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The FreeFileSync project is 100% dependent from ad revenue and donations to stay alive. Instead of the ads, and
after FreeFileSync has proven useful to you, please think about supporting with a donation.
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.
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.
Should I use 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, FreeFileSync 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 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.
Is FreeFileSync still showing an advertisement in its installer?
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!
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 for a certain time to also
download future updates of the FreeFileSync Donation Edition.
Just like the standard edition, the FreeFileSync Donation Edition has an unlimited usage duration,
even when the update period has expired.
Donation amounts that are between or above the numbers shown in the table are calculated accordingly,
e.g. a €15 donation corresponds to 8 months, a €100 donation to 5 years, etc.
The FreeFileSync Donation Edition is expected to be used by a single user (on up to 3 devices),
but support for multiple users is available.
This includes command line parameters that help to integrate into systems for mass deployment.
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.
In order to extend the FreeFileSync Donation Edition to support installations on
more than 3 devices, please use the donation buttons on the right:
When the portable FreeFileSync installation variant 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:
/dir="Installation path" /install_type=local or portable /create_shortcuts=yes or no /disable_updates
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, 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 internet to get this classification. By their very nature,
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 as they 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 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.
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:
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.
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.
If creating the dump file fails with Access denied, check that Process Explorer is running with elevated rights:
Menu → File → Show Details for All ProcessesHow 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.
2. Check user account: Verify that Task Scheduler is using the same user account that you used during your manual testing.
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
You can switch between the two path formats from the drop down menu of FreeFileSync's folder input fields:
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.
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.
FreeFileSync's default filter excludes a few items that are generally not relevant for synchronization,
such as $Recycle.Bin, desktop.ini, and thumbs.db.
You may clear the filter settings to get an accurate account on file stats.
How can I fix the error "Cannot read/write permissions of <file path>"?
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
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.
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.