Domain
Name Service (DNS for short) is that magical protocol that allows your computer
to turn meaningless domain names like www.slackware.com into meaningful IP
address like 64.57.102.34. Computers can't route packets to www.slackware.com,
but they can route packets to that domain name's IP address. This gives us a
convenient way to remember machines. Without DNS we'd have to keep a mental
database of just what IP address belongs to what computer, and that's assuming
the IP address doesn't change. Clearly using names for computers is better, but
how do we map names to IP addresses?
host
can do this for us. host is used to map names to IP addresses. It is a very
quick and simple utility without a lot of functions.
|
www.slackware.com
is an alias for slackware.com.
slackware.com
has address 64.57.102.34
|
But
let's say for some reason we want to map an IP address to a domain name; what
then?
nslookup
is a tried and true program that has weathered the ages. nslookup has been
deprecated and may be removed from future releases. There is not even a man
page for this program.
|
% nslookup
64.57.102.34
Note: nslookup is deprecated and may be removed
from future releases.
Consider
using the `dig' or `host' programs instead.
Run nslookup with
the
`-sil[ent]' option to prevent this message from appearing.
Server: 192.168.1.254
Address: 192.168.1.254#53
Non-authoritative
answer:
www.slackware.com canonical name = slackware.com.
Name: slackware.com
Address:
64.57.102.34
|
The
meanest dog in the pound, the domain information groper, dig(1) for short, is
the go-to program for finding DNS information. dig can grab just about anything
from a DNS server including reverse lookups, A, CNAME, MX, SP, and TXT records.
dig has many command line options and if you're not familiar with it you should
read through it's extensive man page.
|
% dig
@192.168.1.254 www.slackware.com mx
;
<<>> DiG 9.2.2 <<>> @192.168.1.254 www.slackware.com
mx
;;
global options: printcmd
;;
Got answer:
;;
->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26362
;;
flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 2
;;
QUESTION SECTION:
;www.slackware.com. IN MX
;;
ANSWER SECTION:
www.slackware.com. 76634
IN CNAME slackware.com.
slackware.com. 86400 IN
MX 1 mail.slackware.com.
;;
AUTHORITY SECTION:
slackware.com. 86400 IN
NS ns1.cwo.com.
slackware.com. 86400 IN
NS ns2.cwo.com.
;;
ADDITIONAL SECTION:
ns1.cwo.com. 163033 IN
A 64.57.100.2
ns2.cwo.com. 163033 IN
A 64.57.100.3
;;
Query time: 149 msec
;;
SERVER: 192.168.1.254#53(192.168.1.254)
;;
WHEN: Sat Nov 6 16:59:31 2004
;;
MSG SIZE rcvd: 159
|
This
should give you an idea how dig works. “@192.168.1.254” specifies the dns
server to use. “www.slackware.com” is the domain name I am performing a lookup
on, and “mx” is the type of lookup I am performing. The above query tells me
that e-mail to www.slackware.com will instead be sent to mail.slackware.com for
delivery.
finger(1)
will retrieve information about the specified user. You give finger a username
or an email address and it will try to contact the necessary server and
retrieve the username, office, telephone number, and other pieces of
information. Here is an example:
|
% finger
johnc@idsoftware.com
|
finger
can return the username, mail status, phone numbers, and files referred to as
“dot plan” and “dot project”. Of course, the information returned varies with
each finger server. The one included with Slackware returns the following
information by default:
·
Username
·
Room number
·
Home phone number
·
Work phone number
·
Login status
·
Email status
·
Contents of the .plan file in the user's
home directory
·
Contents of the .project file in the
user's home directory
The first four items can be set with the
chfn command. It stores those values in the /etc/passwd file. To change the
information in your .plan or .project file, just edit them with your favorite
text editor. They must reside in your home directory and must be called .plan
and .project.
Many users finger their own account from
a remote machine to quickly see if they have new email. Or, you can see a
user's plan or current project.
Like many commands, finger has options.
Check the man page for more information on what special options you can use.
Someone
once stated that telnet was the coolest thing he had ever seen on computers.
The ability to remotely log in and do stuff on another computer is what
separates Unix and Unix-like operating systems from other operating systems.
telnet
allows you to log in to a computer, just as if you were sitting at the
terminal. Once your username and password are verified, you are given a shell
prompt. From here, you can do anything requiring a text console. Compose email,
read newsgroups, move files around, and so on. If you are running X and you
telnet to another machine, you can run X programs on the remote computer and
display them on yours.
To
login to a remote machine, use this syntax:
If
the host responds, you will receive a login prompt. Give it your username and
password. That's it. You are now at a shell. To quit your telnet session, use
either the exit command or the logout command.
* Telnet
does not encrypt the information it sends. Everything is sent in plain text,
even passwords. It is not advisable to use telnet over the Internet. Instead,
consider the Secure Shell(PKE). It encrypts all traffic and is available for
free.
Now
that we have convinced you not to use the telnet protocol anymore to log into a
remote machine, we'll show you a couple of useful ways to use telnet.
You
can also use the telnet command to connect to a host on a certain port.
|
% telnet
<hostname> [port]
|
This
can be quite handy when you quickly need to test a certain service, and you
need full control over the commands, and you need to see what exactly is going
on. You can interactively test or use an SMTP server, a POP3 server, an HTTP
server, etc. this way.
In
the next figure you'll see how you can telnet to a HTTP server on port 80, and
get some basic information from it.
Electronic
mail is one of the most popular things one can do on the Internet. In 1998, it
was reported that more electronic mail was sent than regular mail. It is indeed
common and useful.
Under
Slackware, we provide a standard mail server, and several mail clients. All of
the clients discussed below are text-based. A lot of Windows users may be
against this, but you will find that a text based client is very convenient,
especially when checking mail remotely. Fear not, there are many graphical
e-mail clients such as KDE's Kmail. If you wish to use one of those check its
help menu.
pine
is not elm. Or so the saying goes. The University of Washington
created their program for Internet news and email out of a need for an easy
mail reader for their students. pine is one of the most popular email clients
in use today and is available for nearly every flavor of Unix and even Windows.
elm
elm
is another popular text-based email client. Though not quite as user friendly
as pine, it's definitely been around a lot longer.
By
default, you are placed in your inbox. The messages are listed with the message
number, date, sender, and subject. Use the arrow keys to highlight the message
you want. Press Enter to read the message.
To
compose a new message, type m at the main screen. The d key will
flag a message for deletion. And the r key will reply to the current
message you are reading. All of these keys are displayed at the bottom of the
screen with a prompt.
The
man page discusses elm in more detail, so you will probably want to consult
that before using elm.
“All
mail clients suck. This one just sucks less.” mutt's original interface was
based on elm with added features found in other popular mail clients, resulting
in a hybrid mutt.
Some
of mutt's features include:
·
color support
·
message threading
·
MIME and PGP/MIME support
·
pop3 and imap support
·
support for multiple mailbox formats
(mbox, MMDF, MH, maildir)
·
highly
customizabl
nail is a command line driven mail
client. It is very primitive and offers pretty much nothing in the way of user
interfaces. However, mailx is handy for times when you need to quickly mail
something, scripting a bulk mailer, testing your MTA installation or something
similar. Note that Slackware creates symbolic links to nail at /usr/bin/mail
and /usr/bin/mailx. Any of these three commands executes the same program. In
fact, you will most likely see nail referred to as mail.
The basic command line is:
|
% mailx
<subject> <to-addr>
|
mailx reads the message body from
standard input. So you can cat a file into this command to mail it, or you can
just type text and hit Ctrl+D when finished with the message.
