manual.html

主要用于监控网络流量并动态产生可视化结果

<P><I><B>Q:</B> I need a script to make mrtg work with xyz.</I><BR>
<B>A:</B> Probably this has already been done. Check the stuff in
the "contrib" directory. There is a file called 00INDEX in that directory
which tells what you can find there.</P>


<P><I><B>Q:</B> I need more documentation ... </I><BR>

<B>A:</B> Make sure you have checked the files in the doc
directory of the mrtg distribution archive. Most notably  'config.html' and
'mibhelp.txt' and 'squid.txt'. Further there is a host of unsuported,
contributed scripts in the 'contrib'
directory of you mrtg distribution. If you need even more infos, make
sure to check the mailing list archive as well. There has also been an article about SNMP
and mrtg in a backissue of the Linux Journal.
It's author David Guerrero has made it
available on the net.
Check <A HREF="http://www.mec.es/~david/papers/snmp"
>http://www.mec.es/~david/papers/snmp</A>
</P>

<P><I><B>Q:</B> The GIFs created by MRTG look very strange. Not all the
grid lines are drawn and ... </I><BR>

<B>A:</B> Remove the *-{week,day,month,year}.gif files and start MRTG
again.  Using MRTG for the first time, you might have to do this
twice. This will also help, when you introduce new routers into the cfg
file.</P>

<P><I><B>Q:</B> What is my Community Name?</I><BR>
<B>A:</B> Try 'public', as this is the default Community Name.</P>

<P><I><B>Q:</B> I compiled your program and I get the following errors:
at the command line I typed <TT>./mrtg kirit.cfg</TT> and I get :</I>
<PRE>
    Can't locate Socket.pm in @INC at /SNMP_Session.pm line 27. 
    BEGIN failed--compilation aborted at /SNMP_Session.pm line 27.
    BEGIN failed--compilation aborted at ./mrtg line 356.
</PRE>
<B>A:</B> You need to get Perl5 installed properly. Socket.pm comes with
Perl5 and is an integral part of Perl5. Perl5 comes
with compiled in defaults about where it should look for its libraries (eg
Socket.pm). Type <TT>'perl -V'</TT> to see what your perl assumes ... And
get it fixed ... Eg by installing it properly.<P>

<P><I><B>Q:</B>My graphs show a flat, nonzero line during an outage.  What's up with
that?</I></P>

<P><B>A:</B>Well, the short answer is that when an SNMP query goes out
and a response doesn't come back, MRTG has to assume something to put
in the graph, and by default it assumes that the last answer we got
back is probably closer to the truth than zero.  This assumption is
not perfect (as you have noticed), it's a trade-off that happens to
fail during a total outage. If it's an unacceptable trade-off, run at
least MRTG V2.8.4 and use the "unknaszero" option.  You may want to
know what you're trading off, so in the spirit of trade-offs, here's
the long answer:</P>

<P>The problem is that MRTG doesn't know *why* the data didn't come back, all
it knows is that it didn't come back.  It has to do something, and it
assumes it's a stray lost packet rather than an outage.</P>

<P>Why don't we always assume the circuit is down, and use zero, which will
(we think) be more nearly right?  Well, it turns out that you may be
taking advantage of MRTG's "assume last" behaviour without being aware of
it.</P>

<P>MRTG uses SNMP (Simple Network Management Protocol) to collect data, and
SNMP uses UDP (User Datagram Protocol) to ship packets around.  UDP is
connectionless (not guaranteed) - unlike TCP where packets are tracked and
acknowledged and, if needed, re-transmitted end-to end, UDP just throws
packets at the network and hopes they arrive. Sometimes they don't.</P>

<P>One likely cause of lost SNMP data is congestion, another is busy routers.
Other possibilities include transient telecommunications problems, router
buffer overflows (which may or may not be congestion-related), "dirty
lines" (links with high error rates), and acts of God.  These things
happen all the time, we just don't notice because many interactive
services are TCP-based and the lost packets get retransmitted
automatically.</P>

<P>In the above cases where some SNMP packets are lost but traffic is
flowing, assuming zero is the wrong thing to do - you end up with a graph
that looks like it's missing teeth whenever the link fills up.  MRTG
interpolates the lost data to produce a smoother graph which is more
accurate in cases of intermittent packet loss.  But with V2.8.4 and above,
you can use the "unknaszero" option to produce whichever graph is best
under the conditions typical of your network.</P>


