NAGIOS NETWORK MONITORING

"How to Install & configure Nagios on CentOS"

Nagios is an awesome Open Source monitoring tool, its provides you more comprehensive monitoring environment to always keep an eye on your all machines / networks whether you are in a your data centre or just your small labs.

With Nagios, you can monitor your remote hosts and their services remotely on a single window. It shows warnings and indicates if something goes wrong in your servers which eventually helps us to detect some problems before they occur. It helps us to reduce downtime and business losses.

Recently, Nagios released its latest versions Nagios 4.0.1 on 15th October 2013, and its latest stable release of Nagios plugins 1.5.

Installing Nagios 4.0.1 and Nagios Plugin 1.5
-------------------------------------------------------------

Nagios and its plugins will be installed under /usr/local/nagios directory.
Nagios will be configured to monitor few services of your local machine (Disk Usage, CPU Load, Current Users, Total Processes, etc.)

[ Note:- Before to begine, sure update your CentOS sytem by the "#yum update" command ]

Step 1: Install Required Dependencies
We need to install Apache, PHP and some libraries like gcc, glibc, glibc-common and GD libraries and its development libraries before installing Nagios 4.0.1 with source. And to do so we can use yum default package installer.

[root@tecmint]# yum install -y  httpd  php  gcc  glibc  glibc-common  gd gd-devel  make net-snmp   (RedHat / CentOS)

Step 2: Create Nagios User and Group
Create a new nagios user and nagcmd group account and set a password.

[root@tecmint]# useradd nagios
[root@tecmint]# groupadd nagcmd

Next, add both the nagios user and the apache user to the nagcmd group.

[root@tecmint]# usermod -G nagcmd nagios
[root@tecmint]# usermod -G nagcmd apache

Step 3: Download Nagios Core 4.0.1 and Nagios Plugin 1.5

Create a directory for your Nagios installation and all its future downloads.

[root@tecmint]# mkdir /root/nagios
[root@tecmint]# cd /root/nagios

Now download latest Nagios Core 4.0.1 and Nagios plugins 1.5 packages with wget command.

[root@tecmint nagios~]# wget  http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-4.0.1.tar.gz
[root@tecmint nagios~]# wget  https://www.nagios-plugins.org/download/nagios-plugins-1.5.tar.gz

Step 4: Extract Nagios Core and its Plugins

We need to extract downloaded package with tar command as follows.

root@tecmint nagios~]# tar –xvf nagios-4.0.1.tar.gz
[root@tecmint nagios~]# tar –xvf nagios-plugins-1.5.tar.gz

When we extract these tarballs with tar command, two new folders will appear in that directory.

[root@tecmint nagios ~]# ll
total 3712
drwxrwxr-x 18 root root    4096 Oct 17 03:28 nagios-4.0.1
-rw-r--r--  1 root root 1695367 Oct 15 19:49 nagios-4.0.1.tar.gz
drwxr-xr-x 15  200  300    4096 Oct 14 10:18 nagios-plugins-1.5
-rw-r--r--  1 root root 2428258 Oct  2 11:27 nagios-plugins-1.5.tar.g

Configure Nagios Core

Now, first we will configure Nagios Core and to do so we need to go to Nagios directory and run configure file and if everything goes fine, it will show the output in the end as sample output. Please see below

[root@tecmint nagios~]# cd nagios-4.0.1
[root@tecmint nagios-4.0.1 ]# ./configure --with-command-group=nagcmd

Sample output:

Nagios executable:  nagios
Nagios user/group:  nagios,nagios
Command user/group:  nagios,nagcmd
Event Broker:  yes
Install ${prefix}:  /usr/local/nagios
Install ${includedir}:  /usr/local/nagios/include/nagios
Lock file:  ${prefix}/var/nagios.lock
Check result directory:  ${prefix}/var/spool/checkresults
Init directory:  /etc/rc.d/init.d
Apache conf.d directory:  /etc/httpd/conf.d
Mail program:  /bin/mail
Host OS:  linux-gnu

Now, after configuring we need to Compile and install all the binaries with make command and make install command will install all the needed libraries in your machine and we can proceed further.

[root@tecmint nagios-4.0.1 ]# make all
[root@tecmint nagios-4.0.1 ]# make install

Sample output:

*** Main program, CGIs and HTML files installed ***

You can continue with installing Nagios as follows (type 'make'
without any arguments for a list of all possible options):

make install-init
     - This installs the init script in /etc/rc.d/init.d

make install-commandmode
     - This installs and configures permissions on the
       directory for holding the external command file

make install-config
     - This installs sample config files in /usr/local/nagios/etc
------------------------------------------------------------------------------------    
    
Following command will install the init scripts for Nagios.

