</>PC Utility Hub

System File Checker (SFC)

System File Checker is a built-in Windows utility that scans protected system files for corruption and replaces damaged copies automatically. This page is the reference for sfc /scannow: syntax, switches, log analysis, and its limits.

Updated September 8, 2026 · PC Utility Hub Editorial Team

What System File Checker does

System File Checker (SFC) is a command-line tool built into every version of Windows since Windows XP. It compares the protected system files on your PC against a cached, known-good copy stored by Windows and repairs or replaces any file that has been corrupted, deleted, or overwritten by a bad install or malware.

It runs from an elevated Command Prompt or PowerShell window and does not require any download — the tool and its verification database ship with Windows itself.

All SFC switches

sfc /scannow
sfc /verifyonly
sfc /scanfile=C:\Windows\System32\kernel32.dll
sfc /verifyfile=C:\Windows\System32\kernel32.dll
sfc /offbootdir=D:\ /offwindir=D:\Windows
SwitchEffect
/scannowScans all protected system files and repairs any it can, using the cached component store.
/verifyonlyScans files and reports integrity violations without repairing anything.
/scanfile=<path>Scans and repairs a single specified file rather than the entire protected set.
/verifyfile=<path>Verifies a single specified file without repairing it.
/offbootdir=<path>Points SFC at the boot directory of an offline Windows installation, used from recovery media.
/offwindir=<path>Points SFC at the Windows directory of an offline installation, paired with /offbootdir.

How to run it

  1. 1Press Start, type cmd, right-click Command Prompt and choose Run as administrator.
  2. 2Type sfc /scannow and press Enter.
  3. 3Wait for the scan to reach 100% — this can take 10-20 minutes.
  4. 4Read the result: no violations found, repaired successfully, or unable to fix some files.
  5. 5Restart the PC even if no issues were found, then re-check the problem that prompted the scan.

Running SFC offline, from recovery media

If Windows won't boot, run SFC against the offline OS partition from Windows Recovery Environment (WinRE): boot to WinRE, open Command Prompt from Troubleshoot > Advanced options, confirm the Windows drive letter (often not C: in WinRE), then run sfc /scannow with /offbootdir and /offwindir pointing at it.

sfc /scannow /offbootdir=D:\ /offwindir=D:\Windows

Reading CBS.log

SFC writes details to C:\Windows\Logs\CBS\CBS.log. Filter it with findstr to see only SFC-related lines, then look for 'Cannot repair member file' entries, which name the exact file that failed:

findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log > %userprofile%\Desktop\sfcdetails.txt

What SFC cannot fix

SFC repairs individual protected files, but it pulls replacements from the local WinSxS component store. If that store is itself damaged, SFC reports it found corrupt files but could not fix some of them, and no amount of re-running sfc /scannow will help — the source it copies from is broken. SFC also can't fix disk-level or file system corruption, and it can't recover deleted files.

When SFC can't repair everything, the fix is to repair the component store with DISM first — see the DISM guide for the exact commands and error codes.

Get System File Checker

Start the download and follow the setup steps described on this page.

Frequently asked questions

Does SFC need internet access?
No. SFC repairs files from the local WinSxS component cache, not from the internet.
Is sfc /scannow safe?
Yes, it is a read/repair operation on system files only and does not touch personal data.
How long does sfc /scannow take?
Typically 10-20 minutes depending on drive speed and system size.
What if SFC finds errors it can't fix?
Repair the component store with DISM, then run sfc /scannow again.

Related pages