netsnmp 安装与配置

net-snmp installation and configuration
Recently I spent much time to learn SNMP to try to setup a snmp server for the developers. The following is the steps of installation and configuration of net-snmp, a popular and open source snmp server and agent .


DOWNLOAD AND INSTALL
1.download the source.

or the official web:
2.Extract the packet.
tar -zxvf net-snmp-5.4.tar.gz
3.Compile the packet.
cd net-snmp-5.4
./configure (for example ./configure --with-mib-modules="agentx")
make
make test
make install
4.Copy the example configure file
cp EXAMPLE.conf /usr/local/share/snmp/snmpd.conf
5.Modify the configure file as following
Change the COMMUNITY to democommunity which is a community string
6.check the process of snmpd and kill it and then run it
ps -A | grep snmp kill xxxx snmpd -d -L
7.have a try.
snmpget -v 1 -c democommunity localhost system.sysUpTime.0
INSTALL A MIB
1. A mibs file like JM-TEST-1-MIB.txt. the following is the content.

JM-TEST-1-MIB DEFINITIONS ::= BEGINIMPORTS        MODULE-IDENTITY,         OBJECT-TYPE,         INTEGER                 FROM SNMPv2-SMI;jmtest MODULE-IDENTITY    LAST-UPDATED "200203210000Z"    ORGANIZATION "Temple U"    CONTACT-INFO        "None yet."    DESCRIPTION        "AgentX testing MIB"    REVISION     "200203210000Z"    DESCRIPTION        "None yet."    ::= { experimental 72}firstKey OBJECT-TYPE    SYNTAX      INTEGER (0..100)    MAX-ACCESS  read-write    STATUS      current    DESCRIPTION        "Value initialized to 0 and on each          access:         - Return current val.         - increment"    ::= { jmtest 1 }END
2.Copy the mib file to the correct locations
cp JM-TEST-1-MIB.txt /usr/local/share/snmp/mibs
3.Let the snmp tools to recognize the mibs
echo "mibs +JM-TEST-1-MIB" >> /usr/local/share/snmp/snmp.conf
4.Use the snmptranslate to verify if the mib is loaded.
snmptranslate -IR -Tp experimental
and should get the following show:
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
+--experimental(3)
|
+--jmtest(72)
+-- -RW- INTEGER firstKey(1)
Range: 0..100

1. Download the source from , or if this link is broken try the , to your local directory which we will now refer to as $. For this tutorial we will use net-snmp-5.0-pre2.
2. change directory to $, untar and unzip the package using:

   $gunzip net-snmp-5.0.pre2.tar.gz
   $tar xvf net-snmp-5.0.pre2.tar

   This will dump all the souce into $/net-snmp-5.0.pre2
3. To compile to package:

   $./configure --with-mib-modules="agentx"
   $make
   $make install
   $cd local; make install; cd ..
   $cd mibs; make install; cd ..

   The "configure" command configure the agent to use the AgentX protocol. This is a IETF defined protocol that allows a master/client relationship between agents and subagents. The last two command should not theoretically have to be to used ... but without them .. things do not seem to work. Now, we have to setup the snmpd configuration file, before "snmpd" can work properly.
4. Copy the example configuration file:

   $ cp $/EXAMPLE.conf /usr/local/share/snmp/snmpd.conf

5. Now we need to modify /usr/local/share/snmp/snmpd.conf as follows:
   1. Replace COMMUNITY with "democommunity". This is your community string.
   2. Comment out 2^nd "com2sec" line. We do not allow network access for now.
   3. On a new line at the end of the file add "master agentx". This tells the agents to behave as the master in the master/client AgentX protocol.
6. We now need to fix some library links (this is truely awful ... is this a Redhat or a net-snmp "problem"/"feature" ?)(Note: On some machines this is not required e.g RedHat 7.1 ... use your judgement :-))

   $ln -s /usr/local/lib/libnetsnmp-0.5.0.0.2.so /lib/libnetsnmp-0.5.0.0.2.so
   $ln -s /usr/local/lib/libnetsnmpagent-0.5.0.0.2.so /lib/libnetsnmpagent-0.5.0.0.2.so
   $ln -s /usr/local/lib/libnetsnmphelpers-0.5.0.0.2.so /lib/libnetsnmphelpers-0.5.0.0.2.so
   $ln -s /usr/local/lib/libnetsnmpmibs-0.5.0.0.2.so /lib/libnetsnmpmibs-0.5.0.0.2.so

7. To check "snmpd" do:
   become root

   $ ps awwux | grep snmp

   if you see an earlier snmpd deamon ... kill it

   $ cd $/net-snmp-5.0.pre2/agent
   $ ./snmpd -f -L

   This should start the "snmpd" agent but keep it attached to the current terminal (which is useful since we want to kill it very soon).
8. On another window:

   $snmpget -v 1 -c democommunity localhost system.sysUpTime.0

   If snmpd was installed correctly, this gives up the timeticks the snmpd agent has been up (NOT how long your system was up !!). If you get an error .. retrace your steps from the beginning.

   You can now use "^C" to kill the snmpd deamon in the first window.

Writing and installing a MIB

In this part of the the tutorial we will write and install a simple MIB.

