Nagios - NRPE: Command '...' not defined - apache

Question

In /usr/local/nagios/etc/nrpe.cfg I added a new command check_this_process to the already pre-defined ones:
command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10
command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20
command[check_hda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/$
command[check_zombie_procs]=/usr/local/nagios/libexec/check_procs -w 5 -c 10 -s$
command[check_total_procs]=/usr/local/nagios/libexec/check_procs -w 150 -c 200
command[check_this_process]=/usr/local/nagios/libexec/check_procs -w 15 -c 20 -C name
This works:
define service{
use generic-service
host_name my_host
service_description CPU Load
check_command check_nrpe!check_load
}
This doesn't:
define service{
use local-service
host_name my_host
service_description cron
check_command check_nrpe!check_this_process
}
and returns: NRPE: Command 'check_this_process' not defined

Answer 1

The terminology used in the supplied docs is a little confusing, but I'll put it like this:
As written in Page 10 of https://assets.nagios.com/downloads/nagioscore/docs/nrpe/NRPE.pdf, you need to modify /usr/local/nagios/etc/commands.cfg on your Nagios server and add the following to define the check_nrpe command:
define command{
command_name check_nrpe
command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}
On your Nagios server, define your service definition as you've already done:
define service{
use local-service
host_name my_host
service_description cron
check_command check_nrpe!check_this_process
}
On your remote host to be monitored, the following is going to be different depending on whether you installed NRPE:
using the tarball and xinetd as in
https://assets.nagios.com/downloads/nagioscore/docs/nrpe/NRPE.pdf
or using a package manager like yum as in
http://sharadchhetri.com/2013/03/02/how-to-install-and-configure-nagios-nrpe-in-centos-and-red-hat/
If you used the tarball / xinetd method, your NRPE configuration file will likely be located at /usr/local/nagios/etc/nrpe.cfg on your remote-host-to-be-monitored. (To avoid typing that all the time, I'll just call it "my_host").
So, on my_host, modify /usr/local/nagios/etc/nrpe.cfg.
Add
command[check_this_process]=/usr/local/nagios/libexec/check_procs -w 15 -c 20 -C name
So that it looks like:
command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10
command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20
command[check_hda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/$
command[check_zombie_procs]=/usr/local/nagios/libexec/check_procs -w 5 -c 10 -s$
command[check_total_procs]=/usr/local/nagios/libexec/check_procs -w 150 -c 200
command[check_this_process]=/usr/local/nagios/libexec/check_procs -w 15 -c 20 -C name
(Note: the above is assuming you have a process called name. If not, replace name with your real process name: i.e. crond)
Restart xinetd:
service xinetd restart
(NOTE: restarting xinted might not be necessary, but I don't use it so I'm a little fuzzy on this one.)
However, if you installed NRPE on my_host using a package manager like yum, your NRPE configuration file will likely be located at /etc/nagios/nrpe.cfg.
So, on my_host, modify /etc/nagios/nrpe.cfg.
Add
command[check_this_process]=/usr/local/nagios/libexec/check_procs -w 15 -c 20 -C name
So that it looks like:
command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10
command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20
command[check_hda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/$
command[check_zombie_procs]=/usr/local/nagios/libexec/check_procs -w 5 -c 10 -s$
command[check_total_procs]=/usr/local/nagios/libexec/check_procs -w 150 -c 200
command[check_this_process]=/usr/local/nagios/libexec/check_procs -w 15 -c 20 -C name
Restart the nrpe service:
service nrpe restart
Back on your Nagios server, run a verification of your Nagios configuration settings:
nagios -v /usr/local/nagios/etc/nagios.cfg
Check the output for errors.
If there are no errors, restart Nagios:
service nagios restart
On your Nagios server you should have a check_nrpe utility installed somehwere as a result of installing the "check_nrpe plugin" on your Nagios server.
See pages 9 and 10 of: https://assets.nagios.com/downloads/nagioscore/docs/nrpe/NRPE.pdf
This check_nrpe utility will most likely be located at: /usr/local/nagios/libexec/check_nrpe
Using the host information for my_host manually test your NRPE connection from the Nagios server.
Execute the following:
/usr/local/nagios/libexec/check_nrpe -H <IP Address of my_host> -c check_this_process
If everything is setup correctly, you should get some output on the command line.

Answer 2

My trouble-shooting guide for 'NRPE: Command ... not found.' Ordered from most common to least common - in my environment.
Was the NRPE daemon restarted AFTER adding the new command? If it is a new command, then NRPE MUST be restarted.
Typos/spelling errors. Does the configured command name on the Nagios side, match that the one in the NRPE config?
Permissions issues. Does the USER that NRPE runs as, have READABLE and EXECUTABLE access to the actual command being ran? Did you test run the command, as the NRPE user? On that same system? TIP: Use the dash (-) when changing to the NRPE user on Linux (su - ...) so you import said users environment as well.
Path issues. Was the FULL PATH to the actual command put into the NRPE config file? Doing this will normally eliminate issues with PATHs, so don't do it any other way.
Bad commands. Does the actual command really execute? Or is it simply throwing an error and exiting? Do you have the correct version of (INSERT SOMETHING HERE) to run the command, installed on the remote system? You should be able to run any command defined in the nrpe.cfg from the command line, and all new commands should be checked BEFORE being added to the nrpe.cfg.
IF ALL THE ABOVE FAILS: Enable DEBUGGING in NRPE and check the log files (on the remote host). This is a bit of a drawn out process - described in the documentation - read it. It is important to disable DEBUGGING as soon as you get output that looks like it would be useful.
This checklist ASSUMES that you've done the needful things to the various Nagios and NRPE configs to get it working in the first place. Hopefully others will read this before posting yet another question as to why they are seeing this error.