How Exactly Does SFC Fix Corrupt System File?

Question

According to some texts I have read, the System File Checker (
SFC
) is a command-line tool that is used to find corrupt system files, and replace them with healthy copies. |1| These copies would come from what is called Windows component store. In the
SFC
description on Microsoft it is said that the source is the %systemroot%\system32\dllcache folder, but it seems that this folder is not used anymore, and it doesn’t even appear in my system. |1||2|[|3|

Component store is where all system files are located, which is currently in the %windir%/WinSxS. The system files elsewhere are just hard links to the files in the component store. This implies that if we change access a system file using a path outside of WinSxS, the modification would also be present if we access the file from withing WinSxS.|4|

Considering that when
SFC
finds a corrupt file, it means that its counterpart in WinSxS is also corrupt, where the
SFC
tool actually find the file it use to replace the defective file detected?

------------------

Answer 1

C:\Windows\WinSxS\Backup

files here are independant from hard links

Answer 2

Hello,
There are multiple ways the files are replaced.
The files are checked to ensure the correct file is in place.
If not it is checked against the WinSxS folder \Windows\WinSxS or \Windwos\WinSxS\backup
The files in winSxS are the hardlinked to the the Windows Folder such as \Windows or \Windows\System32 to name a couple.
the hardlinks can be broken, files can be replaced. So the WinSxS store is checked first.
if that fails, then the system looks to the Internet where there is a file store on the Microsoft site
files are pulled down from that Store and used to replace the files and generate the hard links again.
Managing the Windows Component Store

Answer 3

Hello,

Thank you for reaching out.

The SFC process is well explained in below Microsoft article which includes to run DISM first to get files from winsxs.

https://support.microsoft.com/en-us/topic/use-the-system-file-checker-tool-to-repair-missing-or-corrupted-system-files-79aa86cb-ca52-166a-92a3-966e85d4094e#:~:text=The%20sfc%20%2Fscannow%20command%20will,the%20Windows%20operating%20system%20folder.

Hope this helps.

Thank you,

Answer 4

One of these links may be useful:

https://support.microsoft.com/en-us/topic/use-the-system-file-checker-tool-to-repair-missing-or-corrupted-system-files-79aa86cb-ca52-166a-92a3-966e85d4094e
https://support.microsoft.com/en-us/windows/using-system-file-checker-in-windows-365e0031-36b1-6031-f804-8fd86e0ef4ca
https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/manage-the-component-store
https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/determine-the-actual-size-of-the-winsxs-folder
https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/clean-up-the-winsxs-folder
https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/reduce-the-size-of-the-component-store-in-an-offline-windows-image
https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/sfc
https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/repair-a-windows-image
https://learn.microsoft.com/en-us/troubleshoot/windows-server/deployment/fix-windows-update-errors
https://www.tenforums.com/tutorials/7808-use-dism-repair-windows-10-image.html
https://www.tenforums.com/tutorials/2895-run-sfc-command-windows-10-a.html

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