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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>

<UL>
<LI><A NAME="tex2html1956"
  HREF="#SECTION001510000000000000000">12.1 <TT>
<FONT COLOR="#0000ff">ssh</FONT></TT>, not <TT>
<FONT COLOR="#0000ff">telnet</FONT></TT> or <TT>
<FONT COLOR="#0000ff">rlogin</FONT></TT></A>
<LI><A NAME="tex2html1957"
  HREF="#SECTION001520000000000000000">12.2 <TT>
<FONT COLOR="#0000ff">rcp</FONT></TT> and <TT>
<FONT COLOR="#0000ff">scp</FONT></TT></A>
<LI><A NAME="tex2html1958"
  HREF="#SECTION001530000000000000000">12.3 <TT>
<FONT COLOR="#0000ff">rsh</FONT></TT></A>
<LI><A NAME="tex2html1959"
  HREF="#SECTION001540000000000000000">12.4 FTP</A>
<LI><A NAME="tex2html1960"
  HREF="#SECTION001550000000000000000">12.5 <TT>
<FONT COLOR="#0000ff">finger</FONT></TT></A>
<LI><A NAME="tex2html1961"
  HREF="#SECTION001560000000000000000">12.6 Sending Files by Email</A>
<UL>
<LI><A NAME="tex2html1962"
  HREF="#SECTION001561000000000000000">12.6.1 <TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT> and <TT>
<FONT COLOR="#0000ff">uudecode</FONT></TT></A>
<LI><A NAME="tex2html1963"
  HREF="#SECTION001562000000000000000">12.6.2 MIME encapsulation</A>
</UL></UL>
<!--End of Table of Child-Links-->
<HR>

<H1><A NAME="SECTION001500000000000000000">
12. Using Internet Services</A>
</H1>

<P>
<A NAME="chap:netservices"></A>
<P>
This chapter summarizes remote access and the various
methods of transferring files and data over the Internet.

<P>

<H1><A NAME="SECTION001510000000000000000">
12.1 <TT>
<FONT COLOR="#0000ff">ssh</FONT></TT>, not <TT>
<FONT COLOR="#0000ff">telnet</FONT></TT> or <TT>
<FONT COLOR="#0000ff">rlogin</FONT></TT></A>
</H1>

<P>
<TT>
<FONT COLOR="#0000ff">telnet</FONT></TT> is a program for talking to a U<SMALL>NIX</SMALL> network service. It is
most often used to do a remote login. Try

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>telnet&nbsp;&#060;remote_machine&#062;</code><br>
<code>telnet&nbsp;localhost</code><br>
</FONT></TD></TR></TABLE><P>
to log in to your remote machine. It needn't matter if there is
no physical network; network services always work regardless
because the machine always has an internal link to itself.

<P>
<TT>
<FONT COLOR="#0000ff">rlogin</FONT></TT> is like a minimal version of <TT>
<FONT COLOR="#0000ff">telnet</FONT></TT>
that allows login access only. You can type

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>rlogin&nbsp;-l&nbsp;&#060;username&#062;&nbsp;&#060;remote_machine&#062;</code><br>
<code>rlogin&nbsp;-l&nbsp;jack&nbsp;localhost</code><br>
</FONT></TD></TR></TABLE><P>
if the system is configured to support remote logins.

<P>
These two services are the domain of old world U<SMALL>NIX</SMALL>;
for security reasons, <TT>
<FONT COLOR="#0000ff">ssh</FONT></TT> is now the preferable service for
logging in remotely:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>ssh&nbsp;[-l&nbsp;&#060;username&#062;]&nbsp;&#060;remote_machine&#062;</code><br>
</FONT></TD></TR></TABLE><P>

<P>
<I>Though <TT>
<FONT COLOR="#0000ff">rlogin</FONT></TT> and <TT>
<FONT COLOR="#0000ff">telnet</FONT></TT> are very convenient,
they should <I>never</I> be used across a public network because
your password can easily be read off the wire as you type it in.</I>

