Detecting multiple logged on users via win32 - winapi

Question

Using the standard win32 api, what's the best way to detect more than one user is logged on? I have an upgrade to our software product that can't be run when more than one user is logged in. (I know this is something to be avoided because of its annoyance factor, but the product is very complicated. You'll have to trust me when I say there really is no other solution.) Thanks.

Answer 1

In order to have more than one user logged in at once, Terminal Services or Fast User Switching must be enabled. Since Fast User Switching is implemented using Terminal Services, you first need to find out if the OS has it enabled. You can use GetVersionEx with an OSVERSIONINFOEX. Check for the VER_SUITE_SINGLEUSERTS and VER_SUITE_TERMINAL flags.
If TS is enabled, you can use WTSEnumerateSessions to find out how many users are logged on. This only works if the "Terminal Services" service is started.
If the machine doesn't support Terminal Services (or if the service isn't started), then you can only have one user logged on.

Answer 2

Here's a solution that works on XP, Server 2003, Vista, and Server 2008. Note, this won't work on Windows 2000, because "LsaEnumerateLogonSessions" is not available on Windows 2000. This code is modified from a Delphi-PRAXIS post.
To compile this, create a new VCL application with a TButton and a TMemo on the form. Then copy and paste this code and it should compile. I tested on XP and Vista and it works well. It will return interactive and remote users.
unit main;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
const
WTS_CURRENT_SERVER_HANDLE = 0;
type
PTOKEN_USER = ^TOKEN_USER;
_TOKEN_USER = record
User: TSidAndAttributes;
end;
TOKEN_USER = _TOKEN_USER;
USHORT = word;
_LSA_UNICODE_STRING = record
Length: USHORT;
MaximumLength: USHORT;
Buffer: LPWSTR;
end;
LSA_UNICODE_STRING = _LSA_UNICODE_STRING;
PLuid = ^LUID;
_LUID = record
LowPart: DWORD;
HighPart: LongInt;
end;
LUID = _LUID;
_SECURITY_LOGON_TYPE = (
seltFiller0, seltFiller1,
Interactive,
Network,
Batch,
Service,
Proxy,
Unlock,
NetworkCleartext,
NewCredentials,
RemoteInteractive,
CachedInteractive,
CachedRemoteInteractive);
SECURITY_LOGON_TYPE = _SECURITY_LOGON_TYPE;
PSECURITY_LOGON_SESSION_DATA = ^SECURITY_LOGON_SESSION_DATA;
_SECURITY_LOGON_SESSION_DATA = record
Size: ULONG;
LogonId: LUID;
UserName: LSA_UNICODE_STRING;
LogonDomain: LSA_UNICODE_STRING;
AuthenticationPackage: LSA_UNICODE_STRING;
LogonType: SECURITY_LOGON_TYPE;
Session: ULONG;
Sid: PSID;
LogonTime: LARGE_INTEGER;
LogonServer: LSA_UNICODE_STRING;
DnsDomainName: LSA_UNICODE_STRING;
Upn: LSA_UNICODE_STRING;
end;
SECURITY_LOGON_SESSION_DATA = _SECURITY_LOGON_SESSION_DATA;
_WTS_INFO_CLASS = (
WTSInitialProgram,
WTSApplicationName,
WTSWorkingDirectory,
WTSOEMId,
WTSSessionId,
WTSUserName,
WTSWinStationName,
WTSDomainName,
WTSConnectState,
WTSClientBuildNumber,
WTSClientName,
WTSClientDirectory,
WTSClientProductId,
WTSClientHardwareId,
WTSClientAddress,
WTSClientDisplay,
WTSClientProtocolType);
WTS_INFO_CLASS = _WTS_INFO_CLASS;
_WTS_CONNECTSTATE_CLASS = (
WTSActive, // User logged on to WinStation
WTSConnected, // WinStation connected to client
WTSConnectQuery, // In the process of connecting to client
WTSShadow, // Shadowing another WinStation
WTSDisconnected, // WinStation logged on without client
WTSIdle, // Waiting for client to connect
