How do I find out which process is locking a file using .NET?

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I've seen several of answers about using Handle or Process Monitor, but I would like to be able to find out in my own code (C#) which process is locking a file.

I have a nasty feeling that I'm going to have to spelunk around in the win32 API, but if anyone has already done this and can put me on the right track, I'd really appreciate the help.

Update
Links to similar questions
  • How does one figure out what process locked a file using c#?
  • Command line tool
  • Across a Network
  • Locking a USB device
  • Unit test fails with locked file
  • deleting locked file

One of the good things about handle.exe is that you can run it as a subprocess and parse the output.

We do this in our deployment script - works like a charm.

How do I find out which process is locking a file using .NET?, "Make sure the disk is not full or write-protected and that the file is not currently in use". How to Solve the Issue. One of the easiest ways to handle locked files or  I’ve seen several of answers about using Handle or Process Monitor, but I would like to be able to find out in my own code (C#) which process is locking a file. I have a nasty feeling that I’m going to have to spelunk around in the win32 API, but if anyone has already done this and can put me on the right track, I’d really appreciate the help.

Long ago it was impossible to reliably get the list of processes locking a file because Windows simply did not track that information. To support the Restart Manager API, that information is now tracked.

I put together code that takes the path of a file and returns a List<Process> of all processes that are locking that file.

using System.Runtime.InteropServices;
using System.Diagnostics;
using System;
using System.Collections.Generic;

static public class FileUtil
{
    [StructLayout(LayoutKind.Sequential)]
    struct RM_UNIQUE_PROCESS
    {
        public int dwProcessId;
        public System.Runtime.InteropServices.ComTypes.FILETIME ProcessStartTime;
    }

    const int RmRebootReasonNone = 0;
    const int CCH_RM_MAX_APP_NAME = 255;
    const int CCH_RM_MAX_SVC_NAME = 63;

    enum RM_APP_TYPE
    {
        RmUnknownApp = 0,
        RmMainWindow = 1,
        RmOtherWindow = 2,
        RmService = 3,
        RmExplorer = 4,
        RmConsole = 5,
        RmCritical = 1000
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    struct RM_PROCESS_INFO
    {
        public RM_UNIQUE_PROCESS Process;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_APP_NAME + 1)]
        public string strAppName;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_SVC_NAME + 1)]
        public string strServiceShortName;

        public RM_APP_TYPE ApplicationType;
        public uint AppStatus;
        public uint TSSessionId;
        [MarshalAs(UnmanagedType.Bool)]
        public bool bRestartable;
    }

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    static extern int RmRegisterResources(uint pSessionHandle,
                                          UInt32 nFiles,
                                          string[] rgsFilenames,
                                          UInt32 nApplications,
                                          [In] RM_UNIQUE_PROCESS[] rgApplications,
                                          UInt32 nServices,
                                          string[] rgsServiceNames);

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Auto)]
    static extern int RmStartSession(out uint pSessionHandle, int dwSessionFlags, string strSessionKey);

    [DllImport("rstrtmgr.dll")]
    static extern int RmEndSession(uint pSessionHandle);

    [DllImport("rstrtmgr.dll")]
    static extern int RmGetList(uint dwSessionHandle,
                                out uint pnProcInfoNeeded,
                                ref uint pnProcInfo,
                                [In, Out] RM_PROCESS_INFO[] rgAffectedApps,
                                ref uint lpdwRebootReasons);

