Default postgres configuration does not "trust" postgres user

[rageshkrishna]

Out of the box, this image does not allow me to run psql commands by using the -U parameter to pass the username. Repro steps and output below:

root@751e37ecfac7:/# sudo service postgresql start
 * Starting PostgreSQL 9.4 database server [ OK ]
root@751e37ecfac7:/# psql -c "create database foo" -U postgres
psql: FATAL:  Peer authentication failed for user "postgres"

Currently, the only way out is to run psql after switching to the postgres user like this:

root@751e37ecfac7:/# sudo su postgres -c 'psql -c "create database foo"'
CREATE DATABASE
root@751e37ecfac7:/#

This works, but it's rather inelegant.

This can be fixed by updating /etc/postgresql/9.4/main/pg_hba.conf to change this line:

local   all             postgres                                peer

to

local   all             postgres                                trust