Elasticsearch index data not found in directory data.path

Hi
in .yml file i have mentioned data.path=custom directory.The index has approximate 500 mb data .
when i CD to the custom directory and do >> ls -lh its only 4.kb
I wonder where all the data resides of elasticsearch index.
OS ubuntu 18
elasticsearch 6.7.1

What is the output from the _cluster/stats?pretty&human API?

This is a very old version and is no longer supported, you need to upgrade please.