How do I login and authenticate to Postgresql after a fresh install?

Did a new install of postgres 8.4 on mint ubuntu. How do I create a user for postgres and login using psql?

When I type psql, it just tells me

psql: FATAL: Ident authentication failed for user "my-ubuntu-username"

There are two methods you can use. Both require creating a user and a database.

By default psql connects to the database with the same name as the user. So there is a convention to make that the "user's database". And there is no reason to break that convention if your user only needs one database. We'll be using mydatabase as the example database name.

1. Using createuser and createdb, we can be explicit about the database name,

    $ sudo -u postgres createuser -s $USER
    $ createdb mydatabase
    $ psql -d mydatabase
   

   You should probably be omitting that entirely and letting all the commands default to the user's name instead.

    $ sudo -u postgres createuser -s $USER
    $ createdb
    $ psql
   

2. Using the SQL administration commands, and connecting with a password over TCP

    $ sudo -u postgres psql postgres
   

And, then in the psql shell

    CREATE ROLE myuser LOGIN PASSWORD 'mypass';
    CREATE DATABASE mydatabase WITH OWNER = myuser;

Then you can login,

    $ psql -h localhost -d mydatabase -U myuser -p <port>

If you don't know the port, you can always get it by running the following, as the postgres user,

    SHOW port;

Or,

    $ grep "port =" /etc/postgresql/*/main/postgresql.conf

Sidenote: the postgres user

I suggest NOT modifying the postgres user.

1. It's normally locked from the OS. No one is supposed to "log in" to the operating system as postgres. You're supposed to have root to get to authenticate as postgres.
2. It's normally not password protected and delegates to the host operating system. This is a good thing. This normally means in order to log in as postgres which is the PostgreSQL equivalent of SQL Server's SA, you have to have write-access to the underlying data files. And, that means that you could normally wreck havoc anyway.
3. By keeping this disabled, you remove the risk of a brute force attack through a named super-user. Concealing and obscuring the name of the superuser has advantages.

by default you would need to use the postgres user:

sudo -u postgres psql postgres

The error your are getting is because your-ubuntu-username is not a valid Postgres user.

You need to tell psql what database username to use

psql -U postgres

You may also need to specify the database to connect to

psql -U postgres -d <dbname>

The main difference between logging in with a postgres user or any other user created by us, is that when using the postgres user it is NOT necessary to specify the host with -h and instead for another user if.

Login with postgres user

$ psql -U postgres 

Creation and login with another user

# CREATE ROLE usertest LOGIN PASSWORD 'pwtest';
# CREATE DATABASE dbtest WITH OWNER = usertest;
# SHOW port;
# \q

$ psql -h localhost -d dbtest -U usertest -p 5432

GL

Source

you can also connect to database as "normal" user (not postgres):

postgres=# \connect opensim Opensim_Tester localhost;

Password for user Opensim_Tester:    

You are now connected to database "opensim" as user "Opensim_Tester" on host "localhost" at port "5432"

If your database client connects with TCP/IP and you have ident auth configured in your pg_hba.conf check that you have an identd installed and running. This is mandatory even if you have only local clients connecting to "localhost".

Also beware that nowadays the identd may have to be IPv6 enabled for Postgresql to welcome clients which connect to localhost.