SFC Scannow: How to Run It and What the Results Mean

Updated 2026-09-10

Somebody told you to run sfc /scannow. You opened a black window, typed it, waited, and got one line back that either sounds fine or sounds alarming - and either way it does not tell you what to do next.

That last line is the whole point of this page. There are only four answers the command can give you, and each one means something specific.

We will also cover the part nobody mentions: what this command does not check, and why "no integrity violations" is not the same as "your computer is fine".

Quick Answer

System File Checker (that is what sfc stands for) compares the files that came with Windows against the originals, and puts back any that were changed or damaged. It repairs Windows itself, nothing else.

It gives one of four answers. If yours says it found corrupt files but could not fix them, go straight to that section - the fix is a different command, run in a particular order.

What SFC Actually Checks

Windows keeps its own copies of the files it shipped with. When you run the command, it walks through the system files one by one, compares each with the stored original, and replaces anything that does not match.

So it is not a virus scan, and it is not a general repair tool. It is a spellcheck for Windows against its own dictionary.

Which brings up the thing that catches almost everybody out. It only looks at files that are part of Windows. All the pieces that arrived later are outside its reach:

• The Visual C++ packages that games and programs install alongside themselves
• The older DirectX components that games add during setup
• Apps from the Microsoft Store, and browser runtimes like WebView2
• Anything from a manufacturer - graphics tools, audio panels, printer software
• Your drivers, your programs and your own files

This matters because of what people conclude from a clean result. A program crashes, you run the scan, it says everything is fine, and you assume the problem must be elsewhere. But if the fault sits in a Visual C++ runtime - which is the cause behind the whole family of missing DLL errors - the scan never looked at it in the first place.

How to Run It Properly

There is an order to this, and it is the opposite of what most advice online says.

SFC repairs damaged files by copying good ones out of a store Windows keeps on your disk. If that store is damaged too, SFC has nothing clean to copy from, and it fails through no fault of its own. So the store gets checked first.

Microsoft says the same thing plainly in its guide to the System File Checker tool: run DISM before running SFC.

Steps:

1. Click Start, type cmd, right-click Command Prompt and choose Run as administrator
2. Type DISM.exe /Online /Cleanup-image /Restorehealth and press Enter
3. Wait. It often sits at 20 percent for several minutes - that is normal, not frozen
4. Then type sfc /scannow and press Enter
5. Wait for it to reach 100 percent and read the last line

Between them, expect 15 to 40 minutes. The computer stays usable, but leave the window alone until it finishes.

The Four Answers It Can Give You

When it finishes, the last line is one of these four. That line is your instruction.

"Windows Resource Protection did not find any integrity violations."
Every Windows file matched its original. Nothing was wrong and nothing was changed. If you still have a problem, it is somewhere the scan does not reach - see the section further down.

"Windows Resource Protection found corrupt files and successfully repaired them."
The best outcome. Something was damaged and has been put back. Restart the computer and check whether your original problem is gone.

"Windows Resource Protection found corrupt files but was unable to fix some of them."
Damage was found, and some of it could not be repaired. This is the one that sends people searching, and it has a proper next step - below.

"Windows Resource Protection could not perform the requested operation."
The scan could not even start properly. Also fixable, also below.

"Found Corrupt Files but Was Unable to Fix Some of Them"

This sounds much worse than it usually is. Nine times out of ten it means exactly what we described earlier: the store SFC copies its replacements from is itself damaged, so there was no clean copy to put back.

Which is why the answer is to repair the store and then scan again.

1. Open Command Prompt as administrator again
2. Type DISM /Online /Cleanup-Image /RestoreHealth and press Enter
3. Let it finish completely, even if it looks stuck partway
4. Restart the computer
5. Run sfc /scannow once more

Most of the time the second scan comes back clean, because now there is something good to copy from.

If it still reports the same thing, the next step is to find out which files failed rather than guessing. That is the section after next.

"Could Not Perform the Requested Operation"

Here the scan did not really run at all. Something blocked it before it started.

Microsoft gives two things to check, and between them they cover almost every case.

Run the scan in Safe Mode. Safe Mode starts Windows with the minimum it needs, so nothing else is holding files open.

1. Click Start, hold Shift and click Restart
2. Choose Troubleshoot, then Advanced options, then Startup Settings, then Restart
3. Press 4 or F4 to start in Safe Mode
4. Open Command Prompt as administrator and run sfc /scannow again

Check that two folders exist. SFC uses them as a waiting area while it swaps files, and if they are missing it cannot work.

1. Press Windows + R, type %WinDir%\WinSxS\Temp and press Enter
2. Look for folders named PendingDeletes and PendingRenames
3. If either is missing, create it with exactly that name, then run the scan again

How to See Which Files It Actually Found

SFC writes everything it did into a log. The log is enormous and mostly unreadable, but there is an official one-line command that pulls out just the relevant part and drops it on your desktop.

1. Open Command Prompt as administrator
2. Type this exactly, then press Enter:
   findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log >"%userprofile%\Desktop\sfcdetails.txt"
3. Open sfcdetails.txt on your desktop
4. Look for lines containing Cannot repair member file - those name the files that failed

Now the trap, and it catches people constantly. That file contains every SFC run ever made on this computer, not just today's. Microsoft says so on the same page.

So a frightening "Cannot repair" line may be two years old and long since sorted. Check the date and time at the start of each line before you react to it. Only entries from your most recent scan describe your situation now.

Once you have a filename, you have something to work with: search that name and you will usually find which component it belongs to and whether it matters. Microsoft's own reference on reading SFC log entries explains the format if you want to go deeper.

One More Thing Most People Forget

A clean result is not a clean bill of health. It is a narrow test that passed.

"Windows Resource Protection did not find any integrity violations" means the files that came with Windows are exactly as they should be. That is all it means. Your actual problem can still be sitting in any of the places the scan never visits.

If your problem survived a clean scan, look at these instead:

• A program crashes or will not start. The fault is usually inside that program or its runtime, not in Windows - our guide on error 0xc0000005 covers that route.
• Updates keep failing. That is its own trail, and error 0x80070643 walks through it.
• The whole computer feels slow. Nothing is damaged - it is load, startup programs or a full disk. See why your computer is so slow.
• Files will not open, or the drive makes noises. That is the drive rather than Windows, and it is a different tool - see our guide on what chkdsk does and when not to run it.
• A missing DLL is named in the error. That points at a runtime package, and our guide on the vcruntime140.dll error deals with it directly.

And the other way round: if nothing is wrong, there is nothing to gain from running this scan "just in case". It takes half an hour and cures nothing that is not broken.

Final Thoughts

SFC is a good tool with one bad habit: it reports back in a single sentence and then leaves you to work out what that sentence meant.

Take the sentence at face value, run DISM before it rather than after, and read the log before you panic about a file you have never heard of. That is the whole technique.

And if the scan comes back clean while your problem is still there, that is useful information too. It means you can stop looking at Windows and start looking at the program that is actually failing.