System File Checker (SFC) is a utility in
Microsoft Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...
that allows users to scan for and restore corrupted Windows system files.
Overview
Microsoft ships this utility with
Windows 98
Windows 98 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. It was the second operating system in the 9x line, as the successor to Windows 95. It was Software ...
,
Windows 2000
Windows 2000 is a major release of the Windows NT operating system developed by Microsoft, targeting the server and business markets. It is the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RT ...
and all subsequent versions of the
Windows NT
Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Original ...
family of operating systems. In
Windows Vista
Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...
,
Windows 7
Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...
and
Windows 10
Windows 10 is a major release of Microsoft's Windows NT operating system. The successor to Windows 8.1, it was Software release cycle#Release to manufacturing (RTM), released to manufacturing on July 15, 2015, and later to retail on July 2 ...
, System File Checker is integrated with
Windows Resource Protection (WRP), which protects
registry keys and folders as well as critical system files. Under Windows Vista,
sfc.exe
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
%WinDir%\System32\dllcache
.
Windows Resource Protection (WRP) works by setting discretionary access-control lists (DACLs) and
access control lists (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
%WinDir%\WinSxS\Backup
.
Permission for full access to modify WRP-protected resources is restricted to the processes using the ''Windows Modules Installer service'' (
TrustedInstaller.exe
). 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.
System File Checker was first introduced on
Windows 98
Windows 98 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. It was the second operating system in the 9x line, as the successor to Windows 95. It was Software ...
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 attributes; therefore, no preventive or reactive measure was available.
All Windows NT-based operating systems since
Windows 2000
Windows 2000 is a major release of the Windows NT operating system developed by Microsoft, targeting the server and business markets. It is the direct successor to Windows NT 4.0, and was Software release life cycle#Release to manufacturing (RT ...
introduced real-time file protection, called Windows File Protection (WFP).
In addition, the System File Checker utility (
sfc.exe
) 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 Me
Windows Me (Millennium Edition) is an operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. It was the successor to Windows 98, and was released to manufacturing on June 19, 2000, and t ...
, as it was replaced with
System File Protection (SFP). Similar to WFP, SFP offered real-time protection.
Issues
The System File Checker component included with versions of Windows 2000 earlier than Service Pack 4 overrode patches distributed by Microsoft; this was rectified in Windows 2000 Service Pack 4.
Usage
In Windows NT-based operating systems, System File Checker can be invoked via
Windows Command Prompt
cmd.exe, a.k.a. Command Prompt, is a shell (computing), shell computer program, program on later versions of Windows (Windows NT, NT and Windows CE, CE families), OS/2,, eComStation, ArcaOS, and ReactOS. In some versions of Windows (Windows C ...
(with Admin privilege), with the following command:
* (to repair problems)
* or (no repair)
If it finds a problem, it will attempt to replace the problematic files from the DLL Cache (
%WinDir%\System32\dllcache
). 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
SourcePath
and
ServicePackSourcePath
. It may keep prompting for the installation media even if the user supplies it if these values are not correctly set.
In Windows Vista and onwards, files are protected using
access control lists (ACLs), and if it finds a problem, it will attempt to replace the problematic files from the Windows Side-by-side Backup (
%WinDir%\WinSxS\Backup
).
[ 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 or a recovery drive which gives access to the Windows Recovery Environment.
In cases where the component store is corrupted, the "System Update Readiness tool" (CheckSUR) can be installed on Windows 7, Windows Vista, Windows Server 2008 R2 or Windows Server 2008, replaced by " Deployment Image Service and Management Tool" (DISM) for Windows 10, Windows 8.1, Windows 8, Windows Server 2012 R2 or Windows Server 2012. This tool checks the store against its own payload and repairs the corruptions that it detects by downloading required files through Windows update.]
References
Further reading
*
*
External links
sfc , Microsoft Docs
Use the System File Checker tool to repair missing or corrupted system files
Description of Windows XP and Windows Server 2003 System File Checker (Sfc.exe)
{{Windows Components
Windows administration
Windows components