Internet RFC/STD/FYI/BCP Archives
Alternate Formats: rfc1635.txt | rfc1635.txt.pdf
Network Working Group P. Deutsch
Request for Comments: 1635 A. Emtage
FYI: 24 Bunyip
Category: Informational A. Marine
NASA NAIC
May 1994
How to Use Anonymous FTP
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
This document provides information for the novice Internet user about
using the File Transfer Protocol (FTP). It explains what FTP is,
what anonymous FTP is, and what an anonymous FTP archive site is. It
shows a sample anonymous FTP session. It also discusses common ways
files are packaged for efficient storage and transmission.
Acknowledgements
This document is the result of work done in the Internet Anonymous
FTP Archives (IAFA) working group of the IETF. Special thanks are
due to Mark Baushke (Cisco), John Curran (BBN), Aydin Edguer (CWRU),
Rafal Maszkowski (Onsala Space Observatory), Marsha Perrott
(PREPnet), Bob Peterson (Texas Instruments), Nathan Torkington
(Victoria University of Wellington), and Stephen Tihor (NYU) for
excellent comments and contributions.
What is FTP?
FTP refers to the File Transfer Protocol [1], one of the protocols
within the TCP/IP protocol suite used on the Internet. The File
Transfer Protocol makes it possible to transfer files from one
computer (or host) on the Internet to another. There are many FTP
implementations built on the specification of the FTP protocol. A
user of an FTP program must log in to both hosts in order to transfer
a file from one to the other.
It is common for a user with files on more than one host to use the
FTP program to transfer files from one host to another. In this
case, the user has an account on both hosts involved, so he has
passwords for both hosts.
However, Internet users may also take advantage of a wealth of
information available from archive sites by using a general purpose
account called "anonymous FTP".
What is an Archive Site?
An archive site is a host that acts as a repository of information,
much like a conventional library. Information stored on these
Internet hosts is made available for users to transfer to their local
sites. Users run software to identify this information and transfer
it to their own hosts. Such a transfer is done with a program that
implements the File Transfer Protocol (FTP).
What is Anonymous FTP?
Anonymous FTP is a means by which archive sites allow general access
to their archives of information. These sites create a special
account called "anonymous". User "anonymous" has limited access
rights to the archive host, as well as some operating restrictions.
In fact, the only operations allowed are logging in using FTP,
listing the contents of a limited set of directories, and retrieving
files. Some sites limit the contents of a directory listing an
anonymous user can see as well. Note that "anonymous" users are not
usually allowed to transfer files TO the archive site, but can only
retrieve files from such a site.
Traditionally, this special anonymous user account accepts any string
as a password, although it is common to use either the password
"guest" or one's electronic mail (e-mail) address. Some archive
sites now explicitly ask for the user's e-mail address and will not
allow login with the "guest" password. Providing an e-mail address
is a courtesy that allows archive site operators to get some idea of
who is using their services.
What Information Do You Need to Know?
To retrieve a specific file, a user needs to know what host it is on,
and the pathname of the file. A pathname tells the directory (and
possibly subdirectories) that house the file, and the name of the
file. Often discussions of available files will not specifically
say, "This file is available for anonymous FTP from X host with Y
pathname". However, if a file is publicly announced as available and
referred to as something like pub/good-stuff on nisc.sri.com, it is a
good assumption that you can try to transfer it.
You may also need to know if your machine uses an ASCII, EBCDIC, or
other character set to know how likely a transfer of binary
information will work, or whether such a transfer will require other
keywords, such as is true for TENEX.
In the general case, you may assume that an ASCII transfer will
always do the right thing for plain text files. However, more and
more information is being stored in various compressed formats (which
are discussed later in this document), so knowing the binary
characteristics of your machine may be important.
A Sample Session
To start an FTP session on a UNIX or VMS host, you type "ftp" and the
host name or host IP address of the machine to which you want to
connect. For example, if you wish to access the NASA Network
Applications and Information Center archive site, you would normally
execute one of the following commands at the UNIX prompt:
ftp naic.nasa.gov
or
ftp 128.102.128.6
Observe that the first form uses the fully-qualified domain name and
the second uses the Internet address for the same host.
The following is an example of connecting to the naic.nasa.gov host
to retrieve STD 9, RFC 959, "File Transfer Protocol (FTP)" [1].
Note several things about the session.
1. Every response the FTP program at the archive site gives
is preceded by a number. These numbers are called
Reply Codes and are defined in the FTP specification,
RFC 959. The text that accompanies these reply codes
can vary in different FTP implementations, and usually does.
Also note that some FTP client implementations (e.g., MVS
systems) may not echo the reply codes or text as
transmitted from the remote host. They may generate their
own status lines or just hide the non-fatal replies
from you. For the purposes of this document, the more
popular UNIX interface to the FTP client will be
presented.
