目錄

1          基本概念

請參閱《TCP-IP詳解卷1》——《第25章SNMP:簡單網路管理協議》

MIBS rfc詳見原始碼目錄下的doc\rfc\smiV2

MIBS總共有三種實體：

1.2.1    scalar：變數，就是一個量（包括整數理、字串型、IPADDRESS等）

snmp認證目前有三個版本：snmpv1、snmpv2、snmpv3

snmpv1（rfc1157）、snmpv2（rfc1901）都是基於密碼字串的認證，且密碼為明文。

snmpv3（rfc2571）認證分為使用USM（基於使用者的安全模式）和VACM（基於檢視的訪問控制模式）。認證的加協議有：MD5、SHA；加密協議有：DES、AES；加密協議用於加密PDU資料。

./configure –help #檢視配置

./configure

make

make install

4          程式

4.1         snmpd:響應snmp

請求包的代理伺服器。

用法：-f 不呼叫fork,即不進入daemon，如果不用這個引數，則進入daemon模式

      -L[efos]日誌輸出到指定的位置

       -Le    Log messages to the standard error stream.

       -Lf FILE

              Log messages to the specified file.

       -Lo    Log messages to the standard output stream.

       -Ls FACILITY

              Log  messages  via  syslog,  using the specified facility

              ('d' for LOG_DAEMON, 'u' for  LOG_USER,  or  '0'-'7'  for

              LOG_LOCAL0 through LOG_LOCAL7).

4.4         snmpget、snmpgetnext、snmpwalk：得到請求

4.10      mib2c：用於從mib檔案生成擴充套件模組c程式碼的工具。

  -V, --version         顯示命令的版本號

SNMP Version 1 or 2c specific

  -c COMMUNITY          設定團體名

SNMP Version 3 specific

  -a PROTOCOL           設定認證協議 (MD5|SHA)

  -A PASSPHRASE         設定認證協議密碼

  -e ENGINE-ID          set security engine ID (e.g. 800000020109840301)

  -E ENGINE-ID          set context engine ID (e.g. 800000020109840301)

  -l LEVEL              set security level (noAuthNoPriv|authNoPriv|authPriv)

  -n CONTEXT            set context name (e.g. bridge1)

  -u USER-NAME          set security name (e.g. bert)

  -x PROTOCOL           設定加密協議 (DES|AES)

  -X PASSPHRASE         設定加密協議密碼

  -Z BOOTS,TIME         set destination engine boots/time

例子：

snmpgetnext -v 1 -c public 127.0.0.1 sysUpTime

snmpget –v 3 –a MD5 –A 1235678 –u name 127.0.0.1 oid

5          配置

用配置工具 snmpconf 進行配置

配置包括三個部分：

###########################################################################

# SECTION: Textual mib parsing

#

#   This section controls the textual mib parser.  Textual

#   mibs are parsed in order to convert OIDs, enumerated

#   lists, and ... to and from textual representations

#   and numerical representations.

# mibs: Specifies a list of mibs to be searched for and loaded.

#   Adding a '+' sign to the front of the argument appends the new

#   mib name to the list of mibs already being searched for.

#   arguments: [+]mibname[:mibname...]

mibs  +/root/test/NET-SNMP-EXAMPLES-MIB.txt

5.2.3    安裝存取控制

###########################################################################

# SECTION: Access Control Setup

#

#   This section defines who is allowed to talk to your running

#   snmp agent.

# rwcommunity: a SNMPv1/SNMPv2c read-write access community name

#   arguments:  community [default|hostname|network/bits] [oid]

rwcommunity  public 127.0.0.1

rwcommunity public 192.168.0.1

# rwuser: a SNMPv3 read-write user

#   arguments:  user [noauth|auth|priv] [restriction_oid]

rwuser  public  #這裡定義使用者名稱和驗證方式，密碼儲存在/var/net-snmp/snmpd.conf中

# rouser: a SNMPv3 read-only user

#   arguments:  user [noauth|auth|priv] [restriction_oid]

rouser  public  #這裡定義使用者名稱和驗證方式，密碼儲存在/var/net-snmp/snmpd.conf中,詳見——用net-snmp-config配置V3

