Resource Library: Multimedia/Resource Library: Multimedia.iso/hypertxt/msdos/montanac/ftp

Text File | 1993-03-08 | 12KB | 321 lines

Extracted from Brendan Kehoe's ZEN AND THE ART OF THE INTERNET  <PERMIT.ZEN>

 Anonymous FTP

FTP (File Transfer Protocol) is the primary method of transferring
files over the Internet.  On many systems, it's also the name of the
program that implements the protocol. Given proper permission, it's
possible to copy a file from a computer in South Africa to one in Los
Angeles at very fast speeds (on the order of 5--10K per second).
This normally requires either a user id on both systems or a special
configuration set up by the system administrator(s).

There is a good way around this restriction---the anonymous FTP
service.  It essentially will let anyone in the world have access to
a certain area of disk space in a non-threatening way.  With this,
people can make files publicly available with little hassle.  Some
systems have dedicated entire disks or even entire computers to
maintaining extensive archives of source code and information.  They
include gatekeeper.dec.com (Digital), wuarchive.wustl.edu (Washington
University in Saint Louis), and archive.cis.ohio-state.edu (The Ohio
State University).

The process involves the ``foreign'' user (someone not on the system
itself) creating an FTP connection and logging into the system as the
user anonymous, with an arbitrary password:

Name (foo.site.com:you): anonymous
Password: [e-mail]

Custom and netiquette dictate that people respond to the
Password: query with an email address so that the sites can
track the level of FTP usage, if they desire.  (Addresses for
information on email addresses).

The speed of the transfer depends on the speed of the underlying
link. A site that has a 9600bps SLIP connection will not get the same
throughput as a system with a 56k leased line (The Physical
Connection, for more on what kinds of connections can exist in a
network).  Also, the traffic of all other users on that link will
affect performance.  If there are thirty people all FTPing from one
site simultaneously, the load on the system (in addition to the
network connection) will degrade the overall throughput of the
transfer.

FTP Etiquette

Lest we forget, the Internet is there for people to do work.  People
using the network and the systems on it are doing so for a purpose,
whether it be research, development, whatever.  Any heavy activity
takes away from the overall performance of the network as a whole.

The effects of an FTP connection on a site and its link can vary; the
general rule of thumb is that any extra traffic created detracts from
the ability of that site's users to perform their tasks.  To help be
considerate of this, it's highly recommended that FTP sessions
be held only after normal business hours for that site, preferably
late at night.  The possible effects of a large transfer will be less
destructive at 2 a.m. than 2 p.m.  Also, remember that if it's past
dinner time in Maine, it's still early afternoon in California---think
in terms of the current time at the site that's being visited, not of
local time.

Basic Commands

While there have been many extensions to the various FTP clients out
there, there is a de facto ``standard'' set that everyone expects to
work.  For more specific information, read the manual for your
specific FTP program.  This section will only skim the bare minimum of
commands needed to operate an FTP session.

 Creating the Connection

The actual command to use FTP will vary among operating systems; for
the sake of clarity, we'll use FTP here, since it's the most
general form.

There are two ways to connect to a system---using its hostname
or its Internet number.  Using the hostname is usually preferred.
However, some sites aren't able to resolve hostnames properly,
and have no alternative.  We'll assume you're able to use hostnames
for simplicity's sake.  The form is

ftp somewhere.domain

Domains for help with reading and using domain names
(in the example below, somewhere.domain is ftp.uu.net).

You must first know the name of the system you want to connect to.
We'll use ftp.uu.net as an example.  On your system, type:

ftp ftp.uu.net

 (the actual syntax will vary depending on the type of system the
connection's being made from).  It will pause momentarily then respond
with the message

Connected to ftp.uu.net.

and an initial prompt will appear:

220 uunet FTP server (Version 5.100 Mon Feb 11 17:13:28 EST 1991) ready.
Name (ftp.uu.net:jm):

to which you should respond with anonymous:

220 uunet FTP server (Version 5.100 Mon Feb 11 17:13:28 EST 1991) ready.
Name (ftp.uu.net:jm): anonymous

The system will then prompt you for a password; as noted previously, a
good response is your email address:

331 Guest login ok, send ident as password.
Password: [e-mail]
230 Guest login ok, access restrictions apply.
ftp>

The password itself will not echo.  This is to protect a user's
security when he or she is using a real account to FTP files between
machines.  Once you reach the ftp> prompt, you know you're
logged in and ready to go.

Notice the ftp.uu.net:joe in the Name: prompt?  That's
another clue that anonymous FTP is special: FTP expects a normal user
accounts to be used for transfers.

 dir
At the ftp> prompt, you can type a number of commands to perform
various functions.  One example is dir---it will list the files
in the current directory. Continuing the example from above:

ftp> dir

200 PORT command successful.
150 Opening ASCII mode data connection for /bin/ls.
total 3116
drwxr-xr-x  2 7        21            512 Nov 21  1988 .forward
-rw-rw-r--  1 7        11              0 Jun 23  1988 .hushlogin
drwxrwxr-x  2 0        21            512 Jun  4  1990 Census
drwxrwxr-x  2 0        120           512 Jan  8 09:36 ClariNet
                ... etc etc ...
-rw-rw-r--  1 7        14          42390 May 20 02:24 newthisweek.Z
                ... etc etc ...
-rw-rw-r--  1 7        14        2018887 May 21 01:01 uumap.tar.Z
drwxrwxr-x  2 7        6            1024 May 11 10:58 uunet-info

226 Transfer complete.
5414 bytes received in 1.1 seconds (4.9 Kbytes/s)
ftp>

The file newthisweek.Z was specifically included because we'll
be using it later.  Just for general information, it happens to be a
listing of all of the files added to UUNET's archives during the past
week.

