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INFO 321Server Technologies II
FTP
Material adapted from Dr. Randy Kaplan
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FTP
◊ FTP = File Transfer Protocol◊ What is it?
• A classic client-server application• Purpose: move data from computer A to
computer B and vice versa
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FTP
◊ What is it?• A client server application• A pair of programs• Allows two computers to communicate
to transfer information• A well defined protocol
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How It Works?
◊ The FTP server is started on a system and waits for incoming requests
◊ The user FTP program is started and the user initiates a transfer
◊ The local FTP program interprets the command and translates the command into the required form for the server
◊ The command is sent to the server
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How It Works?
◊ When the command is received by the FTP server it is decoded and acted upon
◊ The result is returned to the user FTP program over the data link
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FTP
File System
Server PI
Server DTP
User Interface
User PI
User DTP
File System
User
FTP Commands
FTP Replies
Data
Connection
Server FTP User FTP
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FTP
File System
Server PI
Server DTP
User Interface
User PI
User DTP
File System
User
FTP Commands
FTP Replies
Data
Connection
Server FTP User FTP
The server protocol interpreter "listens" on Port L for a connection from a user-PI and establishes a control communication connection. It receives standard FTP commands from the user-PI, sends replies, and governs the server-DTP.
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FTP
File System
Server PI
Server DTP
User Interface
User PI
User DTP
File System
User
FTP Commands
FTP Replies
Data
Connection
Server FTP User FTP
The data transfer process, in its normal "active" state, establishes the data connection with the "listening" data port. It sets up parameters for transfer and storage, and transfers data on command from its PI. The DTP can be placed in a "passive" state to listen for, rather than initiate a connection on the data port.
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FTP
File System
Server PI
Server DTP
User Interface
User PI
User DTP
File System
User
FTP Commands
FTP Replies
Data
Connection
Server FTP User FTP
The data transfer process "listens" on the data port for a connection from a server-FTP process. If two servers are transferring data between them, the user-DTP is inactive.
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FTP
File System
Server PI
Server DTP
User Interface
User PI
User DTP
File System
User
FTP Commands
FTP Replies
Data
Connection
Server FTP User FTP
The user protocol interpreter initiates the control connection from its port U to the server-FTP process, initiates FTP commands, and governs the user-DTP if that process is part of the file transfer.
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Launching FTP, version 1
◊ In order to use FTP, you need to know the name of a host that has an FTP server running
◊ Start from a terminal window or command prompt
◊ To initiate an FTP session and go to a specific server use ftp followed by the hostname• C:\ ftp host.site.tld
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Launching FTP, version 1
◊ After you enter this command, you will be asked for a user name and password
◊ For anonymous login, try• User name is ‘anonymous’• Password is ‘password’
◊ After you log in successfully, an FTP prompt will be displayed• ftp>
Launching FTP, version 2
◊ Or you can start FTP without a hostname• C:\> ftp
◊ When you do this, the FTP prompt is displayed• ftp>
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Launching FTP, version 2
◊ Then connect to an FTP server using the open command• ftp> open ftp-server-name• For example,
ftp> open ftp.sei.cmu.edu
◊ Log in to the server as shown on slide 12
FTP help!
◊ The local help information can be obtained within FTP using the command ? or help• ftp> ?• ftp> help• ftp> help commandname
◊ Help for the remote FTP server can be found with remotehelp• ftp> remotehelp
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Exiting FTP
◊ To log out from the current FTP server, use the disconnect or close commands• ftp> disconnect• ftp> close
◊ To exit FTP completely, enter the command quit or bye• ftp> quit• ftp> bye
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Transfer modes
◊ When transferring a file there are two modes in which a file transfer can occur
◊ ASCII• Transfer files in text mode (text or PDF
files)◊ BINARY
• Transfer files in binary mode (as a sequence of binary digits)
• Used for transferring executables and compressed files
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Transfer modes
◊ The command to set which data transfer mode is in use is ‘type’• ftp> type ascii• ftp> type binary
◊ Or those types are also standalone commands• ftp> ascii• ftp> binary
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Transferring Files
◊ In order to send one file from your computer to the FTP server (upload) use the command put or send• ftp> put filename• ftp> send filename
Transferring Files
◊ In order to transfer one file from the FTP server to your computer (download) use the command get or recv• ftp> get filename• ftp> recv filename
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Multiple file transfers
◊ Transferring multiple files• Sometimes you may wish to transfer a
group of files• You can accomplish this with the mget
command (download) or the mput command (upload)
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Multiple file transfers
◊ For example, if you enter the command• ftp> mget foo*
◊ Then all of the files whose name begin with foo will be downloaded
◊ Likewise to upload a group of files, use the command mput• ftp> mput bar*
◊ All of the files whose name begins with bar will be uploaded to the server
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Navigating in FTP
◊ When you use these commands (get, put) they assume that the activity will take place in the current directory on the FTP server
◊ To see what files are in the current FTP server (remote) directory you can use the command dir or ls• ftp> dir• ftp> ls
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Navigating in FTP
◊ You can change the directory on the remote FTP server by using the command cd• ftp> cd directoryname
◊ You can change the directory on your local computer while in the FTP client by using the command lcd• ftp> lcd directoryname
Navigating in FTP
◊ You can show the current remote directory with the pwd command• ftp> pwd
◊ Remote directories can be created or deleted (if you have permission) with mkdir or rmdir, respectively• ftp> mkdir foldername• ftp> rmdir foldername
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Shell commands
◊ Bang (!) is used to execute a command directly by the shell (outside of FTP)
◊ For example, if you enter• !cd downdir
◊ The cd command will be executed by the shell• This particular result will be the same as
using lcd – just to show the use of bang
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FTP Server Protocol
◊ In order to implement the FTP protocol, the server understands a set of commands issued by the FTP client• See http://ftpguide.com/index.htm
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FTP Protocol
◊ Client-Server Commands◊ Access Control Commands
• USER – accept user name• PASS – accept password• ACCT – set account information, usually tied to
