How to fix FATAL: role "postgres" does not exist in PostgreSQL

First, check what roles currently exist in your PostgreSQL installation. Connect as a superuser and list all roles:

sudo -u postgres psql -c "\\du"

Or using SQL:

SELECT rolname FROM pg_roles ORDER BY rolname;

This shows all roles and their attributes. If the postgres role is missing, you'll need to create it.

If the role doesn't exist, create it using the createuser utility (recommended) or SQL.

Using createuser (from your system terminal):

sudo -u postgres createuser -s postgres

The -s flag makes it a superuser. If you need a password:

sudo -u postgres createuser -s -P postgres

Using SQL (if already connected as a superuser):

CREATE ROLE postgres WITH SUPERUSER CREATEDB CREATEROLE LOGIN;

Or with a password:

CREATE ROLE postgres WITH SUPERUSER CREATEDB CREATEROLE LOGIN PASSWORD 'your_password';

If you're using PostgreSQL in Docker, the postgres role should be created automatically. If it's missing:

1. Ensure you're not connecting to a local PostgreSQL installation instead of the container:

docker ps | grep postgres

2. Check if the container is running and initialized:

docker logs <container_name>

3. If the container postgres is correct but the role is missing, exec into it and create the role:

docker exec -u postgres <container_name> createuser -s postgres

When moving a database between systems, roles don't migrate automatically. Before restoring a dump:

1. Create all required roles on the destination system first
2. Or, dump without role ownership information:

pg_dump --no-owner --no-acl source_db > dump.sql

3. Then restore:

psql -U postgres -d target_db -f dump.sql

Alternatively, edit the dump file to replace role references with existing roles before restoring.

Once created, test that the role works:

# Using peer authentication (OS username matches role name)
sudo -u postgres psql

# Using password authentication (if password is set)
psql -U postgres -h localhost -W

Both should connect successfully without the 'role does not exist' error.