Express the operating systems your module supports in the module's metadata.json, as shown in the following example:

"operatingsystem_support": [
       { "operatingsystem": "RedHat", },
       { "operatingsystem": "Ubuntu", },
]

The Facter facts operatingsystem and operatingsystemrelease are expected. Here's a more complete example:

"operatingsystem_support": [
       {
           "operatingsystem":"RedHat",
           "operatingsystemrelease":[ "5.0", "6.0" ]
       },
       {
           "operatingsystem": "Ubuntu",
           "operatingsystemrelease": [
               "12.04",
               "10.04"
           ]
       }
   ]

Check the metadata.json file for validity afterwards using the new pdk command:

$ pdk validate metadata