Edit your postgres.conf
stats_start_collector = true
This must be set to true for the statistics collector to be launched at all.
stats_command_string = true
This enables monitoring of the current command being executed by any server process. The statistics collector subprocess need not be running to enable this feature.
After restarting postgres the following query will show currently running queries
psql -U postgres template1 -c "select * from pg_stat_activity"
only as user "postgres"