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Subject: Setting up nagios

Nagios is a versatile and functional network management tool with a GUI
(graphicuser interface) comparable to other commercial tools. It is a
system and network monitoring application. It watches hosts and
services that you specify, alerting you when things go bad and when
they get better. Nagios was originally designed to run under Linux, but
now it also runs well on other Unix variants.

Nagios Installation Guides:

This blog is intended to provide you with simple instructions on how to install Nagios from source (code) in Fedora.

Prerequisites:

Before installing Nagios,you need to install the following packages:

Apache

GCC compiler

GD development libraries

You can use yum to install these packages by running the following commands (as root):

yum install httpd

yum install gcc

yum install glibc glibc-common

yum install gd gd-devel

1) Create Account Information

Create a new nagios user account.

/usr/sbin/useradd -m nagios

Create a new nagcmd group for allowing external commands to be
submitted through the web interface. Add both the nagios user and the
apache user to the group.

/usr/sbin/groupadd nagcmd

/usr/sbin/usermod -a -G nagcmd nagios

/usr/sbin/usermod -a -G nagcmd apache

2) Download Nagios:

Create a directory for storing the downloads.

mkdir ~/ssages

cd ~/ssages

wget http://osdn.dl.sourceforge.net/sourceforge/nagios/nagios-3.0.6.tar.gz

3) Compile and Install Nagios

Extract the Nagios source code tarball.

tar xzf nagios-3.0.6.tar.gz

cd nagios-3.0.6

./configure βwith-command-group=nagcmd

make install

make install-init

make install-config

make install-commandmode

nagios-3.0.6

4) Configure the Web Interface

Install the Nagios web config file in the Apache conf.d directory.

make install-webconf

Create a nagiosadmin account for logging into the Nagios web interface.

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

Edit the file
/usr/local/apache/conf/includes/pre_virtualhost_global.conf and append
the following lines to the virtual host directories.

AuthName βNagiosβ

AuthType Basic

AuthUserFile /usr/local/nagios/etc/htpasswd.users

Require valid-user

Restart Apache to make the new settings take effect.

service httpd restart

5) Compile and Install the Nagios Plugins

wget http://osdn.dl.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-1.4.11.tar.gz

cd ~/ssages

tar xzf nagios-plugins-1.4.11.tar.gz

cd nagios-plugins-1.4.11

Compile and install the plugins.

./configure βwith-nagios-user=nagios βwith-nagios-group=nagios

make

make install

6) Start Nagios

Add Nagios to the list of system services and have it automatically start when the system boots.

chkconfig βadd nagios

chkconfig nagios on

Verify the sample Nagios configuration files.

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

If there are no errors, start Nagios.

service nagios start

you can check the Nagios in your browser typing the following url:

http://localhost/nagios

You should now be able to access the Nagios web interface at the URL
below. Youβll be prompted for the username (nagiosadmin) and password
you specified earlier.

NRPE Installation and Configuration

The NRPE addon is designed to allow you to execute Nagios plugins on
remote Linux/Unix machines. The main reason for doing this is to allow
Nagios to monitor βlocalβ resources (like CPU load, memory usage, etc.)
on remote machines. Since these public resources are not usually
exposed to external machines, an agent like NRPE must be installed on
the remote Linux/Unix machines.

The NRPE addon consists of two pieces:

The check_nrpe plugin, which resides on the local monitoring machine.

The NRPE daemon, which runs on the remote Linux/Unix machine.

When Nagios needs to monitor a resource of service from a remote Linux/Unix machine:

Nagios will execute the check_nrpe plugin and tell it what service needs to bechecked.

The check_nrpe plugin contacts the NRPE daemon on the remote host over an (optionally) SSL-protected connection.

The NRPE daemon runs the appropriate Nagios plugin to check the service or resource.

The results from the service check are passed from the NRPE daemon back
to thecheck_nrpe plugin, which then returns the check results to the
Nagios process.

INSTALLATION

Remote Host Setup:

Create a new nagios user account.

/usr/sbin/useradd nagios

Create a directory for storing the downloads.

mkdir ~/ssages

cd ~/ssages

wget http://osdn.dl.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-1.4.11.tar.gz

Extract the Nagios plugins source code tarball.

tar xzf nagios-plugins-1.4.11.tar.gz

cd nagios-plugins-1.4.11

Compile and install the plugins.

./configure

make

make install

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

chown nagios.nagios /usr/local/nagios

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

Install the NRPE daemon:

cd ~/ssages

wget http://osdn.dl.sourceforge.net/sourceforge/nagios/nrpe-2.8.tar.gz

tar xzf nrpe-2.8.tar.gz

cd nrpe-2.8

Compile the NRPE addon.