2. The password you type is never shown on your screen.
3. It is possible to "browse" in archives, but most often users
already know the pathname of the file they want. The pathname
for RFC 959 on this host is files/rfc/rfc959.txt. In the
example, we first connect to the 'files/rfc' directory (cd
files/rfc), then get the specific file we know we want. If you
do not know the name of the file you want, a file called README
or something similar (00README.1ST, AAREAD.ME, INDEX, etc.) is
probably the one to retrieve first.
atlas.arc.nasa.gov% ftp naic.nasa.gov
Connected to naic.nasa.gov.
220 naic.nasa.gov FTP server (Wed May 4 12:15:15 PDT 1994) ready.
Name (naic.nasa.gov:amarine): anonymous
331 Guest login ok, send your complete e-mail address as password.
Password:
230-----------------------------------------------------------------
230-Welcome to the NASA Network Applications and Info Center Archive
230-
230- Access to NAIC's online services is also available through:
230-
230- Gopher - naic.nasa.gov (port 70)
230- World-Wide-Web - http://naic.nasa.gov/naic/naic-home.html
230-
230- If you experience any problems please send email to
230-
230- naic@nasa.gov
230-
230- or call +1 (800) 858-9947
230-----------------------------------------------------------------
230-
230-Please read the file README
230- it was last modified on Fri Dec 10 13:06:33 1993 - 165 days ago
230 Guest login ok, access restrictions apply.
ftp> cd files/rfc
250-Please read the file README.rfc
250- it was last modified on Fri Jul 30 16:47:29 1993 - 298 days ago
250 CWD command successful.
ftp> get rfc959.txt
200 PORT command successful.
150 Opening ASCII mode data connection for rfc959.txt (147316 bytes).
226 Transfer complete.
local: rfc959.txt remote: rfc959.txt
151249 bytes received in 0.9 seconds (1.6e+02 Kbytes/s)
ftp> quit
221 Goodbye.
atlas.arc.nasa.gov%
Variations
The above example is of the FTP program available on UNIX systems.
Other operating systems also make FTP programs available. The actual
commands you type may vary somewhat with other programs. However, in
general, you will do the following with every FTP program:
- Log in to your local host, and invoke the FTP program.
- Open a connection to the host (using either the host name
or its IP address)
- Once connected to the remote host, log in with username
"anonymous".
- Provide either the password "guest" or whatever the password the
site requests.
- Issue whatever FTP commands you require, such as those to
change directories or to retrieve a file.
- When finished, exit the FTP program, which will close your
connection to the archive host.
Friendly Servers
These days, many sites are using a form of FTP that allows them to
display several lines of explanatory text that help direct users
through their archive. The listing of alternative services on
naic.nasa.gov is an example. If these effusive servers confuse the
client you are using, try typing a hyphen ( - ) before your password
when you log in. That should disable the verbose mode of the server.
Other FTP Commands
We have demonstrated some of the commands available with FTP
programs. Many others are possible. For example, once you have
logged in to a remote host:
- You may ask the FTP program to display a list of available
commands, typically by invoking the FTP program without
arguments and typing "help".
- You may view the contents of the directory to which you are
connected. Type "dir" or "ls" to do so.
- You may rename a file by using the "get" command's
optional local file name, which follows the remote file
name on the command line. You probably should rename a
file when the remote file name exceeds your local file
system's naming constraints, e.g., if the remote file
name is too long. An example of using the "get" command
to rename a file when transferring it might be "get
really-long-named-file.txt short.txt".
- You may set BINARY mode to transfer executable programs or files
of data. Type "binary" to do so. Usually
FTP programs assume files use only 7 bits per byte, the norm for
standard ASCII-encoded files. The BINARY command allows you to
transfer files that use the full 8 bits per byte without error,
but this may have implications on how the file is transferred
to your local system.
If you are not sure what format a file is in, you may need to
transfer it a second time in the other mode (BINARY or ASCII)
if your first guess is wrong. The extension at the end of the
file name may give you a clue. File name extensions are
described below.
Because some machines store text files differently than others,
you may have to try your luck if you're not sure what format
a file is in. A good guess is to try ASCII mode first, if
you have grounds to suspect the file is a text file. Otherwise,
try BINARY mode. Try TENEX mode as a last resort.
- You may transfer multiple files at the same time. To set this
mode, type "mget". You then supply a file name pattern that
the remote system understands and it tries to transfer each
file in turn. If your local FTP user agent cannot transform
the remote file names into legal local file names, or if there
are some files that must be transferred in ASCII mode and others
that must be transferred in BINARY mode, you may not be able to
take advantage of this facility.
Full details on the commands and options available are in the FTP
documentation that comes with your system. You can also type "help"
at the FTP command prompt for a list of command options.
