Nagios monitoring

Installation Nagios on EC2 Ami instance and monitor a generic host on Internet.

Installation

Install Nagios core package

sudo yum install nagios

Install plugins. Without the plugins you will not be able to monitor even localhost.

sudo yum install nagios nagios-plugins-all

Install SNMP

yum install net-snmp-utils net-snmp

Post-installation configuration

Set up user name and password. A default username is nagiosadmin

sudo htpasswd -c -b  /etc/nagios/passwd nagiosadmin nagiospassword

Adding host to be monitored

Create new object to monitor

sudo vi /etc/nagios/objects/o2box.cfg

Paste below standard minimum config

# Define a host for the local machine

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               o2box
        alias                   Thomson TG585
        address                 8.8.8.8
        }

###############################################################################
###############################################################################
#
# SERVICE DEFINITIONS
#
###############################################################################
###############################################################################

# Define a service to "ping" the local machine

define service{
        use                             generic-service         ; Name of service template to use
        host_name                       o2box
        service_description             PING
        check_command                   check_ping!100.0,20%!500.0,60%
        }

# Define a service to check HTTP on the local machine.
# Disable notifications for this service by default, as not all users may have HTTP enabled.

define service{
        use                             generic-service         ; Name of service template to use
        host_name                       o2box
        service_description             HTTP
        check_command                   check_http
        notifications_enabled           0
        }

Define host

• use linux-server: We use Linux-Server because its the easiest template to use, more on this later
• host_name o2box: This is the host name, this is how you reference your hosts settings, it doesn’t have to be its address just something meaningful related to the host
• alias Thomson TG585: This is the long name for the host, this is only used for display purposes
• address 8.8.8.8: This is important, its the actual address for the host, either a DNS name or IP address will work here.

Define service

This is were we define the services on each host, for o2box home router we are only going to check if its alive(ping) and check to see if its web server is running (http). We need to two services for this, however the settings are the same for each:

• use this is the service template, use generic-serivce is the standard template.
• host_name This is where we reference what host we want the service connected to, use the name of the host defined earlier.
• service_description This is the name the user will see on the Nagios web page
• check_command This is the command we are going to run to test if the service is running, more on commands later.

Add to /etc/nagios/nagios.cfg following lines in appropriate sections:

cfg_file=/etc/nagios/objects/o2box.cfg

Restart Nagios

sudo service nagios restart

Hosts list should look similar to what we have below

Troubleshooting

If you receive errors after restarting, run verbose mode on the main config

nagios -v /etc/nagios/nagios.cfg

References

• Fedora Quickstart rpm based guide and install from sources
• Nagios on AWS live example