FTP servers. This allows manipulation of remote files over FTP through an interface similar to that used for local files. This is done via an FTP URL, which takes the form ftp://<ftpserveraddress> (e.g., [1]). A password can optionally be given in the URL, e.g.:
ftp://<login>:<password>@<ftpserveraddress>. Most web-browsers require the use of passive mode FTP, which not all FTP servers are capable of handling.
Commands
! escape to the shell
$ execute macro
account send account command to remote server
append append to a file
ascii set ascii transfer type
bell beep when command completed
binary set binary transfer type
bye terminate ftp session and exit
case toggle mget upper/lower case id mapping
cd change remote working directory
cdup change remote working directory to parent directory
chmod change file permissions of remote file
close terminate ftp session
cr toggle carriage return stripping on ascii gets
delete delete remote file
debug toggle/set debugging mode
dir list contents of remote directory
disconnect terminate ftp session
form set file transfer format
get receive file
glob toggle metacharacter expansion of local file names
hash toggle printing '#' for each buffer transferred
help print local help information
idle get (set) idle timer on remote side
image set binary transfer type
lcd change local working directory
ls list contents of remote directory
macdef define a macro
mdelete delete multiple files
mdir list contents of multiple remote directories
mget get multiple files
mkdir make directory on the remote machine
mls list contents of multiple remote directories
mode set file transfer mode
modtime show last modification time of remote file
mput send multiple files
newer get file if remote file is newer than local file
nmap set templates for default file name mapping
nlist nlist contents of remote directory
ntrans set translation table for default file name mapping
open connect to remote tftp
prompt force interactive prompting on multiple commands
proxy issue command on alternate connection
sendport toggle use of PORT cmd for each data connection
put send one file
pwd print working directory on remote machine
quit terminate ftp session and exit
quote send arbitrary ftp command
recv receive file
reget get file restarting at end of local file
rstatus show status of remote machine
rhelp get help from remote server
rename rename file
reset clear queued command replies
restart restart file transfer at bytecount
rmdir remove directory on the remote machine
runique toggle store unique for local files
send send one file
site send site specific command to remote server
Try "rhelp site" or "site help" for more information
size show size of remote file
status show current status
struct set file transfer structure
system show remote system type
sunique toggle store unique on remote machine
tenex set tenex file transfer type
trace toggle packet tracing
type set file transfer type
user send new user information
umask get (set) umask on remote side
verbose toggle verbose mode
? print local help information
References The protocol is standardized in RFC 0959 by the IETF as: |
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