Login Failed with Existing User on PostgreSQL

Question

I just started playing around with PostgreSQL. My goal is to create a new user outside of postgres with all of the same privileges and create a database for my ror app. I'm able to login under postgres. I did create an user named Jason, which is good, however when I do sudo -u username psql I receive the following error...

sudo: unknown user: Jason
sudo: unable to initialize policy plugin

I can determine that the username exists by checking both \dg in my postgres console.

                         List of roles
Role name |                   Attributes                   | Member of 
-----------+------------------------------------------------+-----------
Jason     | Superuser, Create role, Create DB, Replication | {}
postgres  | Superuser, Create role, Create DB, Replication | {}

What's causing this problem? Also, I checked my local pg_hba.conf and have what I believe to be the correct settings.

# Allow replication connections from localhost, by a user with the
# replication privilege.
#local   replication     postgres                                peer
#host    replication     postgres        127.0.0.1/32            md5
#host    replication     postgres        ::1/128                 md5

Answer 1

You are confusing system user with database user. The error message comes from sudo and has nothing to do with PostgreSQL at all.

To log in as database user Jason:

psql -U Jason

You need to supply a password, of course, as long as password-less access is not set up. Peer authentication only works for a system user of the same name ("Jason").
More in the excellent manual about psql here and about authentication methods here.