Core system files of the Windows operating system can be manipulated like any other file on a computer hard drive. While it may be necessary to take ownership first, it is not really too complicated of a process.
Manipulation can either be intended or unintended. An admin who patches system files responsible for theme installations on the operating system does so intentionally for instance, while a computer virus' or trojan's modification of system files is not intended by the user of the system.
Both file manipulations can have a severe impact on system stability. There are other issues that may affect system files; a failing hard drive or crash might have corrupted some files.
The sfc /scannow command recovers Windows system files so that manipulated files, those that are not identical to the original version, are replaced by the verified version during the process if possible.
SFC, which stands for System File Checker, scans all protected Windows operating system files and attempts to replace corrupted, damaged, missing and changed file versions with authorized versions.
The sfc /scannow command needs to be run from an elevated command line prompt. Here is how this is done:
The window title should begin with Administrator which confirms that you launched an elevated command prompt window.
If SFC does not work properly for whatever reason, download and run SFCFix to correct the issue.
Type sfc /scannow to run the file verification scan. Windows will check all system files to make sure they are in their original state. Any file that is not will be replaced by the original copy during the procedure if possible.
The scan will take some time and the verification progress is displayed in the command line window.
The system file check may require access to Windows media files from the original installation source to replace or copy the original files. Make sure you have Windows installation media at hand before you run the check.
You may run sfc /verifyonly to check files for corruption or issues but don't do anything about it. Verifyonly is ideal if you want to find out if issues exist before you decide on what to do about it.
Here is a list of all scan parameters that you can make use of:
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