===== Nagios Centos RHEL Oracle Scientific Linux 6 =====
<code>
sed -i 's/SELINUX=.*/SELINUX=permissive/g' /etc/selinux/config
setenforce 0
yum -y install httpd php gcc glibc glibc-common  gd gd-devel
wget https://github.com/NagiosEnterprises/nagioscore/releases/download/nagios-4.4.5/nagios-4.4.5.tar.gz
/usr/sbin/useradd -m nagios
/usr/sbin/groupadd nagcmd
/usr/sbin/usermod -a -G nagcmd nagios
/usr/sbin/usermod -a -G nagcmd apache
tar zxvf nagios-4.4.5.tar.gz
cd nagios-4.4.5
./configure
make all
make install
make install-init
make install-commandmode
make install-config
make install-webconf
cd ..
wget http://www.nagios-plugins.org/download/nagios-plugins-2.3.2.tar.gz
tar zxvf nagios-plugins-2.3.2.tar.gz
cd nagios-plugins-2.3.2
./configure
make all
make install
chkconfig httpd on
service httpd start
htpasswd -cb /usr/local/nagios/etc/htpasswd.users nagiosadmin manager
chkconfig nagios on
service nagios start
</code>

==== References ====
  * https://computingforgeeks.com/install-and-configure-nagios-4-on-rhel-centos-8/
  * https://www.servernoobs.com/how-to-install-nagios-on-centos-5-or-6/