Bien lire le point 3.8 pour la création d'un utilisateur postgres standard, voilà à quoi ça peut ressembler :
dominique@hal9000:~$ sudo su postgres
postgres@hal9000:/home/dominique/$ psql
psql (10.12 (Ubuntu 10.12-0ubuntu0.18.04.1))
Type "help" for help.
postgres=# CREATE USER lambda;
CREATE ROLE
postgres=# ALTER ROLE lambda WITH CREATEDB;
ALTER ROLE
postgres=# CREATE DATABASE lambdadb OWNER lambda;
CREATE DATABASE
postgres=# ALTER USER lambda WITH ENCRYPTED PASSWORD 'lambdapassword';
ALTER ROLE
postgres=# postgres=# \q
postgres@hal9000:/home/dominique/$
exit
dominique@hal9000:~/$ psql -h localhost -U lambda -d lambdadb
Password for user lambda:
psql (10.12 (Ubuntu 10.12-0ubuntu0.18.04.1))
Type "help" for help.
lambda=>