###########################################################################

# SECTION: Trap Destinations

#

#   Here we define who the agent will send traps to.

# trap2sink: A SNMPv2c trap receiver

#   arguments: host [community] [portnum]

trap2sink 127.0.0.1 public 162

trap2sink 192.168.0.1 public 162

###########################################################################

# SECTION: Extending the Agent

#

#   You can extend the snmp agent to have it return information

#   that you yourself define.

# dlmod: dynamically extend the agent using a shared-object

#   arguments:  module-name module-path

dlmod  notification /data/snmp/test/.libs/ libnetsnmpmibs.so

#authCommunity   TYPES COMMUNITY  [SOURCE [OID | -v VIEW ]]

authCommunity log,execute,net public

[email protected]:~# net-snmp-config --create-snmpv3-user --help

Usage:

net-snmp-create-v3-user [-ro] [-A authpass] [-X privpass]

[-a MD5|SHA] [-x DES|AES] [username]

[email protected]:~# net-snmp-create-v3-user -ro -A SHA -a public1234 -x DES -X abcdefgmok public

adding the following line to /var/net-snmp/snmpd.conf:

createUser public SHA "public1234" DES abcdefgmok

adding the following line to /usr/local/share/snmp/snmpd.conf:

rouser public

net-snmp-create-v3-user實質上是個指令碼檔案

它實質上是把V3的使用者配置（createUser public SHA "public1234" DES abcdefgmok）加到/var/net-snmp/snmpd.conf檔案中。然後agent從這個檔案中讀取v3的使用者配置資訊。然後生成相應的密碼並儲存在這個檔案中。

SNMP Version 3 引數：

  -a PROTOCOL           設定認證協議 (MD5|SHA)

  -A PASSPHRASE         設定認證協議密碼

  -x PROTOCOL           設定加密協議 (DES|AES)

  -X privpass           設定加密協議密碼

6          啟動

執行 snmpd –f –Lo

後臺方式 snmpd

[email protected]:~# snmpget -v 1 -c public 127.0.0.1 UDP-MIB::udpInDatagrams.0

UDP-MIB::udpInDatagrams.0 = Counter32: 7822

如果出現錯誤，請檢查配置是否正確。

8          開發

8.1         程式邏輯

snmpd代理完成兩個功能：

8.1.1    接收網管發過來的snmp包，並對接收到的snmp包進行解析，校驗後，找到並呼叫相應的處理函式進行處理。

下面是處理snmp包的堆疊：

#0 reachalarmSubscriberTable_handler (handler=0x8159980, reginfo=0x8122b78,

reqinfo=0x817d050, requests=0x817d138) at reachalarmSubscriberTable.c:116

#1 0x008e08e6 in netsnmp_call_handler (requests=0x817d138, reqinfo=0x817d050,

reginfo=0x8122b78, next_handler=0x8159980) at agent_handler.c:526

#2 netsnmp_call_next_handler (current=0x8146088, reginfo=0x8122b78,

reqinfo=0x817d050, requests=0x817d138) at agent_handler.c:640

#3 0x008dab83 in netsnmp_table_iterator_helper_handler (handler=0x8146088,

reginfo=0x8122b78, reqinfo=0x817d050, requests=0x817d138)

at helpers/table_iterator.c:936

#4 0x008e08e6 in netsnmp_call_handler (requests=0x817d138, reqinfo=0x817d050,

reginfo=0x8122b78, next_handler=0x8146088) at agent_handler.c:526

#5 netsnmp_call_next_handler (current=0x813dcf0, reginfo=0x8122b78,

reqinfo=0x817d050, requests=0x817d138) at agent_handler.c:640

#6 0x008d268c in table_helper_handler (handler=0x813dcf0, reginfo=0x8122b78,

reqinfo=0x817d050, requests=0x817d138) at helpers/table.c:712

#7 0x008e0291 in netsnmp_call_handler (requests=0x817d138, reqinfo=0x817d050,

reginfo=0x8122b78, next_handler=0x813dcf0) at agent_handler.c:526

#8 netsnmp_call_handlers (reginfo=0x8122b78, reqinfo=0x817d050,

requests=0x817d138) at agent_handler.c:611

#9 0x008efc4a in handle_var_requests (asp=0x817c738) at snmp_agent.c:2676

#10 0x008f0150 in handle_getnext_loop (asp=0x817c738) at snmp_agent.c:3122

#11 0x008f0b0b in handle_pdu (asp=0x817c738) at snmp_agent.c:3499

#12 0x008f0c98 in netsnmp_handle_request (asp=0x817c738, status=0)

