PostgreSQL under Debian by default uses IDENT authentication to authenticate a user connecting to the database. In english this means that you can only connect to the database with the same username as your unix login. This can be edited in /etc/postgres/pg_hba.conf (Host Based Authentication) by changing "ident sameuser" with "trust" to let anyone connect to the database with any username without a password, or "crypt" etc.. The file is well commented, refer to it for more details. If you change debian's default setup, then you may get error messages every day from cron, as the postgres user connects to every database and runs some optimisations.
The Unix root user can "su" to the user named "postgres". This user can then run the shell commands "createdb" and "createuser" - if you create a database user with the same name as a unix account, then that unix account user can connect (when using ident sameuser). If you don't want to use the shell command, the postgres user could run "$ psql template1" to connect via the interactive shell, and then do "> create database <name>;" or "> create user <name>;"
A couple of minor "gotchas". As above, check your pg_hba.conf file. Previously "password" authentication covered all forms of stored password. Now it is strict. If you are using md5 passwords, it MUST be md5. Also, in SQL-land, LIMIT used to be fairly forgiving about its arguments. It would accept MySQL format without blinking. Now it's strict - this caught me out on a basic weblog script I use which had been ported from MySQL. Finally, if you are a Debian user, don't believe the instructions in the update README! psql -e <dumpfile will NOT restore your database...you need to do psql template1 -e <dumpfile>.
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