How to add a host to Nagios server

Adding Linux host to nagios server

Following flow summarizes the above explanation:

Nagios Server (check_nrpe) —–> Remote host (NRPE deamon) —–> check_disk

Nagios Server (check_nrpe) <—– Remote host (NRPE deamon) <—– check_disk (returns disk space usage)

1. How to add Linux client to the Nagios server

To start , In the remote host add nagios user,

# /usr/sbin/useradd nagios
# passwd nagios

We need two packages. Nagios-plugin and Nrpe
---> nagios-plugins-1.4.13.tar.gz ---> nrpe-2.12.tar.gz

# cd /home/nagios/nagios-plugins-1.4.15
# ./configure
# make
# make install

The permissions on the plugin directory and the plugins will need to be fixed at this point, so run the following commands.

# chown nagios.nagios /usr/local/nagios
# chown -R nagios.nagios /usr/local/nagios/libexec

2.Install XINETD
# yum install xinetd

Install the NRPE ( Nagios Remote Plugin Executor ) daemon
Nagios Remote Plugin Executor (NRPE) is a Nagios agent that allows remote systems monitoring using scripts that are hosted on the remote systems. It allows for monitoring resources such as disk usage, system load or number of users currently logged in. Nagios periodically polls the agent on the remote system using the check_nrpe plugin.

The NRPE-plugin is running as a xinetd-service.

# wget http://osdn.dl.sourceforge.net/sourceforge/nagios/nrpe-2.12.tar.gz
# cd /home/nagios/nrpe-2.12/
# ./configure
# make all

Install the NRPE plugin (for testing), daemon, and sample daemon config file.

# make install-plugin
# make install-daemon
# make install-daemon-config

Install the NRPE daemon as a service under xinetd
# cd /home/nagios/nrpe-2.12/
# make install-xinetd

Edit the /etc/xinetd.d/nrpe file and add the IP address of the monitoring server to the only_from directive.

# vim /etc/xinetd.d/nrpe
only_from = 127.0.0.1 192.168.1.67  ------- nagios monitoring server ip

Add the following entry for the NRPE daemon to the /etc/services file.

# vim /etc/services
nrpe 5666/tcp   # NRPE

Restart the xinetd service.
# service xinetd restart

Test the NRPE daemon locally
Its time to see if things are working properly. Make sure the nrpe daemon is running under xinetd.

# netstat -at | grep nrpe
 The output out this command should show something like this:

 tcp 0 0 *:nrpe *:* LISTEN

3. Now back to your Nagios Server, and Install NRPE deamon 

# cd /home/nagios/nrpe-2.12/
# ./configure
# make all

Install the NRPE plugin

# make install-plugin

check of nrpe is working we will check the nrpe in the remote host

# /usr/local/nagios/libexec/check_nrpe -H 192.168.1.240  
 in server machine, give the ip of remote machines, to check whether they are communicating or not.

NRPE v2.12

Now in the nagios server : Go to

# cd /usr/local/nagios/etc/objects/

# cp localhost.cfg remotehost.cfg
# mv localhost.cfg Nagios-Server.cfg

Open remotehost.cfg and edit the hostname and IP adress 

# vim remoteost.cfg
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   localhost
   alias       localhost
   address     192.168.1.240
        }

save and exit

# cd /usr/local/nagios/etc
# vim nagios.cfg

# Definitions for monitoring the local (Linux) host  --------> add and comment lines below this
#cfg_file=/usr/local/nagios/etc/objects/localhost.cfg
cfg_file=/usr/local/nagios/etc/objects/remotehost.cfg

 save and exit

edit remotehost.cfg file 

# cd /usr/local/nagios/etc/objects/
# vim /usr/local/nagios/etc/objects/remotehost.cfg

# Define a host for the local machine

define host{
         use        linux-server
         host_name   cloudcc.ctechz.blogspot.com
         alias       localhost
         address     127.0.0.1
       }

define host{
        use         linux-server           
                                                      
                                                      
        host_name    www.ctechz.com
        alias        ctechz
        address      192.168.1.240
        }

# Define an optional hostgroup for Linux machines

define hostgroup{
     hostgroup_name  linux-servers
     alias           Linux Servers
   members    cloudcc.ctechz.blogspot.com,www.ctechz.com
        } 

# SERVICE DEFINITIONS

define service{
     use        local-service       
     host_name   cloudcc.ctechz.blogspot.com,www.ctechz.com
     service_description  PING
     check_command   check_ping!100.0,20%!500.0,60%
        }

Add the Rest of the services like this 

now check if you nagios server nagios can start without errors

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

If no Errors found while running above command then restart the nagios.

# service nagios restart

http://192.168.1.67/nagios/
Uname : nagiosadmin
Passwd: redhat