Bittorrent Sync Faq


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(updated February 25, 2013)

Thanks for your interest in BitTorrent Sync! We will keep this post updated with answers to frequently asked questions and fixes for common issues with Sync.

Can other BitTorrent users see my shared files?
No. BitTorrent Sync is based on the BitTorrent protocol, but all the traffic is encrypted using a private key derived from the shared secret. Your files can be viewed and received only by the people with whom you share your private secret.

What is a "secret" and how does it work?
A secret is a key that connects different devices and joins them together. We automatically generate secrets to ensure their uniqueness. Since each secret is 20 bytes long, it is virtually impossible for the same secret to be automatically generated in two separate instances. After a folder is added to BitTorrent Sync, the Secret is stored in its advanced preferences and can be accessed by right click on a folder in the “Folders’ tab.

There are 3 types of Secrets: master (full access) secret, read only secret for one-way sync and one-time secrets (both full access and read-only). Read only and one-time secrets may be generated only for folders operated by master secrets.

If you are concerned about security, BitTorrent Sync provides opportunity to regularly generate new Secrets for a folder, or replace an existing secret with your own Base64 string more than 40 characters long. The new folder secret should be re-entered on all the devices in sync.

How do I connect mobile devices (QR code)?
Mobile device can be connected to a sync folder via a QR code. From your desktop, right-click the folder you want to sync, or go to Folder Preferences, and choose Connect Mobile. The QR code will be displayed. To sync your desktop folder to your mobile device, just scan the QR code using your smartphone.

However, if you don’t have a QR code at hand when adding a sync folder on your Android device, you can enter or paste the secret manually in the secret text field.

How soon does synchronization start?
When a file is added to the shared folder, the changes start syncing immediately (due to system peculiarities, sync on Mac OS X 10.6 may be delayed up to 10 minutes). If you change a file inside a shared folder, sync will start after the file is saved and/or closed.

It is also possible to change the period of automatic rescanning of sync folders. You can do it in Advanced application preferences - folder_rescan_interval item. Default rescan period equals 600 seconds (10 minutes).

What do the .Sync and .SyncPart extensions mean?
When a file gets .Sync and .SyncPart extension, it means that it is being downloaded or updated at the moment. .SyncPart indicates that file updates come by patching.

What happens if a file is deleted on one of the devices?
Files deleted from a sync folder on your computer are handled depending on your OS preferences (moved to Trash/Recycle Bin/similar folders or deleted completely). On the other syncing devices these files will be moved to the ‘.SyncArchive’ in their sync folders (‘.SyncArchive’ is hidden by default and also stores versions of syncing files).

What if several people make changes to the same file?
When a file is changed on one of the devices, it will be recreated as a new copy and synced to the other devices. We save only the latest version of the file.

What if files with same names are added from different computers?
We give human action first priority and always consider it right. That's why if several files with the same name are added on different devices, BitTorrent Sync will synchronize the file that was the latest added to BitTorrent Sync even if it is not the newest version of the file itself. Previously added files will be deleted, but you can find them in .SyncTrash (if enabled in folder preferences).

What happens when I remove folder from BitTorrent Sync?
If a folder is removed from BitTorrent Sync, all the synced files stay there; incomplete files with the .! sync extension will be deleted.

Does BitTorrent Sync support versioning?
Yes, versioning is available in BitTorrent Sync. It creates and stores all the old copies of edited files for the period of 30 days (this default period can be changed in General advanced preferences - sync_trash_ttl). The versions are stored in the hidden .SyncArchive directory within your sync folder that you can open by right click on the sync folder and choosing ‘Open SyncArchive’.

Old versions of a file are marked by adding numbers to its name, where the file with the highest number is the latest.

Is one-way synchronization possible?
Yes, starting from the version 1.0.95 BitTorrent Sync features one-way synchronization. It is established via read only secret (permanent or one-time). Any folder with a read-only secret will be fully synced, but changes made in this folder will not be synced back.

Do I have an option to ignore some files during sync?
If you have files in your sync folder that you don’t want BitTorrent Sync to track, you can use .SyncIgnore. .SyncIgnore is a UTF-8 encoded .txt file that helps you specify single files, paths and rules for ignoring during the synchronization job. It supports ‘?’ and ‘*‘ wildcard symbols.

Note that .SyncIgnore is applied only to the folder where it is contained and will not work with the files that have already been synced. If you add indexed files to .SyncIgnore, they will be deleted on other syncing devices. In order to avoid this:


1. Remove the folder from sync on all the devices.

2. Modify .SyncIgnore file on all of them so that it contains same info.
3. Re-add the modified folders.

Where can I get the latest version of BitTorrent Sync User Guide?
Since BitTorrent Sync is under active development, we constantly add new features to the app and consequently renew the User Guide. The latest version can always be found here.

I still have questions, who can answer them?
Try looking through the unofficial FAQ or search our forum. There are lots of friendly knowledgeable people there (including the developers) who will help. Feel free to post questions there, too, just make sure your question is not already answered.


BTSync doesn't want to start and exists with Alignment error on ARM.

You need to execute as root "echo 2 > /proc/cpu/alignment" and run btsync.


Is it possible to sync a subfolder of already synced folder?

Yes, it is possible with certain limitations:

 - Both parent folder and child folder must have RW permissions.

 - Both folders are treated as separate sync folder, so additional indexing will be done.

 - Other peers, that have parent secret WILL NOT seed the data to peers, owning secret for child folders.


Some strange files called "," are not synced from my Mac!

These strange files are so-called "Extended attributes" or xattrs. MacOS usually stores Mac-specific data in them. Starting from version 1.3 BTSync tries to sync xattrs as well as regular files. However, some of systems (like Linux) has certain limitations on the xattr naming and sizes and are unable to accept Mac's xattrs. To workaround this you may want to add some exclusions to the .SyncIgnore file on your Mac:


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