Documentation: Fix default enabled features, add troubleshooting hints.

Fixes #6357

doc/2-getting-started.md

@@ -46,6 +46,25 @@ not yet available you will have to use the release tarball which you
 can download from the [Icinga website](https://www.icinga.org/). The
 release tarballs contain an `INSTALL` file with further instructions.
 
+### <a id="installation-enabled-features"></a> Enabled Features during Installation
+
+The default installation will enable three features required for a basic
+Icinga 2 installation:
+
+* `checker` for executing checks
+* `notification` for sending notifications
+* `mainlog` for writing the `icinga2.log ` file
+
+Verify that by calling `icinga2-enable-feature` withour any additional parameters
+and enable the missing features, if any.
+
+    # icinga2-enable-feature
+    Syntax: /usr/sbin/icinga2-enable-feature <features separated with whitespaces>
+        Example: /usr/sbin/icinga2-enable-feature checker notification mainlog
+    Enables the specified feature(s).
+
+    Available features: api checker command compatlog debuglog graphite icingastatus ido-mysql ido-pgsql livestatus mainlog notification perfdata statusdata syslog
+    Enabled features: checker mainlog notification
 
 ### <a id="installation-paths"></a> Installation Paths
 

doc/3-monitoring-basics.md

@@ -321,6 +321,11 @@ object, notifications for all states and types will be sent.
 
 Details on troubleshooting notification problems can be found [here](#troubleshooting).
 
+> **Note**
+>
+> Make sure that the [notification](#features) feature is enabled on your master instance
+> in order to execute notification commands.
+
 You should choose which information you (and your notified users) are interested in
 case of emergency, and also which information does not provide any value to you and
 your environment.
@@ -587,6 +592,11 @@ Please check [Runtime Custom Attributes as Environment Variables](#runtime-custo
 
 `CheckCommand` objects define the command line how a check is called.
 
+> **Note**
+>
+> Make sure that the [checker](#features) feature is enabled in order to
+> execute checks.
+
 #### <a id="command-plugin-integration"></a> Integrate the Plugin with a CheckCommand Definition
 
 `CheckCommand` objects require the [ITL template](#itl-plugin-check-command)
@@ -784,6 +794,11 @@ interfaces (E-Mail, XMPP, IRC, Twitter, etc).
 `NotificationCommand` objects require the [ITL template](#itl-plugin-notification-command)
 `plugin-notification-command` to support native plugin-based notifications.
 
+> **Note**
+>
+> Make sure that the [notification](#features) feature is enabled on your master instance
+> in order to execute notification commands.
+
 Below is an example using runtime macros from Icinga 2 (such as `$service.output$` for
 the current check output) sending an email to the user(s) associated with the
 notification itself (`$user.email$`).

doc/7-troubleshooting.md

@@ -36,6 +36,13 @@ Additionally you can enable the debug log using
 
     # sudo -u icinga /usr/lib/nagios/plugins/check_ping -4 -H 127.0.0.1 -c 5000,100% -w 3000,80%
 
+* Make sure the [checker](#features) feature is enabled.
+
+    # icinga2-enable-feature checker
+    Total params: 1
+    The feature 'checker' is already enabled.
+
+
 ## <a id="notifications-not-sent"></a> Notifications are not sent
 
 * Check the debug log if a notification is triggered
@@ -49,6 +56,12 @@ Verify the following configuration
 * Do the user attributes `states`, `types`, `period` match the notification conditions?
 * Are there any notification `begin` and `end` times configured?
 
+* Make sure the [notification](#features) feature is enabled.
+
+    # icinga2-enable-feature notification
+    Total params: 1
+    The feature 'notification' is already enabled.
+
 * Does the referenced NotificationCommand work executed as Icinga user on the shell?
 
 ## <a id="feature-not-working"></a> Feature is not working