Im always forgetting how to do this. Dont set the password for the linux account postgres, instead set the password for the postgres user in psql.

sudo -u postgres psql postgres

# In psql prompt
\password postgres
# Enter your password

Now when you want to connect to psql use the following command

psql postgres -U postgres

See my other article on setting it up with the current user so your not messing around with the postgres user

Related External Links:

• ServerFault - Default superuser Username and Password after new install