Configuring e mail notificationin nagios core

Configuring e-Mail Notifications in Nagios
Core…
by Andy Grogan on February 24, 2012 · 9 comments

in Exchange 2010 (General), Linux, Linux with Exchange, Monitoring, Nagios, Ubuntu

Linked to my multi part series on using Nagios Core with Exchange server, I would like to explain how
you can configure mail notifications to recipients when status changes occur within the Nagios
monitoring environment.

If you are just joining us here, I recommend that you have a look at the series in its entirety before
reading any further, as there are a few concepts used in this article which were covered in-depth within
previous four parts. You can view them here:

In Part 1
I covered how you can install Nagios Core 3.3.1 onto an existing Ubuntu 11.10 server within
your environment
In Part 2
I covered how you can setup basic monitoring on your first Windows Server – making use of the
NSClient++, I also covered how you could setup a basic “check_nt” monitoring service
In Part 3
I covered how you can install the NRPE daemon onto your Nagios Server – and then use the
NSClient to execute a basic Powershell script and report the output back into the Nagios
interface
In Part 4
I covered how you can build some custom PowerShell scripts to monitor you Exchange
environment

Making Sure that you DNS Configuration is correct
Before you begin to setup the tools which will enable mail notifications to be sent from Nagios, you
should ensure that you destination mail domain can be resolved from your Ubuntu server. I have
assumed that you will be sending notifications to a mailbox within your Exchange infrastructure which
naturally is separate to the Nagios implementation.

In my example, my destination domain is “prepad.com” – therefore in order to check if the Nagios
server can lookup the MX record for that domain you can use the “dig” command like so:

dig prepad.com mx

If everything is ok, you should receive an output to the command similar to that below:

Installing POSTFIX
Postfix is a free MTA for Linux which is designed to be easier to setup and configure than the more
traditional SendMail offering. Combined with Heirloom-MailX (see next section) Nagios can be
configured to use the two products to send e-mail notifications to a designated set of contacts in the
event of an alert being generated.

From the perspective of using Postfix to send e-mail from Nagios – the setup is very simple (e.g. I am
not going to go into huge amounts of detail on how you can configure Postfix).

In order to install Postfix open an SSH session to your Nagios Ubuntu Server using PuTTY and type in
the following command:

sudo apt-get install postfix

You will then be presented with a two step setup Wizard – the first page will ask you what type of
POSTFIX SMTP Server you would like to use – ensure that you have selected the “Internet Site”
option, when done navigate (using TAB) to the “OK” button – see below

You will then be asked to supply a Domain Name which the source e-mails will be sent from – in my
example I have used “nagios.notify” – when you are done tab to the “OK” button – see below

This will then complete the configuration of Postfix.

Installing Heirloom-MailX

Heirloom-MailX is a small binary program that is used by Nagios to send mail to the Postfix mail server
– it is very easy to install.
From the SSH console, type in the following command:

sudo apt-get install heirloom-mailx

Configuring Exchange to accept messages from your Nagios
Server
There are better ways to do this, however if you want to ensure that your Exchange Hub transport
servers are accepting mail from your Nagios server, you should ensure that the Default Receive
Connector on your HT is configured to accept anonymous connections – you can do this by opening up
the Exchange Management Console and navigating to [ Microsoft Exchange On-Premises –> Server
Configuration –> Hub Transport ], then select your HT and then from the low pane (Receive
Connectors) right click on the “Default <Your HT>” – from the context menu that appears choose
“Properties” – see below

From the properties box that appears, click on the “Permission Groups” tab, and then tick the
“Anonymous Users” tick box, and then click on the “OK” button – see below

In the real world, you should probably consider creating a dedicated Receive Connector for the Nagios
instance.

Configuring Nagios to Send Mail Notifications
Now that you have installed the required components to enabled Nagios to send mail notifications, you
will need to download two configurations files from your Nagios Server (using FileZilla and edit them
using Notepad++ – if you need to understand how to do this, please review part 2 of my installing
Nagios for Exchange series).

These files are:

1. commands.cfg
2. contacts.cfg

Which are located in:

/usr/local/nagios/etc/objects

Open the commands.cfg file in Notepad++ and modify the following two lines:

# 'notify-host-by-email' command definition
define command{
command_name notify-host-by-email
command_line /usr/bin/printf "%b" "***** Nagios *****nnNotification Type:
$NOTIFICATIONTYPE$nHost: $HOSTNAME$nState: $HOSTSTATE$nAddress:
$HOSTADDRESS$nInfo: $HOSTOUTPUT$nnDate/Time: $LONGDATETIME$n" | /bin/mailx -s
"** $NOTIFICATIONTYPE$ Host Alert: $HOSTNAME$ is $HOSTSTATE$ **" $CONTACTEMAIL$
}

# 'notify-service-by-email' command definition

define command{
command_name notify-service-by-email
$NOTIFICATIONTYPE$nnService: $SERVICEDESC$nHost: $HOSTALIAS$nAddress:
$HOSTADDRESS$nState: $SERVICESTATE$nnDate/Time: $LONGDATETIME$nnAdditional
Info:nn$SERVICEOUTPUT$n" | /bin/mailx -s "** $NOTIFICATIONTYPE$ Service Alert:
$HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" $CONTACTEMAIL$
}

To look like the following:

# 'notify-host-by-email' command definition
define command{
command_name notify-host-by-email
$NOTIFICATIONTYPE$nHost: $HOSTNAME$nState: $HOSTSTATE$nAddress:
$HOSTADDRESS$nInfo: $HOSTOUTPUT$nnDate/Time: $LONGDATETIME$n" | /usr/bin/mailx
-s "** $NOTIFICATIONTYPE$ Host Alert: $HOSTNAME$ is $HOSTSTATE$ **" $CONTACTEMAIL$
}

# 'notify-service-by-email' command definition
define command{
command_name notify-service-by-email
$NOTIFICATIONTYPE$nnService: $SERVICEDESC$nHost: $HOSTALIAS$nAddress:
$HOSTADDRESS$nState: $SERVICESTATE$nnDate/Time: $LONGDATETIME$nnAdditional
Info:nn$SERVICEOUTPUT$n" | /usr/bin/mailx -s "** $NOTIFICATIONTYPE$ Service
Alert: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" $CONTACTEMAIL$
}

In essence you are changing the /bin/mail part of each command to /usr/bin/mailx

When you are done, save the file and then using FileZilla upload it back to your Nagios Server.

Next open the contacts.cfg file and change the “email” property to that of the account where you would
like the notifications to be sent – see below

define contact{
contact_namenagiosadmin ; Short name of user
use generic-contact ; Inherit default values
from generic-contact template (defined above)
aliasNagios Admin ; Full name of user
email administrator@prepad.com ; <<***** CHANGE THIS
TO YOUR EMAIL ADDRESS ******
}

When you are done, save the file, and upload it back to your Nagios server.

To finish up the configuration, from a PuTTY session type in the following command:

sudo /etc/init.d/nagios restart

For the configuration changes to take effect.

When there is now a problem with either a service or a host, the chosen recipient should receive a mail
notification like the following:

Configuring e mail notificationin nagios core

Configuring e mail notificationin nagios core

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