Install Postgres and first login DB

Install Postgres and first login DB

Setting a password for the postgres user
On Linux systems, there is no default password set.

To set the default password:

Run the psql command from the postgres user account:

sudo -u postgres psql postgres
Set the password:

\password postgres
Enter a password.

Close psql.

\q
Allowing local connections
The file pg_hba.conf governs the basic constraints underlying connection to PostgreSQL. By default, these settings are very conservative. Specifically, local connections are not allowed for the postgres user.

To allow this:

As a super user, open /etc/postgresql/9.6/main/pg_hba.conf (Ubuntu) or /var/lib/pgsql/9.6/data/pg_hba.conf (Red Hat) in a text editor.

Scroll down to the line that describes local socket connections. It may look like this:

local   all             all                                      peer
Change the peer method to md5.

Note

For more information on the various options, please see the PostgreSQL documentation on pg_hba.conf.

To allow connections using pgAdmin, find the line that describes local loopback connections over IPv6:

host    all             all             ::1/128                 ident
Change the ident method to md5.

Save and close the file.

Restart PostgreSQL:

Ubuntu:

sudo service postgresql restart
Red Hat:

sudo service postgresql-9.6 restart
To test your connection using psql, run the following command:

psql -U postgres -W

sources:
http://suite.opengeo.org/docs/latest/dataadmin/pgGettingStarted/firstconnect.html

important:
pg_hba.conf
must be like this: 
# Database administrative login by Unix domain socket
local   all             postgres                                peer

# 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
host    all             all             0.0.0.0/0                 md5