How to detect if machine is joined to domain?

Don't fool with pinvoke if you don't have to.

Reference System.DirectoryServices, then call:

System.DirectoryServices.ActiveDirectory.Domain.GetComputerDomain()

Throws an ActiveDirectoryObjectNotFoundException if the machine is not domain-joined. The Domain object that's returned contains the Name property you're looking for.

You can PInvoke to Win32 API's such as NetGetDcName which will return a null/empty string for a non domain-joined machine.

Even better is NetGetJoinInformation which will tell you explicitly if a machine is unjoined, in a workgroup or in a domain.

Using NetGetJoinInformation I put together this, which worked for me:

public class Test
{
    public static bool IsInDomain()
    {
        Win32.NetJoinStatus status = Win32.NetJoinStatus.NetSetupUnknownStatus;
        IntPtr pDomain = IntPtr.Zero;
        int result = Win32.NetGetJoinInformation(null, out pDomain, out status);
        if (pDomain != IntPtr.Zero)
        {
            Win32.NetApiBufferFree(pDomain);
        }
        if (result == Win32.ErrorSuccess)
        {
            return status == Win32.NetJoinStatus.NetSetupDomainName;
        }
        else
        {
            throw new Exception("Domain Info Get Failed", new Win32Exception());
        }
    }
}

internal class Win32
{
    public const int ErrorSuccess = 0;

    [DllImport("Netapi32.dll", CharSet=CharSet.Unicode, SetLastError=true)]
    public static extern int NetGetJoinInformation(string server, out IntPtr domain, out NetJoinStatus status);

    [DllImport("Netapi32.dll")]
    public static extern int NetApiBufferFree(IntPtr Buffer);

    public enum NetJoinStatus
    {
        NetSetupUnknownStatus = 0,
        NetSetupUnjoined,
        NetSetupWorkgroupName,
        NetSetupDomainName
    }

}

ManagementObject cs;
        using(cs = new ManagementObject("Win32_ComputerSystem.Name='" + System.Environment.MachineName + "'" ))
        {
            cs.Get();
            Console.WriteLine("{0}",cs["domain"].ToString());
        }

That should allow you to get the domain. I believe it will be null or empty if you are part of a workgroup and not a domain.

Make sure to reference System.Management

The Environment variables could work for you.

Environment.UserDomainName

MSDN Link for some more details.

Environment.GetEnvironmentVariable("USERDNSDOMAIN")

I'm not sure this environment variable exists without being in a domain.

Correct me if I'm wrong Windows Admin geeks -- I believe a computer can be in several domains so it may be more important to know what domain, if any, you are in instead of it being in any domain.

The proposed solution above returns false on a domain machine if a local user is logged in.

The most reliable method i have found is via WMI:

http://msdn.microsoft.com/en-us/library/aa394102(v=vs.85).aspx (see domainrole)