Psql: Fatal error: Peer authentication failed for user "user1"

Operating system: DEBIAN8

There may be a warning error when you log in to PG:

$ psql -U user1 -d exampledb
psql: fatal error: peer authentication failed for user "user1"

Open the following file,

 
$ sudo vi /etc/postgresql/9.4/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

Change Peer to MD5:

 
# TYPE DATABASE USER ADDRESS METHOD

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

Then restart the service:

sudo service PostgreSQL restart

You can log in again:

$ psql-u user1-d Exampledb

--End--

Psql: Fatal error: Peer authentication failed for user "user1"