COMMAND
sfc /scannowSystem File Checker
sfc /scannow scans all protected Windows system files and replaces corrupted ones with known-good copies. Run it from an elevated prompt when Windows behaves erratically, crashes or shows missing-component errors. If it cannot repair a file, run DISM first to fix the component store, then run sfc again.
Purpose
System File Checker verifies the integrity of Windows' protected operating-system files against a trusted local copy and restores any that are corrupted, missing or altered. It is a standard early step for unexplained instability, crashes, missing DLL errors and some blue screens.
Run it
Open an elevated prompt (right-click Start → Terminal (Admin)) and run:
sfc /scannowBeginning system scan. This process will take some time.
Verification 100% complete.
Windows Resource Protection did not find any integrity violations.Possible results
| Message | Meaning | Next step |
|---|---|---|
| Did not find any integrity violations | System files are intact | Look elsewhere for the problem |
| Found corrupt files and successfully repaired them | Fixed; details in CBS.log | Reboot and retest |
| Found corrupt files but was unable to fix some of them | Repair source incomplete | Run DISM, then sfc again |
| Windows Resource Protection could not perform the requested operation | A pending repair or servicing issue | Reboot; try in Safe Mode |
The DISM + sfc sequence
For stubborn corruption, repair the component store first, then the files that draw from it:
DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannowDISM fetches healthy component files from Windows Update (or a specified source); sfc then uses the repaired store. See the DISM record.
Reading the log
Detailed results are in C:\Windows\Logs\CBS\CBS.log. To extract just the sfc entries:
findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log > "%userprofile%\Desktop\sfcdetails.txt"Other options
| Option | Effect |
|---|---|
/verifyonly | Scan without repairing |
/scanfile=<path> | Check and repair one file |
/offbootdir + /offwindir | Repair an offline Windows (from recovery) |
Common mistakes
- Running without elevation. sfc requires administrator rights and reports an error otherwise.
- Skipping DISM when sfc cannot repair, then repeating sfc uselessly.
- Interrupting the scan. Let it reach 100%.
- Expecting it to fix application or driver problems. It only covers Windows' own protected files, not third-party software or disk faults (use chkdsk for those).
Frequently asked questions
Should I run sfc or DISM first?
sfc repairs system files using a local cache in the component store (WinSxS). If that store is itself damaged, sfc cannot repair everything. The reliable order for stubborn problems is DISM /RestoreHealth first (which repairs the store), then sfc /scannow.
What does "Windows Resource Protection found corrupt files but was unable to fix some of them" mean?
sfc found damage it could not repair from its cache. Run DISM /Online /Cleanup-Image /RestoreHealth, then sfc /scannow again. If it still fails, the CBS.log names the files; an in-place upgrade repair is the next step.
How long does sfc /scannow take?
Usually 5 to 20 minutes depending on the disk. Do not interrupt it; a partial run leaves the report incomplete.