<P>

<H1><A NAME="SECTION001520000000000000000">
12.2 <TT>
<FONT COLOR="#0000ff">rcp</FONT></TT> and <TT>
<FONT COLOR="#0000ff">scp</FONT></TT></A>
</H1>

<P>

<TT>
<FONT COLOR="#0000ff">rcp</FONT></TT> stands for <I>remote copy</I> and <TT>
<FONT COLOR="#0000ff">scp</FONT></TT> is
the secure version from the <TT>
<FONT COLOR="#0000ff">ssh</FONT></TT> package.
These two commands copy files from one machine to another using a similar
notation to <TT>
<FONT COLOR="#0000ff">cp</FONT></TT>.

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>rcp&nbsp;[-r]&nbsp;[&#060;remote_machine&#062;:]&#060;file&#062;&nbsp;[&#060;remote_machine&#062;:]&#060;file&#062;</code><br>
<code>scp&nbsp;[-l&nbsp;&#060;username&#062;]&nbsp;[-r]&nbsp;[&#060;remote_machine&#062;:]&#060;file&#062;&nbsp;[&#060;remote_machine&#062;:]&#060;file&#062;</code><br>
</FONT></TD></TR></TABLE><P>
Here is an example:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red size="-1">
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>5</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-2"><code>10</code></font><code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue size="-1">
<code>[psheer@cericon]#&nbsp;<font color="navy"><B>rcp&nbsp;/var/spool/mail/psheer&nbsp;&#92;</B></font></code><br>
<code><font color="navy"><B>&nbsp;divinian.cranzgot.co.za:/home/psheer/mail/cericon</B></font></code><br>
<code>[psheer@cericon]#&nbsp;<font color="navy"><B>scp&nbsp;/var/spool/mail/psheer&nbsp;&#92;</B></font></code><br>
<code><font color="navy"><B>&nbsp;divinian.cranzgot.co.za:/home/psheer/mail/cericon</B></font></code><br>
<code>The&nbsp;authenticity&nbsp;of&nbsp;host&nbsp;'divinian.cranzgot.co.za'&nbsp;can't&nbsp;be&nbsp;established.</code><br>
<code>RSA&nbsp;key&nbsp;fingerprint&nbsp;is&nbsp;43:14:36:5d:bf:4f:f3:ac:19:08:5d:4b:70:4a:7e:6a.</code><br>
<code>Are&nbsp;you&nbsp;sure&nbsp;you&nbsp;want&nbsp;to&nbsp;continue&nbsp;connecting&nbsp;(yes/no)?&nbsp;<font color="navy"><B>yes</B></font></code><br>
<code>Warning:&nbsp;Permanently&nbsp;added&nbsp;'divinian.cranzgot.co.za'&nbsp;(RSA)&nbsp;to&nbsp;the&nbsp;list&nbsp;of&nbsp;known&nbsp;hosts.</code><br>
<code>psheer@divinian's&nbsp;password:&nbsp;</code><br>
<code>psheer&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;100%&nbsp;|***************************************|&nbsp;&nbsp;4266&nbsp;KB&nbsp;&nbsp;&nbsp;&nbsp;01:18</code><br>
</FONT></TD></TR></TABLE><P>

<P>
The <TT>
<FONT COLOR="#0000ff">-r</FONT></TT> option copies recursively and
copies can take place in either direction or even between two
nonlocal machines.

<P>
<I><TT>
<FONT COLOR="#0000ff">scp</FONT></TT> should always be used instead of <TT>
<FONT COLOR="#0000ff">rcp</FONT></TT>
for security reasons.</I> Notice also
the warning given by <TT>
<FONT COLOR="#0000ff">scp</FONT></TT> for this first-time
connection. See the <TT>
<FONT COLOR="#0000ff">ssh</FONT></TT> documentation for how
to make your first connection securely. All commands
in the <TT>
<FONT COLOR="#0000ff">ssh</FONT></TT> package have this same behavior.

