Via user guide
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:
- Quit BitTorrent Sync or remove the folder from sync on all the devices.
- Modify .SyncIgnore file on all of them so that it contains same info.
- Run BitTorrent Sync or re-add the modified folders.