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System File Checker


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#1 janeygee

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Posted 21 December 2010 - 11:23 AM

Today I ran the system file checker, ( sfc /scannow) , for the first time in over 12 months probably. I was surprised when the request for me to insert the XP Installation CD, as in the past, this had never occurred. The message was saying that there was a missing DLL. I inserted the CD , and clicked on "Retry". Throughout the whole process, I had to hit "Retry" about 100 times I would think, but eventually got to the end OK.
Later the same day, I ran SFC again, and I had to run through the same procedure !!

I do not have any problems with the way the PC is behaving, but does anyone understand why, having restored all the missing DLLs, they appear still to be missing. Between the 2 runs, I had not uninstalled anything, or re-booted.
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#2 cryptodan

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Posted 21 December 2010 - 11:45 AM

Can you provide examples of the missing dll's? It would greatly help us assist you in your issues.

#3 janeygee

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Posted 21 December 2010 - 03:13 PM

Thanks for rapid respone Cryptodan:

Don't know how to identify missing files ?
When I run sfc /scannow, it scans for about 20 seconds, about 1 cm. along the search bar, and then this message comes onto the screen:

[img]http://<a href="http://s143.photobucket.com/albums/r125/Janeygee1047/?action=view&amp;current=xpsfc.jpg" target="_blank"><img src="http://i143.photobucket.com/albums/r125/Janeygee1047/xpsfc.jpg" border="0" alt="Photobucket"></a>[/img]

When I slect "Retry" , the scan continues, until the same message appears. Eventually, the scan is completed, but no other messages appear.
Immediately after completing the scan first time, I used Belarc Adviser to scan, and everything was shown as up to date.

Thanks for your assistance.

oops, seems I cannot post a screenshot, I'll have a search for a "How to " and retry :blush:

Just to add that the reinstallation disc is about 7 or 8 years old, and is labelled "Operating Sytsem" XP Home Edition incl. Service Pack 1.

Edited by janeygee, 21 December 2010 - 03:31 PM.

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#4 cryptodan

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Posted 21 December 2010 - 05:05 PM

You will need to find your Windows XP Installation CD.

#5 joseibarra

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Posted 21 December 2010 - 06:58 PM

When you install XP, sfc /scannow runs once to populate the dllcache folder with copies of 3498 critical XP system files that are monitored by Windows File Protection. There are probably more than 3498 files in your dllcache folder, but Windows File Protection only looks after 3498 of them to replace any system files that might come up missing. Delete or rename one of the 3498 files and Windows File Protection will quickly and silently replace it and put an event in the Event Log telling you about it.

If you update your system later (like installing SP3) and then run sfc /scannow, it will want to repopulate the dllcache folder with the new versions of file that may not have made it there when the update was installed. What is in the dllcache folder needs to match what the current installation is and sfc /scannow compare what is in the dllcache folder with what it thinks the latest 3498 files are.

When sfc /scannow runs, it is comparing what it finds in the dllcache folder against what it thinks is correct and if it finds a mismatch, it looks to the path where the original installation was from which is usually a CD to try to resolve the mismatch. You can make sfc /scannow behave though by telling it to look for files in another place.

For me, I just copied my entire XP SP3 slip streamed CD to my external drive and tell sfc /scannow to look there and it runs without incident.

By design, sfc /scannow only populates and replaces files missing or corrupted files in the c:\windows\system32\dllcache folder.

sfc /scannow does not and will not replace any files in c:\windows\system, c:\windows\system32, etc. It only cares about maintaining the 3498 "protected files" in the dllcache folder.

That is why is is often going to be a frustrating waste of time to run it with lots of mouse clicking if you are having a problem with your system. Running sfc /scannow will not replace missing or corrupted system files except those in the dllcache folder. It is also hard to stop sfc /scannow sometimes...

It does "feel good" when sfc /scannow runs completely and does not complain, but it is not even looking at your system or system32 folder.

If there are any doubters out there, I can tell you how to do some testing to convince yourself that sfc /scannow will only replace files in the dllcache folder and does nothing to replace missing or corrupted files in any other folder on your system (it took me a little while to get convinced).

Here is an MS article that you can read about it.

http://www.microsoft.com/whdc/archive/wfp.mspx

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#6 janeygee

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Posted 22 December 2010 - 02:42 AM

Cryptodan : I have the XP Installation file which I got when I bought the PC ( old now, Dell Dimension 4600 !).