at snmp_agent.c:3278

#13 0x008f16bc in handle_snmp_packet (magic=0x0, pdu=0x8191178,

session=0x817c898, op=<optimized out>, reqid=<optimized out>)

at snmp_agent.c:1987

#14 handle_snmp_packet (op=1, session=0x817c898, reqid=8, pdu=0x8191178,

magic=0x0) at snmp_agent.c:1889

#15 0x003808a6 in _sess_process_packet (sessp=0x817c6c0, sp=0x817c898,

isp=0x817c860, transport=0x817c6d8, opaque=0x817d618, olength=36,

packetptr=0x8180ba0 "0&\002\001", length=40) at snmp_api.c:5400

#16 0x00381d0b in _sess_read (sessp=0x817c6c0, fdset=0xbfd00128)

at snmp_api.c:5829

#17 0x0038250a in snmp_sess_read2 (sessp=0x817c6c0, fdset=0xbfd00128)

at snmp_api.c:5861

#18 0x003825f4 in snmp_read2 (fdset=0xbfd00128) at snmp_api.c:5463

#19 0x0804bcee in receive () at snmpd.c:1315

#20 main (argc=6, argv=0xbfd00414) at snmpd.c:1105

net-snmp可以進行對snmp包處理程式和告警進行擴充套件。

示例程式存放在原始碼目錄：agent\mibgroup\examples下。

示例MIBS檔案：

mibs\NET-SNMP-MIB.txt

mibs\NET-SNMP-EXAMPLES-MIB.txt

用mg-soft builder生成。

mibs\NET-SNMP-EXAMPLES-MIB.txt

export MIBS=ALL

並把MIBS檔案複製到net-snmp安裝目錄的中的mibs目錄下

MIBS  ALL #搜尋/usr/share/snmp/mibs下的所有檔案

MIBS  +/usr/share/snmp/ NET-SNMP-EXAMPLES-MIB.txt#加入新建立的檔案

[email protected]:~# snmptranslate -TB netSnmpExamples

NET-SNMP-EXAMPLES-MIB::netSnmpExamples

NET-SNMP-EXAMPLES-MIB::netSnmpExampleScalars

NET-SNMP-EXAMPLES-MIB::netSnmpExampleString

NET-SNMP-EXAMPLES-MIB::netSnmpExampleSleeper

解析正確，就說明MIBS檔案配置正確。

8.3.3.1    直接在你想要生成程式碼的目錄下執行下面命令：

mib2c實體名

mib2c會提示你進行操作

[email protected]:~#mib2c netSnmpExamples

writing to -

mib2c has multiple configuration files depending on the type of

code you need to write. You must pick one depending on your need.

You requested mib2c to be run on the following part of the MIB tree:

OID:                              netSnmpExamples

numeric translation:              .1.3.6.1.4.1.8072.2

number of scalars within:         8

number of tables within:          3

number of notifications within:   1

First, do you want to generate code that is compatible with the

ucd-snmp 4.X line of code, or code for the newer Net-SNMP 5.X code

base (which provides a much greater choice of APIs to pick from):

1) ucd-snmp style code

2) Net-SNMP style code

Select your choice :

建議做法是：為每一個實體單獨生成一組檔案。這樣條理比較清楚。

8.3.3.2    如果你清楚模組，可以用下面命令直接指定模板。

mib2c –c 模板檔案實體名

模板檔案位於: /usr/share/snmp/*.conf

實體名：本列中是：netSnmpExamples

注意：模組名不要與已存的的模組名重複，否則會出錯（沒有提示，這就看mib2c先搜尋到哪個MIBS，就應用哪個）。且模組名是大小寫敏感覺的。

執行完後，會生成一組列檔案。

[email protected]:~/test/mib# mib2c netSnmpExampleInteger

writing to -

mib2c has multiple configuration files depending on the type of

code you need to write. You must pick one depending on your need.

