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How to kill remote desktop session for local computer only

I'm using the following code to kill a remote desktop session and the application running in it. It works fine, the only problem is that it kills the specified application for all users.
How do I keep this to just the local machine running a session?
We have multiple users logging in and running this application from a server on their local machines. Most are running using work resources, but some use remote desktop.
No matter how they are logged in when I run my code all users loose their sessions.
private void btnCloseSession_Click(object sender, EventArgs e)
{
if (!runningExclusiveProcess)
{
runningExclusiveProcess = true;
btnCloseSession.Enabled = false;
//check and close Labware if running
if (chkCloseLabware.Checked == true)
{
if (chkExit.Checked == true)
{
KillLabWare();
Close();
}
else
{
KillLabWare();
}
}
Process[] my = Process.GetProcessesByName("mstsc");
//loop thru list to get selected item(s)
ListBox.SelectedObjectCollection selectedItems = new ListBox.SelectedObjectCollection(lstOpenSessions);
selectedItems = lstOpenSessions.SelectedItems;
try
{
//remove credentials
string szTestx = "/delete:GOJO.NET/" + cboServer.Text;
ProcessStartInfo infox = new ProcessStartInfo("cmdkey.exe", szTestx);
Process procx = new Process();
procx.StartInfo = infox;
procx.Start();
if (lstOpenSessions.SelectedIndex != -1)
{
for (int i = selectedItems.Count - 1; i >= 0; i--)
{
//loop thru process to match process vs. list selection(s)
foreach (Process remote in my)
{
if (remote.MainWindowTitle == selectedItems[i].ToString())
{
KillRS(remote.MainWindowTitle);
lstOpenSessions.Items.Remove(selectedItems[i]);
}
}
if (lstOpenSessions.Items.Contains(selectedItems[i].ToString()))
{
lstOpenSessions.Items.Remove(selectedItems[i]);
}
}
}
}
catch (Exception ex)
{
Console.WriteLine("{0} Exception caught.", ex);
}
// If your task is synchronous, then undo your flag here:
runningExclusiveProcess = false;
btnCloseSession.Enabled = true;
}
}
public void KillLabWare()
{
ConnectionOptions con = new ConnectionOptions();
con.Username = cboUserName.Text;
con.Password = txtPassWord.Text;
string strIPAddress = cboServer.Text;
ManagementScope scope = new
ManagementScope(#"\\" + strIPAddress + #"\root\cimv2", con);
scope.Connect();
ObjectQuery query = new ObjectQuery("SELECT * FROM Win32_Process WHERE Name='Labware.exe'");
ManagementObjectSearcher searcher = new
ManagementObjectSearcher(scope, query);
ManagementObjectCollection objectCollection = searcher.Get();
foreach (ManagementObject managementObject in objectCollection)
{
managementObject.InvokeMethod("Terminate", null);
}
}
private void KillRS(string rwt)
{
foreach (Process p in Process.GetProcesses())
{
if (p.MainWindowTitle == rwt)
{
p.Kill();
}
}
}
public static void KillRemoteProcess(Process p, string user, string password)
{
new Process
{
StartInfo = new ProcessStartInfo
{
FileName = "TaskKill.exe",
Arguments = string.Format("/pid {0} /s {1} /u {2} /p {3}", p.Id, p.MachineName, user, password),
WindowStyle = ProcessWindowStyle.Hidden,
CreateNoWindow = true
}
}.Start();
}

It sounds like you are trying to force a specific user to log out? Is this because you find that users are forgetting to log out and constantly consuming licenses?
LabWare Application allows for a time out interval (in minutes) to be set on each user where after the interval has passed, the user will be logged out (licence no longer consumed).
For more information see page 204 of the LabWare 7 Technical Manual.
Alternativley if this is for a scheduler (service or cluster instance) session, this can also be controlled by the application. You can either manually change the shutdown and keep alive flags on the instance record on the Services table (if using Service Manager) or you can write a LIMS Basic event trigger/automation script or scheduled subroutine (or have this as a button on a Visual workflow) to do this for you.
HTH.

