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The FreeFileSync project is 100% dependent on 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.
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.
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
FreeFileSync is designed for local installation and provides the best user experience in this variant.
In order to support restricted scenarios, the 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 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.
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.
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.
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 ProcessesmacOS:
First, check if crash reporting is enabled by entering via command line:
defaults read com.apple.CrashReporter DialogType
If the previous command does not return with crashreport, enable it as follows, then restart the system:
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, System Volume Information, 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.