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I run a Nagios Core server on a LAN. I have 5 windows machines outside the network I am talking to via five ssh tunnels on 5 different ports listening to five custom NSClient++ apps. All is working well with this configuration, however I am noticing that check_nt MEMUSE is giving us odd numbers, when in fact all we want/need is the actual Physical memory.

After much digging I discovered check_nrpe, which look like it will give me the data I'm looking for.

I put the following in the commands.cfg:

define command {
       command_name    CheckWindowsPhysicalMem
       command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -p 5666 -c CheckMEM -a MaxWarn=$ARG1$% MaxCrit=$ARG2$% ShowAll=long type=physical
}

And I put the following in my windows.cfg

define service{
        use                     generic-service
        host_name               HOSTNAME
        service_description     Physical Memory
        check_command           CheckWindowsPhysicalMem!80!90
}

I restarted both nagios and nagios-nrpe-server, and now I'm getting this error:

CHECK_NRPE: Receive header underflow - only 0 bytes received (4 expected)

I am not sure what I missed here, but if seems like a dependency or a package. Google-fu lost on this one.

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    Are you using the same version of nrpe on both sides? I hit this problem trying to connect to a very old nrpe server. – Joachim Breitner Oct 25 '17 at 1:31
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1. Testing NRPE connection

You can test your connection between your windows and Nagios via NRPE like this :

./check_nrpe -H Server
I (0.4.3.143 2015-04-29) seem to be doing fine...

If you don't pass any arguments to your check_nrpe, the server (windows client) will responde with his version number.

2. Testing your command

On your windows client, you can test locally your command in a console with nscp test.

If your command return good result, you can test from your nagios server without arguments :

# ./check_nrpe -H Server -c alias_cpu
OK: CPU load is ok.|'total 5m'=1%;80;90 'total 1m'=1%;80;90 'total 5s'=2%;80;90

3. NRPE arguments

By default, NRPE not allow the send of arguments from Nagios to a remote client for security considerations. So, you must enable it in the nsclient.ini for each windows station.

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