FreeFileSync Locked Files: Files in Use on Windows
Handle files locked by applications without disabling Windows security or risking inconsistent copies.
Quick answer
Close the application that owns a locked file when possible, then rerun the comparison after pending writes finish.
What to check first
Databases, mail stores, virtual machines, and other active application data may require an application-aware snapshot or export.
Windows-specific factors
Do not broadly disable antivirus or permissions to bypass a lock; the lock may protect consistency.
Safer troubleshooting workflow
Use logs to distinguish access-denied, sharing-violation, and missing-file errors before choosing a fix.
How to verify the result
Test restored complex files with the application that uses them, not only by checking file size.
Frequently asked questions
Should I change sync mode to fix this?
Not until the underlying cause is identified. First verify paths, permissions, comparison results, and logs.
Is a successful sync the same as a verified backup?
No. Important data should be checked at the destination and periodically restored to a separate location.
Related: all FreeFileSync Windows guides