Deleting unknown user from ACL

Warning: I thought I'd asked this already...

After transferring some HPFS USB drives from my old PC to the new PC, I've ended up with an unknown user in many of my files. It will be OldPC/Steve, but it manifests itself as S-1-5-21-713417444-3787200217-3968111754-1006 as demonstrated by cacls:

E:\>cacls tracefinal.txt /s
E:\tracefinal.txt "DA;;FA;;;BA)(A;;FA;;;SY)(A;;FA;;;S-1-5-21-713417444-3787200217-3968111754-1006)(A;;0x1200a9;;;BU)"

I can write a script to display the SDDL string for all my files, and to replace the SDDL string with the unknown user excluded, and leave it running for a few weeks (there are millions of files) but is there a better approach?

Use the option "Replace all child object permissions with inheritable permissions from this object" when changing the permissions on the root folder.

logicearth said:

Use the option "Replace all child object permissions with inheritable permissions from this object" when changing the permissions on the root folder.

The particular file that I was referring to does not inherit its' permissions from its' parent folder (the reasons for this are lost in time).

I suspect this will be the case for all such files that I find, as I've used the suggested options when tidying up directories across the four affected USB files.

That is what the option is for, it replaces the current permissions of the child regardless if it inherits from the parent with inheritable permissions from the parent. It is the option you want to use.