The response of staff is correct, but if you want to further automate can do:

$ sudo -u postgres psql -c "ALTER USER postgres PASSWORD 'postgres';"

Done! You saved User = postgres and password = postgres.

If you do not have a password for the User postgres ubuntu do:

$ sudo passwd postgres

This was frustrating, most of the above answers are correct but they fail to mention you have to restart the database service before the changes in the pg_hba.conf file will take affect.

so if you make the changes as mentioned above:

local all postgres ident

then restart as root ( on centos its something like service service postgresql-9.2 restart )
now you should be able to access the db as the user postgres

$psql
psql (9.2.4)
Type "help" for help.

postgres=# 

Hope this adds info for new postgres users

Edit the pg_hba.conf file, e.g. with sudo emacs /etc/postgresql/9.3/main/pg_hba.conf

Change all authentication methods to trust. Change Unix Password for "postgres" user. Restart Server. Login with psql -h localhost -U postgres and use the just set Unix password. If it works you can re-set the pg_hba.conf file to the default values.

If you are trying to login postgres shell as postgres user, then you can use following commands.

switch to postgres user

# su - postgres

login to psql

# psql

Hope that helps

Try to not use the -W parameter and leave the password in blank. Sometimes the user is created with no-password.

If that doesn't work reset the password. There are several ways to do it, but this works on many systems:

$ su root
$ su postgres
$ psql -h localhost
> ALTER USER postgres with password 'YourNewPassword';

For those who are using it first time and have no information regarding what the password is they can follow the below steps(assuming you are on ubuntu):

1. 
   

   Open the file pg_hba.conf in /etc/postgresql/9.x/main

   
   
   

    sudo vi pg_hba.conf 
   

   
   
   

   2.edit the below line

   
   
   

    local all postgres peer
   

   
   
   

   to

   
   
   

    local all postgres trust
   

   
   


2. 
   

   Restart the server

   
   
   

    sudo service postgresql restart
   

   
   



3. Finally you can login without need of a password as shown in the figure

Ref here for more info

As a rule of thumb: YOU SHOULD NEVER EVER SET A PASSWORD FOR THE POSTGRES USER.

If you need a superuser access from pgAdmin, make another superuser. That way, if the credentials for that superuser is compromised, you can always ssh into the actual database host and manually delete the superuser using

sudo -u postgres -c "DROP ROLE superuser;"

I just wanted to add that you should also check if your password is expired.

See Postgres password authentication fails for details.

Here are some combinations which I tried to login:

# login via user foo
psql -Ufoo -h localhost

sudo -u postgres psql postgres

# user foo login to postgres db
psql -Ufoo -h localhost -d postgres

i had a similar problem.
Ubuntu was left me log in in console with any password for superuser.
Except when i connected with -h localhost in psql line command.

I Observed too that "localhost:8080/MyJSPSiteLogIn" - showed: Fatal: autentication error with user "user".

pg_hba.conf was ok.

I noted had two versions of postgres running in the same service.

Solved - uninstalling inutil version.

I hope this will help you short of time.
You can change the password of postgres sql by using bellow command.

Command

sudo -u postgres psql

And next you can update the password

Command

Alter user postgres password 'YOUR_NEW_PASSWORD';