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) this is a great tool for troubleshooting Windows XP problems. 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: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.
Any corrupt, missing or incorrect files would be replaced by this process. However, things can go wrong and the following guide should help!
The complaint with sfc /scannow is the following dialog box appearing:
Why does this Happen?
In your computer’s registry, are several settings that are checked when you run scannow sfc. The Windows File Protection service constantly monitors for any changes to the main system files. Windows XP keeps a cache (copy) of these essential files at the following location:
C:WINDOWS\System32\Dllcache (assuming C: is your system root)
Normally this dllcache file is hidden. If you want to see this, you have to enable “Show hidden file” option from tools-folder option. If the Dllcache folder, or part of it, has become corrupted for some reason then you will be prompted for the XP CD.
How to perform start sfc /scannow command without windowsXP CD ?
If you have a copy of i386 folder in your system you can perform sfc /scannow without windowsXP CD. But you have to change windows default searching path from registry. By default it will be your CD drive.
How to change the windows sfc/scannow default searching path ?
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:\ (assuming you copied i386 folder in C drive)
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!
Other Problems with sfc /scannow
1. Has the CD Drive’s drive letter changed (perhaps by the addition of another hard drive, partition, or removable drive) since Windows XP was first installed? If so, simply edit the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Setup\SourcePath to reflect the changed drive letter.
After you restart the computer, Windows file protection and sfc /scannow uses the new source path instead of prompting for the Windows XP installation CD-ROM
2. Has the registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Setup\SourcePath got an incorrect entry? The SourcePath entry does NOT include the path location till the I386 folder. It completes one folder ahead to reach the I386 folder.
Example:
If the I386 directory is at C:\I386, the SourcePath value would be C:\
3. If the problem persists and you have the correct path for your I386 folder then the I386 folder is corrupted. To solve this problem copy I386 folder from the CD-ROM to your system restart the system and then
perform sfc /scannow again.
4. You do not have an XP retail CD with an I386 folder on it. If you have a restore CD from your PC manufacturer then you may have to explore the CD to find the folder.
5. You still keep being prompted for the XP CD yet you have done all in this article! There is another setting in the registry that may be causing the problem. Navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SourcePath
Make sure the entry here is the same path to the I386 folder as used above.
6. Systems administrators can enforce security policies that may include changes to the Windows File Protection settings. You will need to speak with your network administrator about this, but it is important to bear in mind when Windows starts up, the Windows File Protection service synchronizes (copies) the Windows file protection settings from the following registry key:
HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows NT\Windows File Protection
to the following registry key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
Therefore, if any of the following values are present in the HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows NT\Windows File Protection key, they will take precedence over the same values under the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon key.
This will not effect scannow sfc so much, but WILL make an impact if any of the other sfc.exe “switches” have been used! (More about these at the end of this article.)
7. 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
How sfc is handling Windows Updates
You may be asking yourself how does sfc.exe know how to check for updated Windows system files? during OS upgrades, service pack installations etc.. the dllcache folder should be updated with these new files.
As an example the recent Windows XP Hotfix – KB828535 updated the system file wkssvc.dll A new version of the file was placed in C:\WINDOWS\system32 and a copy in the cache: C:\WINDOWS\system32\dllcache A copy of the old system file is archived in: C:\WINDOWS\$NtUninstallKB828535$
There is another location the Windows File protection service uses and that is the I386 folder in C:\WINDOWS\ServicePackFiles When you install a service pack, like SP1. Any new system drivers are cached in this location too.
If you have odd problems with running scannow sfc and nothing else in the article has resolved it, then take a look at the entry in:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\
CurrentVersion\Setup\ServicePackSourcePath
This should be pointing to the location C:\WINDOWS\ServicePackFiles (assuming C:\ is the boot drive.)
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Now i understand that how to change sfc scan dir… thanks a lot
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