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<!-- ISBN=0672311739 //-->
<!-- TITLE=RED HAT LINUX 2ND EDITION //-->
<!-- AUTHOR=DAVID PITTS ET AL //-->
<!-- PUBLISHER=MACMILLAN //-->
<!-- IMPRINT=SAMS PUBLISHING //-->
<!-- PUBLICATION DATE=1998 //-->
<!-- CHAPTER=08 //-->
<!-- PAGES=0131-0152 //-->
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<P><CENTER>
<a href="0135-0138.html">Previous</A> | <a href="../ewtoc.html">Table of Contents</A> | <a href="0142-0144.html">Next</A>
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<A NAME="PAGENUM-139"><P>Page 139</P></A>
<P>where <n> is the number of attempts. For example, the following line disconnects a user
from the FTP server after three failed attempts:
</P>
<!-- CODE SNIP //-->
<PRE>
loginfails 3
</PRE>
<!-- END CODE SNIP //-->
<H5><A NAME="ch08_ 14">
private
</A></H5>
<P>You might find it convenient to be able to share files with other users via FTP without
having to place the file in a 100 percent public place or having to give these users a real account on
the server. The clients use the SITE GROUP and SITE
GPASS commands so that they can change into privileged groups that require passwords.
</P>
<P>For your FTP server to support this capability, you need to set the
private flag using the command
</P>
<!-- CODE SNIP //-->
<PRE>
private <switch>
</PRE>
<!-- END CODE SNIP //-->
<P>where <switch> is either the string YES to turn it on or
NO to turn it off.
</P>
<P>Because you need to require passwords for these special groups, you need to use the
/etc/ftpgroups file. The format of an access group in
/etc/ftpgroups is
</P>
<!-- CODE SNIP //-->
<PRE>
access_group_name:encrypted_password:real_group
</PRE>
<!-- END CODE SNIP //-->
<P>where access_group_name is the name that the client uses to reference the special
group, encrypted_password is the password users need to supply (via
SITE GPASS) to access the group, and real_group is the actual group referenced in the
/etc/group file.
</P>
<CENTER>
<TABLE BGCOLOR="#FFFF99">
<TR><TD><B>
TIP
</B></TD></TR>
<TR><TD>
<BLOCKQUOTE>
To create the encrypted_password entry, use the UNIX
crypt function. To make generating the encrypted password easier, use the following Perl script:
<!-- CODE //-->
<PRE>
#!/usr/bin/perl
print "Enter password to encrypt: ";
chop ($password=<STDIN>);
print "The encrypted password is: ",crypt($password,$password);
</PRE>
<!-- END CODE //-->
</BLOCKQUOTE></TD></TR>
</TABLE></CENTER>
<H4>
Controlling Banner Messages
</H4>
<P>It is often useful to provide messages to FTP users when they connect to your site or specify
a special action. These commands allow you to specify these instances as well as the
corresponding messages. Using them is a great way to make your site self-documenting.
</P>
<H5><A NAME="ch08_ 15">
banner
</A></H5>
<P>The banner command allows you to display a sign onscreen before the client has to provide
a login and password combination. The format of this command is
</P>
<!-- CODE SNIP //-->
<PRE>
banner <path>
</PRE>
<!-- END CODE SNIP //-->
<A NAME="PAGENUM-140"><P>Page 140</P></A>
<P>where <path> is the full pathname of the file you want to display. Consider this example:
</P>
<!-- CODE SNIP //-->
<PRE>
banner /home/ftp/.banner
</PRE>
<!-- END CODE SNIP //-->
<H5><A NAME="ch08_ 16">
email
</A></H5>
<P>The email command allows you to specify the site maintainer's e-mail address. Some
error messages or information requests provide the information given in this line on demand.
The default value in the /etc/ftpaccess file is
root@localhost.
</P>
<P>The format of the email command is
</P>
<!-- CODE SNIP //-->
<PRE>
email <address>
</PRE>
<!-- END CODE SNIP //-->
<P>where <address> is the full e-mail address of the site maintainer.
</P>
<P>Creating an e-mail alias "FTP" that forwards to the system administrators is generally
good practice. Providing this kind of information in the sign-on banner is also a good idea so
that users know whom to contact if they cannot log in to the system.