    /// <summary>
    /// Find out what process(es) have a lock on the specified file.
    /// </summary>
    /// <param name="path">Path of the file.</param>
    /// <returns>Processes locking the file</returns>
    /// <remarks>See also:
    /// http://msdn.microsoft.com/en-us/library/windows/desktop/aa373661(v=vs.85).aspx
    /// http://wyupdate.googlecode.com/svn-history/r401/trunk/frmFilesInUse.cs (no copyright in code at time of viewing)
    /// 
    /// </remarks>
    static public List<Process> WhoIsLocking(string path)
    {
        uint handle;
        string key = Guid.NewGuid().ToString();
        List<Process> processes = new List<Process>();

        int res = RmStartSession(out handle, 0, key);
        if (res != 0) throw new Exception("Could not begin restart session.  Unable to determine file locker.");

        try
        {
            const int ERROR_MORE_DATA = 234;
            uint pnProcInfoNeeded = 0,
                 pnProcInfo = 0,
                 lpdwRebootReasons = RmRebootReasonNone;

            string[] resources = new string[] { path }; // Just checking on one resource.

            res = RmRegisterResources(handle, (uint)resources.Length, resources, 0, null, 0, null);

            if (res != 0) throw new Exception("Could not register resource.");                                    

            //Note: there's a race condition here -- the first call to RmGetList() returns
            //      the total number of process. However, when we call RmGetList() again to get
            //      the actual processes this number may have increased.
            res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, null, ref lpdwRebootReasons);

            if (res == ERROR_MORE_DATA)
            {
                // Create an array to store the process results
                RM_PROCESS_INFO[] processInfo = new RM_PROCESS_INFO[pnProcInfoNeeded];
                pnProcInfo = pnProcInfoNeeded;

                // Get the list
                res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, processInfo, ref lpdwRebootReasons);
                if (res == 0)
                {
                    processes = new List<Process>((int)pnProcInfo);

                    // Enumerate all of the results and add them to the 
                    // list to be returned
                    for (int i = 0; i < pnProcInfo; i++)
                    {
                        try
                        {
                            processes.Add(Process.GetProcessById(processInfo[i].Process.dwProcessId));
                        }
                        // catch the error -- in case the process is no longer running
                        catch (ArgumentException) { }
                    }
                }
                else throw new Exception("Could not list processes locking resource.");                    
            }
            else if (res != 0) throw new Exception("Could not list processes locking resource. Failed to get size of result.");                    
        }
        finally
        {
            RmEndSession(handle);
        }

        return processes;
    }
}

Using from Limited Permission (e.g. IIS)

This call accesses the registry. If the process does not have permission to do so, you will get ERROR_WRITE_FAULT, meaning An operation was unable to read or write to the registry. You could selectively grant permission to your restricted account to the necessary part of the registry. It is more secure though to have your limited access process set a flag (e.g. in the database or the file system, or by using an interprocess communication mechanism such as queue or named pipe) and have a second process call the Restart Manager API.

Granting other-than-minimal permissions to the IIS user is a security risk.

How to Identify which Windows Process is Locking a File or Folder , When you attempt to delete a file or folder which is in use by a process, the File In Use dialog For investigating processes and locked files, Windows Sysinternals Process Explorer is probably OpenedFilesView from Nirsoft.net (3rd party)  Process Explorer from Sysinternals can find also the process which are locking a file. Just use Find, Find Handle or Dll in the main menu. Enter the path of the file in the textbox, then click Search. – Maxence Apr 24 '15 at 8:38

It is very complex to invoke Win32 from C#.

You should use the tool Handle.exe.

After that your C# code have to be the following:

string fileName = @"c:\aaa.doc";//Path to locked file

Process tool = new Process();
tool.StartInfo.FileName = "handle.exe";
tool.StartInfo.Arguments = fileName+" /accepteula";
tool.StartInfo.UseShellExecute = false;
tool.StartInfo.RedirectStandardOutput = true;
tool.Start();           
tool.WaitForExit();
string outputTool = tool.StandardOutput.ReadToEnd();

string matchPattern = @"(?<=\s+pid:\s+)\b(\d+)\b(?=\s+)";
foreach(Match match in Regex.Matches(outputTool, matchPattern))
{
    Process.GetProcessById(int.Parse(match.Value)).Kill();
}

Find Which Process Has Locked a File Without 3rd Party Tools , but i cannot find in each process, which file they are using(locking), find-out-​which-process-is-locking-a-file-using-net <DllImport("rstrtmgr.dll",  4. You will see the associated handles for the file in the Associated Handles tab. Right click on the process which is locking the file and then click on “End Process” to end the process on your computer. After ending the particular service, try to modify/ delete the file again. This time, you will be able to do it.

