Logoff interactive users in Windows from a service

Question

I'm trying to figure out a way to log off users in local Windows sessions from a Windows Service written in C#.

Here's the background to the problem: I need to manage the computer usage time of a set of users; when their allotted time expires I want to log them off. This is in the context of a W2K8 domain. Unfortunately the login time controls in Windows simply disconnect the user from server resources; there is no way to force their sessions to terminate via this method.

My approach is to build a Windows Service that I will deploy across the domain; the service will run on every client computer. At regular intervals the service will enumerate logged-in users on the computer, call out to a database to add the logged-in time since the last call to the total for the day, and if they have reached their maximum, log them out (with a five minute warning). Note - these are NOT terminal services sessions, they are regular local interactive logons. Note also that there may be multiple logons on a machine due to the "switch user" functionality in Win7 & Vista. All my client PCs will be running Win7. The Windows Service will be running as Local System so privileges should not be a problem.

I can successfully construct a list of logged-in users on the machine by user name using WMI. Here's a snippet of that code:

---

        List<string> loggedInUsers = new List<string>();
        ManagementClass mc = new ManagementClass("Win32_Process");
        ManagementObjectCollection moc = mc.GetInstances();

        foreach (ManagementObject mo in moc)
        {
            ROOT.CIMV2.Process process = new ROOT.CIMV2.Process(mo);
            string domain, user;
            uint pid;
            process.GetOwner(out domain, out user);
            pid = process.ProcessId;
            if (process.Name.Trim().ToLower() == "explorer.exe")
                loggedInUsers.Add(user);
        }
        return loggedInUsers;

---

However, I am struggling to find a method that will allow me to log off a selected user's session. I know I can shut down the machine, but I don't want that - that will kill all users' sessions.

Any ideas anyone? Thanks for reading this lengthy post!

Snowden

Sounds like you might need to get ahold of, and kill, each user's window station: msdn.microsoft.com/en-us/library/ms681928(v=VS.85).aspx -- and you might have to do that via Win32 calls. Which you can do from .NET, though it's a hassle. – Partisan

You can use WMI to log off the active console session (via Win32Shutdown) but I don't think it works with multiple users. – Fulmar

@Ed - thanks for that suggestion, I learnt about Window Stations from following up on that. From what I can see though (and I could be wrong) it looks like it will only work if executed within the user's session. I don't think I can kill their window station from another session. – Snowden

@Fulmar - thank you for your suggestion. If all else fails I can fall back to that approach, and just deal with the disconnected sessions if/when they become active again. – Snowden

Answer 1

You could use following P/Invoke calls to achieve this. Below sample works only with Admin Rights

        [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern bool WTSLogoffSession(IntPtr hServer, int SessionId, bool bWait);

    [DllImport("Wtsapi32.dll")]
    static extern bool WTSQuerySessionInformation(
        System.IntPtr hServer, int sessionId, WTS_INFO_CLASS wtsInfoClass, out System.IntPtr ppBuffer, out uint pBytesReturned);

    [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern IntPtr WTSOpenServer([MarshalAs(UnmanagedType.LPStr)] String pServerName);

    [DllImport("wtsapi32.dll")]
    static extern void WTSCloseServer(IntPtr hServer);

    [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern Int32 WTSEnumerateSessions(IntPtr hServer, [MarshalAs(UnmanagedType.U4)] Int32 Reserved, [MarshalAs(UnmanagedType.U4)] Int32 Version, ref IntPtr ppSessionInfo, [MarshalAs(UnmanagedType.U4)] ref Int32 pCount);

    [DllImport("wtsapi32.dll")]
    static extern void WTSFreeMemory(IntPtr pMemory);

Here is a sample implementation to lookup all the users and their sessions, and then logging off one of the user.

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

namespace ConsoleApplication1
{
 [StructLayout(LayoutKind.Sequential)]
internal struct WTS_SESSION_INFO
{
    public Int32 SessionID;
    [MarshalAs(UnmanagedType.LPStr)]
    public String pWinStationName;
    public WTS_CONNECTSTATE_CLASS State;
}

internal enum WTS_CONNECTSTATE_CLASS
{
    WTSActive,
    WTSConnected,
    WTSConnectQuery,
    WTSShadow,
    WTSDisconnected,
    WTSIdle,
    WTSListen,
    WTSReset,
    WTSDown,
    WTSInit
}

internal enum WTS_INFO_CLASS
{
    WTSInitialProgram,
    WTSApplicationName,
    WTSWorkingDirectory,
    WTSOEMId,
    WTSSessionId,
    WTSUserName,
    WTSWinStationName,
    WTSDomainName,
    WTSConnectState,
    WTSClientBuildNumber,
    WTSClientName,
    WTSClientDirectory,
    WTSClientProductId,
    WTSClientHardwareId,
    WTSClientAddress,
    WTSClientDisplay,
    WTSClientProtocolType,
    WTSIdleTime,
    WTSLogonTime,
    WTSIncomingBytes,
    WTSOutgoingBytes,
    WTSIncomingFrames,
    WTSOutgoingFrames,
    WTSClientInfo,
    WTSSessionInfo
}

class Program
{
    [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern bool WTSLogoffSession(IntPtr hServer, int SessionId, bool bWait);

