Helping people with computers... one answer at a time.
The System File Checker is a little known utility that validates that Windows own files are undamaged. It's a simple to run command line program.
What is the System File Checker, and how do I run it?
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Windows XP works very hard to maintain the integrity of the system files on your machine. If you try to replace one of the "protected" files, you may get an informative message that the operating system has put the old approved version back. Not all files are under system file protection and even for those that are, there are ways around it. Occasionally system files become corrupt.
Enter the SFC, the System File Checker.
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SFC is a good utility to run when you suspect that system files have been somehow corrupted. It validates the digital signatures of all of the Windows system files and restores any that it finds are incorrect. It will use the on-disk cache if possible, but SFC may require that you provide your original installation CD or a location with an image thereof. (See this prior article about not having an installation CD on some of the alternatives if that's the case.)
To run the system file checker press Start, Run, and then type in SFC, followed by its options.
The most common usage of SFC is this:
SFC /scannow
This causes SFC to scan your system immediately. SFC can take a few minutes to run. As I said above, have your installation CD or equivalent available in case SFC needs to replace a damaged file.
While it's not documented anywhere, if SFC replaces any system files, I'd reboot. I just like to make absolutely certain that the file replacement actually takes effect.
The Microsoft knowledgebase includes more detailed SFC documentation, including more options to check at boot time, control the size of the system file protection cache, and so on. Speaking of which, the knowledgebase also includes System File Protection documentation, covering the mechanism Windows XP uses to keep your system files safe automatically.
UPDATE: If you have no CD, but you do have an I386 directory or CD image somewhere, check out this article: How do I tell Windows where my I386 folder has moved? Once you make the changes therein, you should be able to run SFC to completion.
Article C1896 - February 28, 2004
Leo A. Notenboom has been playing with computers since he
was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed.
After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers
to common computer and technical questions. More about Leo.
"You must be an administrator running a console session in order to use the windows file checker utility" ok so HOW do I change this so I can run an SFC scan and fix my bad images? please help
11-Aug-2011
Posted by: Heidi at August 11, 2011 5:33 AM
@Heidi
This happens if you are running Windows 7. It's the User Account Control protecting you computer against unauthorized access.
To get around this click on the Start Button, select All Programs, scroll to the Accessories folder, then right click on Command Prompt and select Run as Administrator.
Posted by: Mark J at August 11, 2011 7:42 AMYou the MAN,man.Check this guy out,he's absolutely awesome!!!!
Posted by: Pat at January 12, 2012 2:45 PMYou didn't explain how to run SFC from a command prompt but Heidi did in her comment.
Posted by: Ike Nash at February 2, 2012 11:07 AMThanks Heidi...
I ran an sfc /scannow twice after copying i386 folder to my C: drive to check for errors, and both times it's filled up my HD up to 2G worth of space. Is there a way to delete this built-up cache of files? Thanks, Leo!
Posted by: vk1drums at April 26, 2012 4:50 PM