screwed up authentication

debian jessie 9.3 latest upgrade

su - postgres
password:  xxxxx
==> Authentication failure

edited pg_hba.conf  ==> local  all  all  trust
restarted

still failure

sudo -u postgres
pgsql
===> access

okay, figure this is a problem with postgresql user vs linux user - but
how to fix ?   is it easier to remove and reinstall postgres ??   or
maybe it is not worth bothering to fix and just use sudo ?

other created users and databases are okay and work from node scripts