A copy of the UNIX version of the FTP documentation is available from
the online manual. If your UNIX site has the manuals installed, type
the following at the UNIX prompt:
% man ftp
The Packaging and Naming of Files
Several widely used conventions allow for efficient storage and
transmission of information stored at archive sites.
Information stored on archive sites is often "transformed" in three
common ways. "Compressing" (reducing the size of) the stored
information makes more space available on the archive, and reduces
the amount of data actually transferred across the network.
"Bundling" several files into one larger file maintains the internal
directory structure of the components, and allows users to transfer
only one larger object rather than several (sometimes hundreds) of
smaller files.
In addition, binary data is often converted into an ASCII format for
transmission, a process referred to in this document as
"transformation". Traditionally, Internet RFC 822-based electronic
mail and USENET protocols did not allow the transmission of "binary"
(8-bit) data; therefore, files in binary format had to be transformed
into printable 7-bit ASCII before being transmission.
On many systems, various file naming conventions are used to help the
remote user to determine the format of the stored information without
first having to retrieve the files. Below we list the more common
compression, bundling, and transformation conventions used on the
Internet. This list is not intended to be exhaustive. In all cases
public domain or freely-available implementations of the programs
associated with these mechanisms are available on the network.
1) compress/uncompress
Filenames terminating in ".Z" normally signify files that have been
compressed by the standard UNIX Lempel-Ziv "compress" utility.
There is an equivalent program called "uncompress" to reverse the
process and return the file to its original state. No bundling
mechanism is provided, and the resulting files are always in binary
format, regardless of the original format of the input data.
2) atob/btoa
Performs a transformation of ASCII to binary (atob) and the reverse
(btoa) in a standard format. Files so transformed often have
filenames terminated with ".atob". No bundling or compression
mechanisms are used.
3) atox/xtoa
A data transformation standard used to convert binary
files to transferable ASCII format. Sometimes used in
preference to other similar mechanisms because it is more
space efficient; however, it is not a compression
mechanism per se. It is just more efficient in the
transformation from one format to the other. Filenames of
files in this format often have the ".atox" extension.
4) uuencode/uudecode
Transforms binary to ASCII ("uuencode") and the reverse
("uudecode") transformation in a standard manner.
Originally used in the UUCP ("Unix to Unix CoPy")
mail/USENET system. No bundling or compression mechanisms
are used. Naming conventions often add a .uu at the end
of the file name.
5) tar/untar
Originally a UNIX based utility for bundling (and
unbundling) several files and directories into (and from)
a single file (the acronym stands for "Tape ARchive").
Standard format provides no compression mechanism. The
resulting bundled file is always in binary format
regardless of whether the constituent files are binary or
not. Naming conventions usually hold that the filename of
a "tarfile" contain the sequence ".tar" or "-tar".
6) zip/unzip
Often used in IBM PC environments, these complementary programs
provide both bundling and compression mechanisms. The resulting
files are always in binary format. Files resulting from the "zip"
program are by convention terminated with the ".zip" filename
extension.
7) arc/unarc
Often used in IBM PC environments, these complementary programs
provide both bundling and compression mechanisms. The resulting
files are always in binary format. Files stored in this format
often have a ".arc" filename extension.
8) binhex
Used in the Apple MacIntosh environment, the binhex
process provides bundling as well as binary to ASCII data
transformations. Files in this format by convention have
a filename extension of ".hqx".
9) shar
Bourse shell archives package text or binary files into a
single longer file which, when executed, will create the
component files. Because this format is vulnerable to
misuse, most users use a special tool called unshar to
decode these archives. By convention, files in this
format have a filename extension of ".shar".
10) VMS_SHARE
DCL archives package text or binary files into a single
longer file which, when executed, will created the
component files. Because this format is vulnerable to
misuse, care must be take to examine such an archive
before executing it. By convention, files in this format
have a filename extension of ".shar".
11) Multipart shar/vms_share files
Sometimes these shell archive files are broken into
multiple small parts to simplify their transfer over other
forms of fileservers that share the same archive tree. In
such cases, the parts of the files are usually suffixed
with a part number (e.g., xyz.01 xyz.02 xyz.03 ... or even
.01-of-05). Collect all the parts, concatenate them on
your local system, and then apply the procedure listed
above for a simple shar or vms_share file to the
concatenated file you just made.
12) zoo
The zoo program implements compression/decompression and
bundling/unbundling in a single program. Utilities
supporting the zoo format exist on a wide variety of
systems, including Unix, MS-DOS, Macintosh, OS/2, Atari
ST, and VAX VMS. Files created by the "zoo" programs by
convention end with the ".zoo" filename extension. Zoo is
a popular distribution format due to the availability of
free implementations (both source and executable code) on
a wide variety of operating systems.
