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

You can edit your .conf files with privileges using an editor, for my case it is nano.

$sudo nano /etc/postgresql/14/main/pg_ident.conf

Map your user by adding this line

# MAPNAME       SYSTEM-USERNAME         PG-USERNAME
user1           <computer-username>     postgres

Replace the <computer-username> with the System-Username, which can be found using the whoami command. Type in your terminal:

$whoami

Then go ahead to the pg_hba.conf with privileges

$sudo nano /etc/postgresql/14/main/pg_hba.conf

Add your postgres user, with method=peer, as shown below:

# TYPE  DATABASE        USER            ADDRESS                 METHOD
local   all             postgres                                peer

This worked for me.