./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

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

nrpe 5666/tcp# NRPE

Next we add an init script for nrpe. For this,

cd nrp-2.12/

cp ./src/nrpe /usr/sbin/

cp ./sample-config/nrpe.cfg /etc /

cat init-script.in > /etc/init.d/nrpe

mod a+x /etc/init.d/nrpe

open the /etc/init.d/nrpe and edit

NrpeBin=/usr/sbin/nrpe

NrpeCfg=/usr/local/nagios/etc/nrpe.conf

Then restart nrpe services

/etc/init.d/nrpe restart

Then edit the nrpe configuration file and allow the monitoring hoast ipaddress.

allowed_hosts=ipaddress of monitoring host

Next to open nrpe port in the firewall.

vi /etc/apf/conf.apf

edit the follwing section and add the port number 5666

IG_tcp_cports=β5666,20β¦β¦β¦..etcβ

Restart the services

/etc/init.d/apf restart

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

Monitoring Host Setup

For monitoring remote host, you need to install nrpe plugin to the monitoring host. For this,

cd ~/ssages

wget http://osdn.dl.sourceforge.net/sourceforge/nagios/nrpe-2.8.tar.gz

tar xzf nrpe-2.8.tar.gz

cd nrpe-2.8/

Compile the NRPE addon.

./configure

make all

Install the NRPE plugin.

make install-plugin

Create a command definition

vi /usr/local/nagios/etc/commands.cfg

and add the following definition to the file:

define command{

command_name check_nrpe

command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$

}

You can insert each remote system services in one file. For that you have to edit the configuration file

vi /usr/local/nagios/etc/nagios.cfg

and append the following line.

cfg_file=/usr/local/nagios/etc/objects/remotehost.cfg

Create host and service definitions

First create a new template for each different type of host youβll be monitoring. Letβs create a new template for linux boxes.

edit /usr/local/nagios/etc/objects/templates.cfg and add the following lines,

define host{

name linux-box ; Name of this template

use generic-host ; Inherit default values

check_period 24Γ7

check_interval 5

retry_interval 1

max_check_attempts 10

check_command check-host-alive

notification_period 24Γ7

notification_interval 30

notification_options d,r

contact_groups admins

register 0 ; DONT REGISTER THIS - ITS A TEMPLATE

}

Notice that the linux-box template definition is inheriting default
values from the generic-host template, which is defined in the
localhost.cfg file.

Next, define a new host for the remote Linux/Unix box that references the newly created linux-box host template.

For this edit /usr/local/nagios/etc/objects/remotehost.cfg

define host{

use linux-box ; Inherit default values from a template

host_name remotehost ; The name weβre giving to this server

address 192.168.0.1 ; IP address of the server

check_command check-host-alive

}

Then define contact name and contact goup name in same file

define contact{

contact_name clientcontact

host_name remote_host

use generic-contact

alias Nagios client

email remotehost@gmail.com

}

define contactgroup{

contactgroup_name groupname

host_name remote_host

alias Nagios group

members clientcontact,membersof remote_host

}

Now define some services to monitor the remote Linux/Unix box. These
service definitions will use the commands that have been defined in the
nrpe.cfg file in the remote host.

The following service will monitor the CPU load in the remote host. The
βcheck_loadβ argument that is passed to the check_nrpe command
definition tells the NRPE daemon to run the βcheck_loadβ command as
defined in the nrpe.cfg file.

define service{

use generic-service

host_name remotehost

service_description CPU Load

check_command check_nrpe!check_load

}

The following service will monitor the the number of currently logged-in users in the remote host.

define service{

use generic-service

host_name remotehost

service_description Current Users

check_command check_nrpe!check_users

}

The following service will monitor the free drive space on /dev/hda1 in the remote host.

define service{

use generic-service

host_name remotehost

service_description /dev/hda1 Free Space

check_command check_nrpe!check_hda1

}

The following service will monitor the total number of processes in the remote host.

define service{

use generic-service

host_name remotehost

service_description Total Processes

check_command check_nrpe!check_total_procs

}

The following service will monitor the number of zombie processes in the remote host.

define service{

use generic-service

host_name remotehost

service_description Zombie Processes

check_command check_nrpe!check_zombie_procs

}

The following service will monitor http status in the remote host.

define service{

use generic-service

host_name remote_host

service_description HyperVM

check_command check_nrpe!check_http

}

Restarting Nagios:

Verify your Nagios configuration files.

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

If there are errors, fix them. If everything is fine, restart Nagios.

service nagios restart

Remote Host Configuration:

Edit the nrpe configuration file and add the folowing lines:

vi /usr/local/nagios/etc/nrpe.cfg

command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10

command[check_load]=/usr/local/nagios/libexec/check_load -w 15,10,5 -c 30,25,20

command[check_hda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/hda1

command[check_zombie_procs]=/usr/local/nagios/libexec/check_procs -w 5 -c 10 -s Z

command[check_http]=/usr/local/nagios/libexec/check_http -H 127.0.0.1 -w 5 -c 10

Restart the nrpe:

/etc/init.d/nrpe restart

Make sure you add nrpe to chkconfig in server being monitored so it will be automatically restart when the server is rebooted:

chkconfig --add nrpe

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