Zen and the Art of Internet by Brendan P. Kehoe (best books to read .TXT) 📖

are vital to proper delivery.

Bounced Mail

When an email address is incorrect in some way (the system's name is wrong, the domain doesn't exist, whatever), the mail system will bounce the message back to the sender, much the same way that the Postal Service does when you send a letter to a bad street address. The message will include the reason for the bounce; a common error is addressing mail to an account name that doesn't exist. For example, writing to Lisa Simpson at Widener University's Computer Science department will fail, because she doesn't have an account. {Though if she asked, we'd certainly give her one.}

From: Mail Delivery Subsystem Date: Sat, 25 May 91 16:45:14 -0400 To: mg@gracie.com Cc: Postmaster@cs.widener.edu Subject: Returned mail: User unknown

----- Transcript of session follows ----- While talking to cs.widener.edu: >>> RCPT To:lsimpson@cs.widener.edu <<< 550 lsimpson@cs.widener.edu... User unknown 550 lsimpson... User unknown

As you can see, a carbon copy of the message (the Cc: header entry) was sent to the postmaster of Widener's CS department. The Postmaster is responsible for maintaining a reliable mail system on his system. Usually postmasters at sites will attempt to aid you in getting your mail where it's supposed to go. If a typing error was made, then try re-sending the message. If you're sure that the address is correct, contact the postmaster of the site directly and ask him how to properly address it.

The message also includes the text of the mail, so you don't have to retype everything you wrote.

----- Unsent message follows ----- Received: by cs.widener.edu id AA06528; Sat, 25 May 91 16:45:14 -0400 Date: Sat, 25 May 91 16:45:14 -0400 From: Matt Groening mg@gracie.com Message-Id: 9105252045.AA06528@gracie.com To: lsimpson@cs.widener.edu Subject: Scripting your future episodes Reply-To: writing-group@gracie.com

.... verbiage ...

The full text of the message is returned intact, including any headers that were added. This can be cut out with an editor and fed right back into the mail system with a proper address, making redelivery a relatively painless process.

Mailing Lists

People that share common interests are inclined to discuss their hobby or interest at every available opportunity. One modern way to aid in this exchange of information is by using a mailing list---usually an email address that redistributes all mail sent to it back out to a list of addresses. For example, the Sun Managers mailing list (of interest to people that administer computers manufactured by Sun) has the address sun-managers@eecs.nwu.edu. Any mail sent to that address will ``explode'' out to each person named in a file maintained on a computer at Northwestern University.

Administrative tasks (sometimes referred to as administrivia) are often handled through other addresses, typically with the suffix -request. To continue the above, a request to be added to or deleted from the Sun Managers list should be sent to sun-managers-request@eecs.nwu.edu.

When in doubt, try to write to the -request version of a mailing list address first; the other people on the list aren't interested in your desire to be added or deleted, and can certainly do nothing to expedite your request. Often if the administrator of a list is busy (remember, this is all peripheral to real jobs and real work), many users find it necessary to ask again and again, often with harsher and harsher language, to be removed from a list. This does nothing more than waste traffic and bother everyone else receiving the messages. If, after a reasonable amount of time, you still haven't succeeded to be removed from a mailing list, write to the postmaster at that site and see if they can help.

Exercise caution when replying to a message sent by a mailing list. If you wish to respond to the author only, make sure that the only address you're replying to is that person, and not the entire list. Often messages of the sort ``Yes, I agree with you completely!'' will appear on a list, boring the daylights out of the other readers. Likewise, if you explicitly do want to send the message to the whole list, you'll save yourself some time by checking to make sure it's indeed headed to the whole list and not a single person.

A list of the currently available mailing lists is available in at least two places; the first is in a file on ftp.nisc.sri.com called interest-groups under the netinfo/ directory. It's updated fairly regularly, but is large (presently around 700K), so only get it every once in a while. The other list is maintained by Gene Spafford (spaf@cs.purdue.edu), and is posted in parts to the newsgroup news.lists semi-regularly. (Usenet News, for info on how to read that and other newsgroups.)

Listservs

On BITNET there's an automated system for maintaining discussion lists called the listserv. Rather than have an already harried and overworked human take care of additions and removals from a list, a program performs these and other tasks by responding to a set of user-driven commands.

Areas of interest are wide and varied---ETHICS-L deals with ethics in computing, while ADND-L has to do with a role-playing game. A full list of the available BITNET lists can be obtained by writing to LISTSERV@BITNIC.BITNET with a body containing the command

list global

However, be sparing in your use of this---see if it's already on your system somewhere. The reply is quite large.

The most fundamental command is subscribe. It will tell the listserv to add the sender to a specific list. The usage is

subscribe foo-l Your Real Name

It will respond with a message either saying that you've been added to the list, or that the request has been passed on to the system on which the list is actually maintained.

The mate to subscribe is, naturally, unsubscribe. It will remove a given address from a BITNET list. It, along with all other listserv commands, can be abbreviated---subscribe as sub, unsubscribe as unsub, etc. For a full list of the available listserv commands, write to LISTSERV@BITNIC.BITNET, giving it the command help.

As an aside, there have been implementations of the listserv system for non-BITNET hosts (more specifically, Unix systems). One of the most complete is available on cs.bu.edu in the directory pub/listserv.

``I made this letter longer than usual because I lack the time to make it shorter.'' Pascal, Provincial Letters XVI

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: jm@south.america.org

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: jm@south.america.org 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