What causes ORA-01034?

Oracle database service is stopped or crashed. The TNS listener is not running on the target host. Incorrect host, port, or service name in the connection string. Firewall blocks the connection to the Oracle port. The Oracle instance was shut down for maintenance

How do I fix ORA-01034?

Step 1: Verify the Oracle listener is running on the target host: `lsnrctl status`.. Step 2: Start Oracle if stopped: `sqlplus / as sysdba` → `STARTUP;`.. Step 3: Verify network connectivity: `telnet 1521`.. Step 4: Check firewall rules and security groups for port 1521 (or custom port).. Step 5: Validate the connection string service name matches `lsnrctl services` output.

Critical severityconnectivity

Oracle Database Error:
ORA-01034

What does this error mean?

The Oracle database instance is not running or is not accessible at the specified host and port.

Common causes

1Oracle database service is stopped or crashed
2The TNS listener is not running on the target host
3Incorrect host, port, or service name in the connection string
4Firewall blocks the connection to the Oracle port
5The Oracle instance was shut down for maintenance

How to fix it

1Step 1: Verify the Oracle listener is running on the target host: `lsnrctl status`.
2Step 2: Start Oracle if stopped: `sqlplus / as sysdba` → `STARTUP;`.
3Step 3: Verify network connectivity: `telnet <oracle_host> 1521`.
4Step 4: Check firewall rules and security groups for port 1521 (or custom port).
5Step 5: Validate the connection string service name matches `lsnrctl services` output.

Example log output

ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist

Frequently asked questions

What is the difference between ORA-01034 and ORA-01033?

ORA-01034 means Oracle is completely down (listener unreachable or instance not started). ORA-01033 means Oracle is in the process of starting up or shutting down — it is temporarily unavailable.

Source · docs.oracle.com/error-help/db/ora-01034