The System File Checker or sfc.exe is a utility in Microsoft Windows located in C:\Windows\System32 folder. This utility allows users to scan for and restore corrupt Windows system files.
System File Checker
In Windows 7 & Vista, the System File Checker is integrated with Windows Resource Protection, which protects registry keys and folders as well as critical system files. If any changes are detected to a protected system file, the modified file is restored from a cached copy located in the Windows folder itself.
So if at any point of time if you find that you have hacked some system files or maybe applied some tweaks or replaced system files, maybe while customizing your Windows, and you now find that your Windows is not working properly, you may want to consider running this utility first, before trying a System Restore. To do so, you will have to first open an elevated command prompt window.
To run the System File Checker in Windows 8, Windows 7 or Windows Vista, type cmd in start search box. In the result, which appear, right click on cmd and select Run As Administrator.
Run sfc /scannow
In the command prompt window which opens, type sfc /scannow and hit Enter.
The sfc utility will run for a while and if any corruptions are found, replace them on re-boot.
In case you are unable to start the System File Checker and you instead get the “Windows Resource Protection Could Not Start the Repair Service” error, you may want to check up if your Windows Modules Installer service has been Disabled. To do so, type services.msc in start search and hit Enter. The status of this services should be set to Manual.
Some more sfc switches:
Scan once at next boot: sfc /scanonce
Scan at every boot: sfc /scanboot
Purge File Cache: sfc /purgecache
Return to Default Setting: sfc /revert
You can also use the sfc.exe program to help you troubleshoot crashes that occur in the user mode part of Windows 7 & Vista. These crashes may be related to missing or damaged operating system files. To do so you may have to access the log files.
How to view the log file.
The sfc.exe program writes the details of each verification operation and of each repair operation to the CBS.log file. Each sfc.exe program entry in this file has an [SR] tag. The CBS.log file is located in the %windir%\Logs\CBS folder.
You can search for [SR] tags to help locate SFC.exe program entries. To perform this kind of search and to redirect the results to a text file, follow these steps:
Click Start, type cmd in the Start Search box, right-click cmd in the Programs list, and then click Run as administrator.
Type the following command, and hit Enter:
findstr /c:”[SR]” %windir%\logs\cbs\cbs.log >sfcdetails.txt
The sfcdetails.txt file includes the entries that are logged every time that the SFC.exe program runs on the computer.
How to interpret the log file entries:
The sfc.exe program verifies files in groups of 100. Therefore, there will be many groups of SFC.exe program entries. Each entry has the following format: date time entry_type details. For more details on how to interpret, visit KB928228.
Go here if you find that System File Checker (SFC) cannot repair corrupted member file.