FreeFileSync Open Source File Synchronization

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Frequently Asked Questions


  1. General
  2. Installation
  3. Troubleshooting



What are the basic steps to use FreeFileSync?
  1. Choose left and right directories.
    FreeFileSync: Choose left and right directories


  2. Compare them.
    FreeFileSync: Start comparison


  3. Select synchronization settings.
    FreeFileSync: Select synchronization settings


  4. Press Synchronize to begin synchronization.
    FreeFileSync: Press Synchronize to begin synchronization

For more detailed explanations on how to set up the most common synchronization scenarios, have a look at the FreeFileSync video tutorials.

Where can I find information about FreeFileSync's advanced features? Show help file For the most up to date description of FreeFileSync, visit the Online Manual. Press F1 while running FreeFileSync.

If internet access is not available, an offline version of the manual can be found in the FreeFileSync installation folder.

After you've become comfortable with using FreeFileSync, be sure to read chapter Tips and Tricks!

Which features make FreeFileSync unique?
  • Download and use for free... (but you may donate to support)
  • No ads in the installer or application
  • Synchronize folders on network shares and local drives
  • Synchronize mobile devices via MTP (Android, iPhone, tablet, digital camera)
  • Synchronize with Google Drive cloud storage
  • Free FTP client: synchronize via FTP (File Transfer Protocol) and FTPS (SSL/TLS)
  • Access files online using SFTP (SSH File Transfer Protocol)
  • No artificial limits on the number of files to sync
  • Detect moved and renamed files and folders
  • Get sync results as an email notification
  • Manage versions and keep a history of deleted/updated files
  • Compare and synchronize multiple files in parallel
  • Show drive space usage as a directory tree
  • Copy locked files (Volume Shadow Copy Service)
  • Detect conflicts and propagate deletions
  • Compare files by content
  • Configure handling of Symbolic Links, NTFS Junctions and WSL Symlinks
  • Automate sync as a batch job
  • Process multiple folder pairs
  • Comprehensive and detailed error reporting
  • Copy NTFS extended attributes (compressed, encrypted, sparse)
  • Copy NTFS security permissions
  • Copy NTFS Alternate Data Streams
  • Copy HFS+ extended attributes and ACLs
  • Support long file paths with more than 260 characters
  • Fail-safe file copy prevents data corruption
  • Cross-platform: Runs on Windows, Linux, macOS
  • Use macros %time%, %date%, et al. for recurring backups
  • Expand environment variables like %UserProfile%
  • Access variable-drive-letters by volume name (USB sticks)
  • Native 64-bit support
  • Prevent disc space bottlenecks via optimal sync sequence
  • Full Unicode support
  • Highly optimized run time performance
  • Include and exclude files via filter
  • FreeFileSync portable and local installation available
  • Handle daylight saving time changes on FAT/FAT32
  • Case-sensitive synchronization
  • Serialize multiple users accessing the same (network) folder via folder locking
  • Fully localized user interface available in 30+ languages:

Which operating systems does FreeFileSync support? FreeFileSync runs natively on all 32 and 64-bit Windows versions.
FreeFileSync runs on all recent editions of macOS.
FreeFileSync is supported on all major Linux distributions.


(*) Supported until FreeFileSync 10.11

Are there limitations on the number of files to sync? FreeFileSync imposes no artificial limitations on how many files you can sync. Practically speaking, the only limiting factor for extremely large sync jobs is the amount of free memory available: For each 1 GB of RAM, FreeFileSync can synchronize roughly 1.7 million file pairs at a time.

Is FreeFileSync free for commercial use? Yes, FreeFileSync may be used in business, commercial, and government environments without cost.

May I distribute the FreeFileSync installation package? You are permitted to distribute the software subject to the following conditions:
The software must be distributed free of charge and without modification to the contents of the installer package. Redistributing the installer package with any files added, removed, or modified is prohibited. The inclusion of the installer package or any of the included files in a different archive, or in a different installer is forbidden. For example, the integration into a third-party automated installation mechanism is forbidden without the prior permission of the author.



Do I need to uninstall FreeFileSync before installing a newer version? No, you can safely install a new version of FreeFileSync into a directory that contains an old version. FreeFileSync will recognize the previous installation and clean up thoroughly should you choose to uninstall at a later time.

No, FreeFileSync is completely ad-free! Before version 10, FreeFileSync had shown a single advertisement during installation to help fund the project. Beginning with FreeFileSync 10, the project is now fully relying on donations from users to finance its ongoing expenses in software development and support.
Thanks to everyone who is contributing to make this possible!


FreeFileSync Installer

What are the benefits of the FreeFileSync Donation Edition? Everyone who donates is eligible to download a special version of FreeFileSync without any advertisements, including a few of bonus features. The FreeFileSync Donation Edition is a thank-you for supporting the FreeFileSync project!

