[SOLVED] psql: error: connection to server on socket "/var/run/postgresql/.s.PGSQL.5432" failed: FATAL: Peer authentication failed for user "postgres" (Ubuntu)

Issue

When I try to open psql with this command:

psql -U postgres

I get this error:

psql: error: connection to server on socket "/var/run/postgresql/.s.PGSQL.5432" failed: FATAL:  Peer authentication failed for user "postgres"

But it connects successfully when I use:

sudo -u postgres psql

Can someone please explain what is happening and how to diagnose/fix this problem? My pg_hba.conf contains the following:

# 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                                     md5
# IPv4 local connections:
host    all             all             127.0.0.1/32            scram-sha-256
# IPv6 local connections:
host    all             all             ::1/128                 scram-sha-256
# Allow replication connections from localhost, by a user with the
# replication privilege.
local   replication     all                                     peer

Solution

Peer authentication means that the connection is only allowed if the name of the database user is the same as the name of the operating system user.

So if you run psql -U postgres as operating system user root or jimmy, it won't work.

You can specify a mapping between operating system users and database users in pg_ident.conf.

Answered By - Laurenz Albe

Answer Checked By - Mary Flores (WPSolving Volunteer)