snmp_agent_api − embedding an agent into a external application


#include <ucd-snmp/ucd-snmp-config.h>
#include <ucd-snmp/ucd-snmp-includes.h>
#include <ucd-snmp/ucd-snmp-agent-includes.h>

main () {
  int agentx_subagent=1; /* change this if you’re a master agent */


 /* if we’re an agentx subagent */
  if (agentx_subagent) {
      /* make us a agentx client. */
      ds_set_boolean(DS_APPLICATION_ID, DS_AGENT_ROLE, 1);


 /* initialize your mib code here */

 /* yourappname will be used to read yourappname.conf files. */

 /* If we’re going to be a snmp master agent */
  if (!agentx_subagent)
      init_master_agent(161, NULL, NULL);  /* open port 161 (UDP:snmp) */

 /* you’re main loop here... */
  while(whatever) {
      /* if you use select(), see snmp_api(3) */
      /*     --- OR ---  */
      agent_check_and_process(0); /* 0 == don’t block */

 /* at shutdown time */

cc ... -lucdagent -lucdmibs -lsnmp # other libraries may be needed here


Our goal is to create a easy to use interface to the ucd-snmp package such that you can take code that you have written that has been designed to be a ucd-snmp mib module and embed it into an external application where you can either chose to be a SNMP master agent or an AgentX sub-agent using the same mib module code. Our suggestion is that you use our (or another) SNMP agent as the AgentX master agent and chose to become an AgentX subagent which then attaches to the master.

Starting with version 4.1, the ucd-snmp package provides a pair of libraries that enables easy embedding of an SNMP or AgentX agent into an external software package. AgentX is an extensible protocol designed to allow multiple SNMP sub-agents all run on one machine under a single SNMP master agent. It is defined in RFC 2741.

You will need to perform a few tasks in order to accomplish this. First off, you will need to initialize both the SNMP library and the SNMP agent library. As indicated above, this is done slightly differently depending on whether or not you are going to perform as a master agent or an AgentX sub-agent.


If you intend to operate as an AgentX sub-agent, you will have to configured the ucd-snmp package as follows:

./configure --with-mib-modules="agentx/subagent"

Additionally, you will need to link against the libucdmibs library and call subagent_pre_init() as indicated above.


In order to make use of any of the above API, you will need to clinch against at least two libraries: the libucdagent library and the libsnmp library. Additionally, if you plan to make use of any of the code in the agent’s mib modules (like the AgentX subagent support), you will need to link against the libucdmibs library as well.



Logs error output from the SNMP agent to the standard error stream.


Please see the default_store(3) manual page for more information about this API.

init_agent(char *name)

Initializes the embedded agent. This should be called before the init_snmp() call. name is used to dictate what .conf file to read when init_snmp() is called later.

init_snmp(char *name)

Initializes the SNMP library. Note that one of the things this will do will be to read configuration files in an effort to configure your application. It will attempt to read the configuration files named by the name string that you passed in. It can be used to configure access control, for instance. Please see the read_config(3), snmp_config(5), and snmpd.conf(5) manual pages for further details on this subject.

init_master_agent(port, NULL, NULL)

Initializes the master agent and opens all its necessary ports. port is the port you want to listen for SNMP requests on.

agent_check_and_process(int block)

This checks for packets arriving on the SNMP port and processes them if some are found. If block is non-zero, the function call will block until a packet arrives or an alarm must be run (see snmp_alarm(3)). The return value from this function is a positive integer if packets were processed, zero if an alarm occurred and -1 if an error occured.

snmp_shutdown(char *name);

This shuts down the agent, saving any needed persistent storage, etc.


select(2), snmp_api(3), default_store(3), snmp_alarm(3), read_config(3), snmp_config(5), snmpd.conf(5)