You requested mib2c to be run on the following part of the MIB tree:

OID:                              netSnmpExampleInteger

numeric translation:              .1.3.6.1.4.1.8072.2.1.1

number of scalars within:         1

number of tables within:          0

number of notifications within:   0

First, do you want to generate code that is compatible with the

ucd-snmp 4.X line of code, or code for the newer Net-SNMP 5.X code

base (which provides a much greater choice of APIs to pick from):

1) ucd-snmp style code

2) Net-SNMP style code

Select your choice : 2

**********************************************************************

GENERATING CODE FOR SCALAR OBJECTS:

**********************************************************************

It looks like you have some scalars in the mib you requested, so I

will now generate code for them if you wish.  You have two choices

for scalar API styles currently.  Pick between them, or choose not

to generate any code for the scalars:

1) If you're writing code for some generic scalars

(by hand use: "mib2c -c mib2c.scalar.conf netSnmpExampleInteger")

2) If you want to magically "tie" integer variables to integer

scalars

(by hand use: "mib2c -c mib2c.int_watch.conf netSnmpExampleInteger")

3) Don't generate any code for the scalars

Select your choice: 1

using the mib2c.scalar.conf configuration file to generate your code.

writing to netSnmpExampleInteger.h

writing to netSnmpExampleInteger.c

**********************************************************************

* NOTE WELL: The code generated by mib2c is only a template. *YOU*  *

* must fill in the code before it'll work most of the time. In many *

* cases, spots that MUST be edited within the files are marked with *

* /* XXX */ or /* TODO */ comments.                                 *

**********************************************************************

running indent on netSnmpExampleInteger.h

running indent on netSnmpExampleInteger.c

[email protected]:~/test/mib# mib2c netSnmpHostsTable

writing to -

mib2c has multiple configuration files depending on the type of

code you need to write. You must pick one depending on your need.

You requested mib2c to be run on the following part of the MIB tree:

OID:                              netSnmpHostsTable

numeric translation:              .1.3.6.1.4.1.8072.2.2.2

number of scalars within:         0

number of tables within:          1

number of notifications within:   0

First, do you want to generate code that is compatible with the

ucd-snmp 4.X line of code, or code for the newer Net-SNMP 5.X code

base (which provides a much greater choice of APIs to pick from):

1) ucd-snmp style code

2) Net-SNMP style code

Select your choice : 2

**********************************************************************

GENERATING CODE FOR TABLES:

**********************************************************************

The Net-SNMP agent API is extremely extensive and, in fact, lets

each programmer write agent code according to the style that works

best for them based on their experience and their preference.  We're

going to ask you a serious of questions that will help mib2c

generate code that best suits *your* needs, as the programmer that

will be responsible for taking the code and further refining it.  If

you don't like how the results look, you are always welcome to

re-run mib2c and select a different set of options.

There are essentially two tasks involved in processing requests

for OIDs within a MIB table - firstly identifying the relevant row

of the table for a given request, and then returning (or updating)

the appropriate column value within that row.  Many MIB tables model

the state of some external system (the kernel, a device, processes,

etc), and the MIB implementation module (the code we're about to

produce a template for) acts as an interface between this underlying

system and the SNMP side.  Other tables hold data internally that is

only available within the agent itself, or at least the master copy

of the data is held within the agent.

There are a number of different code templates that can be used to

implement MIB tables, using various approaches to these two tasks.

There are three basic approaches to identifying the relevant row:

1) Pass the request through to the table-specific code, and

identify the requested row there (for both GET and GETNEXT

requests).  This is typically the most efficient way to get

up-to-date information, but relies on suitable

  (programmer-provided) code within the MIB handler.

Most importantly, you should be an expert to use this choice.

This will produce code based on the table_dataset handler.

2) Have table-specific code to provide information about which

rows exist in the table (by iterating through them in turn),

but utilise standard helper code to select the appropriate

row for a given request.  This is particularly suitable for

tables where the data is naturally stored in a "random" order

(or differently to the MIB table index), or where rows are

frequently added to or removed from the table.

However searching for the requested row is not very efficient,

and performance can be slow - particularly for large tables with

many rows.

3) Hold a locally cached copy of the contents of the table (or at

least a cache of which rows are valid), and utilise standard

helper code to select the appropriate row.  This is

significantly faster than the iterator-based approach, but

cached data is inevitably slightly "stale" with respect to the

data from the underlying system being managed.  This approach,

since it relies on caching of data, is also results in a larger

memory footprint.  It is less appropriate for tables where rows

are frequently added or removed externally to the agent (i.e.,

not via SNMP requests).

This approach can also be used where _all_ use of the table is

via SNMP, and there is no external "underlying system".  In

this case, the local cache is the canonical version of the

table.

