From Observium

Follow these steps to add a new operating system:

• Create a file in includes/discovery/os, which fills the $os variable if you can identify the device as such ($sysObjectID preferred, otherwise $sysDescr or similar). Please use a meaningful name! Preferably the name of the operating system rather than the brand of the device.
• Adjust discovery.php, running specific command based on OS type, if needed.
• Create includes/polling/os/$osname.inc.php, for device specific polling.
• Add an OS text name and possibly other settings in includes/definitions.php
• Create a 32x32 logo, in html/images/os/$osname.png. The file name may also be the manufacturer logo (probably better) - in that case set the "icon" property in the definitions file accordingly.

• When tested and satisfied, please submit a patch to the development team! ;-)