I tried to find some mechanism to get the current machine’s NetBIOS domain name (the machine domain, not user domain), but couldn’t find anything in the usual places (e.g. System.Environment). If you want the fancy-schmancy Active Directory DNS domain then you can use Domain.GetComputerDomain().Name from System.DirectoryServices.ActiveDirectory, or another one that I stumbled across in Reflector was IPGlobalProperties.GetIPGlobalProperties().DomainName that lives in System.Net.NetworkInformation. But a simple way of getting the old-skool NetBIOS/LanManager-style machine domain name proved elusive.

Some googling suggested that WMI would provide the answer but I find WMI a little heavyweight, and not always reliable. The information is also probably in the registry somewhere, although I couldn’t find it after a cursory scan. The proper, supported way it would appear is to use the Network Management API. So my solution entailed P/Invoking to netapi32.dll.

If you’re after the same information I hope you find the code below useful. Once you’ve incorporated this in your project, just call the GetMachineNetBiosDomain method. It will return the machine’s Workgroup name if the machine is not domain-joined.

UPDATE: Now works on 64-bit thanks to update sent by Rp Brongers.

using System;
using System.Runtime.InteropServices;
using System.ComponentModel;

class NetUtil
{
    [DllImport("netapi32.dll", CharSet = CharSet.Auto)]
    static extern int NetWkstaGetInfo(string server,
        int level,
        out IntPtr info);

    [DllImport("netapi32.dll")]
    static extern int NetApiBufferFree(IntPtr pBuf);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    class WKSTA_INFO_100
    {
        public int wki100_platform_id;
        [MarshalAs(UnmanagedType.LPWStr)]
        public string wki100_computername;
        [MarshalAs(UnmanagedType.LPWStr)]
        public string wki100_langroup;
        public int wki100_ver_major;
        public int wki100_ver_minor;
    }

    public static string GetMachineNetBiosDomain()
    {
        IntPtr pBuffer = IntPtr.Zero;

        WKSTA_INFO_100 info;
        int retval = NetWkstaGetInfo(null, 100, out pBuffer);
        if (retval != 0)
            throw new Win32Exception(retval);

        info = (WKSTA_INFO_100)Marshal.PtrToStructure(pBuffer, typeof(WKSTA_INFO_100));
        string domainName = info.wki100_langroup;
        NetApiBufferFree(pBuffer);
        return domainName;
    }
}

At home, our PC running Vista is rarely rebooted and is either in a low power state sleeping or being used by either me or my wife. One thing we’ve taken great advantage since the XP days is Fast User Switching which allows someone else to log in to their desktop whilst yours is kept running in the background. My wife and I had got quite used to doing a quick WinKey+L (as you do) before relinquishing control of the PC to one another. In Windows XP WinKey+L is does a “lock workstation” which in non-domain machines takes you back to the Windows logon screen. Unfortunately on Vista it takes you to a “workstation locked” screen, so you then have another mouse click on the Switch User button (followed by monitor re-syncing itself – why does it do this? All users run at the same screen resolution) to take you to the users screen. Of course there is a “Switch User” command tucked away in the little menu next to the lock button on the start menu – but a quick keystroke is what we’re after here.

So – I go off searching for a shortcut key that does a “switch user” rather than “lock workstation”. After a 20 minutes fruitless Googling for some special key combination, I sat back, thought about it logically and came up with this solution:

1. Create a shortcut on your desktop to TSDISCON (* see below) and call it something like “Switch User”
2. Go the shortcut Properties page and assign a shortcut key. Note that unfortunately you can’t use the Windows Key in your shortcut – so I went for CTRL + ALT + SHIFT + L
3. Right click Start button and choose “Open All Users” and move the shortcut into the Programs folder (confirming the UAC prompt as you go).
4. Log out, and back in again. This is necessary because Explorer hasn’t noticed there’s now a shortcut with a new shortcut key it should be taking notice of.

And that did it. CTRL + ALT + SHIFT + L isn’t quite a neat as WinKey+L but it’s a hell of a lot better than poking around in the Start Menu.

* What is TSDISCON you ask? It’s the Terminal Services Disconnect command. Fast User Switching is all made possible by the core Terminal Services technologies which introduced the concept of multiple Window Stations or “sessions” running concurrently on the one machine. It was of course originally designed to support multiple users connecting concurrently to these sessions over the network using the Remote Desktop Protocol (RDP), but Windows XP took advantage of the multi-session architecture to enable Fast User Switching. (The RDP stuff is still there but hobbled to only allow one user to connect at a a time.)

UPDATE: If you don’t have tsdiscon.exe on your system for some reason (maybe it’s only available in Business/Ultimate or something) then you can use the following C# code (compiled into a Windows EXE using C:WindowsMicrosoft.NETFrameworkv2.0.50727csc.exe if you don’t have Visual Studio) to do the same thing. Tsdiscon.exe is just a wrapper around WTSDisconnectSession. I used Dependency Walker (aka depends.exe) to find out what was being used:

UPDATE 2: For your convenience: I’ve compiled the below and packaged it into a ZIP along with the source for download here.

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();
  }
}