13) gzip/gunzip
The Free Software Foundation GNU project adopted a variant
of the zip compression mechanism as a substitute for the
compress/uncompress commands. The resulting files are
always in binary format. Files resulting from the "gzip"
program are by convention terminated with the ".z" or
".gz" filename extensions. The gunzip program also
recognizes ".tgz" and ".taz" as shorthands for ".tar.z" or
".tar.Z". Also, gunzip can recognize and decompress files
created by the gzip, zip, compress, or pack commands.
The GNU project recently began distributing and using the
gzip/gunzip utilities. Even more recently they changed
the default suffix from .z to .gz, in an attempt to (1)
reduce confusion with .Z, and (2) eliminate a problem with
case-insensitive file systems such as MS-DOS. The gzip
software is freely redistributable and has been ported to
most UNIX systems, as well as Amiga, Atari, MSDOS, OS2,
and VMS systems.
In some cases, a series of the above processes are performed to
produce the final file as stored on the archive. In cases where
multiple transformation processes have been used, tradition holds
that the original (base) filename be changed to reflect these
processes, and that the associated filename extensions be added in
the order in which the processes were performed. For example, a
common procedure is first to bundle the original files and
directories using the "tar" process, then to "compress" the bundled
file. Starting with a base file name of "foobar", the file name in
the archive would become "foobar.tar.Z". As this is a binary file,
it would require a further transformation into printable ASCII by a
program such as "uuencode" in order to be transmitted over
traditional email or USENET facilities, so it might finally be called
"foobar.tar.Z.uu."
Some operating systems can not handle multiple periods; in such cases
they are often replaced by hyphen ( - ), underscore ( _ ), or by
detailed instructions in the "read me" files in the directories.
Compress and Tar
Here is an example of the use of the "compress/uncompress" and
"tar/untar" programs.
Suppose "patch" is a useful public domain program for applying
program patches and updates. You find this file at an archive site
as "patch.tar.Z". Now you know that the ".Z" indicates that the file
was compressed with the UNIX "compress" command, and the ".tar"
indicates that it was tar'ed using the UNIX "tar" tape archive
command.
First retrieve the file onto your machine using anonymous FTP. To
unpack this program, you would first uncompress it by typing:
uncompress patch.tar.Z
This will uncompress the file, and in the process, rename it to
"patch.tar". You can then execute the "tar" command to extract the
individual files.
In the example of patch.tar, you could invoke the command as:
%tar xvf patch.tar
The files would be extracted (that's the 'x' argument to tar) from
the file patch.tar (that's the 'f' argument). Because we use the 'v'
(for verbose) argument, the name of each file is printed as it is
extracted. When tar is complete you should have all the files that
make up the "patch" program in your working directory.
Etiquette
Not every site that supports FTP permits anonymous tranfers. It is
wrong to try to get files from systems that have not advertised the
availability of such a service.
Remember that Internet site administrators for archive sites have
made their systems available out of a sense of community. Rarely are
they fully compensated for the time and effort it takes to administer
such a site. There are some things users can do to make their jobs
somewhat easier, such as checking with local support personnel first
if problems occur before asking the archive administrator for help.
Most archive machines perform other functions as well. Please
respect the needs of their primary users and restrict your FTP access
to non-prime hours (generally between 1900 and 0600 hours local time
for that site) whenever possible. It is especially important to
remember this for sites located on another continent or across a
significant body of water because most such links are relatively slow
and heavily loaded.
In addition, some sites offering anonymous FTP limit the number of
concurrent anonymous FTP logins. If your attempt to log onto such a
site results in an error message to the effect that too many
anonymous FTP users are online, you should wait a while before
attempting another connection rather than retrying immediately.
To reduce redundant storage, you should find out how to make useful
the files you fetch using FTP available to your entire organization.
If you retrieve and test a program that turns out to be useful, you
should probably ask your administrator to consider making the program
generally available, which will reduce the redundant effort and disk
space resulting from multiple individuals installing the same package
in their personal directories.
If you find an interesting file or program on an archive site, tell
others about it. You should not copy the file or program to your own
archive unless you are willing to keep your copy current.
References
[1] Postel, J., and J. Reynolds, "File Transfer Protocol (FTP)", STD
9, RFC 959, USC/Information Sciences Institute, October 1985.
Security Considerations
Security issues are not discussed in this memo.
Authors' Addresses
Peter Deutsch
Bunyip Information Systems
266 Blvd. Neptune
Dorval, Quebec, H9S 2L4
Canada
Phone: (514) 398-3709
EMail: peterd@bunyip.com
Alan Emtage
Bunyip Information Systems
266 Blvd. Neptune
Dorval, Quebec, H9S 2L4
Canada
Phone: (514) 398-3709
EMail: bajan@bunyip.com
April N. Marine
NASA NAIC
M/S 204-14
Ames Research Center
Moffett Field, CA 94035-1000
Phone: (415) 604-0762
EMail: amarine@atlas.arc.nasa.gov