Warning: Failed to connect to the agentx master agent ([NIL]) - snmp

Question

I have installed net-snmp5.7.2 on my system, I have written my app_agent.conf for my application and
agentXSocket udp:X.X.X.X:1610
and exported SNMPCONFIGPATH=path_to_app_agent.conf
I have also wrtten snmpd.conf in /usr/etc/snmp/snmp.conf
trap2sink X.X.X.Y
agentXSocket udp:X.X.X.X:1610
I have two more snmpd.conf present in my /etc/snmp/ and /var/net-snmp/
Config from /etc/snmp:
com2sec notConfigUser default public
com2sec notConfigUser v1 notConfigUser
com2sec notConfigUser v1 notConfigUser
view systemview included .1.3.6.1.2.1.1
view systemview included .1.3.6.1.2.1.25.1.1
access notConfigGroup "" any noauth exact systemview none none
pass .1.3.6.1.4.1.4413.4.1 /usr/bin/ucd5820stat
Config from /var/net-snmp:
setserialno 1322276014
ifXTable .1 14:0 18:0x $
ifXTable .2 14:0 18:0x $
ifXTable .3 14:0 18:0x $
engineBoots 14
oldEngineID 0x80001f888000e17f6964b28450
I have started snmpd and snmptrapd. Now in my code I am calling
netsnmp_ds_set_boolean(NETSNMP_DS_APPLICATION_ID, NETSNMP_DS_AGENT_ROLE, 1);
init_agent("app_agent");
init_snmp("app_agent");
init_snmp is throwing a warning
Warning: Failed to connect to the agentx master agent ([NIL]):
I have no idea why?? Thanks in advance for any help

Answer 1

This is basically saying the sub-agent you wrote failed to connect to NetSNMP master agent, as the message suggested. In Linux, by default agentx will attempt to make the connection via socket using /var/agentx/master. The following hint might help:
Running your sub-agent under appropriate privilege that has access
to sockets e.x. sudo
Check socket setting in your snmpd.conf (which located varies) if not already specified, such as
agentxsocket /var/agentx/master and agentxperms 777 777
Restart NetSNMP for any change to take effect with sudo service snmpd restart; or as an option you can try stop the service with sudo service snmpd stop and run an instance with debugging mode snmpd -f -Lo -Dagentx which most likely will output useful information on sub-agent connection.

Answer 2

I ran into this problem right now with quagga and ospfd and after doing an strace -f -p PID, noticed this among the output:
connect(14, {sa_family=AF_FILE, path="/var/agentx/master"}, 110) = -1 EACCES (Permission denied)
so I:
$ ls -al /var/agentx/
total 8
drwx------ 2 root root 4096 Sep 12 20:50 .
drwxr-xr-x. 27 root root 4096 Sep 12 20:13 ..
srwxrwxrwx 1 root root 0 Sep 12 20:50 master
and then I:
$ chmod 755 /var/agentx/
and immediately zebra and ospfd had their Agentx subnets connect.
$ tail -10f /var/log/quagga/zebra.log
2014/09/12 20:52:59 ZEBRA: snmp[info]: NET-SNMP version 5.5 AgentX subagent connected
$ tail -10f /var/log/quagga/ospfd.log
2014/09/12 20:52:59 OSPF: snmp[info]: NET-SNMP version 5.5 AgentX subagent connected
This is running quagga-0.99.23-2014062401 on RHEL6. hope this helps.

Answer 3

Had a similar problem, whether it be with the unix Sockets or Tcp:localhost:750 i was still getting the same error message:
/var/log/quagga/ospfd.log: warning, failed to connect to Master AgentX [nill] or [tcp:localhost:750].
I resolved the issue by disabling SELINUX.

Answer 4

This is not the answer to your problem, but I too got "Warning: Failed to connect to the agentx master agent ([NIL]):" message when my snmpd service didn't startup properly or went down. For my SNMP Sub-Agent, I used the example they provide, example-demon.c, and found I get this message nonstop (about every second) when processing agent_check_and_process(0) on every loop.
while (true) {
agent_check_and_process(0); /* 0 == don't block */
}
This is how I fixed it.
netsnmp_transport *snmpTransport;
while( true ) {
// Check to see snmpd is still running
snmpTransport = netsnmp_transport_open_client("agentx", NULL);
if (snmpTransport == NULL)
{
// Just went down?
if (snmpAgentDown == false)
{
snmp_log( LOG_INFO, "Net-SNMP Agent is down\n" );
snmpAgentDown = true;
}
Sleep(5000); // Sleep for a 5 sec
} else
{
if (snmpAgentDown)
{
snmp_log( LOG_INFO, "Net-SNMP Agent is back up\n" );
snmpAgentDown = false;
}
// Close connection test
snmpTransport->f_close(snmpTransport); // This burn me without; its needed
netsnmp_transport_free(snmpTransport);
// Process SNMP request and notifications
agent_check_and_process( 0 ); // 0 == don't block, 1 = block
Sleep(1); // Sleep for 1ms; Need to sleep thread, but need subAgent to be responsive too
}
i++;
}
Now if the snmpd goes down, my app can detect it being down and not process agent_check_and_process() stopping the "Warning: Failed to connect to the agentx master agent ([NIL]):" from ever appearing. If snmpd comes back up, then it processes it.
Final Note: I determine that code based off subagent.c file subagent_open_master_session() funtion in net-snmp-5.7.2 package. snmpTransport->f_close(snmpTransport) is also needed and determine that by following what snmp_close() did at the end of subagent_open_master_session() function.

Answer 5

As the subagent of Net-SNMP sometimes unable to read the adress of master agent from the configuration file, so you can even try
/* set the location of master agent */
netsnmp_ds_set_string(NETSNMP_DS_APPLICATION_ID,
NETSNMP_DS_AGENT_X_SOCKET, "udp:X.X.X.X:1610");
Write these lines in the agentx code before calling init_agent().

Answer 6

I have solved problem next comands line in OS Ubuntu 17.07
Change code (add line)
view systemview included .1.3.6.1.2.1.1
view systemview included .1.3.6.1.2.1.2
view systemview included .1.3.6.1.2.1.25.1.1
instead of
view systemview included .1.3.6.1.2.1.1
view systemview included .1.3.6.1.2.1.25.1.1
Write down new line master agentx in /etc/snmpd.conf
Restart snmpd demon:
sudo /etc/init.d/snmpd restart or sudo service snmpd restart