<P>

<H1><A NAME="SECTION001530000000000000000">
12.3 <TT>
<FONT COLOR="#0000ff">rsh</FONT></TT></A>
</H1>

<P>
<TT>
<FONT COLOR="#0000ff">rsh</FONT></TT> (<I>remote shell</I>) is a useful utility for
executing a command on a
remote machine. Here are some
examples:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<font size="-1"><code>5</code></font><code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>[psheer@cericon]#&nbsp;<font color="navy"><B>rsh&nbsp;divinian.cranzgot.co.za&nbsp;hostname</B></font></code><br>
<code>divinian.cranzgot.co.za</code><br>
<code>[psheer@cericon]#&nbsp;<font color="navy"><B>rsh&nbsp;divinian.cranzgot.co.za&nbsp;&#92;</B></font></code><br>
<code><font color="navy"><B>&nbsp;&nbsp;&nbsp;tar&nbsp;-czf&nbsp;-&nbsp;/home/psheer&nbsp;&#124;&nbsp;dd&nbsp;of=/dev/fd0&nbsp;bs=1024</B></font></code><br>
<code>tar:&nbsp;Removing&nbsp;leading&nbsp;`/'&nbsp;from&nbsp;member&nbsp;names</code><br>
<code>20+0&nbsp;records&nbsp;in</code><br>
<code>20+0&nbsp;records&nbsp;out</code><br>
<code>[psheer@cericon]#&nbsp;<font color="navy"><B>cat&nbsp;/var/spool/mail/psheer&nbsp;|&nbsp;rsh&nbsp;divinian.cranzgot.co.za&nbsp;&#92;</B></font></code><br>
<code><font color="navy"><B>&nbsp;&nbsp;&nbsp;sh&nbsp;-c&nbsp;'cat&nbsp;&#062;&#062;&nbsp;/home/psheer/mail/cericon'</B></font></code><br>
</FONT></TD></TR></TABLE><P>
The first command prints the host name of the remote machine.
The second command backs up my <I>remote</I> home directory to my <I>local</I>
floppy disk. (More about <TT>
<FONT COLOR="#0000ff">dd</FONT></TT>
and <TT>
<FONT COLOR="#0000ff">/dev/fd0</FONT></TT> come later.)
The last command appends my local mailbox file to a remote mailbox file.
Notice how stdin, stdout, and stderr
are properly redirected to the local
terminal. After reading Chapter <A HREF="node32.html#chap:xinetd">29</A> see <TT>
<FONT COLOR="#0000ff">rsh</FONT></TT>(8) or
<TT>
<FONT COLOR="#0000ff">in.rshd</FONT></TT>(8) to configure this service.

<P>
<I>Once again, for security reasons <TT>
<FONT COLOR="#0000ff">rsh</FONT></TT> should
never be available across a public network.</I>

<P>

<H1><A NAME="SECTION001540000000000000000">
12.4 FTP</A>
</H1>

<P>
FTP stands for <I>File Transfer Protocol</I>. If FTP is set up
on your local machine, then other machines can download files.
Type

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>ftp&nbsp;metalab.unc.edu</code><br>
</FONT></TD></TR></TABLE><P>
or

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>ncftp&nbsp;metalab.unc.edu</code><br>
</FONT></TD></TR></TABLE><P>

<P>
<TT>
<FONT COLOR="#0000ff">ftp</FONT></TT> is the traditional command-line U<SMALL>NIX</SMALL> FTP
<I>client</I>, <FONT COLOR="#ffa500">[``<I>client</I>'' always indicates
the user program accessing some remote service.]</FONT>while <I>ncftp</I> is a more powerful client that will not
always be installed.

<P>
You will now be inside an FTP <I>session</I>. You will be asked
for a login name and a password. The site
<TT>
<FONT COLOR="#0000ff">metalab.unc.edu</FONT></TT> is one that allows <I>anonymous</I>
logins. This means that you can type <TT>
<FONT COLOR="#0000ff">anonymous</FONT></TT> as your
user name, and then anything you like as a password. You will
notice that the session will ask you for an email address as your
password. Any sequence of letters with an <TT>
<FONT COLOR="#0000ff">@</FONT></TT> symbol will
suffice, but you should put your actual email address out of
politeness.

