Installing and Configuring Nagios

[Leo.Prince]

Hi,

Nagios is a wonderful tool to check and monitor services at a remote host. We can check many services like ping, server load etc. Before we begin, we need to install some packages on the remote host for Nagios to work fine.

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yum install elinks gcc make gcc-c++
yum -y install openssl-devel
useradd nagios
passwd nagios
cd /usr/src/
Then install Nagios plugin and NRPE on remote host.

Install Plug-in

Follow these steps

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wget http://sourceforge.net/projects/nagiosplug/files/nagiosplug/1.4.15/nagios-plugins-1.4.15.tar.gz/download
tar -zxvf nagios-plugins-1.4.15.tar.gz && cd nagios-plugins-1.4.15
./configure --with-nagios-user=nagios --with-nagios-group=nagios
make
make install
chown nagios:nagios /usr/local/nagios
chown -R nagios:nagios /usr/local/nagios/libexec
cd ..
Install NRPE

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wget http://sourceforge.net/projects/nagios/files/nrpe-2.x/nrpe-2.12/nrpe-2.12.tar.gz/download
tar -zxvf nrpe-2.12.tar.gz && cd nrpe-2.12
./configure
make all
make install-plugin
make install-daemon
make install-daemon-config
make install-xinetd
Edit Xinetd NRPE entry

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vi /etc/xinetd.d/nrpe
only_from = 127.0.0.1 Server-IP (nagios monitoring server ip-address is: )
:wq (save and exit)
Edit services file entry

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vi /etc/services
nrpe 5666/tcp # Entry for NRPE daemon
:wq (save and exit)
Restart xinetd

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service xinetd restart
Verify whether NRPE is listening

You can use netstat command to see if it is up and running in the corresponding port

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netstat -at |grep nrpe

# output -: tcp 0 0 *:nrpe *.* LISTEN
Verify to make sure the NRPE is functioning properly

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/usr/local/nagios/libexec/check_nrpe -H localhost
#output NRPE v2.12
Configuring Nagios monitoring server to monitor the remote host

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cd /usr/src
wget http://sourceforge.net/projects/nagios/files/nrpe-2.x/nrpe-2.12/nrpe-2.12.tar.gz/download
tar -zxvf nrpe-2.12.tar.gz && cd nrpe-2.12
yum -y install openssl-devel
yum install perl
./configure
make all
make install-plugin
Create a command definition

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vi /home/nagios/public_html/etc/objects/commands.cfg
Add the following to the file and save

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# NRPE CHECK COMMAND
# Command to use NRPE to check remote host systems
define command{
command_name check_nrpe
command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}
Create configuration file for remote host

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# cp –prf /home/nagios/www/etc/objects/ localhost.cfg /home/nagios/www/etc/objects/remotehost.cfg

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# vi /home/nagios/www/etc/objects/remotehost.cfg
Replace the values “host_name” “alias” “address” with the values that match your setup

The “host_name” you set for the “define_host” section must match the “host_name” in the “define_service” section

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# Define a host for the remote machine
define host{
       use      linux-server     ; Name of host template to use
                                         ; This host definition will inherit all variables that are defined
                                         ; in (or inherited by) the linux-server host template definition.
        host_name         your_host_name
        alias                    your_alias_name
        address              remote_machine_ip
        }
# SERVICE DEFINITIONS
# Define a service to "ping" the local machine

define service{
        use                              generic-service         ; Name of service template to use
        host_name                  your_host_name
        service_description      PING
        check_command          check_ping!100.0,20%!500.0,60%
        }
# Define a service to check the disk space of the root partition.

define service{
        use                             generic-service         ; Name of service template to use
        host_name                 your_host_name
        service_description     Root Partition
        check_command          check_nrpe!check_disk
        }

# Define a service to check the number of currently logged in users on the remotehost.

define service{
        use                             generic-service         ; Name of service template to use
        host_name                 your_host_name
        service_description     Current Users
        check_command         check_nrpe!check_users
        }
# Define a service to check the number of currently running processes on the remote host.

define service{
        use                              generic-service         ; Name of service template to use
        host_name                  your_host_name
        service_description     Total Processes
        check_command          check_nrpe!check_total_procs
        }
# Define a service to check the load on the remote host.

define service{
        use                             generic-service         ; Name of service template to use
        host_name                 your_host_name
        service_description     Current Load
        check_command         check_nrpe!check_load
        }

# Define a service to check SSH on the remote host.
# Disable notifications for this service by default, as not all users may have SSH enabled.
define service{
        use                             generic-service         ; Name of service template to use
        host_name                 your_host_name
        service_description     SSH
        check_command          check_nrpe!check_ssh
        notifications_enabled  0
        }
# Define a service to check HTTP on the remote host.
# Disable notifications for this service by default, as not all users may have HTTP enabled.
define service{
        use                              generic-service         ; Name of service template to use
        host_name                  your_host_name
        service_description      HTTP
        check_command           check_nrpe!check_http
        notifications_enabled   0
        }

Activate the remotehost.cfg template

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vi /usr/local/nagios/etc/nagios.cfg
 #Definitions for monitoring remote Linux machine
cfg_file=/home/nagios/www/etc/objects/remotehost.cfg
Verify Nagios Configuration Files

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/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
/home/nagios/public_html/bin/nagios -v /home/nagios/public_html/etc/nagios.cfg (In nagios host server)
Output :

Things look okay - No serious problems were detected during the pre-flight check


Verify whether nagios monitoring server can talk to the remote host

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/usr/local/nagios/libexec/check_nrpe -H remotehost_ip
NRPE v2.12

Start nagios

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/home/nagios/www/bin/nagios -d /home/nagios/www/etc/nagios.cfg
Restart nagios (if already running)

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kill -HUP <nagios_pid>

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/usr/local/nagios/libexec/check_nrpe -H 62.75.215.12 -c check_load (To check the load of the remote server)

OK - load average: 0.35, 0.30, 0.23|load1=0.350;15.000;30.000;0; load5=0.300;10.000;25.000;0; load15=0.230;5.000;20.000;0;

(Usage: check_nrpe -H <host> [-n] [-u] [-p <port>] [-t <timeout>] [-c <command>] [-a <arglist...>])

That is it. Your nagios server is all set to monitor your remote machine.