Instructions apply to Ubuntu.
Postgres uses the concept of roles to manage authentication and authorization.
Installing postgres will create a Unix user named
postgres and a associated
postgres. Run the below and you should see a user listed.
compgen -u | grep postgres
By default, Postgres uses the
ident authentication system, meaning any Postgres roles are associated with a matching Unix system account. This means that upon a fresh install, you can log into the Postgres prompt as the
postgres Unix user:
sudo -u postgres psql