 Sync files without limits available available
 Ad-free installation available available
 Parallel file copy not available available
 Auto-updater not available available
ZIP file 
Portable version
Windows only
not available available
 Email notifications not available available
 Silent installation not available available
 Price Free You decide
Donation Edition Bonus Features

After donating, you are automatically redirected to a page with the download link and a confirmation email is sent, too. You can then download the Donation Edition and save it for a later installation at any time because it has an unlimited usage duration.

The download page and auto-updater will remain active for some time to download future updates of the FreeFileSync Donation Edition. The update interval is one year, assuming a €20 donation, and adapted otherwise, e.g. 6 months for a €10 donation, 2 years for a €40 donation.

Support for email notifications is linked with the update interval because they are sent using an external service (Mailgun, Amazon SES) with ongoing costs for the FreeFileSync project.
Donate Now
The FreeFileSync Donation Edition is generally expected to be used by the donor and their friends on up to 3 devices.
It is not allowed to publish the Donation Edition online, such as on a public application download website.

How does the portable installation work Local or portable installation FreeFileSync is designed for local installation and provides the best user experience in this variant.
In order to support restricted scenarios, the FreeFileSync Donation Edition also allows for portable installation on memory sticks or external hard drives. However, part of FreeFileSync's functionality may not be available in this case: For example, it will not be possible to manage FreeFileSync configuration files via context menu in Windows Explorer or start batch runs with a few mouse clicks. Therefore local installation is recommended in general.

Note: When the portable FreeFileSync Donation Edition is started for the first time, it adds the current computer to the overall device count (unless already considered).
After that, the portable storage device (USB memory stick or external hard drive) may be used on an unlimited number of computers without increasing the device count ever again.
However, if the portable installation files are copied to a different location on a new computer (instead of running directly from the portable storage device), this will increase the total device count as an additional device installation.

How can I install FreeFileSync silently via command line? The FreeFileSync Donation Edition supports silent installation via the following command line syntax:
FreeFileSync_11.14_[Donation_Edition]_Windows_Setup.exe /silent

Optional Parameters:
/dir="Installation path"
/install_type=local or portable
/create_shortcuts=yes or no
Disables the update prompt when a new FreeFileSync version is available. Instead updates are expected to be installed by a deployment system.

My virus scanner/firewall shows a scary warning. Is there a virus, malware, or trojan? No, FreeFileSync never contains malware or viruses. Both firewalls and virus scanners work with heuristics in addition to searching for known virus patterns. Heuristics are generic algorithms that try to identify malicious behavior by evaluating certain program characteristics according to their proprietary implementation.

Often, these are simplistic algorithms that bluntly flag any software as "dangerous" because it has been newly released or has only a small number of downloads yet, for example the reputation-based heuristic used by Norton by Symantec.
By their very nature, these heuristics cannot be exact and frequently lead to false-positive detections. Occasionally FreeFileSync is a victim of this.

In practice, however, one can distinguish real malware threats from heuristic alerts that contain phrases like *gen*, *generic*, *heur*, *heuristic* or *reputation* as part of the threat signature name. McAfee uses the term *artemis* instead of *heuristic*. For example
Trojan.Win32.Generic!BT, Heur.AdvML.B, WS.Reputation.1 or Artemis!24FFD34B2F78 are typical names used for AV heuristics.

In any case, when in doubt never trust a single anti-virus software and use a well known multi-engine virus scanner like VirusTotal for comparison.



How can I report bugs or suggest new features? The best place to get in contact is via the FreeFileSync Forum. This allows for other FreeFileSync users to share their experience and give immediate feedback. A lot of problems have already been discussed and solved, so searching the forum may be the quickest way to get help.

FreeFileSync has crashed/is hanging! How can I help with trouble shooting? Windows:
Usually, FreeFileSync will generate a mini dump file automatically when it detects a program crash. This file can then be sent to the FreeFileSync development team for further analysis. In some situations this will not work correctly, for example, if the process is hanging for a long time rather than crashing directly. In this case, you can create a dump file manually as follows:

1. Download Process Explorer and reproduce the hang. Now start Process Explorer and right-click on FreeFileSync_x64.exe (or *_win32.exe if you're on 32-bit Windows), select Create Dump and then Create Full Dump.


Create dump file with Process Explorer

2. Next, compress the .dmp file as zip or rar and send it to . If the attachment's size is too large for email, upload it to some free file hoster and send the link instead.

