Nagios can be configured to sent out alerts on the state of the host or host service being monitored via email. This guide will therefore take you through how to configure Nagios Email Notification using Gmail.
The current state of a service or host being monitored is determined by the status of the service or host which can be OK, WARNING, UP, DOWN, etc. and the type of state the service or host which can hard or soft.
In this guide, we are going to use Postfix as out Mail Transfer Agent (MTA). Also, by default, Nagios Mail notification is sent using mail command. Hence, run the command below to install the required packages.
dnf install postfix cyrus-sasl-plain mailx
Configure Postfix to Use Gmail Relay
Enable STARTTLS encryption by changing the line smtp_tls_security_level = may to smtp_tls_security_level = encrypt.
sed -i 's/smtp_tls_security_level = may/smtp_tls_security_level = encrypt/' /etc/postfix/main.cf
If the smtp_tls_security_level option is not set, just insert it;
Define the path to CA certificates. The public root certificates are usually found under /etc/pki/tls/certs/ca-bundle.crt on RHEL derivatives and /etc/ssl/certs/ca-certificates.crt on Debian/Ubuntu systems.
You should be able to receive the mail on your inbox. You can also check the mail logs. The log filename may be different for your case.
tail -f /var/log/maillog
Oct 19 15:01:44 dev-server postfix/smtp[5109]: C7E8C3B5AD: to=[email protected], relay=smtp.gmail.com[74.125.200.109]:587, delay=18, delays=0.04/0.02/16/2.1, dsn=2.0.0, status=sent (250 2.0.0 OK 1571511704 h8sm11800598pfo.64 - gsmtp)
Oct 19 15:01:44 dev-server postfix/qmgr[4574]: C7E8C3B5AD: removed
Create Nagios Contact Object Definition
The first step in configuring is to create a Nagios contacts group that defines who should be notified on the state of a monitored service or host.
Nagios comes with a default contact group, contacts.cfg, located on the default objects definition configurations directory, /usr/local/nagios/etc/objects.
You can modify the default contacts definition configuration file or create your own.
Note that, if you are not using non-default Nagios object definitions directory, you need to configure Nagios to process object definitions in that directory.
For example in the above case, insert the line, cfg_dir=/usr/local/nagios/etc/objects/kifarunix-demo on the Object definitions file section of the /usr/local/nagios/etc/nagios.cfg.
In this guide, we create a custom contacts definition configuration under a custom directory, /usr/local/nagios/etc/objects/kifarunix-demo.
vim /usr/local/nagios/etc/objects/kifarunix-demo/contacts.cfg
define contact{
name kifarunix-demo-contact
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
register 0
}
# Define Individual Contacts
define contact{
contact_name johndoe
use kifarunix-demo-contact
alias John Doe-Oracle DBA
email [email protected]
}
define contact{
contact_name janedoe
use kifarunix-demo-contact
alias Jane Doe-System Admin
email [email protected]
}
# CONTACT GROUP DEFINITION allows multiple contacts to receive alerts
define contactgroup{
contactgroup_name kifarunix-demo-admins
alias Sys-DB Admins
members johndoe,janedoe
}
Modify the contact configuration above accordingly.
If there is no syntax error, restart Nagios service.
systemctl restart nagios
Testing Nagios Mail Alerts Notification
To test if mail notification works, first change the IP address of one of the hosts to an IP that is unreachable such that it looks like the host is down.
Reschedule the next check for the host state. This will automatically sent out an email alert on host DOWN.
If you encounter the error below when rescheduling checks,
Error: Could not open command file '/usr/local/nagios/var/rw/nagios.cmd' for update!
This is due to SELinux. To fix, run journactl -xe. It should show some SELinux commands to execute to fix this. The commands below is what i run myself.
You should be able to manually reschedule Nagios host or service checks.
You should now get the email alert on the host being down.
** PROBLEM Host Alert: web01.kifarunix-demo.com is DOWN **
[email protected]
***** Nagios *****
Notification Type: PROBLEM
Host: web01.kifarunix-demo.com
State: DOWN
Address: 192.168.56.18
Info: CRITICAL - Host Unreachable (192.168.56.18)
Date/Time: Sat Oct 19 15:16:09 EDT 2019
Put back the right server IP and reschedule the check to now. You should be able to get the host status UP alert on the mail.
** RECOVERY Host Alert: web01.kifarunix-demo.com is UP **
[email protected]
***** Nagios *****
Notification Type: RECOVERY
Host: web01.kifarunix-demo.com
State: UP
Address: 192.168.56.128
Info: PING OK - Packet loss = 0%, RTA = 1.36 ms
Date/Time: Sat Oct 19 15:31:13 EDT 2019
You should be able to receive alerts for service/host state changes.
You may also be interested in checking the following tutorials.
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koromicha
I am the Co-founder of Kifarunix.com, Linux and the whole FOSS enthusiast, Linux System Admin and a Blue Teamer who loves to share technological tips and hacks with others as a way of sharing knowledge as:
"In vain have you acquired knowledge if you have not imparted it to others".
