sqlclient_unable_to_establish_sqlconnection Sqlclient Unable To Establish Sqlconnection — SQLSTATE 08001

The client could not establish a connection — typically the server is unreachable or not listening for this client.

• The error is written to the server log and returned to the client carrying SQLSTATE 08001.
• Any driver (libpq, JDBC, psycopg, npgsql, pgx) surfaces this code in its error object so you can branch on it programmatically.
• PL/pgSQL can trap it by name: EXCEPTION WHEN sqlclient_unable_to_establish_sqlconnection THEN.

Severity: ERROR  |  PostgreSQL versions: 12, 13, 14, 15, 16, 17

Commonly coincides with restarts, failover, maintenance, or network events; check server uptime and the log around the timestamp.

The driver failed before authentication completed. PostgreSQL (or the network) refused or never answered the connection attempt.

Common causes:

• Wrong host, port, or database name in the connection string.
• listen_addresses does not include the client's network interface.
• The server is not started, or a firewall blocks port 5432.
• TLS is required but the client is not configured for it.

Steps to resolve 08001:

1. Verify host, port, and database name in the connection string.
2. Set listen_addresses = '*' (or the correct interface) in postgresql.conf and restart.
3. Add a matching pg_hba.conf entry for the client IP, database, and role.
4. Test raw connectivity: psql "host=... port=5432 user=... dbname=..." and pg_isready.
5. Check firewalls/security groups and the required sslmode.

Reference: PostgreSQL error codes — Class 08 (Connection Exception).