Linux details for EC2 hosts 

@Mike Moniz was correct. These are brought in by a process called “Auto Properties” using SNMP, by an installed collector.  The document which describes the simplest way to configure SNMP on a linux server is here, and the document which describes how to set up local collectors in your EC2 environment and configure the LM envision platform to assign the virtual machines to the collectors is here. Once you have everything set up, the collector will periodically run the Auto Properties process and update the metadata in the platform. You can manually run “Active Discovery” on the resources page for a given resource if you’d like to run these processes after making a change.
 

  If you want to automatically attach details beyond what are currently there, there is the option to create “PropertySources” which direct the assigned local collector to run scripts which can produce additional metadata properties. 

Ah, many thanks. I was being a numpty and not looking that far down the properties!😳

Have you tried setting up SNMP monitoring? With that you kernel version will be in system.sysinfo. It will require using your own collector and not just the Cloud Collector.