If you wanna kill remote desktop session or disconnect current RDP session, please read this article:
WTSDisconnectSession function
but if you logout current user, it also disconnect RDP session, here is the code:
using System;
using System.Runtime.InteropServices;
using System.ComponentModel;
class Program
{
[DllImport("wtsapi32.dll", SetLastError = true)]
static extern bool WTSDisconnectSession(IntPtr hServer, int sessionId, bool bWait);
const int WTS_CURRENT_SESSION = -1;
static readonly IntPtr WTS_CURRENT_SERVER_HANDLE = IntPtr.Zero;
static void Main(string[] args)
{
if (!WTSDisconnectSession(WTS_CURRENT_SERVER_HANDLE,
WTS_CURRENT_SESSION, false))
throw new Win32Exception();
}
}
I hope it works, fill free for further info, comment plz
Happy Coding 😎

Single instance dotnetcore cli app on linux

I am interested in how to inforce a single instance policy for dotnetcore console apps. To my surprise it seems like there isn't much out there on the topic. I found this one stacko, How to restrict a program to a single instance, but it doesnt seem to work for me on dotnetcore with ubuntu. Anyone here do this before?

Variation of #MusuNaji's solution at: How to restrict a program to a single instance
private static bool AlreadyRunning()
{
Process[] processes = Process.GetProcesses();
Process currentProc = Process.GetCurrentProcess();
logger.LogDebug("Current proccess: {0}", currentProc.ProcessName);
foreach (Process process in processes)
{
if (currentProc.ProcessName == process.ProcessName && currentProc.Id != process.Id)
{
logger.LogInformation("Another instance of this process is already running: {pid}", process.Id);
return true;
}
}
return false;
}

This is a little more difficult on .NET core than it should be, due to the problem of mutex checking on Linux/MacOS (as reported above). Also Theyouthis's solution isn't helpful as all .NET core apps are run via the CLI which has a process name of 'dotnet' which if you are running multiple .NET core apps on the same machine the duplicate instance check will trigger incorrectly.
A simple way to do this that is also multi-platform robust is to open a file for write when the application starts, and close it at the end. If the file fails to open it is due to another instance running concurrently and you can handle that in the try/catch. Using FileStream to open the file will also create it if it doesn't first exist.
try
{
lockFile = File.OpenWrite("SingleInstance.lck");
}
catch (Exception)
{
Console.WriteLine("ERROR - Server is already running. End that instance before re-running. Exiting in 5 seconds...");
System.Threading.Thread.Sleep(5000);
return;
}

