How to Install Nagios 4.4.3 on CentOS 7

Introduction

Nagios (now known as Nagios Core) is a free and open source computer-software application that monitors systems, networks and infrastructure. Nagios offers monitoring and alerting services for servers, switches, applications and services. It alerts users when things go wrong and alerts them a second time when the problem has been resolved.

Prerequisites

To install Nagios on your server, make sure you are logged into your server with a sudo user.

This guide is based on SELinux being disabled or in permissive mode. To disable SELinux use the below command:

sed -i 's/SELINUX=.*/SELINUX=disabled/g' /etc/selinux/config
setenforce 0

Step 1 - Install Required Dependencies

We need to install Apache, PHP and some libraries like gcc, glibc, glibc-common and GD libraries and its development libraries before installing Nagios with source. To do so, we can use the default package installer yum.

First, install the required packages:

yum install -y httpd httpd-tools php gcc glibc glibc-common gd gd-devel make net-snmp openssl-devel xinetd unzip

Step 2 - Create Nagios User and Group

We must create a user and group that will run the Nagios process. Create a nagios user and nagcmd group with these commands:

useradd nagios
groupadd nagcmd

Then add both the nagios user and the apache user to the nagcmd group.

Then add the user to the group with these commands:

usermod -G nagcmd nagios
usermod -G nagcmd apache

Step 3 - Download Nagios Core and Nagios Plugin

Download the latest Nagios Core 4.4.3 and Nagios plugins 2.2.1 packages. Go to the Nagios downloads page, copy the link address for the latest stable release so you can download it to your Nagios server.

cd /tmp
wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.4.3.tar.gz
wget https://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz

Extract the Nagios Core and Plugins archive with this command:

tar xvf nagios-4.4.3.tar.gz
tar xvf nagios-plugins-2.2.1.tar.gz

Step 4 - Configure Nagios Core

Now we will configure Nagios Core. To do so, we need to go to the Nagios directory and run the configure file. If everything goes fine, it will show the output in the end as sample output. Please see below:

cd nagios-4.4.3
./configure --with-command-group=nagcmd

Sample output:

Creating sample config files in sample-config/ ...


*** Configuration summary for nagios 4.4.3 2019-01-15 ***:

 General Options:
 -------------------------
        Nagios executable:  nagios
        Nagios user/group:  nagios,nagios
       Command user/group:  nagios,nagcmd
             Event Broker:  yes
        Install ${prefix}:  /usr/local/nagios
    Install ${includedir}:  /usr/local/nagios/include/nagios
                Lock file:  /run/nagios.lock
   Check result directory:  /usr/local/nagios/var/spool/checkresults
           Init directory:  /lib/systemd/system
  Apache conf.d directory:  /etc/httpd/conf.d
             Mail program:  /bin/mail
                  Host OS:  linux-gnu
          IOBroker Method:  epoll

 Web Interface Options:
 ------------------------
                 HTML URL:  http://localhost/nagios/
                  CGI URL:  http://localhost/nagios/cgi-bin/
 Traceroute (used by WAP):


Review the options above for accuracy.  If they look okay,
type 'make all' to compile the main program and CGIs.

Now compile Nagios with this command:

make all

Now we can run these make commands to install Nagios, init scripts, and sample configuration files:

make install
make install-init
make install-commandmode
make install-config
make install-webconf

Step 5 - Customize Nagios Configuration

Open the "contacts.cfg" file with your choice of editor and set the email address associated with the nagiosadmin contact to receive email alerts.

vi /usr/local/nagios/etc/objects/contacts.cfg

Sample Output:

###############################################################################
#
# CONTACTS
#
###############################################################################

# Just one contact defined by default - the Nagios admin (that's you)
# This contact definition inherits a lot of default values from the
# 'generic-contact' template which is defined elsewhere.

define contact {

    contact_name            nagiosadmin             ; Short name of user
    use                     generic-contact         ; Inherit default values from generic-contact template (defined above)
    alias                   Nagios Admin            ; Full name of user
    email                   admin@example.com       ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******
}

Step 6 - Configure Web Interface

Use htpasswd to create an admin user, called "nagiosadmin", that can access the Nagios web interface:

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

Enter a password at the prompt. Remember this login, as you will need it to access the Nagios web interface.

Restart Apache to make the new settings take effect.

systemctl start httpd.service

Step 7 - Compile and Install Nagios Plugins

cd /tmp
cd nagios-plugins-2.2.1
./configure --with-nagios-user=nagios --with-nagios-group=nagios
make
make install

Step 8 - Verify Nagios Configuration Files

Verify the Nagios configuration file using the following command:

/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

Sample Output:

Nagios Core 4.4.3
Copyright (c) 2009-present Nagios Core Development Team and Community Contributors
Copyright (c) 1999-2009 Ethan Galstad
Last Modified: 2019-01-15
License: GPL

Website: https://www.nagios.org
Reading configuration data...
   Read main config file okay...
   Read object config files okay...

Running pre-flight check on configuration data...

Checking objects...
        Checked 8 services.
        Checked 1 hosts.
        Checked 1 host groups.
        Checked 0 service groups.
        Checked 1 contacts.
        Checked 1 contact groups.
        Checked 24 commands.
        Checked 5 time periods.
        Checked 0 host escalations.
        Checked 0 service escalations.
Checking for circular paths...
        Checked 1 hosts
        Checked 0 service dependencies
        Checked 0 host dependencies
        Checked 5 timeperiods
Checking global event handlers...
Checking obsessive compulsive processor commands...
Checking misc settings...

Total Warnings: 0
Total Errors:   0

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

Step 9 - Add Nagios Services to System Startup

To make Nagios work across reboots, we need to add nagios and httpd with chkconfig and systemctl command.

systemctl enable nagios
systemctl enable httpd

Restart Nagios to make the new settings take effect.

systemctl restart nagios.service

Step 10 - Access Nagios Web Interface

Open your web browser, and go to your Nagios server:

http://nagios_server_public_ip/nagios

Because we configured Apache to use htpasswd, you must enter the login credentials that you created earlier. We used nagiosadmin as the username.

Conclusion

Finally, you have successfully installed and configured Nagios core service in your server.

How to Install Nagios 4.4.3 on CentOS 7

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