net-snmp安装手记

[清钟沁桐]

对于更多的net-snmp的资料,可以去www.net-snmp.org中获得.

另外,net-snmp在FC6上可以正确编译通过,在FC4上编译时却发现二个错误,一个是找不到libbeencrypt.la这个文件,第二个错
误是无法链接到elf库.

如果出现这二个错误,去网络上下载以下二个软件包进行编译就行了:

1.beecrypt-4.1.2.tar.gz

2.libelf-0.8.10.tar.gz



On Redhat 7.1 or above, NetSnmp has become the default snmp...

But on other linux version. It is still a good guide.

In this tutorial we will

* download and install net-snmp,
* write and install a simple MIB,
* write a subagent to handle to mib.

Download and install net-snmp package

This package was previously known as ucd-snmp

1. Download the source from here, or if this link is broken try the
net-snmp homepage, 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 2nd "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.txt:

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
here. 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
example2.c.

Download example2.c and example1.h

$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.

--by Jaiwant Mulik, March 2002.




------------------------------------------------------------------------------------------------------------------------


linux下安装net-snmp，从源码安装，make的时候报错
cannot find the library `/usr/lib/libbeecrypt.la'
安装beecrypt包后，还是报相同的错，按说应该安装成功了，为什么还很难找到呢？
发现默认安装时，libbeecrypt.la安装在了/usr/local/lib目录下。
建立符号连接 ln -s /usr/local/lib/libbeecrypt.la /usr/lib/
libbeecrypt.la
然后进行安装
./configure --prefix=/usr/local/net-snmp
make
make install
安装成功！