Nagios

Nagios is an open source host, service and network monitoring program. It monitors specified hosts and services, alerting you to any developing issues, errors or improvements. This article describes the installation and configuration of Nagios.

Features

Some of Nagios' features include:

• Monitoring of network services (SMTP, POP3, HTTP, NNTP, PING, etc.)
• Monitoring of host resources (processor load, disk usage, etc.)
• Simple plugin design that allows users to easily develop their own service checks
• Parallelized service checks
• Ability to define network host hierarchy using "parent" hosts, allowing detection of and distinction between hosts that are down and those that are unreachable
• Contact notifications when service or host problems occur and get resolved (via email, pager, or user-defined method)
• Ability to define event handlers to be run during service or host events for proactive problem resolution
• Automatic log file rotation
• Support for implementing redundant monitoring hosts
• Optional web interface for viewing current network status, notification and problem history, log file, etc.

The following installation and configuration were tested using nagios 3.2.0-1, Apache web server 2.2.14-2, and PHP5 5.3.1-3 by awayand.

Webserver

According to the official documentation a webserver is not required, but if you wish to use any of the CGI features then a webserver (apache preferred), PHP (php-apache) for it and the gd library are required. This is assumed for this installation

Installation

Install nagios^AUR from the AUR.

Users may also want to install nagios-plugins^AUR.

Nagios Configuration

Copy the sample config files as root:

 cp /etc/nagios/cgi.cfg.sample /etc/nagios/cgi.cfg
 cp /etc/nagios/resource.cfg.sample /etc/nagios/resource.cfg
 cp /etc/nagios/nagios.cfg.sample /etc/nagios/nagios.cfg
 cp /etc/nagios/objects/commands.cfg.sample /etc/nagios/objects/commands.cfg
 cp /etc/nagios/objects/contacts.cfg.sample /etc/nagios/objects/contacts.cfg
 cp /etc/nagios/objects/localhost.cfg.sample /etc/nagios/objects/localhost.cfg
 cp /etc/nagios/objects/templates.cfg.sample /etc/nagios/objects/templates.cfg
 cp /etc/nagios/objects/timeperiods.cfg.sample /etc/nagios/objects/timeperiods.cfg

Make owner/group for all the files you just copied and belong to root equal to nagios/nagios:

# chown -R nagios:nagios /etc/nagios

Create htpasswd.users file with a username and password, eg. nagiosadmin and secretpass

# htpasswd -c /etc/nagios/htpasswd.users nagiosadmin

If the owner/group of the nagios-plugins you installed are root:root, the following needs to be done:

# chown -R nagios:nagios /usr/share/nagios

Once Nagios is configured, it is time to configure the webserver.

Apache Configuration

Edit /etc/httpd/conf/httpd.conf, add the following to the end of the file:

LoadModule php5_module modules/libphp5.so

# Nagios
Include "conf/extra/nagios.conf"

# PHP
Include "conf/extra/php5_module.conf"

Copy configure file:

# cp /etc/webapps/nagios/apache.example.conf /etc/httpd/conf/extra/nagios.conf

Add the apache user http to the group nagios, otherwise you will get the following error when using nagios:

Could not open command file '/var/nagios/rw/nagios.cmd' for update!: 

# usermod -G nagios -a http

PHP Configuration

Edit /etc/php/php.ini to include /usr/share/nagios in the open_basedir directive.

Example configuration:

open_basedir = /srv/http/:/home/:/tmp/:/usr/share/pear/:/usr/share/webapps:/etc/webapps:/usr/share/nagios

Final Steps

Start/Restart nagios:

# systemctl restart nagios

Start/Restart apache:

# systemctl restart httpd

Now you should be able to access nagios through your webbrowser using the username and password you have created above using htpasswd:

http://localhost/nagios

Plugin check_rdiff

A small guide on monitoring rdiff-backups using a plugin called check_rdiff.

Download and Install

You will need perl installed.

cd
wget http://www.monitoringexchange.org/attachment/download/Check-Plugins/Software/Backup/check_rdiff/check_rdiff
cp check_rdiff /usr/share/nagios/libexec
chown nagios:nagios /usr/share/nagios/libexec/check_rdiff
chmod 755 /usr/share/nagios/libexec/check_rdiff

Enable sudo for user nagios

Since the perl script check_rdiff needs to run as root, you will have to enable sudo for the nagios user:

sudoedit /etc/sudoers

This will open the /etc/sudoers file, then paste the following at the end of the file (you should know how to use the vi editor, if that is the one being used by sudoedit):

nagios  ALL=(root)NOPASSWD:/usr/share/nagios/libexec/check_rdiff

Integrate check_rdiff plugin into nagios

Edit /etc/nagios/objects/commands.cfg to include the following command definition:

# check rdiff-backup
define command{
	command_name	check_rdiff
        command_line    sudo $USER1$/check_rdiff -r $ARG1$ -w $ARG2$ -c $ARG3$ -l $ARG4$ -p $ARG5$ 
	}

Edit /etc/nagios/objects/localhost.cfg to include checking of rdiff-backup on localhost, for example:

define service{
        use                             local-service         ; Name of service template to use
        host_name                       localhost
        service_description             rdiff-backup
	check_command			check_rdiff!/home/x/rdiffbackup!8!10!500!24
        }

Quote from the check_rdiff script content:

The above command checks the repository (-r) which is defined as the destination of the backup, or more specifically, the directory above the rdiff-backup-data directory. It will return warning if the backup hasn't finished by 8am and critical by 10am. It will also return warning if the TotalDestinationSizeChange is greater than 500Mb. It also get the period set to 24hrs (-p). This is important as the plugin will throw a critical if the backup doesn't start in time.

Finally, restart nagios:

# systemctl restart nagios

You can now see the rdiff-backup status by clicking on Services on the left side of the nagios web interface control panel.

Forks

• Icinga is a Nagios fork. More details about the fork can be found at Icinga FAQ: Why a fork?

See also

• nagios.org Official website
• Nagios Plugins the home of the official plugins
• wikipedia.org Wikipedia article
• NagiosExchange overview of plugins, addons, mailing lists for Nagios
• NagiosForge a repository for ad