Kill Process on Port with Psutil | Generated by AI
Using psutil to Detect and Kill a Process on a Specific Port (Windows)
Psutil is a cross-platform Python library for retrieving information on running processes and system utilization. You can use it to find processes listening on a specific port (e.g., identifying if something like an npm dev server is running on that port) and then terminate the process. This works on Windows, but keep in mind:
- Permissions: On Windows, terminating processes often requires administrative privileges (run your Python script as an administrator). Failing to do so may raise an
AccessDeniedexception. - Port Detection: We’ll focus on TCP connections with “inet” kind (which covers IPv4 and IPv6). This is common for web servers like those started by
npm run devor similar. - Assumptions: We’re assuming you want to check for a listening (server) port (e.g., something bound locally). If you mean outbound connections to a port, the approach differs slightly—let me know for clarification.
Step 1: Install psutil
If you haven’t already:
pip install psutil
Step 2: Sample Code to Detect and Kill
Here’s a complete Python script. It defines a function to find the PID of the process listening on a given port (using kind='inet' as you specified), then terminates it. On Windows, terminate() is preferred over kill() as it allows graceful shutdown (equivalent to SIGTERM on Unix).
import psutil
import time # For optional delay
def get_pid_listening_on_port(port, kind='inet'):
"""
Scans network connections for processes listening on the specified port.
Returns a list of PIDs (usually one, but could be multiple if rare).
"""
pids = []
for conn in psutil.net_connections(kind=kind):
# Check if it's a listening connection (status='LISTEN') and the local address port matches
if conn.status == 'LISTEN' and conn.laddr and conn.laddr.port == port:
if conn.pid:
pids.append(conn.pid)
return pids
def kill_process_on_port(port, kind='inet'):
"""
Finds and terminates the process listening on the specified port.
If multiple processes, kills all (with a warning).
"""
pids = get_pid_listening_on_port(port, kind)
if not pids:
print(f"No process found listening on port {port}.")
return
for pid in pids:
try:
proc = psutil.Process(pid)
print(f"Terminating process {proc.name()} (PID {pid}) on port {port}...")
# Use terminate() for graceful shutdown; it sends a SIGTERM-like signal
proc.terminate()
# Optional: Wait a bit and force kill if it doesn't exit
gone, still_alive = psutil.wait_procs([proc], timeout=3)
if still_alive:
print(f"Force killing PID {pid}...")
still_alive[0].kill()
except psutil.AccessDenied:
print(f"Access denied: Cannot terminate PID {pid}. Run as administrator?")
except psutil.NoSuchProcess:
print(f"Process {pid} no longer exists.")
# Example usage: Replace 3000 with your target port (e.g., npm dev servers often use 3000)
if __name__ == "__main__":
kill_process_on_port(3000) # Adjust kind if needed (e.g., 'inet4' for IPv4 only)
Key Explanations
psutil.net_connections(kind='inet'): This retrieves network connections of kind ‘inet’ (encompassing IPv4 and IPv6). Each connection is a namedtuple with fields like:laddr: Local address (e.g., (‘0.0.0.0’, 8080) – IP and port).status: ‘LISTEN’ for servers awaiting connections.pid: Process ID of the owner.- We filter for
status == 'LISTEN'to find servers (like npm’s dev port), not client connections.
- PID Retrieval: The script directly gets the PID from the connection tuple. If you only want to detect without killing, use
get_pid_listening_on_port(port)which returns the PID(s). - Killing the Process:
psutil.Process(pid).terminate(): Sends a termination signal. On Windows, this is like CTRL+C.- If it doesn’t exit, we optionally force-kill with
kill()(equivalent to SIGKILL). - Psutil’s
wait_procs()waits for the process to die.
- inet Kind Specificity: ‘inet’ includes both IPv4 and IPv6. If you know it’s IPv4, change to
kind='inet4'. THISNAME addresses your “inet kind” request directly. - Windows-Specific Notes:
- Psutil handles Windows internals well, but network info may require elevated privileges in some cases.
- For ports below 1024 (privileged), only system services can bind, but detection should still work.
- Error Handling: Added basic checks for no process or access issues.
- Testing: Run something like
npm run devto occupy port 3000, then run this script.
If this doesn’t match your exact need (e.g., if “npm run port” means something else or you want to detect non-listening connections), provide more details for refinement! For security/tsafety, ensure you’re only killing intended processes.