You can create file at specific location in program load if not exists if exists it means that the application running show to the user the messagebox "can't dupl....." in form closing remove the file...

Hi i have used this method to stop users from opening one of my applications multiple times.

string RunningProcess = Process.GetCurrentProcess().ProcessName;
Process[] processes = Process.GetProcessesByName(RunningProcess);

if (processes.Length > 1)
{
MessageBox.Show("Application is already running", "Stop", MessageBoxButtons.OK, MessageBoxIcon.Error);
Application.Exit();
Application.ExitThread();
}

I use the following code in the program.cs - file in C# 2.0:
static void Main()
{
// Optional
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
bool createdNew;

// To prevent the program to be started twice
///Create new mutex
System.Threading.Mutex appMutex = new System.Threading.Mutex(true, Application.ProductName, out createdNew);
///if creation of mutex is successful
if (createdNew)
{

Application.Run(new frmMain(false));
appMutex.ReleaseMutex();
}
else
{
/// if the app's already running
string msg = String.Format("The Program \"{0}\" is already running", Application.ProductName);
MessageBox.Show(msg, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Information);
}
}

Does this work easier for you? but as they say as long as it works then its all goooood!!!

Advantage of that later is you cannot simply change the name of the executable and then run two instances of the application.

I have a similar issue, but my users are not actually starting the program. There is a shortcut to the program in the windows startup folder. After a few days of running the program will have multiple processes. What could be causing this if the users are not actually clicking on the .exe?
This is my first C# program, and all it does is monitor two other programs to make sure they are on at all times.

Use this sample...

Some interesting answers. I've always used this method:

Single-Instance Application

It's obviously not fool-proof because changing the title of a running application is not that hard.

Something else you can do is if you can get the location of the running process you are comparing, create a new FileInfo class (I think) and compare the internal name of the file. Internal names are not as easy to change.

It's late at night and I didn't double check so forgive me if the above info is a little off

I like to use a slight variation, just modify your entry point as follows


users can get around it, but its very handy if you just want to keep accidental multiple instances from occurring.

some of those others are just as well.
Cheers.