Joseibarra : I think I understand what you have said. Initially I did wonder whether the "Service Packs" would have any effect, in view of the fact that when SFC finds a problem, it asks for the initial install disc to be made available, which as you point out does not have SP2 or 3 on !
I have read about "Slip streaming SP2 and 3 " onto a new install disc, but I have never had the confidence to try it ............... althouygh I think I should search for an "Idiots Guide" and do it.
You mention copying SP3 to an external hard disc, and getting SFC to check there ........ how do I do that.

In essence, are you saying that, Unless I have a new installation disc, including the slip streamed service packs, running SFC is a waste of time ?

I am still learning !!!
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#7 cryptodan

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Posted 22 December 2010 - 04:04 AM

What prompted you to run sfc /scannow?

#8 janeygee

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Posted 22 December 2010 - 04:43 AM

Cryptodan :
Cannot really remeber, other than I had a done acomplete defrag, deleted lots of EMails, emptied Recycle bin, etc.etc. and just decided to run it. As I said, I had no indications of any problems with the PC, and still don't. It's just that many years ago when I first got it, and when I was just learning, I tried lots of these RUN commands, just to experiment. Using SFC in the past I had never been "asked" to insert the Installation disc.
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#9 joseibarra

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Posted 22 December 2010 - 07:07 AM

Well, not a waste of time exactly, but it will not straighten out any files you think are missing or corrupt from your Windows system folders (except dllcache). It f-e-e-e-e-ls good! I will never even suggest running it for any problem (I used to before I knew better).

I have not slipstreamed in a while but one of these other Bleepers can point to the most current instructions, which if you carefully follow, will work the first time.

What I did was take my Windows SP2 installation CD, downloaded SP3, then (following the good directions I found here) made a new folder on my system and merged the two pieces into one, then from that, made a new Windows XP installation CD with SP3 already on it. Keep that new CD handy for future problems or use it for your sfc /scannow runs. Save your old Windows XP SP2 CD for some rainy day.

Then I copied my entire SP3 CD out to an external drive and told sfc /scannow to look for files there when doing it's comparison check. In all my experimentings, it is easier for me to just have the Windows XP SP3 installation on an external drive so I never have to pull out CDs.

I think I used the following article to modify my system to tell sfc /scannow to look on my external drive. Some of the discussion leads you to think that sfc /scannow will replace missing or corrupt "system" files, but it does not. If your system came with SP3 installed, there may also be an up to date i386 folder on another partition and you can tell sfc /scannow to look there.

http://www.updatexp.com/scannow-sfc.html

If you think you are having some system problem - if you are seeing some weirdness and feel that running sfc /scannow is the first thing to do, it will not help you unless you are missing files from your dllcache folder and you would probably not know that. You can empty your dllcache folder of the protected 3498 files and your system will still work just fine. If you run sfc /scannow successfully, it will repopulate the emptied dllcache folder - that is what it does. sfc /scannow only cares about keeping the dllcache folder up to date.

Files that come "into play" for running XP are mostly (not all of course) going to be in the %Systemroot%\system or %Systemroot%\system32 folder and sfc /scannow is only concerned about missing or corrupt files in this folder:

%Systemroot%\system32\dllcache

There was a time when I used to suggest running sfc /scannow but I never saw it actually fix anything. Mostly it just complained like yours did. Then when I learned how it really works and proved it to myself, I will never suggest running it for anything - it is a waste of time for troubleshooting (but feels good). If it ever does find anything to do, you have some other problem to fix.

I attached the list of the 3498 files that Windows File Protection monitors on your running system and it is the same list that sfc /scannow uses when asked to check the dllcache folder (it IS the XP Protected File list). Rename or delete any one of those files on your healthy system and Windows File Protection will replace it. You will never get a chance to run sfc /scannow since Windows File Protection will replace the missing file in about 1 second.

Edited by joseibarra, 22 December 2010 - 07:08 AM.

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#10 janeygee

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Posted 22 December 2010 - 07:14 AM

Thanks Joseibarra:
I understand the principals of what you say, and I will try the slipstreaming and check SFC again, just for the hell of it. But I feel happier now anyway
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#11 cryptodan

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Posted 22 December 2010 - 02:42 PM

If nothing prompted you to Run SFC, then I would just ignore it.

#12 janeygee

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Posted 22 December 2010 - 03:49 PM

Cryptodan:
It seems as though its pretty redundant anyway.
I hope you pick up my future problems as quick , thanks for your time.
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