USER• CWD – change working directory• CDUP – change to parent directory• SMNT – mount a different file system• REIN – reinitialize; terminate the session• QUIT – also terminates a session
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Access Control Commands
◊ USER• The USER commands identifies the user
to the server• This information is required to gain
access to the FTP server and the files that can be transferred
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Access Control Commands
◊ PASS• The PASS command will always follow
the USER command• It specifies a password to enable a user
to gain access to the FTP server
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Access Control Commands
◊ QUIT• This command terminates a session for
a user• If there is no transfer then the server
will close the control connection• If there is a transfer in progress, the
connection will remain open until a result
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FTP Protocol
◊ Client-Server Commands◊ Transfer Parameter Commands
• PORT – specify data port to be used• PASV – requests server to listen on a
given port• TYPE – same as the previous type
command• STRU – specifies the file structure code• MODE – set send/receive mode
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Transfer Parameter Commands
◊ TYPE• The TYPE command is used to specify
the type of data that will be transferred during a file transfer task
• The codes used in the command that specify the data type are as follows –A = ASCIIE = EBCDICI = IMAGE (Binary transfer)L = BYTE
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Transfer Parameter Commands
◊ MODE• The modes that are used to transfer
data areStreamBlockCompressed
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FTP Protocol◊ Client-Server Commands◊ FTP Service Commands
• RETR – transfer a file• STOR – accept incoming
data• STOU – accept unique file• APPE – append existing file• ALLO – allocate space• REST – set restart point• RNFR – rename from• RNTO – rename to• ABOR – abort previous cmd
• DELE – delete file• RMD – remove directory• MKD – make directory• PWD – print working dir.• LIST – transfer a list of
files• NLST – transfer list of file
names• SITE – set server services• SYST – identify server OS• STAT – send status• HELP – send command list • NOOP – a server ping
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FTP Service Commands
◊ RETR (Retrieve)• This command causes the server to
transfer a file to the computer at the other end of the connection
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FTP Service Commands
◊ STOR (Store)• Causes a file to be transferred from the
computer at the other end of the connection and store on the server
• If the file exists it is overwritten• If the file does not exist, it is created
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FTP Service Commands
◊ APPE (Append)• This command causes the server to
append data transferred from the computer at the other end of the connection to be appended to the named file on the server
• If the file exists, data is appended• If the file does not exists, the file is create
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FTP Service Commands
◊ RNFR (Rename from)• This is one of a pair of commands used
to rename a file• This command specifies the file that is
to be renamed• The command is immediately followed
by a RNTO command (Rename to)
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FTP Service Commands
◊ RNTO (Rename to)• The second of the rename commands• Specifies the new name of the file
◊ ABOR (Abort)• This command tells the server to stop
whatever it was doing; this includes aborting the last command and any data transfer associated with that command
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FTP Service Commands
◊ DELE (Delete file)• This command causes the named file to
be deleted from the server site
◊ RMD (Remove Directory)• This command causes the specified
directory to be removed from the server• The path can be absolute or relative
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FTP Service Commands
◊ MKD (Make directory)• This command creates the specified
directory on the server
◊ PWD (Print working directory)• Causes the current directory name to be
returned as the result (on the server)
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FTP Service Commands
◊ LIST (List)• If the pathname specifies a directory
then the files in the directory are transferred
• If the pathname specifies a group of files then the files specified are transferred
• If the pathname names a file then information about the file is sent
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FTP Service Commands
◊ STAT (Status)• Causes a status response to be send• If no argument is specified then the
server returns general information about the status of the server
• If the command is sent during a file transfer, the server will respond with the status of the transfer
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FTP Service Commands
◊ HELP• Causes the server to send helpful
information about the implementation over the connection
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FTP Protocol
◊ FTP Replies• The purpose of replies from the server
to the client is for the client to understand the precise status of the server after a request was made
• An FTP reply consists of –A 3 digit codeSome textHere are some examples
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Installing FTP (Server)
◊ Most OS that make FTP available, come with the FTP server installed
◊ For example, one of the package options during the Linux installation is FTP
◊ On Windows, the FTP server can be loaded as an optional piece of IIS software and then started
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Installing FTP (Windows)The FTP server is part of the IIS option in the Windows Components dialog.
This dialog is accessible through the control panel and Add/Remove Programs.
Installing FTP (Windows 2003)
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Windows FTP Services
◊ In order to check to see if your FTP services are running, in the Control Panel double click on Internet Information Services
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Windows FTP Services
◊ A control panel will be displayed
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Windows FTP Services
Click on FTP Sites
Make sure thestatus of the site is running
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Example
FTP into your own FTP server
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Example
Log in anonymously
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Example
Identify local and remote directories
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Example
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Example
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Example
◊ Why did this problem occur?• On the server side, permissions were
not set so that the anonymous log on could have access to the directory to store the file
◊ How do you fix it?
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Example
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Try to open this file …
◊ Why?
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Example
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On the server side …
◊ Try to open the file again …
FTP Summary
◊ So to use FTP effectively, need to know• Host FTP server• Login information (if not anonymous)• File location(s), both remotely and
locally• File types (binary or ascii)
