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    <p>
      <b>Note:</b>  Much of this tutorial requires <a
	href="http://prdownloads.sourceforge.net/net-snmp/ucd-snmp-4.2.6.tar.gz">ucd-snmp-4.2.2 or higher</a>!,
	so make sure you get it before running the commands found in
	this tutorial.</b> 
      <p><b>Note:</b>  A new tutorial for net-snmp 5.0 and above <a
      href="/tutorial-5">is available</a> as well.  The commands is
      the ucd-snmp specific tutorial will not work as expected if you
      are using net-snmp and not ucd-snmp.
      <br><br>
    <hr>
    <h1>Dynamic Module Creation for the ucd-snmp agent</h1>
    <p>
      Now, lets take the ustScalarSet mib module we created in the <a
      href="../mib_module">previous example</a> and make it work as a
      dynamicly loadable shared object.

    <p><b>Note:</b> For this to work, you must have compiled the
      ucd-snmp package with dynamicly loadable module support turned
      on, as well as built it with --enable-shared turned on .  It's
      on by default, if your system supports it, in version 4.2 and
      higher.  You can check your agent but looking at the output of
      the "snmpd -H" command for the "dlmod" token.  If its listed,
      the compiled agent supports it.

    <p><b>Note:</b> You should also re-compile
      the agent <b>without</b> the ustScalarSet code by removing it
      from the list of --with-mib-modules option, or else this example
      won't work correctly.

    <p><b>Note:</b> All command line options below assume you have an
    appropriately setup ~/.snmp/snmp.conf file that allows you to not
    have to specify a snmp version number, community name, username,
    or whatever else in order to talk to your agent.  The agent, of
    course, must have a matching /usr/local/share/snmp/snmpd.conf file 
    (or equivalent).

    <p>
      Here are the files discussed in this example so you can download
      them:
      <center>
      <table border=1>
	<tr bgcolor="#d0d0ff"><th>File</th><th>Description</th></tr>
	<tr bgcolor="#d0d0ff"><td><a
	href="../demoapp/Makefile">Makefile</a></td><td>A simple makefile 
	used to build the projects</td>
	<tr bgcolor="#d0d0ff"><td><a
	href="../mib_module/UCD-SNMP-TUTORIAL-MIB.txt">UCD-SNMP-TUTORIAL-MIB.txt</a></td><td>The MIB we'll be writing
	code for</td>
	<tr bgcolor="#d0d0ff"><td><a
	href="../mib_module/ustScalarSet.h">ustScalarSet.h</a></td><td>The mib module's header file</td>
	<tr bgcolor="#d0d0ff"><td><a
	href="../mib_module/ustScalarSet.c">ustScalarSet.c</a></td><td>The mib module's C source code</td>
      </table>
      </center>
      <hr>
    <p>
      The shared object loader calls the "init_ustScalarSet()"
      function when the module gets loaded, and calls the
      "deinit_ustScalarSet()" when (and if) the module is unloaded.
      These function names to use are built by adding the shared
      object's module name (UCD-DLMOD-MIB::dlmodName) to the `init_'
      and `deinit_' prefixes.
      <p>
      Steps to build the shared object:
      <ol>
	<li>First off we must get the 
<a href="../demoapp/Makefile">Makefile</a> file, the <a
href="../mib_module/ustScalarSet.h">ustScalarSet.h</a> file, and the <a
href="../mib_module/ustScalarSet.c">ustScalarSet.c</a> file.
	<li><b>make ustScalarSet.so</b>
    </ol>
    <p>
      Steps to test the shared object:
      <ol>
      <li> Start the snmpd and watch the dlmod and ustScalarSet
      modules interact using the debugging flag (this assumes you
      already have <a
      href="http://www.net-snmp.org/FAQ.html#I_don_t_understand_the_new_access_control_stuff___what_does_it_mean_">access control</a> set up properly for your agent):
	<p><ul>
	  <li> % <b>snmpd -f -L -DustScalarSet,dlmod </b>
	</ul><p>
      <li> In another window, test to make sure that the agent doesn't 
      currently support the ustScalarSet (if you get different results 
      running this command you need to recompile the ucd-snmp agent
      without the ustScalarSet mib module compiled in directly):
	<p><ul>
	  <li> % <b>snmpget  localhost UCD-SNMP-TUTORIAL-MIB::ustSSSimpleString.0 </b>
	<p><pre>
ustSSSimpleString.0 = No Such Object available on this agent
	    </pre>	</ul><p>

      <li> Then, run snmpset to create a new row in the dlmod table:
	<p><ul>
	  <li> % <b>snmpset  localhost UCD-DLMOD-MIB::dlmodStatus.1 i create </b>
<p><pre>
dlmodStatus.1 = create(6)
</pre>
	<p></ul>
      <li> See that the row was created:
	<p><ul>
	    <li> % <b>snmptable  localhost UCD-DLMOD-MIB::dlmodTable </b>
<p><pre>
SNMP table: dlmodTable

 dlmodName dlmodPath dlmodError dlmodStatus
                                   unloaded
</pre><p>
	</ul>
      <li> Then set the properties of the row up to point to our new
      object and to give it a name:
	<p><ul>
	  <li> % <b>snmpset localhost UCD-DLMOD-MIB::dlmodName.1 s "ustScalarSet" UCD-DLMOD-MIB::dlmodPath.1 s "/path/to/ustScalarSet.so" </b>
<p><pre>
dlmodName.1 = "ustScalarSet" 
dlmodName.1 = "/path/to/ustScalarSet.so"
</pre>
	  <li> % <b>snmptable  localhost UCD-DLMOD-MIB::dlmodTable </b>
<p><pre>
SNMP table: dlmodTable

    dlmodName dlmodPath                 dlmodError   dlmodStatus
 ustScalarSet /path/to/ustScalarSet.so                  unloaded
</pre><p>
	</ul>
	<li> Finally, load the shared object into the running agent:
	<p><ul>
	  <li> % <b>snmpset  localhost UCD-DLMOD-MIB::dlmodStatus.1 i load </b>
<p><pre>
dlmodName.1 = ustScalarSet
dlmodName.1 = /path/to/ustScalarSet.so
</pre>
	  <li> % <b>snmptable  localhost UCD-DLMOD-MIB::dlmodTable </b>
<p><pre>
SNMP table: dlmodTable

    dlmodName                      dlmodPath dlmodError dlmodStatus
 ustScalarSet /path/to/ustScalarSet.so                 loaded
</pre><p>
	</ul>
      <li> If everything above was done correctly, then the following
	command should work and will access the shared object's data:
	<p><ul><li> % <b>snmpget  localhost UCD-SNMP-TUTORIAL-MIB::ustSSSimpleString.0 </b>
<p><pre>
ustSSSimpleString.0 = "Hello World"
</pre><p>
	</ul>
    </ol>
    <hr>
    <p> You can also load shared objects using the "dlmod" token in the
    snmpd.conf file by putting a line like this in your snmpd.conf file:
<p><pre>
      dlmod ustScalarSet /path/to/ustScalarSet.so
    </pre>  
    <p>The first argument specifies the shared object's module name
      (UCD-DLMOD-MIB::dlmodName) and second argument specifies the
      full pathname of the shared object file.
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