What is the reason for different value after reg add from within a C# application and query the value from within a cmd window?

Question

I have a program coded in C# that opens a cmd console and adds/modifies a registry value.

After the console outputs that the task completed, I test with reg query if the registry value really changed. There is no problem. I get value 0x1 as expected by me.

But when I query this registry from outside the current cmd window like another cmd executed by me as admin, the value is 0x0 on reg query .

How is this possible?

Here is my C# code:

string command = @"/K reg add HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock /t REG_DWORD /f /v AllowDevelopmentWithoutDevLicense /d 1";

        Process proc = Process.Start("cmd.exe", command);

Query from inside the executed cmd by the program:

reg query HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock
    AllowDevelopmentWithoutDevLicense    REG_DWORD    0x1

From outside:

reg query HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock
    AllowDevelopmentWithoutDevLicense    REG_DWORD    0x0
    AllowAllTrustedApps    REG_DWORD    0x0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock\AllowDevelopmentWithoutDevLicense
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock\AllowDevelopmentWithoutDevLicense=1

Answer 1

When a 32-bit application on a 64-bit Windows accesses the registry key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

it is redirected by Windows registry redirector to

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\AppModelUnlock

whereby a 64-bit application really accesses

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

The difference between the two registry paths is Wow6432Node visible by default only for 64-bit applications on Windows x64.

See the Microsoft developer article Registry Keys Affected by WOW64 .

And for completeness see also:

• File System Redirector
• WOW64 Implementation Details

There are 32-bit cmd.exe and reg.exe on 64-bit Windows in directory %SystemRoot%\\SysWow64 being %SystemRoot%\\System32 for 32-bit applications and 64-bit cmd.exe and reg.exe in %SystemRoot%\\System32 .

Your C# application is most likely compiled as 32-bit application and therefore calls 32-bit cmd.exe which calls 32-bit reg.exe .

You could workaround this from within the 32-bit application by calling explicitly %SystemRoot%\\Sysnative\\cmd.exe .

But be aware of the fact that %SystemRoot%\\Sysnative does not exist on 32-bit Windows and also does not exist for 64-bit applications on 64-bit Windows. ( Sysnative is a special alias, not a hard link, junction or a real folder.)

Therefore your 32-bit C# application needs first to check if %SystemRoot%\\Sysnative\\cmd.exe exists and use this path to edit the 64-bit registry value using 64-bit cmd and reg . But on 32-bit Windows %SystemRoot%\\System32.exe\\cmd.exe must be called by the 32-bit C# application. By the way: %SystemRoot% references the value of environment variable SystemRoot .

See also the answers on:

• Why can a double clicked batch file not find a registry value for deletion?
• Changing value of registry key with getRuntime().exec(cmd) does not change registry value even the operation ended successfully (Java, but same issue)

NOTE 1:

Running cmd.exe is not needed at all. It is possible to run directly on 32-bit Windows

%SystemRoot%\System32\reg.exe

or on 64-bit Windows

%SystemRoot%\Sysnative\reg.exe

from a 32-bit application.

NOTE 2:

And last but not least a C# application does not need to use reg.exe at all as .NET Framework has built-in support for accessing Windows registry - the Registry.SetValue Method . Microsoft even added some examples in an example code block.

KEY_WOW64_64KEY can be used in a 32-bit application to explicitly access always the 64-bit registry key as explained on Microsoft documentation page Accessing an Alternate Registry View .