I am travelling from India to Greece in the month of June and hold Indian passport. My flight is via Paris with a layover of 9 hours and wish to roam around in Paris in the meanwhile. What are the visa rules for this
The rule is that you will enter the Schengen area in Paris and will be free to leave and return to the airport. Your flight from Paris to Greece is an internal Schengen flight, effectively a domestic flight, with no systematic immigration controls.
If there is a passport check (either at random or because of emergency measures as noted in a comment), it will not create additional visa requirements. Such a passport check will not result in any stamps in your passport, because you will not be leaving or entering the Schengen area.