The System File Checker (SFC) is a built-in command-line utility in Microsoft Windows operating systems designed to scan for and restore corrupted, missing, or damaged system files. It helps maintain the integrity of your operating system by replacing problematic files with good copies from a cached backup. If you are experiencing unusual system crashes, slow performance, or strange errors on your Windows PC, the SFC scan can be very helpful for you. In this article, we’ll explain what System File Checker is, how it works, and how you can use it to keep your system running smoothly.
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What Is System File Checker (SFC)?
System File Checker, commonly known as SFC scan and is executed as the sfc /scannow command. Its primary function is to scan, verify, and repair corrupted or missing system files that are essential for the operating system to function correctly. This tool was first introduced with Windows 98 and has continued to evolve across different Windows versions, including Windows 10 and Windows 11.
Microsoft Windows relies on thousands of system files to execute tasks, from launching applications to managing hardware. These files can become corrupted due to software conflicts, malware, improper shutdowns, or hardware failures. This can lead to a wide range of issues, from application crashes and system freezes to blue screens of death (BSODs) and boot problems. The System File Checker command sfc /scannow detects these problems and restores the integrity of system files by replacing corrupted or missing files with their original versions from a cached copy stored on your system.
How Does Windows System File Checker Work?
When you run the SFC utility, it performs a detailed scan of all protected operating system files. Compare the files on your system with the versions stored in a cache (the Windows File Protection cache) or from the original installation media. If any file is found to be missing, damaged, or corrupted, SFC attempts to repair or replace it using a cached copy located in a compressed folder at C:\Windows\System32\dllcache. If the correct version is not available in the cache, it may pull from the Windows installation media or request access to Windows Update.
- Step 01: SFC scans the protected system files on your computer.
- Step 02: It compares each scanned file against a known, good version stored in the Windows File Protection (WFP) cache.
- Step 03: If a file is found to be corrupted, missing, or altered, SFC attempts to replace it with the correct version from the WFP cache or from the Windows installation source files.
- Step 04: After the scan, SFC provides a report indicating whether any issues were found and whether they were repaired.
How do I run System File Checker scan?
If you suspect system file corruption, experience frequent crashes, error messages, or unusual behavior in Windows, running SFC can help identify and repair corrupt system files that might be causing these problems.
- Press Win + S to open the search bar, Type cmd or Command Prompt.
- Right-click on “Command Prompt” and select “Run as administrator.” Alternatively, you can use Windows PowerShell by searching for it in the same way.
- In the Command Prompt window, type sfc /scannow and press Enter.
- The /scannow parameter instructs SFC to scan all protected system files and repair any issues found.
- This will initiate a full system scan for all protected system files and replace corrupted files with a cached copy that is located in a compressed folder at %WinDir% \System32\dllcache.
Note: Here %WinDir% placeholder represents the Windows operating system folder. For example, C:\Windows.
- The above scanning process can take anywhere from 5 to 20 minutes, depending on your system’s performance and the extent of file corruption.
What if the SFC utility results in Windows Resource Protection: Could Not Start the Repair Service?
In case running the sfc /scannow command results in “Windows Resource Protection Could Not Start the Repair Service” error. This is because its related services are not running.
- Press Windows + R, type services.msc, and ok.
- Here, scroll down to look for a service named Background Intelligent Transfer Service (BITS)
- Check and make sure the status of this service is set to Manual.
- Otherwise, double-click on it to change the startup type manually and start the service.
- Now again run the sfc /scannow command, I am sure this time there is no more errors occur.
Windows System File Checker Scan results
Once the system file checker completes its job, you will see one of the following messages:
# Windows Resource Protection did not find any integrity violations
- The above message indicates that there are no missing or corrupted system files on your PC.
# Windows Resource Protection could not perform the requested operation
- If you get this message, you might need to run the System File Checker in Safe mode again. We recommend running System File Checker once again in normal mode before trying that in safe mode.
# Windows Resource Protection found corrupt files and successfully repaired them.
- You will get the above message when the System File Checker detects corrupt or missing files and manages to repair them without any issues.
# Windows Resource Protection found corrupt files but was unable to fix some of them.
- If you get this message, you can either try running the System File Checker tool again or view the log file (%WinDir%LogsCBSCBS.log) and then manually replace corrupted files.
How to view the details of an SFC scan
The SFC scan results are stored on a CBS.Log file, located at C:\Windows\Logs\CBS\CBS.log. If you are looking to view the details of the sfc scan results, you need to make a readable copy on your desktop.
- Open Command Prompt as administrator.
- Type the following command to extract SFC details into a readable file
findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log >"%userprofile%\Desktop\sfclogs.txt"
- This will create a sfclogs text document on the Desktop.
- Open the sfclogs.txt located on the desktop with Notepad.
- The file will contain all the details of the scanned system files and information for files that couldn’t be repaired.
What to Do If SFC Cannot Fix the Problem?
If SFC fails to repair files, you can use the Deployment Imaging Service and Management Tool (DISM) to fix the underlying Windows image:
Open Command Prompt as administrator and run these three commands one by one:
DISM /Online /Cleanup-Image /CheckHealth
DISM /Online /Cleanup-Image /ScanHealth
DISM /Online /Cleanup-Image /RestoreHealth
Once DISM completes successfully, run sfc /scannow again to repair system files.
FAQs About System File Checker (SFC)
Does SFC delete personal files?
- No. SFC only scans and repairs protected Windows system files. Your personal files, apps, and settings remain untouched.
How long does SFC take to run?
- The scan usually takes 10 to 30 minutes, depending on your system’s speed and the number of files.
Can I use my PC while SFC is running?
- Yes, but it’s recommended to avoid heavy tasks while the scan is running for best performance and accurate results.
Should I run DISM or SFC first?
- Start with sfc /scannow. If it fails, then use DISM /RestoreHealth, followed by SFC again.
Does SFC work on Windows 11?
- Yes. SFC works on Windows 11, Windows 10, and older Windows versions as well.