Here is my implementation using Named pipes. It supports passing arguments from the second instance.
Note: I did not test on Linux or Mac but it should work in theory.
Usage
public static int Main(string[] args)
{
instanceManager = new SingleInstanceManager("8A3B7DE2-6AB4-4983-BBC0-DF985AB56703");
if (!instanceManager.Start())
{
return 0; // exit, if same app is running
}
instanceManager.SecondInstanceLaunched += InstanceManager_SecondInstanceLaunched;
// Initialize app. Below is an example in WPF.
app = new App();
app.InitializeComponent();
return app.Run();
}
private static void InstanceManager_SecondInstanceLaunched(object sender, SecondInstanceLaunchedEventArgs e)
{
app.Dispatcher.Invoke(() => new MainWindow().Show());
}
Your Copy-and-paste code
public class SingleInstanceManager
{
private readonly string applicationId;
public SingleInstanceManager(string applicationId)
{
this.applicationId = applicationId;
}
/// <summary>
/// Detect if this is the first instance. If it is, start a named pipe server to listen for subsequent instances. Otherwise, send <see cref="Environment.GetCommandLineArgs()"/> to the first instance.
/// </summary>
/// <returns>True if this is tthe first instance. Otherwise, false.</returns>
public bool Start()
{
using var client = new NamedPipeClientStream(applicationId);
try
{
client.Connect(0);
}
catch (TimeoutException)
{
Task.Run(() => StartListeningServer());
return true;
}
var args = Environment.GetCommandLineArgs();
using (var writer = new BinaryWriter(client, Encoding.UTF8))
{
writer.Write(args.Length);
for (int i = 0; i < args.Length; i++)
{
writer.Write(args[i]);
}
}
return false;
}
private void StartListeningServer()
{
var server = new NamedPipeServerStream(applicationId);
server.WaitForConnection();
using (var reader = new BinaryReader(server, Encoding.UTF8))
{
var argc = reader.ReadInt32();
var args = new string[argc];
for (int i = 0; i < argc; i++)
{
args[i] = reader.ReadString();
}
SecondInstanceLaunched?.Invoke(this, new SecondInstanceLaunchedEventArgs { Arguments = args });
}
StartListeningServer();
}
public event EventHandler<SecondInstanceLaunchedEventArgs> SecondInstanceLaunched;
}
public class SecondInstanceLaunchedEventArgs
{
public string[] Arguments { get; set; }
}
Unit test
[TestClass]
public class SingleInstanceManagerTests
{
[TestMethod]
public void SingleInstanceManagerTest()
{
var id = Guid.NewGuid().ToString();
var manager = new SingleInstanceManager(id);
string[] receivedArguments = null;
var correctArgCount = Environment.GetCommandLineArgs().Length;
manager.SecondInstanceLaunched += (sender, e) => receivedArguments = e.Arguments;
var instance1 = manager.Start();
Thread.Sleep(200);
var manager2 = new SingleInstanceManager(id);
Assert.IsFalse(manager2.Start());
Thread.Sleep(200);
Assert.IsTrue(instance1);
Assert.IsNotNull(receivedArguments);
Assert.AreEqual(correctArgCount, receivedArguments.Length);
var receivedArguments2 = receivedArguments;
var manager3 = new SingleInstanceManager(id);
Thread.Sleep(200);
Assert.IsFalse(manager3.Start());
Assert.AreNotSame(receivedArguments, receivedArguments2);
Assert.AreEqual(correctArgCount, receivedArguments.Length);
}
}

The downside of deandob's solution is that one can launch the application from another path. So you may prefer some static path or a tmp path for all users.
Here is my attempt:
//second instance launch guard
var tempPath = Environment.GetEnvironmentVariable("TEMP", EnvironmentVariableTarget.Machine)
??
Path.GetTempPath();
var lockPath = Path.Combine(tempPath, "SingleInstance.lock");
await using var lockFile = File.OpenWrite(lockPath);
here I'm trying to get TEMP system variable at the scope of machine (not the user TEMP) and if its empty - fallback to the user's temp folder on windows or shared /tmp on some linuxes.

Getting the Drive letter of USB drive inserted

I have detected the insertion of USB drive in my WPF application by following suggestions in given link How do I detect when a removable disk is inserted using C#?
but I am unable to figure out the Drive letter of the detected USB drive; my Code is given below
static ManagementEventWatcher w = null;
static void AddInsertUSBHandler()
{
WqlEventQuery q;
ManagementScope scope = new ManagementScope("root\\CIMV2");
scope.Options.EnablePrivileges = true;
try {
q = new WqlEventQuery();
q.EventClassName = "__InstanceCreationEvent";
q.WithinInterval = new TimeSpan(0, 0, 3);
q.Condition = "TargetInstance ISA 'Win32_USBControllerdevice'";
w = new ManagementEventWatcher(scope, q);
w.EventArrived += USBInserted;
w.Start();
}
catch (Exception e) {
Console.WriteLine(e.Message);
if (w != null)
{
w.Stop();
}
}
}
static void USBInserted(object sender, EventArgs e)
{
Console.WriteLine("A USB device inserted");
}
Kindly guide me if possible.