    [DllImport("Wtsapi32.dll")]
    static extern bool WTSQuerySessionInformation(
        System.IntPtr hServer, int sessionId, WTS_INFO_CLASS wtsInfoClass, out System.IntPtr ppBuffer, out uint pBytesReturned);

    [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern IntPtr WTSOpenServer([MarshalAs(UnmanagedType.LPStr)] String pServerName);

    [DllImport("wtsapi32.dll")]
    static extern void WTSCloseServer(IntPtr hServer);

    [DllImport("wtsapi32.dll", SetLastError = true)]
    static extern Int32 WTSEnumerateSessions(IntPtr hServer, [MarshalAs(UnmanagedType.U4)] Int32 Reserved, [MarshalAs(UnmanagedType.U4)] Int32 Version, ref IntPtr ppSessionInfo, [MarshalAs(UnmanagedType.U4)] ref Int32 pCount);

    [DllImport("wtsapi32.dll")]
    static extern void WTSFreeMemory(IntPtr pMemory);

    internal static List<int> GetSessionIDs(IntPtr server)
    {
        List<int> sessionIds = new List<int>();
        IntPtr buffer = IntPtr.Zero;
        int count = 0;
        int retval = WTSEnumerateSessions(server, 0, 1, ref buffer, ref count);
        int dataSize = Marshal.SizeOf(typeof(WTS_SESSION_INFO));
        Int64 current = (int)buffer;

        if (retval != 0)
        {
            for (int i = 0; i < count; i++)
            {
                WTS_SESSION_INFO si = (WTS_SESSION_INFO)Marshal.PtrToStructure((IntPtr)current, typeof(WTS_SESSION_INFO));
                current += dataSize;
                sessionIds.Add(si.SessionID);
            }
            WTSFreeMemory(buffer);
        }
        return sessionIds;
    }

    internal static bool LogOffUser(string userName, IntPtr server)
    {

        userName = userName.Trim().ToUpper();
        List<int> sessions = GetSessionIDs(server);
        Dictionary<string, int> userSessionDictionary = GetUserSessionDictionary(server, sessions);
        if (userSessionDictionary.ContainsKey(userName))
            return WTSLogoffSession(server, userSessionDictionary[userName], true);
        else
            return false;
    }

    private static Dictionary<string, int> GetUserSessionDictionary(IntPtr server, List<int> sessions)
    {
        Dictionary<string, int> userSession = new Dictionary<string, int>();

        foreach (var sessionId in sessions)
        {
            string uName = GetUserName(sessionId, server);
            if (!string.IsNullOrWhiteSpace(uName))
                userSession.Add(uName, sessionId);
        }
        return userSession;
    }

    internal static string GetUserName(int sessionId, IntPtr server)
    {
        IntPtr buffer = IntPtr.Zero;
        uint count = 0;
        string userName = string.Empty;
        try
        {
            WTSQuerySessionInformation(server, sessionId, WTS_INFO_CLASS.WTSUserName, out buffer, out count);
            userName = Marshal.PtrToStringAnsi(buffer).ToUpper().Trim();
        }
        finally
        {
            WTSFreeMemory(buffer);
        }
        return userName;
    }

    static void Main(string[] args)
    {
        string input = string.Empty;
        Console.Write("Enter ServerName<Enter 0 to default to local>:");
        input = Console.ReadLine();
        IntPtr server = WTSOpenServer(input.Trim()[0] == '0' ? Environment.MachineName : input.Trim());
        try
        {
            do
            {
                Console.WriteLine("Please Enter L => list sessions, G => Logoff a user, END => exit.");
                input = Console.ReadLine();
                if (string.IsNullOrWhiteSpace(input))
                    continue;
                else if (input.ToUpper().Trim()[0] == 'L')
                {
                    Dictionary<string, int> userSessionDict = GetUserSessionDictionary(server, GetSessionIDs(server));
                    foreach (var userSession in userSessionDict)
                    {
                        Console.WriteLine(string.Format("{0} is logged in {1} session", userSession.Key, userSession.Value));
                    }
                }
                else if (input.ToUpper().Trim()[0] == 'G')
                {
                    Console.Write("Enter UserName:");
                    input = Console.ReadLine();
                    LogOffUser(input, server);
                }

            } while (input.ToUpper() != "END");
        }
        finally
        {
            WTSCloseServer(server);
        }
    }
}
}

Tompion

thank you for your very comprehensive reply. This looks promising. I will give it a shot and see what happens. – Snowden

@multiSingularity, did this technique work? If not either comment your issue or edit question so that anyone can take a look at it and solve. – Tompion

sorry for the long delay getting back to you... this is a personal project and work has been ridiculously busy... haven't had a chance to get back to this till now! Your solution worked perfectly - thank you so much. – Snowden

Hi all, Logoff function is not working in win10 and win 7. Any help – Undertook