Unable to discover only Linux machines in VCenter vm discovery schedule

1.I have setup VCenter Cloud discovery schedule and It could find the windows servers

2.It couldn't able to classify only Linux servers , do i need to setup SSH credential separately ? or do i miss any other configuration ?

3.Do i need to enable ports for all esx servers separately if i do Cloud discovery ?

4.I have setup proper VMware credential following below conditions 

"The VMware credentials must have read-only role and License Admin privilege in vCenter..  The credential must be given "Read-Only" defined at "Global".