4) Do not generate code for the tables.

Select the option that best fits your requirements: 2

Having identified the appropriate row for a given request, there are

three basic styles of code for returning (or updating) the requested

column value from within this row:

1) A single handler routine, which contains all the code needed to

handle GET and SET requests for each of the column objects.

The code typically looks like a single function with a large 'case'

statement covering each of the columns.

This will produce code based on the 'iterator' hepler.

2) A set of individual routines, each of which is concerned

with a particular aspect of processing the request.

Each column object within the table has one routine for

retrieving the current value, and another for setting a new one.

This will produce code based on the 'iterate_access' hepler.

3) A (different) set of individual routines, each of which is

smaller and more tightly focused than the code generated by

style 2.  The aim here is to reduce the amount of SNMP specific

knowledge required to implement a module, and hide much of the

SNMP terminology and processing within standard generated code

(which can simply be used sight unseen).

This will produce code based on the 'mfd' hepler ('MIB for Dummies').

4) Do not generate code for the tables.

(In all cases, GETNEXT requests are automatically converted

into the equivalent GET request, so the MIB specific code

  need only be concerned with GET and SET requests.).

Select the code style you wish to use: 1

The same template code can be generated using

mib2c -c mib2c.iterate.conf netSnmpHostsTable

This framework can work in one of two ways:

1)  Hold a local cached copy of some external data

which is then used to service incoming requests.

2)  Query the external data directly for each request.

The first is typically more efficient, but results in

slightly "stale" data (depending on the expiration timeout

for the cache) and greater memory usage. The second can

provide more up-to-date information, but at the cost of

higher processing overheads.

Which is more appropriate for your needs?

Select your choice : 1

writing to netSnmpHostsTable.h

writing to netSnmpHostsTable.c

**********************************************************************

* NOTE WELL: The code generated by mib2c is only a template. *YOU*  *

* must fill in the code before it'll work most of the time. In many *

* cases, spots that MUST be edited within the files are marked with *

* /* XXX */ or /* TODO */ comments.                                 *

**********************************************************************

running indent on netSnmpHostsTable.h

running indent on netSnmpHostsTable.c

[email protected]:~/test/mib# mib2c netSnmpExampleHeartbeatNotification

writing to -

mib2c has multiple configuration files depending on the type of

code you need to write. You must pick one depending on your need.

You requested mib2c to be run on the following part of the MIB tree:

OID:                              netSnmpExampleHeartbeatNotification

numeric translation:              .1.3.6.1.4.1.8072.2.3.0.1

number of scalars within:         0

number of tables within:          0

number of notifications within:   1

First, do you want to generate code that is compatible with the

ucd-snmp 4.X line of code, or code for the newer Net-SNMP 5.X code

base (which provides a much greater choice of APIs to pick from):

1) ucd-snmp style code

2) Net-SNMP style code

Select your choice : 2

**********************************************************************

GENERATING CODE FOR NOTIFICATIONS:

**********************************************************************

Would you like to generate code for sending notifications from within

the agent?

"y" or "n": y

using mib2c.notify.conf to generate code for sending notifications

writing to netSnmpExampleHeartbeatNotification.h

writing to netSnmpExampleHeartbeatNotification.c

# GENERATING HEADER FILE DEFINITIONS

#

#   To generate just a header with a define for each column number in

#   your table:

#

#     mib2c -c mib2c.column_defines.conf netSnmpExampleHeartbeatNotification

#

#   To generate just a header with a define for each enum for any

#   column containing enums:

#

#     mib2c -c mib2c.column_enums.conf netSnmpExampleHeartbeatNotification

**********************************************************************

* NOTE WELL: The code generated by mib2c is only a template. *YOU*  *

* must fill in the code before it'll work most of the time. In many *

* cases, spots that MUST be edited within the files are marked with *

* /* XXX */ or /* TODO */ comments.                                 *

**********************************************************************

running indent on netSnmpExampleHeartbeatNotification.c

running indent on netSnmpExampleHeartbeatNotification.h

scalar實體和table實體其實是一類程式碼，只是處理的複雜度不一樣。

程式碼的核心，就是初始化函式時（程式初始化載入或動態庫載入），向代理(snmpd)註冊了回撥處理函式，當(snmpd)接收到一個snmp請求包時，它會先對包進行校驗，如果校驗不通過，會返回相應的錯誤。如果通過後，它會解析請求包，並把請求包的內容轉換成請求結構（netsnmp_agent_request_info【包含請求包的pdu資訊】，netsnmp_request_info【包含請求包的vb資訊】）。匹配到相關的oid時，就呼叫相應的註冊處理函式並傳入請求結構給處理函式，處理函式只需要根據結構中的內容進行相應的業務處理就可以了。

