Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
that allows users to scan for and restore corruptions in Windows system files. This utility is available on Windows 98
Windows 98
Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid...
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
Windows Server 2003 is a server operating system produced by Microsoft, introduced on 24 April 2003. An updated version, Windows Server 2003 R2, was released to manufacturing on 6 December 2005...
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
Windows Resource Protection is a feature in Windows Vista that replaces Windows File Protection. It protects registry keys and folders in addition to critical system files. The way it protects resources differs entirely from the method used by Windows File Protection.- Overview :Windows File...
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
Windows Resource Protection is a feature in Windows Vista that replaces Windows File Protection. It protects registry keys and folders in addition to critical system files. The way it protects resources differs entirely from the method used by Windows File Protection.- Overview :Windows File...
The Windows Registry is a hierarchical database that stores configuration settings and options on Microsoft Windows operating systems. It contains settings for low-level operating system components as well as the applications running on the platform: the kernel, device drivers, services, SAM, user...
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 works by registering for notification of file changes in Winlogon
Winlogon
In computing, Winlogon is the component of Microsoft Windows operating systems that is responsible for handling the secure attention sequence, loading the user profile on logon, and optionally locking the computer when a screensaver is running...
. 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 works by setting discretionary access control lists (DACLs) and access control list
Access control list
An access control list , with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject...
s (ACLs) defined for protected resources. 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
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
, 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
In computing, DLL Hell is a term for the complications that arise when working with dynamic link libraries used with Microsoft Windows operating systems, particularly legacy 16-bit editions which all run in a single memory space....
.
System File Checker was first introduced on Windows 98
Windows 98
Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid...
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
File attribute
A file attribute is metadata that describes or is associated with a computer file. For example, an operating system often keeps track of the date a file was created and last modified, as well as the file's size and extension . File permissions are also kept track of...
s; therefore, no preventive or reactive measure was available.
All Windows NT-based operating systems since Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
Windows File Protection , a sub-system included in Microsoft Windows operating systems of the Windows 2000 and Windows XP era, aims to prevent programs from replacing critical Windows system files. Protecting core system files mitigates problems such as DLL hell with programs and the operating system...
(WFP).
In addition, the System File Checker utility (sfc.exe) was reimplemented as a more robust command-line utility that integrated with Windows File Protection
Windows File Protection
Windows File Protection , a sub-system included in Microsoft Windows operating systems of the Windows 2000 and Windows XP era, aims to prevent programs from replacing critical Windows system files. Protecting core system files mitigates problems such as DLL hell with programs and the operating system...
. Unlike the Windows 98 SFC utility, the new utility forces a scan of protected system files using Windows File Protection
Windows File Protection
Windows File Protection , a sub-system included in Microsoft Windows operating systems of the Windows 2000 and Windows XP era, aims to prevent programs from replacing critical Windows system files. Protecting core system files mitigates problems such as DLL hell with programs and the operating system...
and allows the immediate silent restoration of system files from the DLLCache folder or installation media.
Windows Millennium Edition, or Windows Me , is a graphical operating system released on September 14, 2000 by Microsoft, and was the last operating system released in the Windows 9x series. Support for Windows Me ended on July 11, 2006....
, System File Checker was replaced with System File Protection (SFP). Similar to Windows File Protection, System File Protection offered real-time protection. The stand-alone SFC utility was removed and not available on Windows Me.
Issues
System File Checker included with a version Windows 2000 earlier than Service Pack 4 are known to override patches distributed by Microsoft. This problem has since been rectified in Windows 2000 Service Pack 4.
Usage
In Windows NT-based operating systems, System File Checker can be invoked via Command Prompt
Command Prompt
Command Prompt is the Microsoft-supplied command-line interpreter on OS/2, Windows CE and on Windows NT-based operating systems...
, with the following command:
sfc /scannow
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.
An access control list , with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject...
s (ACLs), however the above command has not changed.
System File Checker in Windows Vista and later Windows operating systems can scan specific individual 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 which gives access to the Windows Recovery Environment.
System File Checker was first introduced on Windows 98