Hope this helps, its code based on Neeraj Dubbey’s answer.
We run code in a continuous multithreaded loop that keeps checking for a change in connected USB devices. Because we keep track of previously connected devices we can compare it against a new list of devices. We can also determine if a device is removed using the same method.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Management;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace Usb_Test
{
class Program
{
private static List<USBDeviceInfo> previousDecices = new List<USBDeviceInfo>();
static void Main(string[] args)
{
Thread thread = new Thread(DeviceDetection);
thread.Start();
Console.Read();
}
static void DeviceDetection()
{
while (true)
{
List<USBDeviceInfo> devices = new List<USBDeviceInfo>();
ManagementObjectCollection collection;
using (var searcher = new ManagementObjectSearcher(#"Select * From Win32_USBHub"))
collection = searcher.Get();
foreach (var device in collection)
{
devices.Add(new USBDeviceInfo(
(string)device.GetPropertyValue("DeviceID")
));
}
if (previousDecices == null || !previousDecices.Any()) // So we don't detect already plugged in devices the first time.
previousDecices = devices;
var insertionDevices = devices.Where(d => !previousDecices.Any(d2 => d2.DeviceID == d.DeviceID));
if (insertionDevices != null && insertionDevices.Any())
{
foreach(var value in insertionDevices)
{
Console.WriteLine("Inserted: " + value.DeviceID); // Add your own event for the insertion of devices.
}
}
var removedDevices = previousDecices.Where(d => !devices.Any(d2 => d2.DeviceID == d.DeviceID));
if (removedDevices != null && removedDevices.Any())
{
foreach (var value in removedDevices)
{
Console.WriteLine("Removed: " + value.DeviceID); // Add your own event for the removal of devices.
}
}
previousDecices = devices;
collection.Dispose();
}
}
}
class USBDeviceInfo
{
public USBDeviceInfo(string deviceID)
{
this.DeviceID = deviceID;
}
public string DeviceID { get; private set; }
}
}
However this is not a great solution, you're a lot better off listening for WM_DEVICECHANGE.
Windows will send WM_DEVICECHANGE message to all applications whenever
some hardware change occurs, including when a flash drive (or other
removable device) is inserted or removed. The WParam parameter of this
message contains code which specifies exactly what event occurred. For
our purpose only the following events are interesting:
DBT_DEVICEARRIVAL - sent after a device or piece of media has been
inserted. Your program will receive this message when the device is
ready for use, at about the time when Explorer displays the dialog
which lets you choose what to do with the inserted media.
DBT_DEVICEQUERYREMOVE - sent when the system requests permission to
remove a device or piece of media. Any application can deny this
request and cancel the removal. This is the important event if you
need to perform some action on the flash drive before it is removed,
e.g. encrypt some files on it. Your program can deny this request
which will cause Windows to display the well-known message saying that
the device cannot be removed now.
DBT_DEVICEREMOVECOMPLETE - sent after a device has been removed. When
your program receives this event, the device is no longer available —
at the time when Windows display its "device has been removed" bubble
to the user.
Here are some links that each detail an answer on how to do this in C#:
http://www.codeproject.com/Articles/18062/Detecting-USB-Drive-Removal-in-a-C-Program
http://www.codeproject.com/Articles/60579/A-USB-Library-to-Detect-USB-Devices
Both solution should work, and you can always adapt them to fit your needs.

Hey try this console based code afetr adding the reference of System.Management in project
namespace ConsoleApplication1
{
using System;
using System.Collections.Generic;
using System.Management; // need to add System.Management to your project references.
class Program
{
static void Main(string[] args)
{
var usbDevices = GetUSBDevices();
foreach (var usbDevice in usbDevices)
{
Console.WriteLine("Device ID: {0}", usbDevice.DeviceID);
}
Console.Read();
}
static List<USBDeviceInfo> GetUSBDevices()
{
List<USBDeviceInfo> devices = new List<USBDeviceInfo>();
ManagementObjectCollection collection;
using (var searcher = new ManagementObjectSearcher(#"Select * From Win32_USBHub"))
collection = searcher.Get();
foreach (var device in collection)
{
devices.Add(new USBDeviceInfo(
(string)device.GetPropertyValue("DeviceID")
));
}
collection.Dispose();
return devices;
}
}
class USBDeviceInfo
{
public USBDeviceInfo(string deviceID)
{
this.DeviceID = deviceID;
}
public string DeviceID { get; private set; }
}