/** Initializes the netSnmpExampleInteger module */

void

init_netSnmpExampleInteger(void)

{

    const oid netSnmpExampleInteger_oid[] = { 1,3,6,1,4,1,8072,2,1,1 };

  DEBUGMSGTL(("netSnmpExampleInteger", "Initializing\n"));

    netsnmp_register_scalar(

       netsnmp_create_handler_registration("netSnmpExampleInteger", handle_netSn

mpExampleInteger,

                              netSnmpExampleInteger_oid, OID_LENGTH(netSnmpExamp

leInteger_oid),

                               HANDLER_CAN_RWRITE

        ));

}

初始函式呼叫netsnmp_create_handler_registration向snmpd註冊netSnmpExampleInteger_oid的處理函式handle_netSnmpExampleInteger。

函式定義：

int

handle_netSnmpExampleInteger(netsnmp_mib_handler *handler,

                          netsnmp_handler_registration *reginfo,

                          netsnmp_agent_request_info   *reqinfo,

                          netsnmp_request_info         *requests)

當snmpd呼叫它時，便會把相應的snmp包的資訊從這幾個引數中傳進來。其中reqinfo就是snmp請求包被snmpd解析後得到的結構，包含了請求包的會話和pdu資訊；requests:主要包含了 VB 資訊。

/** @struct netsnmp_agent_request_info_s

* The agent transaction request structure

*/

    typedef struct netsnmp_agent_request_info_s {

        int             mode;

     /** pdu contains authinfo, eg */

/*        netsnmp_pdu    *pdu;    */

        struct netsnmp_agent_session_s *asp;    /* may not be needed */

        /*

* can be used to pass information on a per-pdu basis from a

* helper to the later handlers

*/

        netsnmp_data_list *agent_data;

} netsnmp_agent_request_info;

typedef struct netsnmp_agent_session_s {

        int             mode;

       netsnmp_session *session;

netsnmp_pdu    *pdu;

netsnmp_pdu    *orig_pdu;

        int             rw;

        int             exact;

        int             status;

        int             index;

        int             oldmode;

        struct netsnmp_agent_session_s *next;

        /*

* new API pointers

*/

        netsnmp_agent_request_info *reqinfo;

        netsnmp_request_info *requests;

        netsnmp_tree_cache *treecache;

        netsnmp_variable_list **bulkcache;

        int             treecache_len;  /* length of cache array */

        int             treecache_num; /* number of current cache entries */

        netsnmp_cachemap *cache_store;

        int             vbcount;

    } netsnmp_agent_session;

typedef struct netsnmp_request_info_s {

     /**

 * variable bindings

     */

        netsnmp_variable_list *requestvb;

     /**

     * can be used to pass information on a per-request basis from a

     * helper to the later handlers

     */

        netsnmp_data_list *parent_data;

       /*

* pointer to the agent_request_info for this request

*/

       struct netsnmp_agent_request_info_s *agent_req_info;

     /** don't free, reference to (struct tree)->end */

        oid            *range_end;

        size_t          range_end_len;

       /*

* flags

*/

        int             delegated;

        int             processed;

        int             inclusive;

        int             status;

     /** index in original pdu */

        int             index;

       /** get-bulk */

        int             repeat;

        int             orig_repeat;

        netsnmp_variable_list *requestvb_start;

       /* internal use */

        struct netsnmp_request_info_s *next;

        struct netsnmp_request_info_s *prev;

        struct netsnmp_subtree_s      *subtree;

} netsnmp_request_info;

每次處理一個SNMP請求，就呼叫一次註冊函式。從模板生成的檔案，可以很容易看出：通過requests遍歷vb。致於如何處理，你可以用模板生成的方法做，也可以按自己的想法做，你可以把這個看成應用程式的main函式就好了：）

例子可以看net-snmp自帶的示例程式。原始碼目錄\agent\mibgroup\examples\notification.c

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