How to install Nagios core 4 on Centos 7 / RHEL 7 and Monitor Servers

Today, i’m going to explain how to install nagios core 4.x on centos 7 /RHEL 7 and how to monitor linux & windows servers. Here, i will divide this tutorial in three parts:

1/ How to install nagios core 4.x on Centos 7 / RHEL 7.
2/ How to monitor a Centos 7 Linux remote host using nagios core.
3/ How to monitor a windows server remote host using nagios core.

What will do in this first tutorial:
1/ Install Prerequisites.
2/ Download and Install Nagios core 4.x.
3/ Download and Install Nagios Plugins.
4/ Download and Install NRPE.
5/ Configure Nagios.

I/Install Prerequisites

Because we are building Nagios Core from source, we must install a few development libraries that will allow us to complete the build and to set up the Nagios web interface.

[root@nagios ~]# yum install httpd php php-cli gcc glibc glibc-common gd gd-devel net-snmp openssl-devel wget unzip -y 

 

Now, let’s create a user and group for Nagios to use

[root@nagios ~]# useradd nagios
[root@nagios ~]# groupadd nagcmd
[root@nagios ~]# usermod -a -G nagcmd nagios
[root@nagios ~]# usermod -a -G nagcmd apache 

 

II/Download and Install Nagios

Let’s download nagios and extract it:

[root@nagios ~]# cd /tmp
[root@nagios tmp]# wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.1.1.tar.gz
[root@nagios tmp]# tar zxf nagios-4.1.1.tar.gz
[root@nagios tmp]# tar zxf nagios-plugins-2.1.1.tar.gz
[root@nagios tmp]# cd nagios-4.1.1 

 

Now,let’s start compiling Nagios:

[root@nagios nagios-4.1.1]# ./configure --with-nagios-group=nagios --with-command-group=nagcmd
[root@nagios nagios-4.1.1]#  make all
[root@nagios nagios-4.1.1]# make install
[root@nagios nagios-4.1.1]# make install-init
[root@nagios nagios-4.1.1]# make install-config
[root@nagios nagios-4.1.1]# make install-commandmode
[root@nagios nagios-4.1.1]# make install-webconf 

 

After finishing,we need now to create a password for the nagiosadmin user that will be used for accessing to Nagios web GUI.

[root@nagios1 ~]# htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin 

 

By the way you can create another user but you should edit /usr/local/nagios/etc/cgi.cfg and change all the “nagiosadmin” references to the user that you have created.

III/Download and Install Nagios Plugins

Let’s download nagios Plugins and extract it:

[root@nagios ~]# cd /tmp
[root@nagios ~]# wget http://www.nagios-plugins.org/download/nagios-plugins-2.1.1.tar.gz
[root@nagios ~]# tar xzf nagios-plugins-2.1.1.tar.gz
[root@nagios ~]# cd nagios-plugins-2.1.1 

 

Let’s compile:

[root@nagios1 nagios-plugins-2.1.1]# ./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
[root@nagios nagios-plugins-2.1.1]# make all
[root@nagios nagios-plugins-2.1.1]# make install 

 

III/Download and Install NRPE

[root@nagios ~]# cd /tmp
[root@nagios ~]# wget http://downloads.sourceforge.net/project/nagios/nrpe-2.x/nrpe-2.15/nrpe-2.15.tar.gz
[root@nagios ~]# tar xzf nrpe-2.15.tar.gz
[root@nagios ~]# cd nrpe-2.15/ 

 

Let’s install the nrpe addon and plugins:

[root@nagios nrpe-2.15]# 
[root@nagios nrpe-2.15]# ./configure --enable-command-args --with-nagios-user=nagios --with-nagios-group=nagios
[root@nagios nrpe-2.15]# make all
[root@nagios nrpe-2.15]# make install-plugin 

 

IV/Configure Nagios

– First, let’s create a directory called ” servers” where we will put the remote servers configuration files which will be monitored:

[root@nagios ~]# vim /usr/local/nagios/etc/nagios.cfg

 
And uncomment this line

cfg_dir=/usr/local/nagios/etc/servers

 
Now let’s create the directory:

[root@nagios ~]# mkdir /usr/local/nagios/etc/servers
[root@nagios ~]# chown -R nagios.nagios /usr/local/nagios

 

– In order to use the check_nrpe plugin we need to create a command definition in the file commands.cfg:

[root@nagios ~]# vim /usr/local/nagios/etc/objects/commands.cfg 

 

Add the following lines in the end of the file :

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

 

Finally let’s enable and start nagios service

[root@nagios ~]# systemctl enable nagios && systemctl start nagios

 

That’s it for now, You can open your preferred browser and check if everything works properly http://you_nagios_ip_address/nagios and dont forget to start apache and open http service on your firewall.

 
We hope this tutorial was enough Helpful. If you need more information, or have any questions, just comment below and we will be glad to assist you!