<P>
The FTP session is like a reduced shell. You can type <TT>
<FONT COLOR="#0000ff">cd</FONT></TT>,
<TT>
<FONT COLOR="#0000ff">ls</FONT></TT>, and <TT>
<FONT COLOR="#0000ff">ls -al</FONT></TT> to view file lists. <TT>
<FONT COLOR="#0000ff">help</FONT></TT> brings up
a list of commands, and you can also type <TT>
<FONT COLOR="#0000ff">help &lt;command&gt;</FONT></TT>
to get help on a specific command. You can download a file by using
the <TT>
<FONT COLOR="#0000ff">get &lt;filename&gt;</FONT></TT> command, but before you do this, you
must set the <I>transfer type</I> to <I>binary</I>. The
<I>transfer type</I> indicates whether or not newline
characters will be translated to DOS format. Typing
<TT>
<FONT COLOR="#0000ff">ascii</FONT></TT> turns on this feature, while <TT>
<FONT COLOR="#0000ff">binary</FONT></TT> turns it off.
You may also want to enter <TT>
<FONT COLOR="#0000ff">hash</FONT></TT> which will print a
<TT>
<FONT COLOR="#0000ff">#</FONT></TT> for every 1024 bytes of download. This is useful for
watching the progress of a download. Go to a directory that has a <TT>
<FONT COLOR="#0000ff">README</FONT></TT>
file in it and enter

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>get&nbsp;README</code><br>
</FONT></TD></TR></TABLE><P>
The file will be downloaded into your current directory.

<P>
You can also <TT>
<FONT COLOR="#0000ff">cd</FONT></TT> to the <TT>
<FONT COLOR="#0000ff">/incoming</FONT></TT> directory and
upload files. Try

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>put&nbsp;README</code><br>
</FONT></TD></TR></TABLE><P>
to upload the file that you have just downloaded. Most FTP sites
have an <TT>
<FONT COLOR="#0000ff">/incoming</FONT></TT> directory that is flushed periodically.

<P>
FTP allows far more than just uploading of files, although the
administrator has the option to restrict access to any further
features. You can create directories, change ownerships, and do
almost anything you can on a local file system.

<P>
If you have several machines on a trusted <I>LAN</I>
(<I>Local Area Network</I>--that is,
your private office or home network), all should have FTP
enabled to allow users to easily copy files between machines.
How to install and configure one of the many available FTP
servers will become obvious later in this book.

<P>

<H1><A NAME="SECTION001550000000000000000">
12.5 <TT>
<FONT COLOR="#0000ff">finger</FONT></TT></A>
</H1>

<P>
<TT>
<FONT COLOR="#0000ff">finger</FONT></TT> is a service for remotely listing who is logged in on a remote system.
Try <TT>
<FONT COLOR="#0000ff">finger @&#60;hostname&#62;</FONT></TT> to see who is logged in on
<TT>
<FONT COLOR="#0000ff">&#60;hostname&#62;</FONT></TT>. The <I>finger</I> service will often be disabled on
machines for security reasons.

<P>

<H1><A NAME="SECTION001560000000000000000">
12.6 Sending Files by Email</A>
</H1>

<P>
<A NAME="sec:filesoveremail"></A>
<P>
Mail is being used more and more for transferring files
between machines. It is bad practice to send mail messages over
64 kilobytes over the Internet because it tends to excessively
load mail servers. Any file larger than 64 kilobytes should be
uploaded by FTP onto some common FTP server. Most small images
are smaller than this size, hence sending a small
JPEG <FONT COLOR="#ffa500">[A common Internet image file format. These are
especially compressed and are usually under 100 kilobytes for a
typical screen-sized photograph.]</FONT> image is considered
acceptable.