<A HREF="http://www.ltinet.net/info/mrtg/noflashmrtg.htm">Official MRTG FAQ Site</A> and browse the
<A HREF="http://www.ee.ethz.ch/~slist/mrtg">MRTG Mailing list Archives</A>.</B>
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<A NAME="NEWSGROUP"></A>
<TABLE WIDTH="100%" BGCOLOR=silver CELLSPACING=0 CELLPADDING=4><TR><TD>
<FONT COLOR=black SIZE="+2"><B>A newsgroup for MRTG</B></FONT></TD></TR></TABLE>
<P>For discussion of MRTG or related topics on the UseNet, please send your posts to:

<DIV ALIGN=CENTER><B><A HREF="news:comp.dcom.net-management">comp.dcom.net-management</A></B></DIV>

</P>

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<A NAME="LIST"></A>
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<FONT COLOR=black SIZE="+2"><B>MRTG Mailing List</B></FONT></TD></TR></TABLE>


<P>There are two mailing lists for MRTG available. One is called
'mrtg' and is a discussion list for users and developers. The other is
called 'mrtg-announce' and is a low volume list for MRTG
related announcements.</P>
 
<P> To subscribe to these mailing lists, send a message with the subject
line <B>subscribe</B> to either <B>[e-mail]</B> or
<B>[e-mail]</B>. For posting to the mrtg list
use the address <B>[e-mail]</B>.</P>

<P>Further information about the usage of the mailing lists is
available by sending a message with the subject line '<I>help</I>' to
either one of the request addresses.</P>

<P>For past activity there is also a mailing list archive available:
<A HREF="http://www.ee.ethz.ch/~slist/mrtg"
>http://www.ee.ethz.ch/~slist/mrtg</A>
</P>

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<A NAME="NT"></A>
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<FONT COLOR=black SIZE="+2"><B>
Installing MRTG on Windows NT
</B></FONT></TD></TR></TABLE>

<P><I>By Stuart Schneider &lt;[e-mail]&gt;</I></P>

<P>To setup mrtg on a WindowsNT system, you can follow the instructions
already provided for UNIX systems with the following addition:</P>

<P>6.5. Change the $main::OS setting at the top of the mrtg script to
equal 'NT'.</P>

<P>Or, for those who need a little extra help, follow these steps:</P>
<UL>
  <LI>
      Download and unpack mrtg-2.8.12.zip from:
      <A HREF="http://ee-staff.ethz.ch/~oetiker/webtools/mrtg/pub/"
      >http://ee-staff.ethz.ch/~oetiker/webtools/mrtg/pub/</A>.
  </LI>

  <LI>
      Download and install the latest version of Perl 5 for Win32 from
      <A HREF="http://www.ActiveState.com">ActiveState</A>.
  </LI>

  <LI> Edit the main run/mrtg script downloaded in step #1 and remove the
      "#" from the beginning of the line that reads "$main::OS = 'NT';".
  </LI>

  <LI>   Use run\cfgmaker or manually configure your mrtg.cfg file. Be sure
the SNMP Service is installed and running on the device/computer you are
attempting to monitor.
      (Documentation on the structure of the file is in the file
      doc\config.txt and in doc\sample-mrtg.cfg.)</LI>
  <LI>Add the lines:
<pre>
RunAsDaemon: Yes
Interval: 5
</pre>
      To your mrtg.cfg file.
  </LI>
  <LI>
      Execute your mrtg with your mrtg.cfg file as argument.
<pre>
cd \mrtg-2.8.12
perl mrtg mrtg.cfg
</pre>
      At first, expect some output from the script as it creates the necessary databases.
      after about 15 minutes all should be quiet. If you have errors in your mrtg.cfg file
      Mrtg will tell you right after you try to start it.
  </LI>

  <LI> Might want to create a link in your autostart folder for mrtg so that it
      gets launched everytime your start your machine.
  </LI>

     </UL> 
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  <TD BGCOLOR="#ff0000">&nbsp;</TD><TD>
<P><B>NEW:</B> For more verbose instructions, check out the
<A HREF="http://ee-staff.ethz.ch/~oetiker/webtools/mrtg/nt-guide.html">The MRTG Guide for Windows NT Users</A>
by <A HREF="mailto:[e-mail]">David S. Divins</A></P></TD>
<TD BGCOLOR="#ff0000">&nbsp;</TD></TR></TABLE>

</UL>

<HR NOSHADE SIZE=2>

<P>If you have any questions about this program,
or have it up and running,<BR>
we would like to hear from you: </P>

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  <TD><FONT FACE="Arial,Helvetica" SIZE=2>
  <A HREF="http://ee-staff.ethz.ch/~oetiker">Tobias Oetiker</A>
  <A HREF="mailto:[e-mail]">&lt;[e-mail]&gt;</A> 
  and&nbsp;<A HREF="http://www.bungi.com">Dave&nbsp;Rand</A>&nbsp;<A HREF="mailto:[e-mail]">&lt;[e-mail]&gt;</A></FONT>
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