WTSListen, // WinStation is listening for connection
WTSReset, // WinStation is being reset
WTSDown, // WinStation is down due to error
WTSInit); // WinStation in initialization
WTS_CONNECTSTATE_CLASS = _WTS_CONNECTSTATE_CLASS;
function LsaFreeReturnBuffer(Buffer: pointer): Integer; stdcall;
function WTSGetActiveConsoleSessionId: DWORD; external 'Kernel32.dll';
function LsaGetLogonSessionData(LogonId: PLUID;
var ppLogonSessionData: PSECURITY_LOGON_SESSION_DATA): LongInt; stdcall;
external 'Secur32.dll';
function LsaNtStatusToWinError(Status: cardinal): ULONG; stdcall;
external 'Advapi32.dll';
function LsaEnumerateLogonSessions(Count: PULONG; List: PLUID): LongInt;
stdcall; external 'Secur32.dll';
function WTSQuerySessionInformationA(hServer: THandle; SessionId: DWORD;
WTSInfoClass: WTS_INFO_CLASS; var pBuffer: Pointer;
var pBytesReturned: DWORD): BOOL; stdcall; external 'Wtsapi32.dll';
type
TForm1 = class(TForm)
Button1: TButton;
Memo1: TMemo;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
function LsaFreeReturnBuffer; external 'secur32.dll' name 'LsaFreeReturnBuffer';
procedure GetActiveUserNames(var slUserList : TStringList);
var
Count: cardinal;
List: PLUID;
sessionData: PSECURITY_LOGON_SESSION_DATA;
i1: integer;
SizeNeeded, SizeNeeded2: DWORD;
OwnerName, DomainName: PChar;
OwnerType: SID_NAME_USE;
pBuffer: Pointer;
pBytesreturned: DWord;
sUser : string;
begin
//result:= '';
//Listing LogOnSessions
i1:= lsaNtStatusToWinError(LsaEnumerateLogonSessions(#Count, #List));
try
if i1 = 0 then
begin
i1:= -1;
if Count > 0 then
begin
repeat
inc(i1);
LsaGetLogonSessionData(List, sessionData);
//Checks if it is an interactive session
sUser := sessionData.UserName.Buffer;
if (sessionData.LogonType = Interactive)
or (sessionData.LogonType = RemoteInteractive)
or (sessionData.LogonType = CachedInteractive)
or (sessionData.LogonType = CachedRemoteInteractive) then
begin
//
SizeNeeded := MAX_PATH;
SizeNeeded2:= MAX_PATH;
GetMem(OwnerName, MAX_PATH);
GetMem(DomainName, MAX_PATH);
try
if LookupAccountSID(nil, sessionData.SID, OwnerName,
SizeNeeded, DomainName,SizeNeeded2,
OwnerType) then
begin
if OwnerType = 1 then //This is a USER account SID (SidTypeUser=1)
begin
sUser := AnsiUpperCase(sessionData.LogonDomain.Buffer);
sUser := sUser + '\';
sUser := sUser + AnsiUpperCase(sessionData.UserName.Buffer);
slUserList.Add(sUser);
// if sessionData.Session = WTSGetActiveConsoleSessionId then
// begin
// //Wenn Benutzer aktiv
// try
// if WTSQuerySessionInformationA
// (WTS_CURRENT_SERVER_HANDLE,
// sessionData.Session, WTSConnectState,
// pBuffer,
// pBytesreturned) then
// begin
// if WTS_CONNECTSTATE_CLASS(pBuffer^) = WTSActive then
// begin
// //result:= sessionData.UserName.Buffer;
// slUserList.Add(sessionData.UserName.Buffer);
// end;
// end;
// finally
// LSAFreeReturnBuffer(pBuffer);
// end;
//end;
end;
end;
finally
FreeMem(OwnerName);
FreeMem(DomainName);
end;
end;
inc(List);
try
LSAFreeReturnBuffer(sessionData);
except
end;
until (i1 = Count-1);// or (result <> '');
end;
end;
finally
LSAFreeReturnBuffer(List);
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
slUsers : TStringList;
begin
slUsers := TStringList.Create;
slUsers.Duplicates := dupIgnore;
slUsers.Sorted := True;
try
GetActiveUserNames(slUsers);
Memo1.Lines.AddStrings(slUsers);
finally
FreeAndNil(slUsers)
end;
end;
end.

Answer 3

This might be a roundabout way, but run down the process list and see who the process owners are.