Installing and configuring Nagios

Nagios is a powerful monitoring system and here we will learn how to monitor MySQL through Nagios. We will be installing Nagios, required plugins and configuring it to monitor MySQL Database Server.
Let’s unleash the power step by step:
Installing and configuring Nagios
1. Download the nagios and plugins
Download following files from Nagios.org and move to /home/downloads
nagios-3.0.1.tar.gz
nagios-plugins-1.4.11.tar.gz
2. Take care of the prerequisites
Make sure apache is working on the server by verifying from browser: http://localhost
Verify whether gcc is installed
[root@localhost]#rpm -qa | grep gcc
gcc-3.4.6-8
compat-gcc-32-3.2.3-47.3
libgcc-3.4.6-8
compat-libgcc-296-2.96-132.7.2
compat-gcc-32-c++-3.2.3-47.3
gcc-c++-3.4.6-8
Verify whether GD is installed
[root@localhost]# rpm -qa gd
gd-2.0.28-5.4E
3. Create user and group for nagios
[root@localhost]# useradd nagios
[root@localhost]# passwd nagios
[root@localhost]# groupadd nagcmd
[root@localhost]# usermod -G nagcmd nagios
[root@localhost]# usermod -G nagcmd apache
4. Install nagios
[root@localhost]# tar xvf nagios-3.0.1.tar.gz
[root@localhost]# cd nagios-3.0.1
[root@localhost]# ./configure --with-command-group=nagcmd
[root@localhost]# make all
[root@localhost]# make install
[root@localhost]# make install-config
[root@localhost]# make install-commandmode
Following are some additional parameters that you can pass to ./configure to customize your installation. I used only --with-command-group as shown above.
--prefix /opt/nagios Where to put the Nagios files
--with-cgiurl /nagios/cgi-bin Web server url where the cgi's will be available
--with-htmurl /nagios Web server url where nagios will be available
--with-nagios-user nagios user account under which Nagios will run
--with-nagios-group nagios group account under which Nagios will run
--with-command-group nagcmd group account which will allow the apache user to submit
commands to Nagios
At the end of the configure output, it will display a summary as shown below:
*** Configuration summary for nagios 3.0.1 05-28-2008 ***:

General Options:
-------------------------
Nagios executable: nagios
Nagios user/group: nagios,nagios
Command user/group: nagios,nagcmd
Embedded Perl: no
Event Broker: yes
Install ${prefix}: /usr/local/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

Web Interface Options:
------------------------
HTML URL: http://localhost/nagios/
CGI URL: http://localhost/nagios/cgi-bin/
Traceroute (used by WAP): /bin/traceroute
5. Configure the web interface.
[root@localhost]# make install-webconf
[root@localhost# htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
New password:
Re-type new password:
Adding password for user nagiosadmin
6. Compile and install nagios plugins
[root@localhost]# tar xvf nagios-plugins-1.4.11.tar.gz
[root@localhost]# cd nagios-plugins-1.4.11
[root@localhost]# ./configure --with-nagios-user=nagios --with-nagios-group=nagios
[root@localhost]# make
[root@localhost]# make install
Note: On Red Hat, the ./configure command mentioned above did not work and was hanging at the when it was displaying the message: checking for redhat spopen problem… Add –enable-redhat-pthread-workaround to the ./configure command as a work-around for the above problem as shown below.
[root@localhost]# ./configure --with-nagios-user=nagios --with-nagios-group=nagios --enable-redhat-pthread-workaround
7. Start Nagios
Add the nagios to the startup routine:
[root@localhost]# chkconfig --add nagios
[root@localhost]# chkconfig nagios on
Verify to make sure there are no errors in the nagios configuration file:
[root@localhost]# /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

Total Warnings: 0
Total Errors: 0
Things look okay - No serious problems were detected during the pre-flight check
Start the nagios
[root@localhost]# service nagios start
Starting nagios: done.
8. Login to web interface
Nagios Web URL: http://localhost/nagios/
Use the userid, password that was created from step#5 above.

III. Configuration files overview
.
The first configuration to modify is to change the default value of email address in /usr/local/nagios/etc/objects/contacts.cfg file to your email address.
Following are the three major configuration files located under /usr/local/nagios/etc

1. nagios.cfg – This is the primary Nagios configuration file where lot of global parameters that controls the nagios can be defined.
2. cgi.cfg - This files has configuration information for nagios web interface.
3. resource.cfg – If you have to pass some sensitive information (username, password etc.) to a plugin to monitor a specific service, you can define them here. This file is readable only by nagios user and group.
Following are the other configuration files under /usr/local/nagios/etc/objects directory:

contacts.cfg: All the contacts who needs to be notified should be defined here. You can specify name, email address, what type of notifications they need to receive and what is the time period this particular contact should be receiving notifications etc.
commands.cfg – All the commands to check services are defined here. You can use $HOSTNAME$ and $HOSTADDRESS$ macro on the command execution that will substitute the corresponding hostname or host ip-address automatically.
timeperiods.cfg – Define the timeperiods. for e.g. if you want a service to be monitored only during the business hours, define a time period called businesshours and specify the hours that you would like to monitor.
templates.cfg – Multiple host or service definition that has similar characteristics can use a template, where all the common characteristics can be defined. Use template is a time saver.
localhost.cfg – Defines the monitoring for the local host. This is a sample configuration file that comes with nagios installation that you can use as a baseline to define other hosts that you would like to monitor.
printer.cfg – Sample config file for printer
switch.cfg – Sample config file for switch
windows.cfg – Sample config file for a windows machine