Set-ItemProperty creates a duplicate registry key

Question

I am trying to activate Long path names in Windows 10 1903.

When I run as administrator in Windows PowerShell :

Set-ItemProperty -path 'HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem' -Name 'LongPathsEnabled' -value '1'

I see that a new registry key has been created, instead of overwriting existing one.

Thanks for your help.

Answer 1

• There is no reason to assume a bug here - your command should work as intended, but it does the wrong thing (see below).

• The symptom you show - duplicate value names in a registry key - are inconsistent with the command in your question.

  • The underlying native registry APIs do not allow creating values with duplicate names in a given registry key; if they did - which would be a serious bug - the problem would lie there, not in PowerShell.

  • If the registry editor really shows two values whose names appear to be identical, the only plausible explanation is that they contain invisible characters that makes them different.

---

As for what you tried:

The system-known LongPathsEnabled registry value of key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem is a 64-bit integer, of registry type REG_DWORD, equivalent to a [uint32] instance in .NET / PowerShell.

By using -Value '1' in your Set-ItemProperty call, you're letting it infer what registry type to write the value as, and that is REG_SZ, i.e. a literal string:

• However, if the target value already exists, and is of - the correct - type REG_DWORD, PowerShell will convert the string for you.

• By contrast, if no such value exists yet, you'll - incorrectly - create a REG_SZ value.

---

Your own answer now uses -Value 1, which makes the 1 implicitly an [int] (System.Int32), in which case PowerShell correctly infers REG_DWORD.

However - both for readability and robustness - consider using the -Type parameter to explicitly indicate the type of registry value you're planning to create (command spread across multiple lines for readability - note the ` chars. at the end of the interior lines, which must be the very last char. on their respective lines):

Set-ItemProperty 'HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem' `
  -Name 'LongPathsEnabled' `
  -Value 1 `
  -Type DWord

The -Type argument is of type Microsoft.Win32.RegistryValueKind, which, when you create or set a value, must be one of the following values (shown here mapped to their REG_* values):

String        # REG_SZ
ExpandString  # REG_EXPAND_SZ
Binary        # REG_BINARY
DWord         # REG_DWORD
MultiString   # REG_MULTI_SZ
QWord         # REG_QWORD

The full list of native REG_* types can be found here.