BitTorrent Sync FAQ *unofficial*

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Firstly, a big welcome to all you new BitTorrent Sync users!


Don't know where to begin with Sync? - Check out the Getting Started guide or explore the new Sync Help Center.

The forum has exploded into life since BitTorrent Sync first went "public" on Tuesday 23rd April 2013, so I thought I'd make a supplementary post to compliment the official "BitTorrent Sync FAQ"

I'll keep this updated with simple, concise answers to common questions that keep cropping up, and which aren't, as yet, covered elsewhere.


Having a problem with Sync? Be sure to check out the Unofficial Troubleshooting FAQ as well!


Where can I download the latest version of BitTorrent Sync?

Right here: (Changelog)

Installing on a NAS? See Supported NAS

Other unofficial, user-contributed, packages: Ubuntu/Debian (Servers) | Ubunti/Debian (Desktops) | Gentoo ebuild

Note: If you currently use the auto-update feature of BitTorrent Sync, it may inform you that your "Client version is up to date" despite a newer build being available. This is intentional whilst Sync remains in "beta" - new builds are currently announced here in the forums in the first instance. Not every "beta" build is pushed via auto-update, only those considered significant/more stable. Even then these may not be pushed out to existing users via auto update until several days/weeks after they are first announced on the forums - therefore, before reporting any issues/bugs with Sync, please the pinned topics at the top of this forum to find the latest beta version of Sync, and ensure you're running this first)

Will BitTorrent Sync remain free, or will they start charging for it once it comes out of beta?

BitTorrent Sync will remain free! :)

From BitTorrent:

"If tomorrow we want to charge you $100 for 10Kb transferred, stop everything related to the app or try to force you not to use BitTorrent Sync, we just physically can't achieve that!

BitTorrent Sync will work tomorrow exactly like it works today, no matter what we will do. And it will work exactly like today even 10 years from now, of course, if we will have computers in future :)" (Source)

...and in publicising the start of the "beta" phase on 17 July 2013, the team commented: "And don’t worry. BitTorrent Sync is still free, simple to use, and secure. Pretty awesome, huh?"

Is BitTorrent Sync open-source?

BitTorrent Sync isn't open source software, although the developers have previously commented "Never say never - we still consider this option" (Source). There's also a related discussion on whether Sync will be open source here


Some unofficial open-source projects related to Sync that you may be interested in contributing code to include:

What data is collected/seen by BitTorrent Inc when I use Sync?

According to BitTorrent Inc, "There are 3 points of contact with BitTorrent infrastructure: tracker, relay, and check for update service. If you don't use any of these - we will not get any information about you." For more information on what data is seen by BitTorrent Inc, please see this thread

How secure are "keys"... can they be "guessed"?

In a nut shell, "keys" (formally known as "secrets") are extremely secure, and can't realistically be simply "guessed" by others.

You can find out more in this blog post. Additionally, there are plenty of existing topics discussing this particular topic too: (1 | 2 | 3 | 4 | 5 | 6 | 7). Please review/contribute to these threads before considering opening ANOTHER thread on this subject!

Is there an API available?

Yes! - An API is available with Sync 1.2 and later. Please see the API documentation

There is also a dedicated "API wishlist" thread for contributing your suggestions for API functionality n future updates.

Is there an Android/iPhone Mobile App?

Android_Icon.png The official android app is available in the Google Play Store and requires Android 2.2 or higher, and is currently only supported on ARM architecture (for x86 architecture support please see this thread).


Iphone_Icon.png The official iOS app is available in the iTunes Store and requires iOS 5.0 or higher.

Windows_Phone_Icon.png A Windows Phone app is also available from the Windows Store and requires Windows Phone 8 or higher.

An Amazon Kindle app is available in the Amazon App Store.


You can also request mobile-specific features for the various Sync mobile clients in this thread.


Blackberry_Icon.png What about Blackberry support? See this post

Can I control how frequently syncing occurs?

Syncing happens in real time. In addition, as a fall back, BitTorrent Sync also rescans files/folders every 10 minutes by default. If you're running BitTorrent Sync 1.1.12 (or later), you can now configure this interval via the advanced "folder_rescan_interval" setting (default value is "600" (seconds) = 10 minutes)

Will me devices still sync when switched off?

BitTorrent Sync is not a cloud storage solution like SkyDrive/DropBox/GDrive, etc - it doesn't sync your files to a "cloud", therefore for one device to sync with another, both devices need to be online.

