When working with PostgreSQL, you might encounter the frustrating error:

FATAL: Ident authentication failed for user "your_username"

This typically occurs when PostgreSQL is configured to use ident or peer authentication methods, which rely on the operating system's user authentication rather than password-based authentication.

The error usually appears in these situations:

• Fresh PostgreSQL installation with default configuration
• When connecting via localhost without proper authentication setup
• When the system username doesn't match the PostgreSQL username
• When pg_hba.conf is configured to require ident authentication

First, examine your pg_hba.conf file (usually located in /etc/postgresql/[version]/main/):

# Example pg_hba.conf entry causing the issue
local   all             all                                     ident

The "ident" method here is the culprit. You can verify this by running:

sudo cat /etc/postgresql/12/main/pg_hba.conf | grep -v "^#" | grep -v "^$"

The simplest solution is to modify pg_hba.conf to use md5 or trust authentication:

# Change from:
local   all             all                                     ident

# To either:
local   all             all                                     md5
# Or (less secure, for development only):
local   all             all                                     trust

After making changes, reload PostgreSQL:

sudo systemctl reload postgresql

If you prefer to keep ident authentication, ensure your system username matches your PostgreSQL username:

# Create matching system user
sudo adduser postgres_user
sudo -u postgres_user psql

When using psql, specify the correct authentication parameters:

psql -U username -h localhost -d database_name

Or in a connection string:

const { Client } = require('pg');
const client = new Client({
  user: 'your_username',
  host: 'localhost',
  database: 'your_database',
  password: 'your_password',
  port: 5432,
});
client.connect();

If issues persist, check PostgreSQL logs:

sudo tail -f /var/log/postgresql/postgresql-12-main.log

And verify your user exists in PostgreSQL:

sudo -u postgres psql -c "\du"

---

When PostgreSQL throws the "Ident authentication failed" error, it's fundamentally about connection security. PostgreSQL supports multiple authentication methods, and ident is one that's often misunderstood.

# Typical pg_hba.conf entry causing this issue:
host    all             all             127.0.0.1/32            ident

The error typically manifests in these scenarios:

• Local development setups where ident was configured by default
• Docker containers with improper user mapping
• CI/CD pipelines with service account authentication issues

Let's examine a complete debugging session:

$ psql -U myuser -h localhost mydb
psql: FATAL:  Ident authentication failed for user "myuser"

# Check current authentication method:
$ grep -A5 'local.*all' /etc/postgresql/14/main/pg_hba.conf
local   all             all                                     ident

For development environments, consider these alternatives to ident:

# Recommended pg_hba.conf modifications:

# For local connections (peer is better than ident)
local   all             all                                     peer

# For TCP/IP connections
host    all             all             127.0.0.1/32            md5
host    all             all             ::1/128                 md5

In production environments, you should implement more robust authentication:

# Example for production pg_hba.conf
hostssl all             all             10.0.0.0/8              scram-sha-256
hostssl all             all             192.168.0.0/16          scram-sha-256

1. Verify pg_hba.conf location (show config_file; in psql)
2. Check the exact matching rule for your connection
3. Confirm operating system user mapping
4. Test with alternative authentication methods