Configure Nagios Monitoring

Prerequisite

Before you begin verify you server and client configuration. From the server test client connection.

$ /usr/lib64/nagios/plugins/check_nrpe -H <client_ip_or_hostname>
NRPE v2.14

To setup server, see http://magnus-k-karlsson.blogspot.se/2014/01/install-nagios-core-35-on-rhel-6-from.html.

And for client, see http://magnus-k-karlsson.blogspot.se/2014/01/install-nagios-agent-nrpe-on-rhel-6.html

Client Nagios Plugins Configuration

First decide what you want to monitor. Then find a plugin that do the job. The standard plugins are documented here (http://nagios-plugins.org/doc/man/index.html).

You could also get help documentation for a specific plugin by executing it with option '--help'.

$ /usr/lib64/nagios/plugins/check_disk --help
check_disk v1.4.16 (nagios-plugins 1.4.16)

After you have tested it and is satisfied, you now define it as a nagios command.

$ vi /etc/nrpe.d/commands.cfg
...
command[check_sda2_disk]=/usr/lib64/nagios/plugins/check_disk -w 20% -c 15% -p /dev/sda2
...

Restart nrpe to let new configuration take effect.

$ service nrpe restart
Shutting down nrpe:                                        [  OK  ]
Starting nrpe:                                             [  OK  ]

Server Nagios Plugins Configuration

From the server test that you can call the client nrpe command.

$ /usr/lib64/nagios/plugins/check_nrpe -H <client_ip_or_hostname> -c check_sda2_disk

If this did not work, go back to the prerequisites and verify you server and client installation. If good, lets continue and define the nrpe command on the server.

$ vi /etc/nagios/conf.d/server1.domain.local.cfg
...
# 'check_nrpe' command definition
define command{
        command_name    check_nrpe
        command_line    $USER1$/check_nrpe -H <client_ip_or_hostname> -c $ARG1$
        }
...

Then we need to define a service that will run this command.

$ vi /etc/nagios/conf.d/server1.domain.local.cfg
...
define service{
        use                             generic-service         ; Name of service template to use
        host_name                       yourhostname.domain.local
        service_description             Checks partition sda2 at 20 proc and 15 proc
        check_command                   check_nrpe!check_sda2_disk
        }
...

Finally you will need to define a host, if you have not already done that.

$ vi /etc/nagios/conf.d/server1.domain.local.cfg
...
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               yourhostname.domain.local
        alias                   yourhostname.domain.local
        address                 192.168.1.117
        }
...

Before we restart the nagios server, you can test you new configuration

$ nagios -v /etc/nagios/nagios.cfg 

Nagios Core 3.5.1
...
Total Warnings: 0
Total Errors:   0
..

If everything is fine, you can now restart you nagios server.

Open you nagios web admin and login in and check you new service.