If you require an always-on "cloud" functionality for Sync, there are a number of companies now offering dedicated BitTorrent Sync solutions, some of which you'll find listed here

Can I use BitTorrent Sync to backup from an internal drive to an externally connected USB drive?

No, BitTorrent Sync will not permit you to sync one folder location on your computer to another location on the same computer (i.e. you can't have two shared folders using the same "secret" on the same device)


Can I force Sync to do local network (LAN) syncing only and not sync via the Internet?

Yes - simply disable the Relay, Tracker, and DHT options (these are per-folder settings). Sync will then no longer connect to any remote devices (outside your local network).

What does the relay.png icon mean?

Sync tries wherever possible to establish "direct" connections between your other devices. Where this is not possible (i.e. router/firewall blocks, etc), Indirect (Relayed) Connections will be established instead.

These "relayed" connections are indicated by a relay.png icon adjacent to each device in a folder's Peer list.

It is preferable to have direct connections wherever possible, as this will generally provide faster transfer speeds over that of a relayed connection.

What are .SyncID, .SyncIgnore, .SyncPart, .SyncTemp .SyncOld and .!Sync files and the .SyncArchive folder?

When you add a new folder to BitTorrent Sync a number of hidden files/folder are automatically created in the folder. The purpose of each are as follows:

.SyncID (pre 1.4) / .sync/ID (1.4+) = A file containing the unique, internal "ID" of the folder. This file should not be manually modified, or deleted. If you do, the folder will no longer be recognized in BitTorrent Sync.

.SyncIgnore (pre 1.4) / .sync/IgnoreList (1.4+) = A user editable file allowing you to "exclude" certain files/sub folders for being sync'd

.sync/StreamsList (1.4+) = A user editable file allowing you to "white list" alternate streams, xattrs and resource forks (mainly for OSX users)

.SyncArchive (pre 1.4) / .sync/Archive (1.4+) = BitTorrent Sync, by default, won't actually delete any of your files/folders. If a corresponding file/folder is deleted on another device, it will simply be "moved" into the .SyncArchive folder on all other devices, rather than being permanently deleted. (In Sync pre v1.1.40, this folder was named .SyncTrash and was later renamed to .SyncArchive as this folder now stores both local files deleted on remote devices, as well as "versioned" files. From Sync 1.4 onwards, this folder has again been renamed to .sync/Archive)

.!Sync files = Temporary files created by BitTorrent Sync when receiving incoming data transfers. Once a file is fully received, it is then renamed to have its .!Sync extension removed i.e. "file.mp3" will become "file.mp3.!Sync" on receiving devices until all data for the file is fully received, at which point it will be renamed back to "file.mp3".

.SyncPart / .SyncTemp = Please see this post

.SyncOld = Usually contains a backup of a file when that file gets transferred to your device partially from another location. After the transfer is successful, the .syncold file gets moved to .SyncArchive folder (if allowed in settings).


Is there a limit on the number/size of files I can sync?

There are no limits imposed on the number, or size, of files you can sync with BitTorrent Sync, however there are two factors to take into account:

  • How much free disc space you have on the devices you're syncing - if you do not have enough free disc space for the files you wish to sync, they will not sync
  • How much free memory your devices have. In 1.1.x builds, memory usage increases by around 300-400 bytes per file being monitored by BitTorrent Sync. Therefore, if you're monitoring/syncing 1 million files, you will need around 300-400 MB of free memory.
Is there a limit on the number of devices I can connect/share with?

As the current free offering of Sync is designed primarily for home/personal use, there is a 50 peer limit per secret. The ability to change/raise this limit will likely be an enterprise/business feature in the future.


When a file changes, does BitTorrent Sync transfer the entire file again, or just the part that's changed?

Files smaller than 4MB are transferred again in their entirety when changes are detected.

Larger files, however, are split into 4MB "chunks" of data, if one chunk changes, but the others don't, only the chunk that's changed will be transferred (instead of the whole file again). (Source)

How long are files kept in .SyncTrash/.SyncArchive for?

From v1.1.30 onwards, deleted files are kept in .SyncArchive (or .SyncTrash pre v1.1.40, or .sync/Archive from 1.4 onwards) for a default period of 30 days, after which they will be automatically removed. You can change this default period by adjusting the advanced "sync_trash_ttl" setting.


What's the difference between "Secrets" and "Keys"?

Nothing! They are the same! In Sync 1.3 (and earlier) the term "Secret" was used. In Sync 1.4 and later, the term "Key" is used instead - they refer to the same thing.

