Nagios and NRPE - There's more ...

Following on from my earlier post: -

Nagios Remote Plugin Executor (NRPE) and xinetd on Red Hat Enterprise Linux

things are starting to become more clear.

As far as I can establish, on the NRPE client/agent side, we have several components at work here.

So we have the NRPE agent itself, as started using xinetd : -

/etc/xinetd.d/nrpe

 
# default: on
# description: NRPE (Nagios Remote Plugin Executor)
service nrpe
{
        flags           = REUSE
        socket_type     = stream    
port = 5666    
        wait            = no
        user            = nagios
group = nagios
        server          = /usr/local/nagios/bin/nrpe
        server_args     = -c /usr/local/nagios/etc/nrpe.cfg --inetd
        log_on_failure  += USERID
        disable         = no
# only_from       = 192.168.153.130
}

and then we have the command(s) that we want to invoke from the Nagios server itself: -

ls -1 /usr/local/nagios/libexec

check_disk
check_load
check_nrpe
check_procs
check_swap
check_users
diskfree.py
hello.pl

and then we have the configuration file that acts as the lookup/aliasing agent: -

cat /usr/local/nagios/etc/nrpe.cfg

…

command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10
command[check_load]=/usr/local/nagios/libexec/check_load -r -w .15,.10,.05 -c .30,.25,.20
command[check_sda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/sda1
command[check_zombie_procs]=/usr/local/nagios/libexec/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/local/nagios/libexec/check_procs -w 150 -c 200
command[sayHello]=/usr/local/nagios/libexec/hello.pl
command[diskFree]=/usr/local/nagios/libexec/diskfree.py
…

This means that, from the Nagios server, I can invoke any of the above commands: -

/usr/local/nagios/libexec/check_nrpe -H mfp.uk.ibm.com -c check_users

USERS OK - 2 users currently logged in |users=2;5;10;0

/usr/local/nagios/libexec/check_nrpe -H mfp.uk.ibm.com -c check_load

CRITICAL - load average: 0.39, 0.24, 0.17|load1=0.390;0.150;0.300;0; load5=0.240;0.100;0.250;0; load15=0.170;0.050;0.200;0; 

/usr/local/nagios/libexec/check_nrpe -H mfp.uk.ibm.com -c check_sda1

DISK OK - free space: /boot 274 MB (55.29% inode=100%);| /boot=222MB;396;446;0;496

/usr/local/nagios/libexec/check_nrpe -H mfp.uk.ibm.com -c check_zombie_procs

PROCS OK: 0 processes with STATE = Z | procs=0;5;10;0;

/usr/local/nagios/libexec/check_nrpe -H mfp.uk.ibm.com -c check_total_procs

PROCS WARNING: 185 processes | procs=185;150;200;0;

/usr/local/nagios/libexec/check_nrpe -H mfp.uk.ibm.com -c sayHello

Hello, World!

/usr/local/nagios/libexec/check_nrpe -H mfp.uk.ibm.com -c diskFree

FREE SPACE OK: '/' is 26.00% full

From a Nagios console perspective, I can define all/any of these

sudo vi /usr/local/nagios/etc/servers/mfp.cfg 

…

define command {
        command_name                    check_nrpe_with_args
        command_line                    $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}
…

define service {
        use                             generic-service
        host_name                       mfp.uk.ibm.com
        service_description             Check_Load
        check_command                   check_nrpe_with_args!check_load
        notifications_enabled           1
}
define service {
        use                             generic-service
        host_name                       mfp.uk.ibm.com
        service_description             Hello_World
        check_command                   check_nrpe!sayHello
        notifications_enabled           0
}
define service {
        use                             generic-service
        host_name                       mfp.uk.ibm.com
        service_description             Disk_Free
        check_command                   check_nrpe!diskFree
        notifications_enabled           0
}
…

sudo systemctl restart nagios.service

and then check the Nagios dashboard: -

Finally, purely for the record, whilst the shipped plugins are mainly C/C++ binaries e.g.

file /usr/lib64/nagios/plugins/check_disk 

/usr/lib64/nagios/plugins/check_disk: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=0f75d7633e74455320d40f0b75071f8eabe148de, stripped

but I also have a Perl script: -

file hello.pl 

hello.pl: Perl script, ASCII text executable

and a Python script: -

file diskfree.py 

diskfree.py: Python script, ASCII text executable

( kudos to Linux Magazine for this latter script )