System File Checker: Difference between revisions

Revision as of 20:01, 3 December 2015

Revision as of 03:36, 8 April 2016

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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]].

<!-- Deleted image removed: [[File:System File Checker running on Windows 98.png|thumb|SFC on Windows 98]] -->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

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==Issues==

The System File Checker component included with versions of Windows 2000 earlier than Service Pack 4 are known to override patches distributed by Microsoft. <ref>

{{cite web

|date=30 October 2006

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</source>

If it finds a problem, it will attempt to replace the problematic files from the ''DLL Cache'' (<code>%WinDir%\System32\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> [http://support.microsoft.com/kb/885522 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] </ref> It may keep prompting for the installation media even if the user supplies it if these values are not correctly set. <ref> [http://support.microsoft.com/kb/900910 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] </ref>

In Windows Vista and onwards, files are protected using [[Access control list]]s (ACLs), however the above command has not changed.