check_nrpe gives "Unable To Read Output" on just one service



I am running the check command on remote servers using check_nrpe on the monitoring server. On all machines apart from 1 it works fine, on the 1 machine it returns “Unable To Read Output”. All other commands on that machine being run by check_nrpe are working fine.

If I run ./ from the command line on this machine it also works fine. It’s only a problem when being run by check_nrpe.

It can’t be a permissions issue as permissions are configured the same for all the other check commands on each machine, it’s not an SSL issue as this produces a different error message.

Thanks In Advance

PS. What extensions are allowed on this forum when sending attachments? I have strace output examples for when check_nrpe works and when it doesn’t.


I’ll read strace output. You could use a pastebin or paste it inline.


Thanks for the response. Please see below for links to pastebin. (this is the command when it doesn’t work). (this is the command when it does work).

For both the above traces, the command is being run by check_nrpe on the monitoring server (once on a machine that does work and once on the machine where it doesn’t).

To be honest I’m not sure these trace files will help, they’re quite large, but if you ‘can’ spot anything that would be fantastic.

Thanks In Advance



Huh, err yes. These traces show absolute correct behavior on both parts…

Where you need to be doing your traces is on the one host you are trying to monitor. Fist trace the precess being run in a shell, then attach to the running nrped with a follow forks(-f). Comparing the output of these traces should indicate where the problem is.
Notice the traces you pasted both have the same function calls, this indicate the flow of the programs are the same… only the data is different.

#5 This is a strace of the command being run from a shell. This is a strace of the NRPE process on the monitored server when check_nrpe -H -c check_network_load -t 30 is run on the monitoring server.

I showed the strace of the NRPE process to my boss and we both seem to think that the correct output is being sent back to the monitoring server (though we are by no means sure).

Hope this is what you need. Thanks again for your help.