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+---
+layout: default
+title: Writing Fact Plugins
+toc: false
+---
+[SimpleRPCAuthorization]: /mcollective/simplerpc/authorization.html
+[Registration]: registration.html
+
+Fact plugins are used during discovery whenever you run the agent with queries like *-W country=de*.
+
+The default setup uses a YAML file typically stored in */etc/mcollective/facts.yaml* to read facts.  There are however many fact systems like Reductive Labs Facter and Opscode Ohai or you can come up with your own.  The facts plugin type lets you write code to access these tools.
+
+Facts at the moment should be simple *variable = value* style flat Hashes, if you have a hierarchical fact system like Ohai you can flatten them into *var.subvar = value* style variables.
+
+## Details
+Implementing a facts plugin is made simple by inheriting from *MCollective::Facts::Base*, in that case you just need to provide 1 method, the YAML plugin code can be seen below:
+
+For releases in the 1.0.x release cycle and older, use this plugin format:
+
+{% highlight ruby linenos %}
+module MCollective
+    module Facts
+        require 'yaml'
+
+        # A factsource that reads a hash of facts from a YAML file
+        class Yaml<Base
+            def self.get_facts
+                config = MCollective::Config.instance
+
+                facts = {}
+
+                YAML.load_file(config.pluginconf["yaml"]).each_pair do |k, v|
+                    facts[k] = v.to_s
+                end
+
+                facts
+            end
+        end
+    end
+end
+{% endhighlight %}
+
+For releases 1.1.x and onward use this format:
+
+{% highlight ruby linenos %}
+module MCollective
+    module Facts
+        require 'yaml'
+
+        class Yaml_facts<Base
+            def load_facts_from_source
+                config = MCollective::Config.instance
+
+                facts = {}
+
+                YAML.load_file(config.pluginconf["yaml"]).each_pair do |k, v|
+                    facts[k] = v.to_s
+                end
+
+                facts
+            end
+        end
+    end
+end
+{% endhighlight %}
+
+If using the newer format in newer releases of mcollective you do not need to worry about caching or
+thread safety as the base class does this for you.  You can force reloading of facts by creating a
+*force_reload?* method that should return *true* or *false*.  Returning *true* will force the cache
+to be rebuilt.
+
+You can see that all you have to do is provide *self.get_facts* which should return a Hash as described above.
+
+There's a sample using Puppet Labs Facter on the plugins project if you wish to see an example that queries an external fact source.
+
+Once you've written your plugin you can save it in the plugins directory and configure mcollective to use it:
+
+{% highlight ini %}
+factsource = yaml
+{% endhighlight %}
+
+This will result in *MCollective::Facts::Yaml* or *MCollective::Facts::Yaml_facts* being used as source for your facts.