The Internet is a world wide network connecting hundreds of regional networks, which in turn connect hundreds of thousands of local area and wide area networks. Communications among users on the Internet, and by users to remote computer databases, is accomplished easily with a widely available set of software tools. This tutorial is intended to introduce you to some of these many tools for communicating with users and online services throughout the Internet. It will also serve as an introduction to some of the online services themselves. It is important to note that as the services undergo changes, some of the specific addresses we note within this document may change.
An excellent reference for this material is the NYSERNet New User's Guide to Useful and Unique Resources on the Internet, which was a source of some of the information appearing in this document. It is available from the UCC at Taylor Hall for the cost of printing. Additional references for this material would include Sun's Using The Network: Beginner Guide, and the Unix manual pages on the software tools discussed in the following sections.
The symbols [RETURN] and [CR] both mean that you are to press the carriage return key on your keyboard. The symbol [ESCAPE] means that you are to press the escape key on your keyboard. The symbol [CONTROL-x] means that you should hold down the control key while pressing the x key.
The UR has a Gigabit backbone (often refered to as the ELAN) that connects systems within the UR). This in turn has multiple redundant highspee connections to the larger Internet.
Due to security concerns, the UR (ITS/NCS) blocks some forms of connections at the border between the UR and the Internet.
Sometimes you may need to move a file (or several files) from one machine to another. Or you may need to give a copy of your files to somebody else. In either case, your task is to cause a copy of your file to be moved across the network to another machine or account.
In this section, we'll talk about a few ways to accomplish this.
Rcp stands for remote copy. Rcp is intended to make it easy to copy a file between two machines on which you have an account. The syntax is similar to that of cp, but you can specify a machine- name as part of the source and/or destination pathname.
The name of a file can be preceded with the name of a computer and a ":". For example "oz.che:list.txt" specifies the file named list.txt in your home directory on oz (assuming that you have the same username on oz).
So you could say:
rcp list.txt oz.che.rochester.edu:list.txt
which would copy list.txt from whatever machine you're logged onto, to your home directory on oz. Similarly:
rcp oz.che.rochester.edu:list.txt list.txt
would copy list.txt from your home directory on oz to your current directory on whatever machine you're logged into. Please note though - you do NOT need to do this for files in your home directory. Your home directory is the same on all UNIX systems on the HSEAS production network. In other words, the file you are trying to copy already exists and is in fact the same object.
Rcp doesn't know how to prompt you for a username or password. So rcp works best if your username is the same on both machines, and both machines "trust" each other. In general, HSEAS machines are configured to trust other machines in the same department.
Ftp stands for
To run ftp, issue the command "ftp" followed by the name of the computer to
exchange files with. E.g., to transfer files to/from the host
blurf.blarf.com - assuming you had an account there -
Ftp will attempt to establish communications with the other computer. Once
it has contacted the other computer, ftp will prompt you for the username
and the password of the account on the other computer you want to use for
transferring files. Once you're "logged on" to the other computer, ftp will
prompt you for your next command.
Some of the commands you can issue are:
In addition, it's possible for the system manager of the remote machine to
configure it to allow anybody to login and transfer files to/from a special
directory. This is known as "anonymous ftp". If the remote machine is
configured for anonymous ftp, use the username anonymous, and use your email
address as your password. Note that the username anonymous is only valid for
ftp, e.g. you can't telnet to that machine and login as "anonymous".
Remember that you're a guest when you use anonymous ftp.
There are lots of other commands available in ftp. Look at the man page for
more details.
You can also use electronic mail to transfer text files around. Mail is a
convenient method to transfer text to another account either locally, or on
another machine. When the recipient receives your mail, they will need to
save it to a file, and then edit out the header that mail prepends to a
file.
Mail can only transfer text files (also known as ASCII files). Before
sending a non-text file, such as an executable program or an image file, it
is necessary to translate the file into text. The program uuencode can
translate non-text files into text; the companion program uudecode undoes
the translation, producing the original file.
Fortunately, most modern mail programs, even the text-based mailers like
Pine, have the ability to easily handle 'metamail' (mail that is more
than just simple text). These mailers can automatically "attach"
non-text files (e.g., images, sound files, executables, moives, etc.),
performing the binary-to-ascii-text encoding (and decoding) for you.
Most MacOS and Windows mailers (Eudora, Outlook) and most GUI mailers
(Thunderbird, Netscape) of course do this quite well.
Another form of communication is to actually login to another computer and
use it interactively. There are several methods available to do this from
the HSEAS Unix computers.