Printing from Adobe with Citrix

Greetings,
I've attempted to shrink the code down as much as I can. Basically we use the Adobe Acrobat standard 6 Com libraries to print. It works as well as any batch pdf print solution that I've seen, but I can't seem to make it work with Citrix. Citrix appears to remap the netowrk printing locations and I can't seem to make it work with out existing solution. All the code runs on Citirix it just doesn't print anything. When it runs locally it runs and prints just fine.
Any help would be greatly appreciated,
Thank you,
Brian
private void btnTest_Click(object sender, EventArgs e)
{
try
{
Cursor.Current = Cursors.WaitCursor;
PrintDialog PrintDialog1 = new PrintDialog();
PrintDialog1.ShowDialog();
CAcroAVDoc acroDoc = null;
const string fileName = #"SomeFile.pdf";
var acroApp = instantiateAcrobat();
acroDoc = GetAcrobatAVDoc();
acroDoc.Open(fileName, "");
CAcroPDDoc pdDoc = (CAcroPDDoc)acroDoc.GetPDDoc();
int numPages = pdDoc.GetNumPages();
UnManagedMethods.SetDefaultPrinter(PrintDialog1.PrinterSettings.PrinterName);
acroDoc.PrintPagesSilent(0, numPages - 1, 2, 1, 0);
MessageBox.Show("Printed!!");
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
private static CAcroAVDoc GetAcrobatAVDoc()
{
Type acroApp = Type.GetTypeFromProgID("AcroExch.AVDoc", true);
return (CAcroAVDoc)Activator.CreateInstance(acroApp);
}
private static CAcroApp instantiateAcrobat()
{
killAllAcrobatProcesses();
Type acroApp = Type.GetTypeFromProgID("AcroExch.App", true);
return (CAcroApp)Activator.CreateInstance(acroApp);
}
private static void killAllAcrobatProcesses()
{
Process[] acrobatProcesses = Process.GetProcessesByName("Acrobat");
if (acrobatProcesses.Length > 0)
{
foreach (Process process in acrobatProcesses)
{
process.Kill();
}
}
Process[] acroRd32Processes = Process.GetProcessesByName("AcroRd32");
if (acroRd32Processes.Length > 0)
{
foreach (Process process in acroRd32Processes)
{
process.Kill();
}
}
}

If anyone is interested this was fixed by installing the printer on the citrix box outside of Citrix. The trick was to remote desktop into the citrix box install the printer get the application working so it will print. Then when you log on through citrix printing worked just fine. It seems very obvious in retrospect.

C# check if a COM (Serial) port is already open

Is there an easy way of programmatically checking if a serial COM port is already open/being used?
Normally I would use:
try
{
// open port
}
catch (Exception ex)
{
// handle the exception
}
However, I would like to programatically check so I can attempt to use another COM port or some such.

I needed something similar some time ago, to search for a device.
I obtained a list of available COM ports and then simply iterated over them, if it didn't throw an exception i tried to communicate with the device. A bit rough but working.
var portNames = SerialPort.GetPortNames();
foreach(var port in portNames) {
//Try for every portName and break on the first working
}

