How do I kill the process using port 1521?

On macOS & Linux, run: "lsnrctl stop". On Windows PowerShell (as Admin), run: "Stop-Service OracleOraDB* -Force".

Why am I getting "port 1521 already in use" (EADDRINUSE)?

This occurs when another background instance of tnslsnr, oracle or a zombie process is already bound to port 1521. Use the kill commands above to free the port immediately.

Database

Risk: High

Port 1521 — Oracle Database Listener

Q: Is Port 1521 safe to expose to the public internet?

Risk level is High. Oracle listeners can reveal database version information and SID names. Implement Valid Node Checking (COST) to restrict unauthorized client hosts.

Port 1521 is the default port for the Oracle Database TNS (Transparent Network Substrate) Listener.

PORT NUMBER

1521

PROTOCOL

TCP

DEFAULT PROCESS

tnslsnr, oracle

FIREWALL TARGET

1521/tcp

Instant Terminal Fixes for Port 1521

macOS & Linux Terminal

1. Check who is listening on port 1521:

lsnrctl status

2. Kill process occupying port 1521 (EADDRINUSE fix):

lsnrctl stop

3. UFW Firewall Allow rule:

sudo ufw deny 1521

Windows PowerShell (Admin)

1. Check listening port:

Get-NetTCPConnection -LocalPort 1521

2. Force kill process on port 1521:

Stop-Service OracleOraDB* -Force

3. Docker Port Forwarding Mapping:

docker run -p 1521:1521 -d container-registry.oracle.com/database/free:latest

Common Error Encountered

ORA-12541: TNS:no listener on port 1521

Security Advisory & Hardening

Oracle listeners can reveal database version information and SID names. Implement Valid Node Checking (COST) to restrict unauthorized client hosts.

Frequently Asked Questions

Port 1521 Questions & Answers

Common questions regarding default services, kill commands, and firewall configurations.

Port 1521 is commonly used for Oracle Database Listener. Port 1521 is the default port for the Oracle Database TNS (Transparent Network Substrate) Listener.

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