<P>

<H2><A NAME="SECTION001561000000000000000">
12.6.1 <TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT> and <TT>
<FONT COLOR="#0000ff">uudecode</FONT></TT></A>
</H2>

<P>
If you must send files by mail then you can do it by using
<TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT>. This utility packs binary files
into a format that mail servers can handle. If you send a mail
message containing arbitrary binary data, it will more than
likely be corrupted on the way because mail agents are only
designed to handle a limited range of characters.
<TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT> represents a binary file with
allowable characters, albeit taking up slightly more space.

<P>
Here is a neat trick to pack up a directory and send it
to someone by mail.

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>tar&nbsp;-czf&nbsp;-&nbsp;&#060;mydir&#062;&nbsp;|&nbsp;uuencode&nbsp;&#060;mydir&#062;.tar.gz&nbsp;\</code><br>
<code>&nbsp;&nbsp;&nbsp;&nbsp;|&nbsp;mail&nbsp;-s&nbsp;"Here&nbsp;are&nbsp;some&nbsp;files"&nbsp;&#060;user&#062;@&#060;machine&#062;</code><br>
</FONT></TD></TR></TABLE><P>

<P>
To unpack a <TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT>d file, use the <TT>
<FONT COLOR="#0000ff">uudecode</FONT></TT>
command:

<P><TABLE nowrap="1" width="100%" border="0" cellspacing="0" cellpadding="0">
<TR>
<TD valign="top" class="source" width="2%"><FONT color=red>
<code>&nbsp;</code><br>
</FONT></TD><TD valign="top" class="source" bgcolor="#FFE0C0"><FONT color=blue>
<code>uudecode&nbsp;&#060;myfile&#062;.uu</code><br>
</FONT></TD></TR></TABLE><P>

<P>

<H2><A NAME="SECTION001562000000000000000">
12.6.2 MIME encapsulation</A>
</H2>

<P>
<A NAME="sec:mimeencap"></A>
<P>
Most graphical mail readers have the ability to <I>attach</I> files to
mail messages and read these attachments. The way they do this
is not with <TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT> but in a special format known as
<I>MIME encapsulation</I>. MIME (<I>Multipurpose Internet
Mail Extensions</I>) is a way of representing multiple
files inside a single mail message. The way binary data is
handled is similar to <TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT>, but in a format known
as <I>base64</I>.

<P>
Each MIME attachment to a mail message has a particular type,
known as the <I>MIME type</I>. MIME types
merely classify the attached file as an image, an audio clip,
a formatted document, or some other type of data. The MIME type
is a text tag with the format
<TT>
<FONT COLOR="#0000ff">&#60;major&#62;/&#60;minor&#62;</FONT></TT>.
The <TT>
<FONT COLOR="#0000ff">major</FONT></TT> part is called the <I>major MIME type</I> and the
<TT>
<FONT COLOR="#0000ff">minor</FONT></TT> part is called the <I>minor MIME type</I>. Available
major types match all the kinds of files that you would expect to
exist. They are usually one of <TT>
<FONT COLOR="#0000ff">application</FONT></TT>, <TT>
<FONT COLOR="#0000ff">audio</FONT></TT>,
<TT>
<FONT COLOR="#0000ff">image</FONT></TT>, <TT>
<FONT COLOR="#0000ff">message</FONT></TT>, <TT>
<FONT COLOR="#0000ff">text</FONT></TT>, or <TT>
<FONT COLOR="#0000ff">video</FONT></TT>.
The <TT>
<FONT COLOR="#0000ff">application</FONT></TT> type means a file format specific to
a particular utility. The minor MIME types run into the hundreds.
A long list of MIME types can be found in <TT>
<FONT COLOR="#0000ff">/etc/mime.types</FONT></TT>.

<P>
If needed, some useful command-line utilities in the
same vein as <TT>
<FONT COLOR="#0000ff">uuencode</FONT></TT> can create and extract MIME
messages. These are <TT>
<FONT COLOR="#0000ff">mpack</FONT></TT>,
<TT>
<FONT COLOR="#0000ff">munpack</FONT></TT>, and <TT>
<FONT COLOR="#0000ff">mmencode</FONT></TT>
(or <TT>
<FONT COLOR="#0000ff">mimencode</FONT></TT>).

<P>
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