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.

[[email protected] ~]# 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

[[email protected] ~]# useradd nagios
[[email protected] ~]# groupadd nagcmd
[[email protected] ~]# usermod -a -G nagcmd nagios
[[email protected] ~]# usermod -a -G nagcmd apache 

 

II/Download and Install Nagios

Let’s download nagios and extract it:

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

 

Now,let’s start compiling Nagios:

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

[[email protected] ~]# 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:

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

 

Let’s compile:

[[email protected] nagios-plugins-2.1.1]# ./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
[[email protected] nagios-plugins-2.1.1]# make all
[[email protected] nagios-plugins-2.1.1]# make install 

 

III/Download and Install NRPE

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

 

Let’s install the nrpe addon and plugins:

[[email protected] nrpe-2.15]# 
[[email protected] nrpe-2.15]# ./configure --enable-command-args --with-nagios-user=nagios --with-nagios-group=nagios
[[email protected] nrpe-2.15]# make all
[[email protected] 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:

[[email protected] ~]# vim /usr/local/nagios/etc/nagios.cfg

 
And uncomment this line

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

 
Now let’s create the directory:

[[email protected] ~]# mkdir /usr/local/nagios/etc/servers
[[email protected] ~]# 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:

[[email protected] ~]# 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

[r[email protected] ~]# 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!