Find the Process Listening on a Port

Objective

Determine which process is listening on a specific network port.

Prerequisites

• Shell access to the Linux host.
• Permissions to inspect network sockets and process information (typically root for unprivileged processes).

Procedure

1. Use ss to list sockets bound to the port:

   ss -tlnp | grep ':<port>'

2. If ss is unavailable, use netstat:

   netstat -tlnp | grep ':<port>'

3. Extract the process ID from the output and inspect the process:

   ps -fp <pid>

4. For UDP ports, replace -t with -u:

   ss -ulnp | grep ':<port>'

Verification

• Confirm the PID in the ss or netstat output matches the expected service.
• Verify the service is functional using its native health check or by connecting to the port.