Installing Nagios On Debian Lenny And Monitoring A Debian Lenny Server - Page 2

7. Introduce Localservices From server1 To The Monitor Server

We need to change our hostconfig we created in step 5 to monitor the new services we can now discover with nrpe.

monitor:~# nano /etc/nagios3/conf.d/server1_nagios2.cfg

Add this to the end of the file:

define service{
        use                     generic-service
        host_name               server1
        service_description     Current Load
        check_command           check_nrpe_1arg!check_load
}
define service{
        use                     generic-service
        host_name               server1
        service_description     Current Users
        check_command           check_nrpe_1arg!check_users
}
define service{
        use                     generic-service
        host_name               server1
        service_description     Disk Space
        check_command           check_nrpe_1arg!check_hda1
}
define service{
        use                     generic-service
        host_name               server1
        service_description     Total Processes
        check_command           check_nrpe_1arg!check_total_procs
}

Do a restart of the nagios service:

monitor:~# /etc/init.d/nagios3 restart

In the webservice you should now be able to see the added services and slowly they should pick up, beside one of them, the Check for the Disk Space will most likely fail cause you have no /dev/hda1 partition nor device.

Change this check on the monitor1 server to reflect the actual partition that we want to check. In my case the machine sits on a virtual server host by xen, we can determine the used partition by using the following command on server1:

server1:~# df -h

Filesystem            Size  Used Avail Use% Mounted on
 /dev/mapper/iscsi1-root
                       7.3G  714M  6.2G  11% /
 tmpfs                 137M     0  137M   0% /lib/init/rw
 udev                   10M  568K  9.5M   6% /dev
 tmpfs                 137M     0  137M   0% /dev/shm
 /dev/xvda1            228M  9.5M  207M   5% /boot

This will show us the partitions and the mountpoints of them, in my case the actual 'root' partition is /dev/mapper/iscsi1-root and i discovered this by looking for the mountpoint '/'.

Now we can continue to change our nrpe config on the server to make this check working. For this we open the nrpe.cfg file again:

server1:~# nano /etc/nagios/nrpe.cfg

Then we go to the line which contains (line 201 by default):

command[check_hda1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/hda1

And change it to:

command[check_iscsi1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/mapper/iscsi1-root

Change the hostconfig on the Nagios server to reflect these changes:

monitor:~# nano /etc/nagios3/conf.d/server1_nagios2.cfg

From:

define service{
        use                     generic-service
        host_name               server1
        service_description     Disk Space
        check_command           check_nrpe_1arg!check_hda1
}

To:

define service{
        use                     generic-service
        host_name               server1
        service_description     Disk Space
        check_command           check_nrpe_1arg!check_iscsi1
}

Restart both services.

server1:~# /etc/init.d/nagios-nrpe-server restart
 monitor:~# /etc/init.d/nagios3 restart

8. Configure Notifications Per Mail

You want to be notified per email when a service gets into critical status. So we have to configure the email address for the user nagiosadmin.

Go into the file /etc/nagios3/conf.d/contacts_nagios2.cfg and change the email address to your own one. If you want to add more users, just copy the 'define contact' section, create a second one with it and add your user(s) to the contactgroup below.

define contact{
        contact_name                    root
        alias                           Root
        service_notification_period     24x7
        host_notification_period        24x7
        service_notification_options    w,u,c,r
        host_notification_options       d,r
        service_notification_commands   notify-service-by-email
        host_notification_commands      notify-host-by-email
        email                           [email protected]
        }
		
define contact{
        contact_name                    example
        alias                           example
        service_notification_period     24x7
        host_notification_period        24x7
        service_notification_options    w,u,c,r
        host_notification_options       d,r
        service_notification_commands   notify-service-by-email
        host_notification_commands      notify-host-by-email
        email                           [email protected]
        }
define contactgroup{
        contactgroup_name       admins
        alias                   Nagios Administrators
        members                 root,example
        }

To activate simple mail notification we have to enable the smtp transport of the Debian system, because all that Nagios does is to give over the message with a Linux pipe to the standard program /usr/bin/mail.

We have to install Postfix and set up a basic configuration to let the Nagios server send out emails by himself.

monitor:~# apt-get install postfix mailx

Now configure Postfix as "Internet Site" and set a domain where the Nagios mails will come from.

After this do a restart and stop the apache service on the testserver:

monitor:~# /etc/init.d/nagios3 restart
 server1:~# /etc/init.d/apache2 stop

This will create a notification message which should be received if you set your email address in the file contacts_nagios2.cfg.

Misc: About Icinga

Icinga is a Nagios fork with a larger developer community and will most likely be the software in the future to use, you will find howtos about Icinga on HowtoForge and you can reuse your custom plugins with Icinga as the Nagios plugins can be used to.

I would recommend anyone to play around with Nagios and Icinga.