netchx/netch · error · MessageException

The {0} port is in use.

Error message

The {0} port is in use.

What it means

Thrown by MainController.PortCheck when PortHelper.CheckPort raises PortInUseException — an active TCP or UDP listener already exists on the requested port (checked via IPGlobalProperties.GetActiveTcpListeners/GetActiveUdpListeners). The formatted message includes the human-readable portName and the port number.

Source

Thrown at Netch/Controllers/MainController.cs:142

        }
        catch (Exception e)
        {
            Log.Error(e, "MainController Stop Error");
        }

        ServerController = null;
        ModeController = null;
    }

    public static void PortCheck(ushort port, string portName, PortType portType = PortType.Both)
    {
        try
        {
            PortHelper.CheckPort(port, portType);
        }
        catch (PortInUseException)
        {
            throw new MessageException(i18N.TranslateFormat("The {0} port is in use.", $"{portName} ({port})"));
        }
        catch (PortReservedException)
        {
            throw new MessageException(i18N.TranslateFormat("The {0} port is reserved by system.", $"{portName} ({port})"));
        }
    }

    public static void TryReleaseTcpPort(ushort port, string portName)
    {
        foreach (var p in PortHelper.GetProcessByUsedTcpPort(port))
        {
            var fileName = p.MainModule?.FileName;
            if (fileName == null)
                continue;

            if (fileName.StartsWith(Global.NetchDir))
            {
                p.Kill();

View on GitHub (pinned to 9d99eb1c5a)

Solutions

1. Identify the holder: `netstat -ano | findstr :<port>` then tasklist / find the PID.
2. Stop the conflicting application or pick a different port in Settings.
3. Use MainController.TryReleaseTcpPort if the holder is another Netch process (it auto-kills Netch-owned processes).
4. Restart Netch cleanly so stale listeners are released.

MainController.PortCheck(port, portName, PortType.Both);
// throws MessageException("The {portName} (port) port is in use.") if a listener exists

try { MainController.PortCheck(port, portName); }
catch (MessageException ex) when (ex.Message.Contains("port is in use"))
{
    // prompt the user to change the port or stop the conflicting app
    SuggestAlternatePort(port);
}

When it happens

Trigger: Another application (or a previous, not-fully-stopped Netch process) is bound to the Socks5 local port, the mode controller's port, or the AioDNS port; calling PortCheck for a port a non-Netch app holds.

Common situations: Netch crashed without releasing its Socks5 port and is restarted; another proxy client (Clash, v2rayN) uses the same port; a development server occupies the port.

Related errors

• The {0} port is reserved by system.
• The {0} port is used by {1}.
• DNS format invalid
• Lookup Server hostname failed
• Invalid tcp type {server.FakeType}

AI-assisted analysis of netchx/netch@9d99eb1c5a (2026-08-13). Data as JSON: /api/errors/2898484cdc56538e. Report an issue: GitHub.