Installation

Add RPMForge Yum Repository

It is recommended that you configure yum-priorities prior to following this tutorial to avoid having base CentOS packages being overwritten by the RPMForge repository. Instructions to do so can be found on the CentOS Wiki.

• For x86 (32-bit) systems
  • rpm -Uhv http://apt.sw.be/redhat/el5/en/i386/...l5.rf.i386.rpm

• For x64 (64-bit) systems
  • rpm -Uhv http://apt.sw.be/redhat/el5/en/x86_6....rf.x86_64.rpm

Install & Configure Prerequisites

• Install Apache
  • yum install httpd php gcc glibc glibc-common gd gd-devel

• Configure Apache to start on boot
  • chkconfig httpd on

• Configure iptables to allow Apache traffic
  • /sbin/iptables -I INPUT -p tcp --dport 80 -j ACCEPT
  • /etc/init.d/iptables save
  • /etc/init.d/iptables restart

Install Nagios & Nrpe

• Install Nagios (Server Side)
  
  [mylogin@hostname nagios]# yum install nagios nagios-plugins nagios-plugins-nrpe nagios-devel
• Install Nagios (Client Side)

[mylogin@hostname nagios]# yum install nagios nagios-plugins nagios-plugins-nrpe nagios-devel nagios-nrpe

• Create the default Nagios web access user & set a password
  • htpasswd -c /etc/nagios/htpasswd.users nagiosadmin

• Verify default config files
  • nagios -v /etc/nagios/nagios.cfg

• Start Nagios
  • /etc/init.d/nagios start

• Start Apache
  • /etc/init.d/httpd start

Verify Install

• Try logging into your new Nagios installation by going to http://YourIpAddress/nagios/ and logging in with nagiosadmin and the password you set.

Nagios Server Configuration

Before starting any configuration make it a habit to backup all configuration files. This will save us a lot of time in troubleshooting. Having a backup will also allow us to restore the most recent configuration to the system. We can also make the backup configuration as a future reference in case we need something :
[mylogin@hostname nagios]# cd /etc
[mylogin@hostname nagios]# cp -frp nagios nagios.backup-<date>
[mylogin@hostname nagios]# cp -rf /etc/nagios/objects/localhost.cfg /etc/nagios/objects/server1.cfg
[mylogin@hostname nagios]# chown -R nagios:nagios server1.cfg
[mylogin@hostname nagios]# nano /etc/nagios/objects/server1.cfg

Code:

define host{
use                     linux-server            ; Name of host template to use
; This host definition will inherit all variables that are defined
; in (or inherited by) the linux-server host template definition.
host_name               server1
alias                   server1
address                 your client server ip
}
define hostgroup{
hostgroup_name  server1-servers ; The name of the hostgroup
alias           server1 Servers ; Long name of the group
members         server1     ; Comma separated list of hosts that belong to this group
}
define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             PING
check_command            check_ping!100.0,20%!500.0,60%
}
 define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             Root Partition
check_command            check_local_disk!20%!10%!/
}
 define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             Current Users
check_command            check_local_users!20!50
}
 define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             Total Processes
check_command            check_local_procs!250!400!RSZDT
}
 # Define a service to check the load on the local machine.
 define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             Current Load
check_command            check_local_load!5.0,4.0,3.0!10.0,6.0,4.0
}
 define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             Swap Usage
check_command            check_local_swap!20!10
}
 define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             SSH
check_command            check_ssh
notifications_enabled        0
}
 define service{
use                             local-service         ; Name of service template to use
host_name                       server1
service_description             HTTP
check_command            check_http
notifications_enabled        0
}

Your Configuration will be like this . Now save that config.

[mylogin@hostname nagios]#service nagios restart
[mylogin@hostname nagios]# chkconfig nagios on
[mylogin@hostname nagios]# service nrpe restart
[mylogin@hostname nagios]# chkconfig nrpe on
[mylogin@hostname nagios]# nagios -v /etc/nagios/nagios.cfg
Nagios Client Configuration

[mylogin@hostname nagios]# nano /etc/nagios/nrpe.cfg
change server_address=127.0.0.1 to your nagios server ip
[mylogin@hostname nagios]# service nagios restart
[mylogin@hostname nagios]# chkconfig nagios on
[mylogin@hostname nagios]# service nrpe restart
[mylogin@hostname nagios]# chkconfig nrpe on

http://docs.cslabs.clarkson.edu/wiki...os_on_CentOS_5

read my whole post i explain how to config it properly . Its not copy of that post .