Elevate Process Explorer If creating the dump file fails with Access denied, check that Process Explorer is running with elevated rights: Menu → File → Show Details for All Processes
First, check if crash reporting is enabled by entering via command line:
defaults read DialogType

If the previous command does not return with crashreport, enable it as follows, then restart the system:
defaults write DialogType crashreport

When FreeFileSync is crashing you will now see a crash dialog:
macOS Crash Dialog
On this dialog click Report..., then Show Details, and copy all the information. You may now report these crash details on the FreeFileSync Forum or by sending an email to .

How can I record a trace file for troubleshooting file access errors? Windows:
1. Download Process Monitor and start it with filter settings reset to default. Now retry the operation with FreeFileSync that you want to trace, switch back to Process Monitor and save the trace as a .pml file.

2. You may compress this file as zip or rar and send it to . If the attachment's size is too large for email, upload it to some free file hoster and send the link instead.

sudo dtruss -d COMMAND_TO_TRACE &> ~/Desktop/trace.txt
Prerequisite: Start macOS Recovery (press and hold Command + R during start up) and enter csrutil enable --without dtrace into the Terminal, then restart: shutdown -r now.

strace COMMAND_TO_TRACE &> ~/Desktop/trace.txt

Why are network shares not found when synchronizing via Task Scheduler? 1. Test access rights: Make sure the network share was set up correctly by testing access manually with Windows Explorer and FreeFileSync.

2. Check user account: Verify that Task Scheduler is using the same user account that you used during your manual testing.
Task Scheduler security settings

3. Use UNC syntax (\\server\share): If you have mapped a network share to a local drive letter, and have set up Windows Task Scheduler to use a different user account, FreeFileSync will not be able to see the network mapping.
Access may fail even when the user account is the same, see the caveat below.

Mapped network drives are tied to a specific user session and other user accounts do not have access. In fact they may have mapped the same drive letters to completely different network shares.

Solution: Don't use drive mappings, but UNC syntax instead. You can switch between the two path formats from the drop down menu of FreeFileSync's folder input fields:
Mapped network drive alias

Caveat: Even if you are using the very same user in both Task Scheduler and in your testing, FreeFileSync may still fail to access a mapped network drive when run from the Scheduler:
For example, if you've created a non-persistent drive mapping ("Reconnect at sign-in" unchecked), the mapping will be visible only to the current user session and not to other sessions.
Map a network share
Now if you have enabled "Run with highest privileges" in Task Scheduler, a new user session with elevated rights will be created. This session corresponds to the same user account, but it will not have access to the non-persistent drive mapping, because it's a different session after all.
Had you used a persistent drive mapping instead or not run with highest privileges, this scenario would have worked.

Why does Windows Explorer show a different number of items? When synchronizing with FreeFileSync and comparing the number of items of the source and target folders with Windows Explorer, consider the following possible explanations for a mismatch.
If you still find yourself unable to explain the difference, drill down into specific folders with both applications until you find an actual file/folder that is handled differently. This should reveal what the problem is.


  • Filter settings: FreeFileSync's default filter excludes a few items that are generally not relevant for synchronization, such as $Recycle.Bin, System Volume Information, and thumbs.db. You may clear the filter settings to get an accurate account on file stats.


  • Symlink settings: By default FreeFileSync skips symbolic links.


  • Ignored errors: Check if FreeFileSync reported errors during comparison.


  • Long file paths: Unlike FreeFileSync, Windows Explorer is not able to handle file paths longer than 260 characters. Consequently, Explorer will not count files/folders with such long paths.


  • Bugs: Windows Explorer sometimes gets its numbers mixed up.

How can I fix the error "Cannot read/write permissions of <file path>"? Uncheck copy NTFS permissions Copying NTFS permissions is not needed in general and is best left disabled. Go to Menu → tools → options and ensure permission copying is unchecked.
If you are an administrator and really need to preserve DACL, SACL, Owner and Group permissions, make sure the FreeFileSync process is running with admin rights.

Why are some files still different after synchronization? Certain system software has the unfortunate habit of adding hidden alternate data streams (ADS) to newly created files. The files' modification times are then set to the current time as a consequence of this write access. Since this happens directly after FreeFileSync has copied the files, the next comparison will detect this modification just like any other external change.

To resolve this problem you first need to identify which software is responsible for the file changes by using a tool like Process Monitor. Then see if the software has options to disable the unwanted behavior. If not, you can try to file a bug report on the software's support web site, or if nothing else helps, see if you can replace it with an alternative that does not underhandedly modify files.


I have deleted files accidentally. How can I restore them? This depends on how you have set up deletion handling in synchronization settings:


  • Permanent: You can try to recover them using a file un-deletion tool. Depending on whether the physical memory blocks on the hard drive have been overwritten in the meantime, it is possible to partially or even fully restore the files.


  • Recycle Bin: The deleted files are in the Recycle bin, unless they were flushed out by newer files that were moved to the bin later.


  • Versioning: The deleted files are in the directory you have set up.