1. The basics of notifications

Notification in Checkmk involves actively notifying users when the state of a host or service changes. Let us assume that at a certain point in time on the host mywebsrv17 the service HTTP goes from OK to CRIT. Checkmk detects this and by default sends an email including the most important data regarding this event to all contacts for this service. The state later changes again, from CRIT to OK, and the contacts receive another email — this time reporting this event, which is referred to as a recovery.

But this is only the simplest way of notifying. There are numerous ways for you to refine it:

  • You can notify by SMS, pager, Slack, and other Internet services.

  • You can set notifications to specific time periods, for example, to take on-call rosters into account.

  • You can define escalations if the responsible contact does not take action quickly enough.

  • Users can independently 'subscribe' to or unsubscribe from notifications if you want to allow this.

  • You can generally define via rules who is to be notified about what, and when.

However, before you start working with notifications, you should note the following:

  • Notification is an optional feature. Some users do without the notifications because they have a control center that is manned around the clock and that only operates with the status interface.

  • Initially activate the notifications only for yourself and make yourself responsible for everything. Observe over at least a few days how large the number of notifications is.

  • Do not activate notifications for other users until you have reduced the false alarms (false positives) to a minimum. We have described how you can do this in the chapter on fine-tuning monitoring.

2. Preparing for email notifications

The simplest and by far the most common method is to send a notification by email. There is enough space in an email to also include the graphs of metrics as well.

Before you can notify by email, your Checkmk server must be set up for sending emails. For all supported Linux distributions, this boils down to the following:

  1. Install an SMTP server service. This is usually done automatically during the installation of the distribution.

  2. Specify a smarthost. You will usually be asked for this when installing the SMTP server. The smarthost is a mail server in your company that takes over the delivery of emails for Checkmk. Very small companies usually do not have their own smarthost. In this case, you use the SMTP server supplied by your email provider.

If the mail dispatch has been set up correctly, you should be able to send an email from the command line, for instance via this command:

OMD[mysite]:~$ echo "test-content" | mail -s test-subject

The email should be delivered without delay. If this does not work, you will find clues as to the source of the problem in the SMTP server’s log file in the /var/log/ directory. More details on setting up mail delivery under Linux can be found in the article on notifications.

3. Activating email notifications

Once the email dispatch is basically working, activating the notification is very simple. In order for a user to receive notifications by email, the following two conditions must be fulfilled:

  • An email address has been assigned to the user.

  • The user is responsible for hosts or services — through the assignment of contact groups.

You assign email address and contact groups via the user’s properties, as we showed earlier in the chapter on user administration, for instance by adding your email address to the cmkadmin user account and to the Everything contact group.

4. Testing notifications

It would be a bit cumbersome to wait for a real problem or even provoke one to test the notifications. This is easier with Test notifications, a tool with which you can simulate a notification for a host or service and have the notification sent immediately.

You can access the notification test via Setup > Events > Notifications and the Test notifications button:

Dialog for defining the properties of the simulated notification.

Simply select a host and then any state change as the event. By activating the Send out notification checkbox, you specify that the notification is not only simulated but also actually sent.

Click on Test notifications. The Test notifications dialog is hidden and the results are shown. The most important is the summary Analysis results at the top:

The summary for analyzing the simulated notification.

At least one notification rule must take effect and result in a notification. The notification must also have been sent, as indicated by the Notifications have been sent message.

Under Resulting notifications you can then see to whom and via which channel the notification was sent:

The resulting notification for the simulation.

This should immediately result in an email for this simulated problem. A detailed description of the options and the results for the notification test can be found in the article on notifications.

If you have not received a notification in real monitoring, i.e. outside of the simulation, this does not necessarily mean an error. There are situations in which the notifications from Checkmk are deliberately suppressed for example:

  • when the notification has been disabled Master control snap-in;

  • when a host or service is in a scheduled downtime;

  • when a host is DOWN and therefore no notifications are triggered by its services;

  • if the status has changed too often recently and the service has therefore been marked as Icon to indicate a flapping state. flapping.

5. Fine-tuning notifications

You can adapt the notifications in Checkmk to your, or your organization’s, needs in a variety of ways by means of complex rules. You can learn all of the details for this in the article on notifications.

6. Troubleshooting

The notification module in Checkmk is very complex — because it covers many, very different requirements that have proven to be important over many years of practical experience. The question "Why didn’t Checkmk notify here?" will therefore be asked more often than you might expect, especially at the beginning. For this reason, here are a few tips for troubleshooting.

If a notification has not been triggered by a particular service, the first step would be to check the history of the notifications for that service. To do this, open the detail page for that service by clicking in the monitoring on the service. Select Service > Service notifications from the menu. There you will find all notification events for this service listed chronologically from the most recent to the oldest.

Here is an example of a service for which notification was attempted, but for which the sending of emails failed because no SMTP server has been installed.

List of notification events for a service.

You can find even more information in the file ~/var/log/notifiy.log. You can view this as a site user, with the less command, for example:

OMD[mysite]:~$ less var/log/notify.log

If you are not yet familiar with less — with the key combination Shift+G you can jump to the end of a file (which is useful for log files), and quit less with the Q key.

With the tail -f command, you can also observe the file contents 'live' while it is running. This is useful if you are only interested in new messages, i.e. those that only appear after tail has been entered.

Here is an excerpt from the notify.log for a successfully triggered notification:

2024-04-15 16:21:47,912 [20] [cmk.base.notify] Analysing notification (localhost) context with 14 variables
2024-04-15 16:21:47,912 [20] [cmk.base.notify] Global rule 'Notify all contacts of a host/service via HTML email'...
2024-04-15 16:21:47,913 [20] [cmk.base.notify]  -> matches!
2024-04-15 16:21:47,913 [20] [cmk.base.notify]    - adding notification of martin via mail
2024-04-15 16:21:47,913 [20] [cmk.base.notify] Executing 1 notifications:
2024-04-15 16:21:47,913 [20] [cmk.base.notify]   * notifying martin via mail, parameters: graphs_per_notification, notifications_with_graphs, bulk: no
2024-04-15 16:21:47,913 [20] [cmk.utils.notify] sending command LOG;HOST NOTIFICATION: martin;localhost;DOWN;mail;
2024-04-15 16:21:47,913 [20] [cmk.base.notify]      executing /omd/sites/mysite/share/check_mk/notifications/mail
2024-04-15 16:21:48,458 [20] [cmk.base.notify]      Output: Spooled mail to local mail transmission agent
2024-04-15 16:21:48,501 [20] [cmk.utils.notify] sending command LOG;HOST NOTIFICATION RESULT: martin;localhost;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent

By setting up the notifications, you have completed the finishing touches — Your Checkmk system is ready for use! This does not mean, of course, that the full capabilities of Checkmk have been fully explored.

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