[PostgreSQL] Peer authentication failed for user "postgres"

오류

FATAL: Peer authentication failed for user "postgres"

The problem is still your pg_hba.conf file (/etc/postgresql/9.1/main/pg_hba.conf). This line:

local   all             postgres                                peer

를 

local   all             postgres                                md5

이렇게 변경

trust - anyone who can connect to the server is authorized to access the database

peer - use client's operating system user name as database user name to access it.

md5 - password-base authentication