System File Checker (SFC) - Win XP Repair Inbuilt Tool

NOTE: Need windows xp (ver ex: sp2) CD to be inserted in CD DRIVE

How to use the scannow sfc tool in Windows XP

Windows XP has the ability to protect itself from system instability caused by 3rd party software overwriting important system files. This used to be (and still is in fact), a problem with Windows 95 and Windows 98.

With the introduction of Windows Millennium Edition, Microsoft made a real effort to stop this from happening.

Now in Windows XP we have a much more refined protection of these important files....

This system is called:

Windows File Protection

By default, Windows File Protection is always enabled and allows Windows
digitally signed files to replace existing files safely. Currently, signed files are distributed
through:

# Windows Service Packs

# Hotfix distributions

# Operating system upgrades

# Windows Update

# Windows Device Manager

If you introduce a file replacement in any other way, Windows File protection will overwrite your file!

An important part of Windows File Protection is the command line utility:

System File Checker (sfc.exe)

You will often see references to scannow sfc in online newsgroups etc. This is a great tool for troubleshooting Windows XP problems.

How to use scannow sfc...

The main reason for using this utility is when you suspect there may be a problem with a Windows XP system file.

Perhaps you get a dialog box appear informing you of a problem with a .dll file, or your program will just not load! It is therefore worth checking to see if there are any corrupt system files using scannow sfc.

To do this simply go to the Run box on the Start Menu and type in:

System File Checker Utility (Scan Immediately)
sfc /scannow

This command will immediately initiate the Windows File Protection service to scan all protected files and verify their integrity, replacing any files with which it finds a problem.

The following should appear to give an indication of how long the process is taking.

In an ideal world that would be the end of the story... Any corrupt, missing or incorrect files would be replaced by this process.

However, things can go wrong and the following guide should help!

The #1 complaint with scannow sfc is the following dialog box appearing:

Why does this happen?

Well, in your computer's registry, are several settings that are checked when you run scannow sfc.

As mentioned earlier in this article, the Windows File Protection service constantly monitors for any changes to the main system files. Well Windows XP keeps a cache (copy) of these essential files at the following location:

C:WINDOWS\System32\Dllcache (assuming C: is your system root which it probably is.)

NB - The dllcache folder is extremely important so Windows XP hides it from you! To view it go to: My Computer > Tools > Folder Options > View > "uncheck" Hide protected operating system files.

If that's the case on your computer then there is normally no need for the original XP CD to be inserted as your computer has a "copy" it can get hold of in this cache...

But, if the Dllcache folder, or part of it, has become corrupted for some reason then you will be prompted for the XP CD - so your computer can get a clean copy!

Having said that not ALL installations of Windows XP have ALL the system files cached into this folder! You may only have around 50MB of files in this folder under Windows XP depending on the quota settings in the registry. (Under Windows 2003 Server the default is 300MB of system files!)

Annoying, YES!

Is there a workaround YES!

As well as having a cache of all the system files on your PC, I like to have the I386 folder from the XP CD installed on the computer as well. After doing this I then modify the registry to tell it the source path for these files... Why? Well not only does this prevent 99% of request for the the XP CD with Windows File Protection. But the I386 folder also contains many other files that are sometimes needed by the operating system and this stops those requests for the XP CD too!

NB - With today's large hard drives you are not going to notice this 475 MB folder on your computer, but older systems may not have the space for this...

Step 1

You will need to get your XP CD and locate the folder called:

I386

This is a major folder and should be one of the first you see, now copy this onto your hard drive into the system root. For most of you that is going to be C:\ so you should end up with a folder that looks like: C:\I386

-----------------------------

Step 2

Now you will need to tell your computer you now have the files on your PC. We do this is the registry (type regedit in the Run box on the start menu) by navigating to:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Setup

You will see various entries here on the right hand side. The one we want is called:

SourcePath

It probably has an entry pointing to your CD-ROM drive, and that is why it is asking for the XP CD. All we need to do is change it to:

C:\

Simply double click the SourcePatch setting and a new box will pop up allowing you to make the change.

Now restart your computer and try scannow sfc again!

------------------------------

When you run scannow at logon you do not get a progress bar... This can easily be remedied by adding a new DWORD: SFCShowProgress to the registry key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon

the values available are: 0 = disabled, 1 = enabled

------------------------------------

System File Checker Utility (Scan Once At Next Boot)
sfc /scanonce

System File Checker Utility (Scan On Every Boot)
sfc /scanboot

System File Checker Utility (Return to Default Setting)
sfc /revert

System File Checker Utility (Purge File Cache)
sfc /purgecache

System File Checker Utility (Set Cache Size to size x)
sfc /cachesize=x