Configure Email Alert for Nagios

Nagios is an open-source software that can help you monitor your infrastructure 24/7. It has a function that will notify you whenever there's a problem on your servers, switches, applications or services. By sending an email with the information you need to fix the problem.

Click here if you want to know how to install Nagios.

Step 1: Configure contacts.cfg

Edit the contacts.cfg, if the other variables already set just add the others not included.

vi /usr/local/nagios/etc/objects/contacts.cfg

define contact {

Contact_name nagiosadmin

Use generic-contact

Alias Admin

Email admin@localhost.com ←- change to     desired email address

service_notification_period 24x7

host_notification_period 24x7

service_notification_options w,u,c,r,s,f

host_notification_options d,u,r,f,s

service_notification_commands notify-service-by-email

host_notification_commands notify-host-by-email

}

[Esc] :wq

Verify if there's no error.

/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

 Step 2: Install dependencies

Install postfix & mailx

yum install –y postfix mailx

alternatives --set mta /usr/sbin/postfix

If above command not work and you get the output as “/usr/sbin/postfix has not been configured as an alternative for mta“. Use below command. 

alternatives --set mta /usr/sbin/sendmail.postfix

Configure Postfix uncomment and edit

 vi /etc/postfix/main.cf

relayhost = [smtp.gmail.com]:587

smtp_use_tls=yes

smtp_sasl_auth_enable = yes

smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

smtp_sasl_security_options = noanonymous

smtp_sasl_mechanism_filter = plain

smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt

[Esc] :wq

Step 3: Get a unique pass

 Get the unique pass from google

Step 1: Sign in first to the google account you will use.

Step 2: Go to the google account, click your profile and click Google Account

Step 3: Go to Security tab

Step 4: In the “Signing in to Google” make sure the 2 step verification is On if not just click it and wait for the text message of google to turn on the 2 step verification.

Step 5: After you set the 2-step verification click on the app password and request for it

Step 6: Select mail then select the device to receive the unique app pass from google

Step 4: Configure sasl_passwd

vi /etc/postfix/sasl_passwd

[smtp.gmail.com]:587    <your_email_address@gmail.com>:<unique_app_pass_from_google>

[Esc] :wq

postmap /etc/postfix/sasl_passwd

 Step 5: Configure master.cf

vi /etc/postfix/master.cf

Change:

smtp      inet  n       -       n       -       -       smtpd

Into:

587      inet  n       -       n       -       -       smtpd

[Esc] :wq

Step 6: Install mail fonts and start postfix

Install this for the mail font

yum -y install cyrus-sasl cyrus-sasl-plain

service postfix restart

chkconfig postfix on

Step 7: Test to send mail

Test if the mail is sending then check the mail logs.

echo "Test mail from postfix" | mail -s "Test Postfix" <your_email_address>@gmail.com

tail /var/log/maillog