permission denied on socket

-bash-4.2$ psql postgres

psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: Permission denied

        Is the server running locally and accepting connections on that socket?

but when I am trying to connect using the below command I am able to login to the cluster successfully.

-bash-4.2$ psql postgres -h localhost

postgres=#

I am not sure what is causing this issue and what needs to be done to resolve it ?

Regards.