I had issues with stefan's solution. Below is a modified version which seems to work well.

using System;
using System.Collections;
using System.Diagnostics;
using System.Management;
using System.IO;

static class Module1
{
    static internal ArrayList myProcessArray = new ArrayList();
    private static Process myProcess;

    public static void Main()
    {
        string strFile = "c:\\windows\\system32\\msi.dll";
        ArrayList a = getFileProcesses(strFile);
        foreach (Process p in a)
        {
            Debug.Print(p.ProcessName);
        }
    }

    private static ArrayList getFileProcesses(string strFile)
    {
        myProcessArray.Clear();
        Process[] processes = Process.GetProcesses();
        int i = 0;
        for (i = 0; i <= processes.GetUpperBound(0) - 1; i++)
        {
            myProcess = processes[i];
            //if (!myProcess.HasExited) //This will cause an "Access is denied" error
            if (myProcess.Threads.Count > 0)
            {
                try
                {
                    ProcessModuleCollection modules = myProcess.Modules;
                    int j = 0;
                    for (j = 0; j <= modules.Count - 1; j++)
                    {
                        if ((modules[j].FileName.ToLower().CompareTo(strFile.ToLower()) == 0))
                        {
                            myProcessArray.Add(myProcess);
                            break;
                            // TODO: might not be correct. Was : Exit For
                        }
                    }
                }
                catch (Exception exception)
                {
                    //MsgBox(("Error : " & exception.Message)) 
                }
            }
        }

        return myProcessArray;
    }
}

UPDATE

If you just want to know which process(es) are locking a particular DLL, you can execute and parse the output of tasklist /m YourDllName.dll. Works on Windows XP and later. See

What does this do? tasklist /m "mscor*"

how to see which process is using(locking) a file - MSDN, Read(); } public static List<Process> GetProcessesLockingFile(string filePath) { var procs = new List<Process>(); var processListSnapshot  For instance, when trying to delete a folder, Windows reports this: The action can't be completed because the folder is open in another program. IT pro or windows customers would like to find out what program or application is currently using it and preventing me from deleting the file or folder. This Windows PowerShell script will help them find out which process is locking a file or folder.

This works for DLLs locked by other processes. This routine will not find out for example that a text file is locked by a word process.

C#:

using System.Management; 
using System.IO;   

static class Module1 
{ 
static internal ArrayList myProcessArray = new ArrayList(); 
private static Process myProcess; 

public static void Main() 
{ 

    string strFile = "c:\\windows\\system32\\msi.dll"; 
    ArrayList a = getFileProcesses(strFile); 
    foreach (Process p in a) { 
        Debug.Print(p.ProcessName); 
    } 
} 


private static ArrayList getFileProcesses(string strFile) 
{ 
    myProcessArray.Clear(); 
    Process[] processes = Process.GetProcesses; 
    int i = 0; 
    for (i = 0; i <= processes.GetUpperBound(0) - 1; i++) { 
        myProcess = processes(i); 
        if (!myProcess.HasExited) { 
            try { 
                ProcessModuleCollection modules = myProcess.Modules; 
                int j = 0; 
                for (j = 0; j <= modules.Count - 1; j++) { 
                    if ((modules.Item(j).FileName.ToLower.CompareTo(strFile.ToLower) == 0)) { 
                        myProcessArray.Add(myProcess); 
                        break; // TODO: might not be correct. Was : Exit For 
                    } 
                } 
            } 
            catch (Exception exception) { 
            } 
            //MsgBox(("Error : " & exception.Message)) 
        } 
    } 
    return myProcessArray; 
} 
} 

