How to run sfc /scannow System File Checker on external disks

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For correct operation, Windows installs some important system files on your computer. These files are stored in the Windows installation directory and are very important for the Windows operating system. Any corruption or damage to these files can disable certain functions or even freeze the system completely. Users are usually faced with problems where Windows cannot start or gets stuck on a screen. This is mainly caused by errors in these files.

Windows has built-in functionality to repair these important files. The sfc‘ command (System File Checker) is one of those useful commands that can help you repair faulty system files on your Windows installation.

While sfc.exe does its job quite well and helps users replace missing or corrupted system files, you may not be able to boot under Windows to run this command. Therefore, we discussed in this position how to execute this command both internally and externally.

If you can boot on advanced boot options in Windows 10 , click the command prompt and run System File Checker with the following command:

sfc /scannow

However, if you cannot even access advanced boot options, you may need to follow this procedure.

Run sfc /scannow on external disks

June 2020 Update:

We now recommend using this tool for your error. Additionally, this tool fixes common computer errors, protects you against file loss, malware, hardware failures and optimizes your PC for maximum performance. You can fix your PC problems quickly and prevent others from happening with this software:

  • Step 1 : Download PC Repair & Optimizer Tool (Windows 10, 8, 7, XP, Vista – Microsoft Gold Certified).
  • Step 2 : Click “Start Scan” to find Windows registry issues that could be causing PC problems.
  • Step 3 : Click “Repair All” to fix all issues.


If Windows does not load and you want to run System File Checker on the disk, what would you do? Well, you can use an external repair diskette or remove the hard disk and connect it to another running Windows computer to run the SFC scan.

There may be a problem even if you have connected your player to another PC. Windows will run SFC only on the primary Windows installation disk and not on the external disk.

To overcome this, we need to modify our control a little, and it will work surprisingly well with external hard disks.

Perform offline system file scanning

To execute SFC commands on an external hard disk, do the following :

Open a high command prompt window (administrator) and execute this command :


Don’t forget to replace’c:’ with the letter of your external drive in the command. Also replace c:windows with the directory where Windows was installed (‘Windows’ by default).

It may take some time to complete the entire analysis process and once it is completed, you will receive an appropriate response to the results of the analysis. The answer is very similar to the one you received if you were using SFC normally on your computer.

All errors found and reported are recorded in a CBS.log file. You can consult this file for more details about bugs and corrupted files. Here is the complete answer you will see on a successful scan:

Windows Resource Protection successfully found and repaired corrupted files. Details are included in CBS.log %WinDir%LogsCBSCBS.log

You can use the same command if you use an external repair drive on your PC. Other switches of the ‘sfc’ command also work here.

You can use this command to repair your drive if the Windows operating system cannot boot or if you are using an external repair drive.

Related Topics:

  • Run System File Checker in Safe Mode or Startup Time
  • System File Checker does not work, does not work or cannot repair
  • Windows Resource Protection found corrupted files but could not repair some of them
  • Windows Resource Protection could not start repair service.

RECOMMENDED: Click here to troubleshoot Windows errors and optimize system performance

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