System File Checker: Difference between revisions

Revision as of 01:30, 3 July 2022

Latest revision as of 20:03, 26 January 2025

(11 intermediate revisions by 11 users not shown)

Line 1:

{{Short description|Windows system file utility}}

{{Infobox software

| name = SFCsfc

| logo =

| screenshot =

| screenshot size =

| caption =

| developer = [[Microsoft]]

| released = {{Start date and age|1998|06|25}}

| latest release version =

| latest release date =

| operating system = [[Microsoft Windows]]

| genre = [[System software|System utility]]

| license = [[Proprietary software|Proprietary]] [[commercial software]]

| website = {{URL|https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/sfc}}

}}

'''System File Checker''' ('''SFC'''<ref>

{{cite book

| last1 = Boswell

Line 35:

Microsoft ships this utility with [[Windows 98]], [[Windows 2000]] and all subsequent versions of the [[Windows NT]] family of operating systems. In [[Windows Vista]], [[Windows 7]] and [[Windows 10]], System File Checker is integrated with [[Windows Resource Protection]] (WRP), which protects [[Windows Registry|registry]] keys and folders as well as critical system files. Under Windows Vista, <code>sfc.exe</code> can be used to check specific folder paths, including the Windows folder and the boot folder.

[[Windows File Protection]] (WFP) works by registering for notification of file changes in [[Winlogon]]. If any changes are detected to a protected system file, the modified file is restored from a cached copy located in a compressed folder at <code>%WinDir%\System32\dllcache</code>.

[[Windows Resource Protection]] (WRP) works by setting discretionary access-control lists (DACLs) and [[access control list]]s (ACLs) defined for protected resources. If any changes are detected to a protected system file, the modified file is restored from a cached copy located in a folder at <code>%WinDir%\WinSxS\Backup</code>.<ref name=":0">{{Cite web |last=stevewhims |date=2021-01-07 |title=Protected Resource List - Win32 apps |url=https://learn.microsoft.com/en-us/windows/win32/wfp/protected-file-list |access-date=2024-03-15 |website=learn.microsoft.com |language=en-us}}</ref> Permission for full access to modify WRP-protected resources is restricted to the processes using the ''Windows Modules Installer service'' (<code>TrustedInstaller.exe</code>). Administrators no longer have full rights to system files.

==History==

Due to problems with Windows applications being able to overwrite system files in [[Windows 95]], Microsoft has since implemented a number of security measures to protect system files from malicious attacks, corruptions, or problems such as [[DLL hell|DLL Hell]].

System File Checker was first introduced on [[Windows 98]] as a GUI utility. It offered scanning and restoration of corrupted system files by matching the version number against a database containing the original version number of the files in a fresh Windows 98 installation. This method of file protection was basic. It determined system files by [[file extension]] and [[file path]]. It was able to restore files from the installation media or a source specified by the user. Windows 98 did not offer real-time system file protection beyond [[file attribute]]s; therefore, no preventive or reactive measure was available.

All Windows NT-based operating systems since [[Windows 2000]] introduced real-time file protection, called [[Windows File Protection]] (WFP).<ref>{{cite web

|publisher=[[Microsoft]]

|date=December 15, 2003

Line 55 ⟶ 57:

In addition, the System File Checker utility (<code>sfc.exe</code>) was reimplemented as a more robust command-line utility that integrated with WFP. Unlike the Windows 98 SFC utility, the new utility forces a scan of protected system files using Windows File Protection and allows the immediate silent restoration of system files from the ''DLLCache'' folder or installation media.

SFC did not appear on [[Windows MEMe]],<ref>{{cite web

|first=Lincoln

|last=Spector

Line 92 ⟶ 94:

==Usage==

In Windows NT-based operating systems, System File Checker can be invoked via [[cmd.exe|Windows Command Prompt]] (with Admin privilege<ref>{{cite web | title=SFC - System File CheckerWindows CMD | website=SS64.com | url=https://ss64.com/nt/sfc.html | access-date=2023-09-12}}</ref>), with the following command:

* {{code|sfc /scannow}} (to repair problems)

<syntaxhighlight lang="dos">

* or {{code|sfc /scannow verifyonly}} (tono repair problems)

</syntaxhighlight>

or

<syntaxhighlight lang="dos">

sfc /verifyonly (no repair)

</syntaxhighlight>

If it finds a problem, it will attempt to replace the problematic files from the ''DLL Cache'' (<code>%WinDir%\System32\Dllcache\dllcache</code>). If the file is not in the DLL Cache or the DLL Cache is corrupted, the user will be prompted to insert the Windows installation media or provide the network installation path. System File Checker determines the Windows installation source path from the registry values <code>SourcePath</code> and <code>ServicePackSourcePath</code>.<ref>{{cite web|url=http://support.microsoft.com/kb/885522|title=System File Checker does not accept a network ___location that contains the installer CD when you use the scannow switch in Windows XP SP2 or in Windows Server 2003|date=January 13, 2005|work=Support|publisher=[[Microsoft]]|url-status=dead|archive-url=https://web.archive.org/web/20070116014009/http://support.microsoft.com/kb/885522/|archive-date=January 16, 2007}}</ref> It may keep prompting for the installation media even if the user supplies it if these values are not correctly set.<ref>{{cite web|url=http://support.microsoft.com/kb/900910|title=You are prompted to insert a Windows XP SP2 CD when you try to run the System File Checker tool on a Windows XP SP2-based computer|date=July 5, 2005|work=Support|publisher=[[Microsoft]]|url-status=live|archive-url=https://web.archive.org/web/20070207090302/http://support.microsoft.com/kb/900910|archive-date=February 7, 2007}}</ref>

In Windows Vista and onwards, files are protected using [[Accessaccess control list]]s (ACLs), howeverand if it finds a problem, it will attempt to replace the problematic files from the Windows Side-by-side Backup (<code>%WinDir%\WinSxS\Backup</code>).<ref name=":0" /> However, the above command has not changed.

System File Checker in Windows Vista and later Windows operating systems can scan specified files. Also, scans can be performed against an offline Windows installation folder to replace corrupt files, in case the Windows installation is not bootable. For performing offline scans, System File Checker must be run from another working installation of Windows Vista or a later operating system or from the Windows setup DVD<ref>{{Cite web|url=http://www.craxworld.com/system-file-checker-tool-windows-11822/|title=Run System File Checker Tool to Repair Windows 10/8/7 files|last=kumar|first=Rohit|date=26 July 2016|website=Craxworld|publisher=Self Published|url-status=dead|archive-url=https://web.archive.org/web/20160911000021/http://www.craxworld.com/system-file-checker-tool-windows-11822/|archive-date=September 11, 2016}}</ref> or a recovery drive which gives access to the [[Windows Recovery Environment]].