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NRPE - Command ’[Your Plugin]’ Not Defined

Problem Description

This KB article addresses the following NRPE error:

NRPE - Command '[Your Plugin]' Not Defined


Assumed Knowledge

The following KB article contains an explanation of how NRPE works and may need to be referenced to completely understand the problem and solution that is provided here:

NRPE - Agent and Plugin Explained


Troubleshooting The Error

This error is very straight forward. Usually this is caused by a mismatch between the command name declared in Nagios XI to be check through NRPE and the actual command name of the command directive in the remote host's nrpe.cfg file. For more information please refer to the following KB article:

NRPE - Return Code Of 127 Is Out Of Bounds - Plugin May Be Missing


However you may also receive a similar error when trying to pass the -c argument, for example:

./check_nrpe -H -t 30 -c check_users -a -w 5 -c 10


The following error message is produced:

NRPE: Command '10' not defined


This problem will occur in versions of check_nrpe before v3. What is happening here is that the initial -c check_users is being overwritten by the -a -w 5 -c 10, as check_nrpe thinks the -c 10 argument is the command argument, not one of the -a arguments.

If the arguments were enclosed in single quotes -a '-w 5 -c 10' then everything in the single quotes is sent as a string and not interpreted by the check_nrpe plugin. However your goal may be to have a dynamic command in your NRPE client and let Nagios XI send the arguments as multiple arguments. The solution is to upgrade the check_nrpe command on your Nagios XI server to the latest version, you don't specifically need up update the NRPE clients to fix the problem. Please refer to the following documentation on how to upgrade the check_nrpe command, it's at the end of the documentation under Install check_nrpe Plugin Only:



The other solution is to change how you are sending the arguments to the NRPE client and also change the command definition on your NRPE client. Please refer to the following KB article as there are several examples that show how:

NRPE - CHECK_NRPE: Received 0 Bytes From Daemon. Check The Remote Server Logs For Error Messages




Final Thoughts

For any support related questions please visit the Nagios Support Forums at:


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