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New to using the command prompt? Check out the Windows Command Prompt Beginner’s Guide
If you’ve ever asked a PC help question in a forum, it’s likely someone suggested you check for corrupted or out of version protected system files. To do this:
- Open a Command Prompt (Click Start, type cmd, and click cmd.exe.)
- Type sfc /scannow and press Enter
What Does the sfc /scannow Command Do?
System File Checker (SFC) verifies all protected system files are current and complete. If they’re not, it replaces them to bring them into currency.
Here’s what Microsoft say (applies to Windows XP):
System File Checker gives an administrator the ability to scan all protected files to verify their versions. If System File Checker discovers that a protected file has been overwritten, it retrieves the correct version of the file from the cache folder* (%Systemroot%\System32\Dllcache) or the Windows installation source files, and then replaces the incorrect file. System File Checker also checks and repopulates the cache folder. You must be logged on as an administrator or as a member of the Administrators group to run System File Checker. [1]
*The DLL cache folder is replaced in Windows Vista and 7 with Windows File Protection (files are kept in C:\Windows\winsxs\Backup.) Thank you Marc Liron, Microsoft MVP, for this information.
This is a good thing. If something doesn’t seem right on your PC, run this command to give you peace of mind and a good start.
More information:
- SFC Usage Windows 7/Vista
- SFC Usage Windows XP
1 Description of Windows XP and Windows Server 2003 System File Checker (Sfc.exe)
About Rich
Rich is the owner and creator of Windows Guides; he spends his time breaking things on his PC so he can write how-to guides to fix them.
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yeas Superb Tip….. I really like this command ;
Well, anyone who doesn’t know about this needs to. It’s as basic a necessity as “copy and paste” or “ctrl+alt+del” It should be run at the conclusion of every instance of removing malware, just to be sure.
I did it but the report said that it found some corrupt files but could not fix all of them. What should I do?
Thank you Marc. I’ve updated the guide to reflect the information you provided.
Hi I’m having problems with scannow, iv followed all instructions and had no luck.
I have a blue screen error which is c000021a- aknow.dll file is corrupt.
Iv have tried everything from chkdsk and scannow to offline scannow and all the options on Windows disk. I don’t have any image files or backups to go on so that’s no good.
On the scannow it says that it cannot complete because of Windows resource protection. Same as if I do it offline.
I also cannot boot into any of the safe modes or last know good configurations. All I can do is use the windows cds which doesn’t help and I can’t get past the Windows loading screen without the bsod. Iv tried everything for days with no luck. I don’t want to reinstall Windows or take it to a shop.
It’s Windows 7 32bit home premium.
If someone has a solution pls email me.
Thankyou.