This is how I did it:
[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
internal static extern SafeFileHandle CreateFile(string lpFileName, int dwDesiredAccess, int dwShareMode, IntPtr securityAttrs, int dwCreationDisposition, int dwFlagsAndAttributes, IntPtr hTemplateFile);
then later on
int dwFlagsAndAttributes = 0x40000000;
var portName = "COM5";
var isValid = SerialPort.GetPortNames().Any(x => string.Compare(x, portName, true) == 0);
if (!isValid)
throw new System.IO.IOException(string.Format("{0} port was not found", portName));
//Borrowed from Microsoft's Serial Port Open Method :)
SafeFileHandle hFile = CreateFile(#"\\.\" + portName, -1073741824, 0, IntPtr.Zero, 3, dwFlagsAndAttributes, IntPtr.Zero);
if (hFile.IsInvalid)
throw new System.IO.IOException(string.Format("{0} port is already open", portName));
hFile.Close();
using (var serialPort = new SerialPort(portName, 115200, Parity.None, 8, StopBits.One))
{
serialPort.Open();
}

For people that cannot use SerialPort.GetPortNames(); because they are not targeting .net framework (like in my case I am using .Net Core and NOT .Net Framework) here is what I ended up doing:
In command prompt if you type mode you get something like this:
mode is an executable located at C:\Windows\System32\mode.com. Just parse the results of that executable with a regex like this:
// Code that answers the question
var proc = new Process
{
StartInfo = new ProcessStartInfo
{
FileName = #"C:\Windows\System32\mode.com",
UseShellExecute = false,
RedirectStandardOutput = true,
CreateNoWindow = true
}
};
proc.Start();
proc.WaitForExit(4000); // wait up to 4 seconds. It usually takes less than a second
// get ports being used
var output = proc.StandardOutput.ReadToEnd();
Now if you want to parse the output this is how I do it:
List<string> comPortsBeingUsed = new List<string>();
Regex.Replace(output, #"(?xi) status [\s\w]+? (COM\d) \b ", regexCapture =>
{
comPortsBeingUsed.Add(regexCapture.Groups[1].Value);
return null;
});
foreach(var item in comPortsBeingUsed)
{
Console.WriteLine($"COM port {item} is in use");
}

I wanted to open the next available port and did it like this.
Please note, is it not for WPF but for Windows Forms.
I populated a combobox with the com ports available.
Then I try to open the first one. If it fails, I select the next available item from the combobox. If the selected index did not change in the end, there were no alternate com ports available and we show a message.
private void GetPortNames()
{
comboBoxComPort.Items.Clear();
foreach (string s in SerialPort.GetPortNames())
{
comboBoxComPort.Items.Add(s);
}
comboBoxComPort.SelectedIndex = 0;
}
private void OpenSerialPort()
{
try
{
serialPort1.PortName = comboBoxComPort.SelectedItem.ToString();
serialPort1.Open();
}
catch (Exception ex)
{
int SelectedIndex = comboBoxComPort.SelectedIndex;
if (comboBoxComPort.SelectedIndex >= comboBoxComPort.Items.Count - 1)
{
comboBoxComPort.SelectedIndex = 0;
}
else
{
comboBoxComPort.SelectedIndex++;
}
if (comboBoxComPort.SelectedIndex == SelectedIndex)
{
buttonOpenClose.Text = "Open Port";
MessageBox.Show("Error accessing port." + Environment.NewLine + ex.Message, "Port Error!!!", MessageBoxButtons.OK);
}
else
{
OpenSerialPort();
}
}
if (serialPort1.IsOpen)
{
StartAsyncSerialReading();
}
}

The SerialPort class has an Open method, which will throw a few exceptions.
The reference above contains detailed examples.
See also, the IsOpen property.
A simple test:
using System;
using System.IO.Ports;
using System.Collections.Generic;
using System.Text;
namespace SerPort1
{
class Program
{
static private SerialPort MyPort;
static void Main(string[] args)
{
MyPort = new SerialPort("COM1");
OpenMyPort();
Console.WriteLine("BaudRate {0}", MyPort.BaudRate);
OpenMyPort();
MyPort.Close();
Console.ReadLine();
}
private static void OpenMyPort()
{
try
{
MyPort.Open();
}
catch (Exception ex)
{
Console.WriteLine("Error opening my port: {0}", ex.Message);
}
}
}
}

