Unable to connect to PostgreSQL server: FATAL: Peer authentication failed for user "postgres"

Question

How can how to access postgres databases from adminer?

I have changed the password for the user postgres:

$ sudo -u postgres psql
$ postgres=# alter user postgres password 'secret';

Result:

ALTER ROLE

But I still get this error on the adminer:

Unable to connect to PostgreSQL server: FATAL: Peer authentication failed for user "postgres"

Any ideas why?

I have these two users:

postgres=# \du
                                   List of roles
 Role name |                         Attributes                         | Member of 
-----------+------------------------------------------------------------+-----------
 postgres  | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
 root      | Superuser, Create role, Create DB                          | {}

But I did not set password for user root when I created it with this command:

sudo -u postgres createuser --interactive

Output (why doesn't it ask for password??):

Enter name of role to add: root
Shall the new role be a superuser? (y/n) y

But I still get the error on adminer:

Unable to connect to PostgreSQL server: FATAL: Peer authentication failed for user "root"

EDIT:

THis is some bits of my pg_hba.conf

sudo nano /etc/postgresql/9.5/main/pg_hba.conf

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     peer
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5
# 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

I changed peer to ident:

# Database administrative login by Unix domain socket
local   all             postgres                                ident

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     ident
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5
# 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

Then restarted my machine. but still no luck.

Answer 1

Got my answer from here:

local   all             postgres                                md5

and then restart the service:

sudo systemctl restart postgresql.service