This will fix your ability to log in as root on postgresql

Fixing the root issue with postgrepsql

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3 steps only!

sudo -u postgres psql
CREATE USER root SUPERUSER;
CREATE ROLE root SUPERUSER LOGIN PASSWORD 'password';

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How to Create a Superuser in PostgreSQL

To run psql using "UNIX USER" postgres, you need to invoke "sudo -u postgres psql", which switches to "UNIX USER" postgres and run the psql command.