After reinstalling Windows, the advanced security settings for other hard drives in the system have retained previous installation settings, e.g. the owner is an unknown SID and so on.

I would like to restore these permissions to match the actual installation.

After some search, it appears that the following command may be appropriate:

icacls "full path to the folder" /reset /t /c /l


Is this the right way for restoring default permissions on a hard drive?

  • The command won't harm anything but you need to instead take ownership of the files. This requires you to be an Administrator on the system.
    – Ramhound
    Dec 6, 2021 at 18:51
  • Alright, who shall I set the owner as ? Me, SYSTEM, TrustedInstaller like in C: etc.
    – aybe
    Dec 6, 2021 at 18:54
  • I assume your talking about a system disk from another machine? If that is the case simply taking ownership of an Administrator that currently exists should be enough. You can also assign the owner to the machine's Administrators user group.
    – Ramhound
    Dec 6, 2021 at 18:56
  • No, it isn't the system hard drive, it's another drive with documents, etc.
    – aybe
    Dec 6, 2021 at 19:03
  • External dives by default should allow read & write permissions from everyone. The only way this is NOT the case, is if the drive is a system drive (i.e. Windows was installed to it) or the permissions were modified manually. Is the existence of an unknown user SID a simply annoyance or is it preventing you from altering files contained on the drive.
    – Ramhound
    Dec 6, 2021 at 19:09

1 Answer 1


After thoroughly looking at the problem, here's my own answer to the question of whether non-system, non-external drives permissions should be reset to match the newly installed operating system (same version).

This is what an internal drive's security permissions are after:

  • deleting the partitions
  • creating one partition and format it in Explorer




Principal Access
Adminsitrators (Computer name\Administrators) Full control
Authenticated Users Modify
SYSTEM Full control
Users (Computer name\Users) Read & execute

Permissions properties (all of them):

Property Value
Type Allow
Inherited from None
Applies to This folder, subfolders and files

Basically, if the permissions do match, there's absolutely nothing to do because these are well-known SIDs, i.e. they point exactly to the same principal even though the computer operating system has been reinstalled.

But as @Ramhound pointed out, you may eventually have to take ownership for the drive:

enter image description here

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