1. First write the mib that you want to implement. For our tutorial we write a simple MIB called :

   JM-TEST-1-MIB DEFINITIONS ::= BEGIN
   
   IMPORTS
           MODULE-IDENTITY, 
           OBJECT-TYPE, 
           INTEGER 
                   FROM SNMPv2-SMI;
   
   jmtest MODULE-IDENTITY
       LAST-UPDATED "200203210000Z"
       ORGANIZATION "Temple U"
       CONTACT-INFO
           "None yet."
       DESCRIPTION
           "AgentX testing MIB"
       REVISION     "200203210000Z"
       DESCRIPTION
           "None yet."
       ::= { experimental 72}
   
   firstKey OBJECT-TYPE
       SYNTAX      INTEGER (0..100)
       MAX-ACCESS  read-write
       STATUS      current
       DESCRIPTION
           "Value initialized to 0 and on each 
            access:
            - Return current val.
            - increment"
   
       ::= { jmtest 1 }
   
   END

   This mib represents a resource "firstKey" whose initial value is 0 and whose value gets incremented every time it is queried.

   Note that this MIB will be registered under the 1.3.6.1.3.72 heirarchy. This choice is arbitrary and should only be used for experiments. For real world implementation you should get a "real" OID. Existing OIDs and guidelines on getting new ones can be fo und . This page is maintained by the current (March 2002) IETF/IESG chair, so he probably knows what he is talking about.

   Copy this mib into the mibs directory

   $cp JM-TEST-1-MIB.txt /usr/local/share/snmp/mibs

2. Now we need to get the SNMP tools to recognise this MIB. So:

   $echo "mibs +JM-TEST-1-MIB" >> /usr/local/share/snmp/snmp.conf

   This adds a directive to the snmp tools configuration asking them load our mib.
3. To verify if our MIB is loaded use the verstile snmptranslate command:

   $snmptranslate -IR -Tp experimental

   This command will draw the present tree under the experimental branch. Omit the last parameter and you will get the whole tree (as currenly understood by the snmp tools). The output should look like:

   Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
   +--experimental(3)
      |
      +--jmtest(72)
         +-- -RW- INTEGER   firstKey(1)
                  Range: 0..100

   If you get the above output, then we are in good shape so far. The real work, howeve still remains. We must now write the subagent that will handle queries on under this OID branch.

Writing and installing a subagent

In this section we will write and install a subagent that serves the mib we installed in the previous section.

The subagent is an independent program that communicates with the master agent (snmpd in our case) using the AgentX protocol.

The basic steps of writing the code is as follows:

1. Write the agent code in a C file, say example.c. This can be done using the mib2c tool.
2. Create the subagent executable using the net-snmp-config tool.

mib2c is (supposed to) take in the MIB definition as spit out the subagent code. However (as far as I could figure out) the mib2c program distributed with this version of net-snmp does not generate code for simple scalar mibs, instead dealing with mibs th at have tables.

So for an example of subagent code for simple scalar objects look at $/agent/mibgroups/example/example.c.

We have adapted example.c for our mib (JM-TEST-1-MIB.txt) as .

Download and

$mkdir $/agent/mibgroup/examples/subagent
$cp example2.c $/agent/mibgroup/examples/subagent
$cp example.h $/agent/mibgroup/examples/subagent

Now we create the executable using the net-snmp-config tools as:

$net-snmp-config --compile-subagent example2 example2.c -I../../../mibgroup

This produces a executable called example2. example2 is our subagent. Voila !

To test whether things are still working.

In first window:

$cd $/agent
$./snmpd -f -L -D

This will start the snmpd deamon in the debugging mode (you will see LOTS of messages).

In the second window:

$cd agent/mibgroup/examples/subagent
$./example2

Finally in the third window, the command and output should look like (output is shown in bold):

[root@x mibs]# snmpget -v 1 -c democommunity localhost firstKey.0
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
JM-TEST-1-MIB::firstKey.0 = 1
[root@x mibs]# snmpget -v 1 -c democommunity localhost 1.3.6.1.3.72.1.0
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
JM-TEST-1-MIB::firstKey.0 = 2
[root@x mibs]# snmpset -v 1 -c democommunity localhost 1.3.6.1.3.72.1.0 i 10
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
JM-TEST-1-MIB::firstKey.0 = 10
[root@x mibs]# snmpget -v 1 -c democommunity localhost firstKey.0
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
JM-TEST-1-MIB::firstKey.0 = 10
[root@x mibs]# snmpget -v 1 -c democommunity localhost 1.3.6.1.3.72.1.0
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
JM-TEST-1-MIB::firstKey.0 = 11
[root@x mibs]# snmpget -v 1 -c democommunity localhost 1.3.6.1.3.72.1.0
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
JM-TEST-1-MIB::firstKey.0 = 12
[root@x mibs]# snmpwalk -v 1 -c democommunity localhost firstKey        
Unlinked OID in JM-TEST-1-MIB: jmtest ::= { experimental 72 }
JM-TEST-1-MIB::firstKey.0 = 13

In the output above notice that every snmpget query returns an increasing value of "firstKey" and snmpset lets us set "firstKey" to an arbitrary value (within a defined range).

We now have a working subagent. In real applications the subagent could be embedded in the application to be managed.