如何在用户下登录数据库？

Question

我在Linux mint 18上安装了postres9。我以默认的postres用户登录。我尝试创建新用户并以该用户身份登录。

kalinin@lenovo ~ $ sudo -i -u postgres
postgres@lenovo ~ $ psql
psql (9.5.16)
Type "help" for help.

postgres=# CREATE DATABASE db_test;
CREATE DATABASE
postgres=# CREATE USER user_test WITH PASSWORD 'qwerty';
CREATE ROLE
postgres=# 
postgres=# 
postgres=# GRANT ALL PRIVILEGES ON DATABASE "db_test" to user_test;
GRANT
postgres=# \du
                                   List of roles
 Role name |                         Attributes                         | Member of 
-----------+------------------------------------------------------------+-----------
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
 user_test |                                                            | {}

postgres=# \l
                                   List of databases
    Name     |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges    
-------------+----------+----------+-------------+-------------+------------------------
 db_test     | postgres | UTF8     | ru_RU.UTF-8 | ru_RU.UTF-8 | =Tc/postgres          +
             |          |          |             |             | postgres=CTc/postgres +
             |          |          |             |             | user_test=CTc/postgres
 postgres    | postgres | UTF8     | ru_RU.UTF-8 | ru_RU.UTF-8 | 

postgres=# \q
postgres@lenovo ~ $ exit
logout
kalinin@lenovo ~ $ sudo -i -u user_test
sudo: unknown user: user_test
sudo: unable to initialize policy plugin

您会看到我正在使用密码和新数据库创建新用户的情况。之后，我从postgres退出，然后再次尝试登录。但是登录失败。请帮助修复它。