PostgreSQL Peer Authentication Failed Fix

Install PostgreSQL:

Ubuntu/Debian:

sudo apt update
sudo apt install postgresql postgresql-contrib -y

Check if PostgreSQL is running:

sudo systemctl status postgresql

Start it if needed:

sudo systemctl start postgresql

Enable auto-start:

sudo systemctl enable postgresql

Trying this usually fails:

psql -U postgres
FATAL:  Peer authentication failed for user "postgres"

This happens because PostgreSQL uses peer authentication by default on local connections. This means Linux user must match PostgreSQL user, If your Linux session user is ex-introvert and you try connecting as postgres, PostgreSQL rejects the connection.

Temporary solution:

sudo -u postgres psql

This switches to the Linux postgres user before opening PostgreSQL.

Set a password for postgres:

ALTER USER postgres PASSWORD 'yourpassword';
\q

Open PostgreSQL authentication config:

sudo nano /etc/postgresql/[Version_number]/main/pg_hba.conf

[Version_number] may differ, check it manually with < ls /etc/postgresql/ > or use tab for auto completion Find this line:

local   all             postgres                                peer

change it to :

local   all             postgres                                md5

You may also find:

local   all             all                                     peer

change it to :

local   all             all                                     md5

Save the file and Restart PostgreSQL:

sudo systemctl restart postgresql

Now connect using:

psql -U postgres -W

-W forces password authentication.

You should now connect successfully.