[root@tecmint nagios-4.0.1 ]# make install-init

To make nagios work from command line we need to install command-mode.

[root@tecmint nagios-4.0.1 ]# make install-commandmode

Next, install sample nagios files, please run following command.

[root@tecmint nagios-4.0.1 ]# make install-config

Sample output:

/usr/bin/install -c -m 775 -o nagios -g nagios -d /usr/local/nagios/etc
/usr/bin/install -c -m 775 -o nagios -g nagios -d /usr/local/nagios/etc/objects
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/nagios.cfg /usr/local/nagios/etc/nagios.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/cgi.cfg /usr/local/nagios/etc/cgi.cfg
/usr/bin/install -c -b -m 660 -o nagios -g nagios sample-config/resource.cfg /usr/local/nagios/etc/resource.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/templates.cfg /usr/local/nagios/etc/objects/templates.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/commands.cfg /usr/local/nagios/etc/objects/commands.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/contacts.cfg /usr/local/nagios/etc/objects/contacts.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/timeperiods.cfg /usr/local/nagios/etc/objects/timeperiods.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/localhost.cfg /usr/local/nagios/etc/objects/localhost.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/windows.cfg /usr/local/nagios/etc/objects/windows.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/printer.cfg /usr/local/nagios/etc/objects/printer.cfg
/usr/bin/install -c -b -m 664 -o nagios -g nagios sample-config/template-object/switch.cfg /usr/local/nagios/etc/objects/switch.cfg

*** Config files installed ***

Remember, these are *SAMPLE* config files.  You'll need to read
the documentation for more information on how to actually define
services, hosts, etc. to fit your particular needs.
------------------------------------------------------------------------------------------------

Step 5: Customizing Nagios Configuration

Open the “contacts.cfg” file with your choice of editor and set the email address associated with the nagiosadmin contact definition to receiving email alerts.

# vi /usr/local/nagios/etc/objects/contacts.cfg

Sample Output

###############################################################################
###############################################################################
#
# CONTACTS
#
###############################################################################
###############################################################################

# Just one contact defined by default - the Nagios admin (that's you)
# This contact definition inherits a lot of default values from the 'generic-contact'
# template which is defined elsewhere.

define contact{
       contact_name                    nagiosadmin             ; Short name of user
       use                             generic-contact         ; Inherit default values from generic-contact template (defined above)
       alias                           Nagios Admin            ; Full name of user

       email                           tecmint@tecmint.com     ; *** CHANGE THIS TO YOUR EMAIL ADDRESS ****
       }

Step 6: Install and Configure Web Interface for Nagios

We are done with all configuration in the backend, now we will configure Web Interface For Nagios with following command. The below command will Configure Web interface for Nagios and a web admin user will be created “nagiosadmin”.

[root@tecmint nagios-4.0.1 ]# make install-webconf

In this step, we will be creating a password for “nagiosadmin”. After executing this command, please provide a password twice and keep it remember because this password will be used when you login in the Nagios Web interface.

[root@tecmint nagios-4.0.1]# htpasswd -s -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
New password:
Re-type new password:
Adding password for user nagiosadmin

Restart Apache to make the new settings take effect.

[root@tecmint ]# service httpd start         (On RedHat / CentOS)

Step 7: Compile and Install Nagios Plugin

We have downloaded nagios plugins in /root/nagios, Go there and configure and install it as directed below.

[root@tecmint nagios]# cd /root/nagios
[root@tecmint nagios]# cd nagios-plugins-1.5
[root@tecmint nagios]# ./configure --with-nagios-user=nagios --with-nagios-group=nagios
[root@tecmint nagios]# make
[root@tecmint nagios]# make install

Step 8: Verify Nagios Configuration Files

Now we are all done with Nagios configuration and its time to verify it and to do so please insert following command. If everything goes smooth it will show up similar to below output.

[root@tecmint nagios]# /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

Sample Output

/usr/bin/install -c -m 644 sample-config/httpd.conf /etc/httpd/conf.d/nagios.conf

*** Nagios/Apache conf file installed ***

 /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
...
...
Total Warnings: 0
Total Errors:   0

Step 9: Add Nagios Services to System Start-up

To make Nagios work across reboots, we need to add nagios and httpd with chkconfig command.

[root@tecmint ]# chkconfig --add nagios
[root@tecmint ]# chkconfig --level 35 nagios on
[root@tecmint ]# chkconfig --add httpd
[root@tecmint ]# chkconfig --level 35 httpd on

Restart Nagios to make the new settings take effect.

[root@tecmint ]# service nagios start (On RedHat / CentOS)

Step 10: Login to the Nagios Web Interface
Your nagios is ready to work, please open it in your browser with “http://Your-server-IP-address/nagios” or “http://FQDN/nagios” and Provide the username “nagiosadmin” and password.
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