Install ppostgress in Debian and Ubuntu Linux

On Linux, after a fresh install ( apt install postgresql , dnf install postgresql-server , etc.): 

 

 

 

 

 

 

 

 

 

 Default user: postgres — both as a Linux system user and as the PostgreSQL superuser role. 

 Default password: none. There is no preset password. 

 

 

 

 

 

 

 

 

 

 By default the postgres role uses peer authentication for local connections, which means PostgreSQL trusts the OS user. So you log in like this: 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 bash 

 

 

 

 

 

 

 

 

 

 

 sudo -u postgres psql 

 No password prompt — it works because you're acting as the Linux postgres user, and PostgreSQL matches that to the postgres role. 

 If you want to use the script I just made (which connects over TCP with a password), you need to set a password first: 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 bash 

 

 

 

 

 

 

 

 

 

 

 sudo -u postgres psql 

 Then inside psql : 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 sql 

 

 

 

 

 

 

 

 

 

 

 ALTER USER postgres WITH PASSWORD 'your_password_here';

\q 

 You may also need to allow password logins over TCP. Edit pg_hba.conf (usually at /etc/postgresql/<version>/main/pg_hba.conf on Debian/Ubuntu, or /var/lib/pgsql/data/pg_hba.conf on RHEL/Fedora) and find lines like: 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 local all postgres peer

host all all 127.0.0.1/32 ident 

 Change the method to scram-sha-256 (modern) or md5 (older): 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 local all postgres scram-sha-256

host all all 127.0.0.1/32 scram-sha-256 

 Then reload: 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 bash 

 

 

 

 

 

 

 

 

 

 

 sudo systemctl reload postgresql 

 After that, psql -U postgres -h localhost will prompt for the password you set, and the Python script will work with host=localhost , user=postgres , and your chosen password. 

 One caveat: some distros (notably certain Docker images or the official PostgreSQL apt repo) behave a little differently. The Docker postgres image, for instance, requires you to set POSTGRES_PASSWORD as an env var at container creation. But for a plain Linux package install, the answer is: user postgres , no password, peer auth.