The directory shown is on a machine running the Unix operating
system---the dir command will produce different results on other
operating systems (e.g. TOPS, VMS, et al.).  Learning to recognize
different formats will take some time.  After a few weeks of
traversing the Internet, it proves easier to see, for example, how
large a file is on an operating system you're otherwise not acquainted
with.

With many FTP implementations, it's also possible to take the output
of dir and put it into a file on the local system with

ftp> dir n* outfilename

the contents of which can then be read outside of the live FTP
connection; this is particularly useful for systems with very long
directories (like ftp.uu.net).  The above example would put the
names of every file that begins with an n into the local file
outfilename.

 cd

At the beginning of an FTP session, the user is in a ``top-level''
directory.  Most things are in directories below it (e.g. /pub).  To
change the current directory, one uses the cd command.  To change to
the directory pub, for example, one would type

ftp> cd pub

which would elicit the response

250 CWD command successful.

Meaning the ``Change Working Directory'' command (cd) worked
properly.  Moving ``up'' a directory is more system-specific---in Unix
use the command cd .., and in VMS, cd [-].

 get and put

The actual transfer is performed with the get and put
commands.  To get a file from the remote computer to the local
system, the command takes the form:

ftp> get filename

where filename is the file on the remote system.  Again using
ftp.uu.net as an example, the file newthisweek.Z can be
retrieved with

ftp> get newthisweek.Z
200 PORT command successful.
150 Opening ASCII mode data connection for newthisweek.Z (42390 bytes).
226 Transfer complete.
local: newthisweek.Z remote: newthisweek.Z
42553 bytes received in 6.9 seconds (6 Kbytes/s)
ftp>

The section below on using binary mode instead of ASCII will describe
why this particular choice will result in a corrupt and subsequently
unusable file.

If, for some reason, you want to save a file under a different name
(e.g. your system can only have 14-character filenames, or can only
have one dot in the name), you can specify what the local filename
should be by providing get with an additional argument

ftp> get newthisweek.Z uunet-new

which will place the contents of the file newthisweek.Z in
uunet-new on the local system.

The transfer works the other way, too.  The put command will
transfer a file from the local system to the remote system.  If the
permissions are set up for an FTP session to write to a remote
directory, a file can be sent with

ftp> put filename

As with get, put will take a third argument, letting you
specify a different name for the file on the remote system.

 ASCII vs Binary

In the example above, the file newthisweek.Z was transferred, but
supposedly not correctly.  The reason is this: in a normal ASCII
transfer (the default), certain characters are translated between
systems, to help make text files more readable.  However, when binary
files (those containing non-ASCII characters) are transferred, this
translation should not take place.  One example is a binary
program---a few changed characters can render it completely useless.

To avoid this problem, it's possible to be in one of two modes---ASCII
or binary.  In binary mode, the file isn't translated in any way.
What's on the remote system is precisely what's received.  The
commands to go between the two modes are:

ftp> ascii
200 Type set to A.   (Note the A, which signifies ASCII mode.)

ftp> binary
200 Type set to I.   (Set to Image format, for pure binary transfers.)


Note that each command need only be done once to take effect; if the
user types binary, all transfers in that session are done in
binary mode (that is, unless ascii is typed later).

The transfer of newthisweek.Z will work if done as:

ftp> binary
200 Type set to I.
ftp> get newthisweek.Z
200 PORT command successful.
150 Opening BINARY mode data connection for newthisweek.Z (42390 bytes).
226 Transfer complete.
local: newthisweek.Z remote: newthisweek.Z
42390 bytes received in 7.2 seconds (5.8 Kbytes/s)


Note: The file size (42390) is different from that done
in ASCII mode (42553) bytes; and the number 42390 matches the one
in the listing of UUNET's top directory.  We can be relatively sure
that we've received the file without any problems.

 mget and mput

The commands mget and mput allow for multiple file
transfers using wildcards to get several files, or a whole set of
files at once, rather than having to do it manually one by one.  For
example, to get all files that begin with the letter f, one
would type

ftp> mget f*

Similarly, to put all of the local files that end with .c:

ftp> mput *.c

Rather than reiterate what's been written a hundred times before,
consult a local manual for more information on wildcard matching
(every DOS manual, for example, has a section on it).

Normally, FTP assumes a user wants to be prompted for every file in a
mget or mput operation.  You'll often need to get a whole set of
files and not have each of them confirmed---you know they're all
right.  In that case, use the prompt command to turn the queries off.

ftp> prompt
Interactive mode off.

Likewise, to turn it back on, the prompt command should simply
be issued again.

Joe Granrose's List
Monthly, Joe Granrose ([e-mail]) posts to Usenet
(Usenet News) an extensive list of sites offering anonymous FTP
service.  It's available in a number of ways:

The Usenet groups comp.misc and comp.sources.wanted

Anonymous FTP from pilot.njin.net [128.6.7.38], in
/pub/ftp-list.

Write to [e-mail] with a Subject: line of listserv-request
and a message body of send help.  Please don't bother Joe with your
requests---the server will provide you with the list.