PostgreSQL supports multiple client authentication methods including: trust, reject, md5, password, gss, sspi, krb5, ident, peer, ldap, radius, cert, and pam. Here we’re only going to concern ourselves with two: ident and md5.
When connecting to PostgreSQL on Linux for the first time many admins have questions, especially if those admins are from the MySQL world. By default, when PostgreSQL is installed, a postgres user is also added.
If you run the command:
… you’ll see the postgres user.