May 06, 2024

Nagios Monitoring Server Setup

Nagios Core

Nagios core is an open source system monitoring system used to monitor network infrastructure and other computer systems. This application can be configured in Linux or Unix servers, while also supporting remote hosts using operating systems such as windows. Nagios core is comparatively lightweight, easier to configure and deploy.

The necessity of an alert system is self-evident as most companies, including smaller businesses, may have their own critical infrastructure. In order to maintain streamline production or continued services while ensuring quality of services, alerts can be useful to know beforehand when a failure might occur. Generally it makes the monitoring process easier as well and easier to visualize thanks to the monitoring process being automated.

Server Configuration

Nagios Core Installation

In the following installation, CentOS will be used as the server(i.e., Master) and the client(i.e., Slave) will be a fedora Operating System.

I would advise you to visit Nagios Quick Start Guide (Docs) and choose your specific operating system accordingly.

The following bash scripts can be used to install the core.

# Dependancies

yum install -y gcc glibc glibc-common wget unzip httpd php gd gd-devel perl postfix
yum install openssl-devel

#Download Nagios core

## Check github https://github.com/NagiosEnterprises/nagioscore/releases

## Check SourceForge.net as well

wget -o nagiosCore.tar.gz https://github.com/NagiosEnterprises/nagioscore/releases/download/nagios-4.5.2/nagios-4.5.2.tar.gz

# Extract and compile

tar xzf nagiosCore.tar.gz

cd nagios-4.5.2 #

./configure --with-command-group=nagcmd

# Run these commands sequentually

make all

make install-groups-users

## Binaries
make install
make install-init
make install-config // Sample files to get started with clients

make install-daemoninit  
systemctl enable httpd.service

make install-commandmode

make install-config

#Apache Config Files

make install-webconf

#Firewall Config

firewall-cmd --zone=public --add-port=80/tcp  
firewall-cmd --zone=public --add-port=80/tcp --permanent

# Create user account (admin)

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

# Start and Test

## Apache Webserver Start -> Runs the webapp

systemctl start httpd.service

## Nagios Service

systemctl start nagios.service

Afterwords go to http://localhost/nagios, you may also replace the localhost with server IP address.

Nagios Plugins

The plugins are open sourced scripts written to monitor certain services. There are over thousands of plugins that can be found in the Nagios Exchange Website, and we can also define our own plugins as well if we need to.

#Dependencies yum install -y gcc glibc glibc-common make gettext automake autoconf wget openssl-devel net-snmp net-snmp-utils epel-release yum --enablerepo=powertools,epel install perl-Net-SNMP

# Download and Compile

cd tmp wget --no-check-certificate -O nagios-plugins.tar.gz https://github.com/nagios-plugins/nagios-plugins/releases/download/release-2.4.9/nagios-plugins-2.4.9.tar.gz tar zxf nagios-plugins.tar.g cd /tmp/nagios-plugins.tar.g/ ./tools/setup ./configure --with-nagios-user=nagios --with-nagios-group=nagios make make install

# Configuration verification /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg # Start Server

## Apache Webserver Start -> Runs the webapp

systemctl enable httpd.service

systemctl start httpd.service

## Nagios Service

systemctl enable nagios.service

systemctl start nagios.service

NRPE

NRPE installation and client remote configurations will be discussed later. NRPE should be installed prior to host configurations. Therefore, read the official documentations until the content are added.

Refer Official Documentations: NRPE Installation Docs

# Remote Host Setup ## Refer Github and download newest nagios plugins wget http://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz tar xzf nagios-plugins-2.2.1.tar.gz cd nagios-plugins-2.2.1 ./configure make make install

## This is unnecessary since we are gonna use groups-user install useradd nagios groupadd nagios usermod -a -G nagios nagios # Only for some systems chown nagios.nagios /usr/local/nagios chown -R nagios.nagios /usr/local/nagios/libexec

# NRPE Daemon Install wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe- 3.2.1/nrpe-3.2.1.tar.gz tar xzf nrpe-3.2.1.tar.gz cd nrpe-nrpe-3.2.1

./configure makeall make install-groups-users make install make install-config

systemctl enable nrpe.service;systemctl start nrpe.service

# Check id NRPE is working correctly /usr/local/nagios/libexec/check_nrpe -H localhost

# add Monitoring Host Ip to allow it to communicate with the host ## This is the place to configure InDirect Commands as well. Check the config file vi /usr/local/nagios/etc/nrpe.cfg

System Checks

Checks is the main purpose and use of Nagios. There are two types of checks that can be performed with the help NRPE on the remote host. However, if the administrator wants to perform self checks, it is advisable to install NRPE on the server itself.

Direct Checks

Used to monitor private (i.e., local) resources. These commands will be configured with in the Server itself.

`In-Direct Checks`

The following method is employed to check public resources or services which might be unreachable for the Monitoring Host(ie. Server). In the following example provided in the documentation the monitoring host requests statistics from the remote host indirectly on the webserver which is unreachable for the monitoring host directly.

Service Check Configurations

Go to “/usr/local/nagios/etc/objects/“, in here you have to create a cfg file to define hosts and services. This can be done either in one or multiple files. Refer to the following example hosts.cfg file.

define host {
    use                     linux-server
    host_name               fedora-client
    alias                   fedora-client
    address                 10.0.1.20
    check_command           check_ping!100.0,20%!500.0,60%
    check_interval          1
}

define service {
    use                     generic-service
    host_name               fedora-client
    service_description     Ping
    check_command           check_ping!100.0,20%!500.0,60%
    check_interval          1
}

define service {
    use                     generic-service
    host_name               fedora-client
    service_description     hda1
    check_command           check_nrpe!check_hda1
    check_interval          1
}

define service {
    use                     generic-service
    host_name               fedora-client
    service_description     Processes
    check_command           check_nrpe!check_total_procs
    check_interval          1
}

define service {
    use                     generic-service
    host_name               fedora-client
    service_description     Zombie_procs
    check_command           check_nrpe!check_zombie_procs
    check_interval          1
}

define service {
    use                     generic-service
    host_name               fedora-client
    service_description     CPU
    check_command           check_nrpe!check_load
    check_interval          1
}

define service {
    use                     generic-service
    host_name               fedora-client
    service_description     Disk Space
    check_command           check_nrpe!check_root
    check_interval          1
}

In the following file we have used predefined plugin commands found in commands.cfg file of the client to check various system statistics and services. There are multiple such service, check the documentations of individual plugins to get a full understanding. Additionally, any command definitions should be added to commands.cfg of the server (/usr/local/nagios/etc/objects).

define command {

command_name check_nrpe
command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$

}

Once the services and hosts are defined, we have to add the file into the nagios.cfg file of the server.

`Enable Service Checks in client(hosts)`

Make sure that the service commands are configured in the host as follows. More commands can be added. We will be editing /usr/local/nagios/etc

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