VB.Net:

Imports System.Management
Imports System.IO

Module Module1
Friend myProcessArray As New ArrayList
Private myProcess As Process

Sub Main()

    Dim strFile As String = "c:\windows\system32\msi.dll"
    Dim a As ArrayList = getFileProcesses(strFile)
    For Each p As Process In a
        Debug.Print(p.ProcessName)
    Next
End Sub


Private Function getFileProcesses(ByVal strFile As String) As ArrayList
    myProcessArray.Clear()
    Dim processes As Process() = Process.GetProcesses
    Dim i As Integer
    For i = 0 To processes.GetUpperBound(0) - 1
        myProcess = processes(i)
        If Not myProcess.HasExited Then
            Try
                Dim modules As ProcessModuleCollection = myProcess.Modules
                Dim j As Integer
                For j = 0 To modules.Count - 1
                    If (modules.Item(j).FileName.ToLower.CompareTo(strFile.ToLower) = 0) Then
                        myProcessArray.Add(myProcess)
                        Exit For
                    End If
                Next j
            Catch exception As Exception
                'MsgBox(("Error : " & exception.Message))
            End Try
        End If
    Next i
    Return myProcessArray
End Function
End Module

[Solved] file is used by another process in c sharp, .Net Core 2.1 was announced recently by Microsoft along with corresponding updates for ASP.Net Core Read more · Tech  How to Identify which Windows Process is Locking a File or Folder. While attempting to delete, move, or rename a file or folder you get a Windows warning message; the Operating System refuses to complete the operation. This article helps identifying the process that currently has a handle on the file or folder you are attempting a maintenance operation on.

How Do I Find Out What Process Has A File Or Folder Locked , If you cannot move, delete or rename a file because because the file is kept open by SYSTEM or some other process you don't know, this post  This could help you: Use PowerShell to find out which process locks a file. It parses the System.Diagnostics.ProcessModuleCollection Modules property of each process and it looks for the file path of the locked file:

How to unlock a file handle locked by SYSTEM or any process in , With this, you can search to find what process(es) have a file open, and you can has implicit file locking, but any unix based OS has shared access by default). Your question is "how to see which process is using a file" although that has nothing to do with a process having a file locked. Processes use all kinds of files including other assemblies like .Dlls that can be shared by many processes and are not locked.

How do you find what process is holding a file open in Windows , Closing the right process will solve this problem. optionally, you can also release the file by closing the handle from OpenedFilesView utility. However, be aware  Next it calls RmGetList method to see how many processes have locks on the file. It calls RmGetList again to get information on the processes. Then code then loops through the results and uses the returned process IDs to get Process objects representing the objects that have the file locked.

Comments
  • Related - stackoverflow.com/questions/3526802/…
  • but handle.exe can't be distributed with your software
  • Good point. This wasn't a problem with the deployment script (used internally), but would be in other scenarios.
  • any full source code sample in C#? valid too for get process is locking a FOLDER ?
  • Check out my answer for a solution that does not require handle.exe stackoverflow.com/a/20623311/141172
  • "You must have administrative privilege to run Handle."
  • Has anyone tried that, it looks that it could really work (for windows above Vista and srv 2008)
  • @Blagoh: I do not believe the Restart Manager is available on Windows XP. You would need to resort to one of the other, less accurate methods posted here.
  • @Blagoh: If you just want to know who is locking a specific DLL, you can use tasklist /m YourDllName.dll and parse the output. See stackoverflow.com/questions/152506/…
  • Only solution that doesn't require 3rd party tools or undocumented API calls. Should well be the accepted answer.
  • I've tried this out (and it works) on Windows 2008R2, Windows 2012R2, Windows 7 and Windows 10. I found that it had to be run with elevated privileges in a lot of circumstances otherwise it fails when trying to get the list of processes locking a file.