show how to ignore kernel message

admin-guide/configuration/icinga2.md

@@ -121,6 +121,8 @@ Whenever you have a use case which is not covered yet, please talk to us.
 
 Most checks can have custom parameters. The variables you can adapt you find as "Custom Variables" in the page of given service. In Hiera you can add below the key `icinga2::service_check::customize` as multi level hash the service name and below the variable name with the new values.
 
+### Example "CPU Usage"
+
 Lets look at the example of `CPU Usage` "service":
 
 !["CPU Usage" service page](icinga2/service_custom_variables.png)
@@ -141,3 +143,17 @@ icinga2::service_check::customize:
 ```
 
 If it is a Linuxfabrik plugin, you find a link at "Notes" which points to the documentation of the check. This might shed more light on the effect of these variables.
+
+### Example "Kernel Ring Buffer (dmesg)'"
+Another check which can easily have false alerts, but also has a big potential to signal severe kernel or hardware issues, is the check of the kernel log (dmesg).
+
+If you conclude that a given message can savely be ingored, you may add it onto the ignore list, where a partial string match will make it ignored in the future:
+```
+icinga2::service_check::customize:
+  'Kernel Ring Buffer (dmesg)':
+    'dmesg_ignore':
+      - 'blk_update_request: I/O error, dev fd0, sector 0'
+      - 'integrity: Problem loading X.509 certificate -126'
+```
+If you think that this log message can be globally ignored, please inform the Linux Team so we can ignore it by default.
+