Rlogin will attempt to open an interactive session with the computer
machine-name. By default, it will attempt to log you in to the remote
computer using your current username. Depending on how the remote computer
is configured, rlogin may prompt you for your password on the remote
machine. If the account you wish to login to has a different username than
your account on the local machine, use the -l option to specify your account
on the remote computer.
Rlogin will terminate when you logout from the remote computer. In addition,
rlogin recognizes some command sequences that are similar to the "~"
sequences in mail. If a new line begins with a "~", the next character is
interpreted as a command. The command "~.", will cause rlogin to log you out
from the remote host and terminate. You can push rlogin into the background
by issuing the command "~[Control-z]".
Rsh will attempt to login to the remote computer machine-name, and execute
the command unix-command on the remote computer for you. If there is any
output from the command, it will print on your screen. Interactive
commands, such as editors, will not work with rsh.
If you invoke rsh without specifying a command to execute, rsh will simply
start a shell on the remote computer, effectively logging you in to the
remote computer in the same manner as rlogin.
We'll tell you about telnet here for historical completeness and because
you may need it to connect to some types of remote sytems. But -
whenever possible, avoid using telnet. It is a very old method of
connecting to systems, and it has many serious flaws, including serious
security flaws. Rlogin/rsh are much better than telnet, and SecureShell
is even better. We strongly recommend you use a SecureShell client when
connecting to HSEAS computers from outside of HSEAS. Many UR departments
have already turned off telnet access to their systems; we are
considering disabling incoming telnet as well.
Telnet? Just say no!
Telnet will establish a terminal connection over the network, in much the
same way that rlogin does. Telnet is more general then rlogin. For example,
while rlogin only works between two computers running Unix, telnet will
allow for connections to many computers which don't run Unix.
Telnet will open a connection with the remote computer named machine-name.
When you logout from the remote computer, telnet will terminate.
The [Control-]] character will put you into telnet's command mode. Type
"help" for a list of commands available in telnet's command mode.
A related program, tn3270, allows for a telnet-like connection to IBM
mainframe computers running the VM operating system.
SecureShell is a telnet/rlogin/rsh replacement that has two things going
for it. First, it is a much better facility (especially on Windows;
Windows telnet clients are horrible. The SecureSHell clients are much
better). Second, it is much more secure. For telnet - and for
rlogin/rsh to un-trusted hosts - your password is passed over the
network in clear text. Anyone with the ability to examine traffic on the
network (which is not hard to do) can capture your password and login
name - and thus have access to anything you do. SecureShell (ssh)
encrypts traffic between the two hosts; someone "sniffing" network
traffic will have a lot of hard work to break that encryption. In
addition, ssh can tunnel X-window traffic nicely. We have more
infomration on SecureShell on our (what else?)
SecureShell page.
Finger is an application that helps in finding out information about users
on your system, or on other systems.
By itself, finger reports on the users currently logged onto your system
Using the form finger address, finger reports on the address. The address
can take three forms:
Prepared by Jim Prescott, Deke Kassabian and John Simonson
Last modifed:
Thursday, 07-Apr-2011 09:22:56 EDT
ftp blurf.blarf.com
Electronic Mail
uuencode input-file final-file-name | mail address
Logging in to Remote Machines
Rlogin (and rsh)
rlogin machine-name [-l username]
rsh machine-name [unix-command]
Telnet
telnet machine-name
SecureShell
Finger
% finger
Login Name TTY Idle When Where
systaff System Staff co 6d Thu 08:07
lho Ling Cherd Ho p0 Tue 00:58 1640commserver.c
dela Del Armstrong p2 32 Tue 09:00 thermal.ceas.roc
zhmo Zhimin Mo p5 30 Tue 16:34 gav226.che.roche
jgp Jim Prescott p7 1 Thu 10:30 socrates.ceas.ro
kaser Bob Kaser p9 33 Fri 09:58 dagger.ceas.roch
QUICK SUMMARY OF NETWORK TOOLS AND SERVICES
Programs:
rcp - remote copy
ftp - file transfer program
Mail - electronic mail
uuencode - encode binary data as ASCII
uudecode - decode uuencoded data
rlogin - remote login
rsh - remote shell
slogin - remote login via secure shell
ssh - remote shell via secure shell
telnet - user interface to a remote system using the TELNET protocol
tn3270 - user interface to a remote IBM mainframe computer
finger - display information about users
whois - query the Internet user address database
rup - get load information on remote machines
rusers - return information about users on remote machines