pysnmp poll specific process index within HOST-RESOURCES-MIB

Question

I have the following code which I've been using to poll with pysnmp. Up until now it has been used to walk but I'd like to be able to get a specific index. For example I'd like to poll HOST-RESOURCES-MIB::hrSWRunPerfMem.999

I can use this to sucessfully get back everything in hrSWRunPerfMem using getCounter('1.1.1.1', 'public', 'HOST-RESOURCES-MIB', 'hrSWRunPerfMem')

However once I try to include the index number getCounter('1.1.1.1', 'public', 'HOST-RESOURCES-MIB', 'hrSWRunPerfMem', indexNum=999) I always get varBindTable == []

from pysnmp.entity.rfc3413.oneliner import cmdgen
from pysnmp.smi import builder, view

def getCounter(ip, community, mibName, counterName, indexNum=None):
    cmdGen = cmdgen.CommandGenerator()
    mibBuilder = cmdGen.mibViewController.mibBuilder
    mibPath = mibBuilder.getMibSources() + (builder.DirMibSource("/path/to/mibs"),)
    mibBuilder.setMibSources(*mibPath)
    mibBuilder.loadModules(mibName)
    mibView = view.MibViewController(mibBuilder)

    retList = []
    if indexNum is not None:
        mibVariable = cmdgen.MibVariable(mibName, counterName, int(indexNum))
    else:
        mibVariable = cmdgen.MibVariable(mibName, counterName)

    errorIndication, errorStatus, errorIndex, varBindTable = cmdGen.nextCmd(cmdgen.CommunityData('test-agent', community),
                                                                            cmdgen.UdpTransportTarget((ip, snmpPort)),
                                                                            mibVariable)

Does anyone have some insight into how to poll specific indexes using pysnmp?

Answer 1

You should be using cmdGen.getCmd() call instead of nextCmd() call. There's no 'next' OID past the leaf one hence empty response.

Here's a bit optimized version of your code. It should run as-is right from your Python prompt:

from pysnmp.entity.rfc3413.oneliner import cmdgen

def getCounter(ip, community, mibName, counterName, indexNum=None):
    if indexNum is not None:
        mibVariable = cmdgen.MibVariable(mibName, counterName, int(indexNum))
    else:
        mibVariable = cmdgen.MibVariable(mibName, counterName)

    cmdGen = cmdgen.CommandGenerator()

    errorIndication, errorStatus, errorIndex, varBindTable = cmdGen.getCmd(
        cmdgen.CommunityData(community),
        cmdgen.UdpTransportTarget((ip, 161)),
        mibVariable.addMibSource("/path/to/mibs")
    )

    if not errorIndication and not errorStatus:
        return varBindTable

#from pysnmp import debug
#debug.setLogger(debug.Debug('msgproc'))

print(getCounter('demo.snmplabs.com',
                 'recorded/linux-full-walk',
                 'HOST-RESOURCES-MIB',
                 'hrSWRunPerfMem',
                  970))

Performance wise, it's recommended to reuse CommandGenerator instance to save on [heavy] snmpEngine initialisation happening under the hood.