Monitoring Linux Client Using Nagios (NRPE)

by Ankam Ravi Kumar · Published December 29, 2015 · Updated August 1, 2017

Monitoring Linux Client Using Nagios. We can monitor the remote Linux client using SNMP and NRPE (Nagios Remote Plugin Executor) client. In this article we are going to see how to setup a Linux client monitoring using NRPE.

In-order to monitor the Linux client using NRPE we have to install NRPE in client and Nagios server as well.

NRPE installation process

After completion of NRPE installation in client you have to configure (define) commands in remote client. To define a commands you have to edit the below file.

In Remote Client Side

# vi /usr/local/nagios/nrpe.cfg

end of nrpe.cfg file you have to define the commands using local plugins (default location is /usr/local/nagios/libexec/) as example shown below

## Example Commands mentioned in Remote Linux Client
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/hda1
command[check_disk]=/usr/local/nagios/libexec/check_disk -w 20% -c 10%
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[check_mem]=/usr/local/nagios/libexec/check_mem_new.sh -w 80 -c 90

Now ensure below things in remote Linux client

Add Nagios server IP address in /etc/xinetd.d/nrpe.cfg
Add NRPE port number to allow NRPE service to communicate wit Nagios server in /etc/services
Check whether NRPE port is listening state using #netstat -at |grep NRPE
Add NRPE port (5666/5667/5668) in allow list of your firewall

In NAGIOS Server

First check using check_nrpe command whether remote client is responding to NRPE or not.

# cd /usr/local/nagios/libexec/

# ./check_nrpe -H <Remote Client IP>
# NRPE v2.15

It means NRPE is working.

Now add NRPE commands to commands.cfg

# vi /usr/local/nagios/etc/objects/commands.cfg

# 'check_ssh' command definition
define command{
    command_name    check_ssh
    command_line    $USER1$/check_ssh $ARG1$ $HOSTADDRESS$
    }

## To call All the remote NRPE commands 

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

## To all all the remote NRPE commands using ssl
define command{
    command_name    check_nrpe_ssl
    command_line    $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
    }

## Check the remote NRPE command using 30seconds time limit
define command{
        command_name    check_nrpe_timeout
        command_line    $USER1$/check_nrpe -n -t 30 -H $HOSTADDRESS$ -c $ARG1$
        }
## Check NRPE without hostname
define command{
    command_name    check_nrpe_without_hostname
    command_line    $USER1$/check_nrpe -n -t 60 -H $ARG1$ -c $ARG2$
    }

# 'check_mem' command definition will check memory utilization
define command{
    command_name    check_mem
    command_line    $USER1$/check_nrpe -n -H $HOSTADDRESS$ -c check_mem $ARG1$ $ARG2$
    }

# 'check_mem_ssl' command definition memory utilization using ssl
define command{
    command_name    check_mem_ssl
    command_line    $USER1$/check_nrpe  -H $HOSTADDRESS$ -c check_mem $ARG1$ $ARG2$
    }


# 'check_disk' command definition Disk space utilization
define command{
    command_name    check_disk
    command_line    $USER1$/check_nrpe -n -H $HOSTADDRESS$ -c check_disk
    }

# 'check_disk_ssl' command definition disk space utilization using ssl
define command{
    command_name    check_disk_ssl
    command_line    $USER1$/check_nrpe  -H $HOSTADDRESS$ -c check_disk
    }

:wq << -- Save & Exit