Monit: email alerting on an SSH logins

The task is to send an email alert when SSH-login was made from a not whitelisted IPs.

Will use Monit here.

Install it:

Configure email settings: set localhost (we have a local eximhere), email’s format and email’s receiver.

Edit the /etc/monit/monitrc file:

...
set mailserver localhost

set mail-format {
  from:    Monit <monit@$HOST>
  subject: monit alert --  $EVENT $SERVICE
  message: $EVENT Service $SERVICE
                Date:        $DATE
                Action:      $ACTION
                Host:        $HOST
                Description: $DESCRIPTION
           
           Your faithful employee,
           Monit
}
...
set alert user@example.com

Now add the rules file /etc/monit/conf.d/ssh_alerts.conf:

check file ssh_logins with path /var/log/auth.log
  ignore match "/etc/monit/whitelist_ips.txt"
  if match "Accepted publickey" then alert

Check the documentation about IGNORE here>>> and about email’s formatting – here>>>.

If instead of key-based authorization password-based is used – change “Accepted publickey” to “Accepted password“.

Now in the /etc/monit/whitelist_ips.txt file add the 1.1.1.1 IP – after testing will set a real one(s):

Restart the monitservice:

Check how it’s working – login to a server:

Check Monit’s logs:

And an email:

Obviously – such an approach may be used for anything just by changing the if match conditions.

For example – I have one site which is inaccessible for all excluding myself, so I added another rule:

check file nginx_web_access with path /var/log/nginx/example.com-access.log
  ignore match "/etc/monit/whitelist_ips.txt"
  if match "GET" then alert

Here on any GET-request from an IP not added to the white list – I’ll get an email alert.

The /etc/monit/whitelist_ips.txt may look like next:

Here is one IP of my job’s network and another one – my home.

Done.