</P>
<H5><A NAME="ch08_ 17">
message
</A></H5>
<P>The message command allows you to set up special messages to be sent to the clients when
they either log in or change into a certain directory. You can specify multiple messages. The
format of this command is
</P>
<!-- CODE SNIP //-->
<PRE>
message <path> <when> {<class> ...}
</PRE>
<!-- END CODE SNIP //-->
<P>where <path> is the full pathname to the file to be displayed,
<when> is the condition under which to display the message, and
<class> is a list of classes to which this message
command applies.
</P>
<P>The <when> parameter should take one of two forms: either
LOGIN or CWD=<dir>. If it is LOGIN, the message is displayed upon a successful login. If the parameter is set to
CWD=<dir>, then the message is displayed when clients enter the
<dir> directory.
</P>
<P>The <class> parameter is optional. You can list multiple classes for a certain message.
This capability is useful if you want only certain messages going to anonymous users and so on.
</P>
<P>The message file itself (specified by
<path>) can contain special flags that the FTP server
substitutes with the appropriate information at runtime. These options are as follows:
</P>
<HR>
<TABLE WIDTH="360">
<TR><TD>
Option
</TD><TD>
Description
</TD></TR>
<TR><TD>
%T
</TD><TD>
Local time
</TD></TR>
<TR><TD>
%F
</TD><TD>
Free space in the partition where
<dir> is located
</TD></TR>
<TR><TD>
%C
</TD><TD>
Current working directory
</TD></TR>
<TR><TD>
%E
</TD><TD>
Site maintainer's e-mail address (specified by the
email command)
</TD></TR>
</TABLE>
<A NAME="PAGENUM-141"><P>Page 141</P></A>
<HR>
<TABLE WIDTH="360">
<TR><TD>
Option
</TD><TD>
Description
</TD></TR>
<TR><TD>
%R
</TD><TD>
Client hostname
</TD></TR>
<TR><TD>
%L
</TD><TD>
Server hostname
</TD></TR>
<TR><TD>
%U
</TD><TD>
Username provided at login time
</TD></TR>
<TR><TD>
%M
</TD><TD>
Maximum number of users allowed in the specified class
</TD></TR>
<TR><TD>
%N
</TD><TD>
Current number of users in specified class
</TD></TR>
</TABLE>
<P>Remember that when messages are triggered by an anonymous user, the message path needs
to be relative to the anonymous FTP directory.
</P>
<P>An example message command is
</P>
<!-- CODE SNIP //-->
<PRE>
message ./.toomany_anon LOGIN anonfolks
</PRE>
<!-- END CODE SNIP //-->
<P>where the file ./.toomany_anon contains
</P>
<!-- CODE SNIP //-->
<PRE>
Sorry %R, but there are already %N users out of a maximum of %M users in
Âyour class. Please try again in a few minutes.
The FTP Administrator (%E)
</PRE>
<!-- END CODE SNIP //-->
<P>If the limit of 25 users is reached at this site, for example, the client sees a message similar to
the following:
</P>
<!-- CODE //-->
<PRE>
Sorry, technics.domain.com, but there are already 25 out of a maximum
Âof 25 users in your class. Please try again in a few minutes.
The FTP Administrator (ftp@domain.com)
</PRE>
<!-- END CODE //-->
<H5><A NAME="ch08_ 18">
readme
</A></H5>
<P>The readme command allows you to specify the conditions under which clients are
notified that a certain file in their current directory was last modified. This command can take the form
</P>
<!-- CODE SNIP //-->
<PRE>
readme <path> <when> <class>
</PRE>
<!-- END CODE SNIP //-->
<P>where <path> is the name of the file to alert the clients about (for example,
README), <when> is similar to the
<when> in the message command, and
<class> is the classes for which this command applies. The
<when> and <class> parameters are optional.
</P>
<P>Remember that when you're specifying a path for anonymous users, the file must be relative
to the anonymous FTP directory.
</P>
<H4><A NAME="ch08_ 19">
Controlling Logging
</A></H4>
<P>As with any complex network service, security quickly becomes an issue. In order to
contend with possible threats, tracking connections made along with the corresponding commands is
a necessity. The following commands allow you to determine how much, if any,
logging should be done by the server software.
</P>
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