Data Transfer Tools: ftp and lftp

This article provides information about FTP (File Transfer Protocol) as a data transfer tool. In particular:

• what is FTP?
• where and how can I use FTP on JASMIN?
• what are its limitations?

What is FTP?  

FTP  is a well-established transfer protocol enabling connections from a client to download files from, or upload files to, a server, although limited in security. A wide variety of client tools are available to the user, 2 implementations of which are available on the JASMIN transfer servers, although no server is provided. ftp is also the name of the basic FTP client program, see below.

Where and how can I use FTP on JASMIN?  

FTP can only be used as a client on JASMIN, to pull data from external FTP servers to local storage on JASMIN, for example a Group Workspace or your home directory. There is no FTP server within JASMIN providing the ability to upload files to these locations. Please use an alternative, more secure method instead. See other Data Transfer Tools such as scp/rsync/sftp, bbcp or GridFTP ( over SSH or using Globus)

On the transfer servers, you can use one of the installed FTP clients to download data from elsewhere. These are:

• ftp basic ftp client. Usage details
• lftp parallel-capable ftp client. Usage details

CEDA however runs 2 FTP servers within the JASMIN environment providing download-only access to the CEDA archive. Access to these is controlled by your CEDA account and any dataset-specific privileges which are associated with that account.

What are its limitations?  

• FTP was never designed as a secure protocol and has several limitations  affecting how it can be used safely within an environment like JASMIN.
• Some external sites offer anonymous FTP download. In this case, no username or password needs to be exchanged and (as long as the data resources do not need to be protected in any way) this can provide a simple but effective data transfer method.
• Few external sites now provide FTP access to protected data resources, hence many data-intensive institutions are now focussing on more sophisticated data delivery methods which can meet the demands of security and performance in a multi-user environment.

Basic client usage: ftp  

The ftp client is available on the transfer servers xfer*.jasmin.ac.uk and high-performance transfer servers hpxfer*.jasmin.ac.uk.

Example 1: Downloading a file to a location on JASMIN from a remote FTP server.

This involves setting up an interactive client session. Once logged in (in this case, using anonymous FTP), you use FTP commands to interact with the remote server and locate and download the data you require. The session is terminated with bye.

ftp someserver.somesite.ac.uk
Trying 123.456.78.123...
Connected to someserver.somesite.ac.uk (123.456.78.123).
220----------------------------------------------------------------------------
220-Welcome message from somesite.ac.uk
220----------------------------------------------------------------------------
220
Name (123.456.78.123:username): anonymous
331 Please specify the password.
Password:

Once connected, the prompt changes to ftp>:

230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
cd /sites/pub/testdir/
(out)(out)250-
250-This is the somesite ftp repository.
250-
250 Directory successfully changed.
get md5.sum
local: md5.sum remote: md5.sum
227 Entering Passive Mode.
150 Opening BINARY mode data connection for md5.sum (45 bytes).
226 Transfer complete.
45 bytes received in 0.00267 secs (16.83 Kbytes/sec)
bye
221 Goodbye.

Full details of commands available within an interactive session with the ftp client are available via the man page (man ftp).

Parallel-capable client usage: lftp  

The alternative client lftp is less verbose, but the basic workflow is the same.

lftp someserver.somesite.ac.uk

Once connected, the prompt changes to lftp and the name of the remote server:

cd /sites/pub/testdir
cd ok, cwd=/sites/pub/testdir/
get md5.sum
45 bytes transferred
bye

The interactive shell provided by lftp also benefits from tab completion and use of up/down arrows for command history.

In fact, lftp can also be used as an SFTP client, with the added benefit that it can handle multiple SFTP transfers in parallel.

In the following example, we connect to a remote SFTP server using the sftp:// syntax. Once logged in to the remote server, the prompt changes and you can enter lftp-specific commands like mirror, in this case with -P 4 as the option to use 4 sftp processes in parallel. Try other values but please consider other users so a suggested limit is 16.

lftp sftp://username@someserver.somesite.ac.uk
Password: (enter password when prompted)

mirror -P 4 sourcedata
bye

Note that if you’re connecting to a JASMIN transfer server in this way, then you would need to make your JASMIN private key available in an ssh agent locally, and you would not be prompted for the password.