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Summary: 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.
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What is the System File Checker, and how do I run it? |
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.
Related:
How do I tell Windows where my I386 folder has moved? You can move the I386 folder, but in order to keep Windows File Protection happy, you'll need to update a registry key as well.
When I use Start-Run and type in a command, why does a window just flash and disappear? Start-Run, or the Run item on Windows Start menu is a way to run any program on your machine. Some will work as expected, but Start-Run of others just produces a quick flash. We'll look at why, and what to do instead.
I have no CD - how do I get at Windows XP setup? If you don't have your Windows installation CD there are still a few things you can do. If you have an image of your CD, you may be able to do more.
Article C1896 - February 28, 2004
I am responding to my own post. I did more searching and found that the files that SFC wasn't able to find and asked for CD2 don't exist for Windows XP Media Center 2005. Here is a Microsoft article that says what should be done. http://support.microsoft.com/kb/909059
Posted by: RB at December 11, 2008 5:18 AMHi Leo,
I recently had a nasty Trojan called Prunnet.exe.
I used various programs to attempt to remove it, which i think has been done successfully.
Anyway, after running the anti-virus/anti-malware programs, I've been getting error messages, and once my computer shutdown because some vital system processes were not running.
I think that the anti-virus programs may have deleted some system files, so i ran system file checker.
After the scan, the scan completed (to my knowledge), but the small "windows file protection" window disappeared.
Does this mean that all the system files are intact and undamaged?
I anxiously await your reply.
27-Jan-2009
...hey, mr. leo... i dunno if this is a virus or what, my laptop got an autorun thing... and i can't delete it, i have an anti virus here but that autorun thing keeps invading my file, even my usb and cp were infected... what should i do>?
Posted by: dhoo at February 22, 2009 6:18 PMI just found this site and so I'm new to finding information here. I was wondering if Mike Creel's question posted on 1/28/08 has been answered and if so it would be great to read it. His question applies to me as well.
Posted by: Erin Lounsbury at February 27, 2009 4:08 PMi cannot send e-mails it constantly asks for identification via distorted letters numbers etc even though i correctly identify them
Posted by: cal at February 28, 2009 2:46 PMLeo,
Posted by: Peter Owens at March 1, 2009 6:46 PMI have only the original XP Pro CD.
Usually this is useless because if I try & use it my system always says "the installed version is more recent".
So for just about EVERYBODY, who has the nearly 100 XP updates, including SP2 & 3, surely the advice you offer, to try & use the original CD is useless.
This is the second comment on this topic which I hope you see fit to address.
I Secode Peter Owens Comment from March 1ST 2009. Please address this issue Leo.
Posted by: Steve at March 9, 2009 11:02 AMLeo, I installed IE 8 on my XP mach. Didn't work. Removed it and IE 7 wouldn't work. Removed it IE 6 worked. Reinstalled IE7 and all fixes & SP3. Works fine. Outlook Express now has a prob. Cannot open any links from outlook. Ran SFC /scannow. Ran to completion no problems. OE still not working for links. Any ideas?
Posted by: Mike Passaretti at April 7, 2009 7:28 PMI am having problems controling iexplorer.exe How do i keep it from Crashing my computer. I'd like free safe download, I have Windows XP home Edition
Thank-you
Posted by: Diane at May 30, 2009 2:13 PMI have Windows XP. I do not have the file
SFC/scannow. Please explain.
14-Jun-2009
Posted by: CD at June 13, 2009 10:12 AM