Internet

Some general remarks

The institute is connected to the Internet 24 hours a day with a 2 Mbps line (as of today, April 2004). This means that you have unrestricted access (so far!) to the Internet all day long, and can do download, browse, send email and any other Internet-related activity you want.

While the Internet is a great source of information (mathematical and otherwise), one should be careful while using it. Try always to use programs that do not transmit passwords in a clear way (for example, use ssh instead of telnet or rsh).

And if you download some program to be executed (run in your account), be sure you know the site from you get the program; otherwise you might end up with all your files removed! Or worse!

telnet

The telnet command allows you to log on in another machine connected to the Internet. The usage is simple:


   telnet remote-machine

A couple of remarks about this program:

The connection is "clear", meaning that all you type can be read by some one (or a program) between your machine and the remote machine. In particular, passwords (and other confidential stuff) are not safe via telnet.
If the connection hangs up you can interrupt it with Ctrl-]
Some times the remote machine does not understand your "TERM" environment (linux is not a valid term in the remote host). Try giving one of the following two commands in the remote machine:
```
   setenv TERM vt100
```
or
```
   export TERM=vt100
```

rsh (and rlogin)

The rlogin program is similar to telnet. The sequence to end a hanging rlogin session is ~. (tilde followed by a period). The rsh works in a similar way if used like


   rsh remote-machine

if your logging name in the remote machine is the same as in the local machine, or


   rsh user-name@remote-machine

if the user name is different.

But with rsh you can also execute commands in a remote machine without having a full session. For example, if you want to see who is logged on in another machine with the who command you can simply do


   rsh remote-machine who

In the School of Maths machines (or at least, in most machines), rsh between two machines works without asking for passwords. It is not a problem but I "feature" I have set up. If you want to copy a file from a remote machine you can use rcp as this:


   rcp user-name@remote-machine:file local-file

ssh

This program is similar to rsh but the communication between the two hosts is encrypted, so it is safe to type passwords (or other confidential stuff). ssh comes with a secure version of rcp called scp. The usage is similar to that of rsh or rcp. The sequence to terminate a hanging ssh session is also the same (~.).

browsing (lynx and mozilla/netscape)

The World Wide Web (www) is a way of sharing information among millions of computers in the Internet. You can browse it with text-base programs (lynx and elinks) or graphics/X-windows ones (netscape and its latest variation, mozilla).

Addresses in the wwww typically start with the http:// string. In the School of Maths, if you call lynx or netscape/mozilla you will start with the School of Maths' homepage. To go to another page use the g key-stroke in lynx or type the address in the box at the top of the netscape window.

You can also start directly at another page with


   lynx http://remote.site.address/file


   mozilla http://remote.site.address/file

ftp

The file transfer protocol (or ftp in short) allows you to transfer files between two machines connected to the Internet. The usage is


   ftp remote.machine

Due to the firewall in the Institute, you might have problems with the above command. Start better with the "passive" option, namely:


   pftp remote.machine

Do not panic, if you started with ftp direcetly you can go to passive mode by typing that word, passive, at any moment of your ftp session.

After the connection is stablished you should give your logging name (in the remote machine) and your password. These are transmitted clear text, so it is not safe. Anonymous ftp is a special account that allows you to transfer certain public files from the remote machine. The logging name is anonymous or ftp and the password is your email address (in the local machine).

Here are some commands for an ftp session

command            action
------------------------------------------------
dir                lists files in remote machine
cd directory       changes to directory in remote machine
lcd directory      changes to directory in local machine
get file           gets file from remote machine to local machine
put file           puts file from local machine in the remote machine
quit               ends ftp session

Be careful when using get since it will overwrite any local file with the same name as the file in the remote machine.

Look at the mail section for more information.

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