Sharing what worked for me (a simple helper method):
private string portName { get; set; } = string.Empty;
/// <summary>
/// Returns SerialPort Port State (Open / Closed)
/// </summary>
/// <returns></returns>
internal bool HasOpenPort()
{
bool portState = false;
if (portName != string.Empty)
{
using (SerialPort serialPort = new SerialPort(portName))
{
foreach (var itm in SerialPort.GetPortNames())
{
if (itm.Contains(serialPort.PortName))
{
if (serialPort.IsOpen) { portState = true; }
else { portState = false; }
}
}
}
}
else { System.Windows.Forms.MessageBox.Show("Error: No Port Specified."); }
return portState;
}
Notes:
- For more advanced technique(s) I recommend using ManagementObjectSearcher Class.
More info Here.
- For Arduino devices I would leave the Port Open.
- Recommend using a Try Catch block if you need to catch exceptions.
- Check also: "TimeoutException"
- More information on how to get SerialPort (Open) Exceptions Here.

public void MobileMessages(string ComNo, string MobileMessage, string MobileNo)
{
if (SerialPort.IsOpen )
SerialPort.Close();
try
{
SerialPort.PortName = ComNo;
SerialPort.BaudRate = 9600;
SerialPort.Parity = Parity.None;
SerialPort.StopBits = StopBits.One;
SerialPort.DataBits = 8;
SerialPort.Handshake = Handshake.RequestToSend;
SerialPort.DtrEnable = true;
SerialPort.RtsEnable = true;
SerialPort.NewLine = Constants.vbCrLf;
string message;
message = MobileMessage;
SerialPort.Open();
if (SerialPort.IsOpen )
{
SerialPort.Write("AT" + Constants.vbCrLf);
SerialPort.Write("AT+CMGF=1" + Constants.vbCrLf);
SerialPort.Write("AT+CMGS=" + Strings.Chr(34) + MobileNo + Strings.Chr(34) + Constants.vbCrLf);
SerialPort.Write(message + Strings.Chr(26));
}
else
("Port not available");
SerialPort.Close();
System.Threading.Thread.Sleep(5000);
}
catch (Exception ex)
{
message.show("The port " + ComNo + " does not exist, change port no ");
}
}

I have been fighting with this problem for a few weeks now. Thanks to the suggestions on here and from the site, https://www.dreamincode.net/forums/topic/91090-c%23-serial-port-unauthorizedaccessexception/ .
I finally came up with a solution that seems to work.
The application I am working on allows a user to connect to a USB device and display data from it.
The Problem I was battling. Along side the application I am writing, I use another serial terminal application for doing my testing. Sometimes I forget to disconnect the COMport being used on the other application. If I do, and try to connect with the application I am writing, I would get an “UnAuthorizedAccessException” error. Along with this exception came some side effects, such as double lines of data being spit out and the application locking up on closing down.
My Solution
Thanks to the advice on here and the other site referenced, this was my solution.
private void checkAndFillPortNameList()
{
SerialPort _testingSerialPort;
AvailablePortNamesFound.Clear();
List<string> availablePortNames = new List<string>();//mySerial.GetAvailablePortNames();
foreach (string portName in SerialPortDataAccess.GetAvailablePortNames())
{
try
{
_testingSerialPort = new SerialPort(portName);
_testingSerialPort.Open();
if (_testingSerialPort.IsOpen)
{
availablePortNames.Add(portName);
_testingSerialPort.Close();
}
}
catch (Exception ex)
{
}
}
availablePortNames.Sort();
AvailablePortNamesFound = new ObservableCollection<string>(availablePortNames);
}
This routine connects to a combobox which holds the available Comports for selection. If a Comport is already, in use by another application, that port name will not appear in the combo box.

You can try folloing code to check whether a port already open or not. I'm assumming you dont know specificaly which port you want to check.
foreach (var portName in Serial.GetPortNames()
{
SerialPort port = new SerialPort(portName);
if (port.IsOpen){
/** do something **/
}
else {
/** do something **/
}
}