FreeFileSync - Open Source File Synchronization

Open Source File Synchronization

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

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, read chapter Tips and Tricks to boost your productivity!

Which features make FreeFileSync unique?
  • Synchronize network shares and local disks
  • Synchronize MTP devices (Android, iPhone, tablet, digital camera)
  • Synchronize via FTP (File Transfer Protocol) and FTPS (SSL/TLS)
  • Synchronize via SFTP (SSH File Transfer Protocol)
  • Detect moved and renamed files and folders
  • Show disk space usage for a directory tree
  • Copy locked files (Volume Shadow Copy Service)
  • Detect conflicts and propagate deletions
  • Compare files by content
  • Configure handling of Symbolic Links
  • 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
  • Support long file paths with more than 260 characters
  • Fail-safe file copy prevents data corruption
  • Cross-platform: Runs on Windows, Linux, macOS
  • Expand environment variables like %UserProfile%
  • Access variable drive letters by volume name (USB sticks)
  • Native 64-bit support
  • Manage versions of deleted/updated files
  • 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
  • Use macros %time%, %date%, et al. for recurring backups
  • Case-sensitive synchronization
  • Built-in locking serializes multiple users synchronizing the same network folder
  • ... download and use for free!

Which operating systems does FreeFileSync support?

FreeFileSync runs natively on all 32 and 64-bit Windows versions.
FreeFileSync runs on all recent 64-bit editions of macOS.
FreeFileSync is supported on all major Linux distributions.


Microsoft Windows Apple macOS Linux
Windows 10
Windows 8.1
Windows 8
Windows 7
Windows Vista
Windows XP
macOS 10.12  – Sierra
OS X 10.11  – El Capitan
OS X 10.10 – Yosemite
OS X 10.9 – Mavericks
OS X 10.8 – Mountain Lion

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 archive. Redistributing this archive with any files added, removed or modified is prohibited. The inclusion of any individual file from this archive in another archive without the prior permission of the author is prohibited.



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.

Should I use local or portable installation? FreeFileSync portable installation

FreeFileSync is designed for local installation and provides the best user experience in this variant.
In order to support restricted scenarios, FreeFileSync also allows for portable installation on USB memory sticks or external hard drives. However part of FreeFileSync's functionality may not be available in this case: For example it won't 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.

The FreeFileSync installer is showing a single advertisement (and only during installation) to help recover part of the software development effort, which is the time and energy invested in application design, implementation and continuous support. Although it's nowhere near enough to allow to focus on FreeFileSync full time, it is more effective than asking for donations only. If nothing else it helps keep the motivation for the project, next to the other big motivation: striving for perfection in software design.

Does FreeFileSync install advertised software silently?

No, FreeFileSync never installs anything without consent. During installation you are provided a single offer screen. If you want to support the FreeFileSync development or find the software that is shown useful, feel free to accept the offer. If not, just decline and nothing other than FreeFileSync will be installed.


single advertisement


For more info about the advertisement integration, see: installCore Installation Guidelines

Is there a version of the FreeFileSync installer without advertisements? FreeFileSync Heart
Yes, everyone who donates is offered a special version of FreeFileSync without any advertisements, including a number 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 not available available
Auto-updater not available available
Portable version (ZIP) not available available
Silent installation not available available
Price Free You decide
Donation Edition Bonus Features

Donation Free updates
€5 1 month
€10 3 months
€15 6 months
€25 1 year
After donating you are automatically redirected to a page with the download link and a confirmation email is sent, too. Depending on the donation amount the download page and auto-updater will remain active to download future FreeFileSync releases for a certain time.

Donation amounts that are between or above the numbers shown in the table are calculated accordingly, e.g. a €20 donation corresponds to 9 months, a €100 donation to 4 years, ect.

Just like the standard edition, the FreeFileSync Donation Edition can be used for an unlimited period of time, even when the free update period has expired.

The FreeFileSync Donation Edition is expected to be used by a single home user, but support for multiple users in companies and institutions is available.

The FreeFileSync Donation Edition can be used to install silently via command line:
C:\>FreeFileSync_9.0_[Donation_Edition]_Windows_Setup.exe /silent

Optional Parameters:
/dir="<Installation Path>"

Note: Some anti-virus programs, most notably Norton by Symantec may falsely flag the installer as dangerous and delete it without providing further info. This is because Norton uses a so-called "reputation-based heuristic", which will simply delete all files that are not well known or commonly downloaded. This simple algorithm is expected to fail with the FreeFileSync Donation Edition which is not widely distributed by design. As a workaround you can try to restore the deleted installer or use a smarter anti-virus program.

How can I get the Donation Edition for multiple users? Multiple Users

The normal FreeFileSync Donation Edition may be used and installed by a single home user on his computer. This includes installation on portable storage devices (USB memory sticks) and even use on different computers, provided that FreeFileSync was already activated (during first start) on the former computer.

Multi-User Licensing
Number of users: months
Include updates for

However if the portable installation files are copied to a different computer (instead of being used directly from a memory stick), this is considered a second installation.

In order to obtain the FreeFileSync Donation Edition licensed for multiple users/installations, please use the donation button here on the side.

My virus scanner/firewall shows a scary warning dialog. Is there a virus, malware or trojan?

No, the FreeFileSync installer 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 it is already sufficient to have a program access the registry or the internet to get this classification. By their very nature heuristics cannot be exact and frequently lead to false positive detections. Occasionally FreeFileSync is victim of this.

In practice however one can distinguish real malware threats from heuristic alerts: later contain phrases like *gen*, *generic*, *heur*, *heuristic* or *reputation* as part of the threat signature name, for example Trojan.Win32.Generic!BT or Heur.AdvML.B or WS.Reputation.1.

Anyway, when in doubt never trust a single anti-virus software and use an online mass virus scanner 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.

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 impact of the following settings.
If you still find yourself unable to explain the difference, drill down into specific mismatching 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 settings exclude a few items that are generally not relevant for synchronization, like the Recycle Bin or desktop.ini, thumbs.db files.


  • Symlink settings: By default FreeFileSync skips symbolic links.


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


  • 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.

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 anti-virus products, for example Comodo v8, write hidden alternate data streams to newly created files. Unfortunately this has the side effect of also setting the file modification time to the current time. Since this happens after FreeFileSync has copied the files, the next comparison will detect this modification just like any other external change.
To resolve this problem file a bug report on the anti-virus software's support web site, use a different anti-virus software that does not modify files or look for options to disable such features (e.g. disable Comodo's "File Source Tracking").

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 undeletion 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.

FreeFileSync has crashed/is hanging! How can I help with trouble shooting?

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:

Download the tool Process Explorer and reproduce the crash/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. Next, compress this file with zip or rar and send it to the email shown in FreeFileSync's about dialog.


Create dump file with Process Explorer 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

How can I record a trace file for troubleshooting file access errors?
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. You may compress this file with zip or rar and send it to the email shown in FreeFileSync's about dialog.

strace COMMAND_TO_TRACE &> ~/Desktop/trace.txt

sudo dtruss -d COMMAND_TO_TRACE &> ~/Desktop/trace.txt