Is "SyncApp" the same as "BitTorrent Sync"?

Yes, "SyncApp" was the former name of "BitTorrent Sync", so if you see lingering references to "SyncApp" in the forums or elsewhere, don't be concerned! - they are one and the same!

How do I use "*" and "?" wildcards in .SyncIgnore files?

"?" is a substitute for a single character instance,

"*" is a substitute for multiple character instances.

Four examples:

  • *.dat would exclude from syncing all .dat files types regardless of name i.e. myfile.dat, anotherfile.dat, ete
  • abc???.dat would exclude from syncing files named "abc123.dat", "abcdef.dat", etc... but wouldn't exclude files named "abc1.dat" or "abcdefg.dat", etc
  • *.mp? would exclude from syncing file types such as .mp3, .mp4, .mpa, etc, but wouldn't exclude file types such as .mpeg
  • /*.avi would exclude from syncing .avi file types contained in the root folder only (any .avi files in sub folders will still sync)
How can I improve sync/transfer speed?

A number of factors can affect how quickly your files transfer between devices. One of the most significant is whether your other devices are connected "directly" (i.e. appear on the same LAN), or "indirectly" (relayed). to determine this, please see "What do the device icons mean?" above.


Generally speaking, "direct" connections are preferable as they are significantly faster than relayed connections. Therefore, the first step to improving sync speed would be to try and ensure that direct connections are established between your devices. If they all reside on the same physical local LAN, this shouldn't be a problem. However, if they are "remote", you could consider establishing an VPN in order to make your remote devices appear as though they're all on the same local LAN.


Once your devices all appear on the same LAN, follow the steps outlined above for "Can I force Sync to do local network (LAN) syncing only and not sync via the Internet?" to restrict syncing to your local LAN.


Next, if possible, assign static IPs to your devices, and then use the "pre-defined hosts" settings (again, these are per folder) to list your devices. At the same time, untick the "Search LAN" option. By doing this, Sync will then know exactly where to connect without having to spend time searching for other devices.


Make sure you've not set any upload/download rate limits in Sync, and set the advanced "rate_limit_local_peers" setting is set to "false"


Another advanced setting that can be set to "false" to potentially further improve transfer speed is the "lan_encrypt_data" setting.


If you have a more powerful device, you could also consider setting "disk_low_priority" to "false", and increasing the size of "recv_buf_size" and "send_buf_size" to get a further speed advantage.


One final thing that can improve overall performance of Sync is how fragmented your hard discs are. The less fragmented, the better nc indexing speed will be - so if you've not de-fragmented your drives for a while, it's worth doing!



Windows_icon24.png Windows-specific:

How to make BitTorrent Sync "Portable"

Running Sync directly from a USB Stick/Memory Card was officially supported up until version 1.2.24. The Sync team have since removed this option in more recent builds whilst they focus on "higher priority" development tasks. "Portable Mode" may return in the future.


In the meantime, there is an unofficial workaround to run the latest builds of 1.3.x in "Portable Mode" directly from your USB Stick/Memory Card, however, do bear in mind that "Portable Mode" is no longer officially supported, and won't work at all with 1.4.x builds.


How to make BitTorrent Sync run as a service

Please see Start Sync as a service on Windows

Is there a Command Line Interface (CLI) for BitTorrent Sync on Windows?

Not at this time! The CLI is only available for Linux builds

Linux_icon24.png Linux-specific:

Is there a MIPS build?

There are no MIPS builds of BitTorrent Sync at the present time, however, according to the developers, "We plan to add MIPS support", although there is no timescale at present.

How do you define multiple shared folders in the config file?

Please see this thread

How do you secure the WebUI with a password?

By default, the web-based User Interface for BitTorrent Sync isn't password protected. To protect your WebUI (recommended) please see this thread



...and finally...

...Please do bear in mind that BitTorrent Sync is currently just a "beta", and therefore it may not currently have all the features/functionality/behavior that you'd ideally like to see! If you experience an issue/bug there are instructions on how to report it here. There is also a dedicated and very active "Feature Requests" forum where you can contribute ideas & suggestions as to what you think would make BitTorrent Sync even better! The developers do read all these feature requests, and are taking note as to the popularity of each suggestion... so give them time, and I'm sure BitTorrent Sync will get ever better! :)

Edited by GreatMarko
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I wish to know how the protocol works, specially how it can find computer A synced with computer B, I know is bittorrent protocol, but obviously you need a tracker, right?, if the tracker, one?, many?, are down by X-Force, how can it work? it can?...

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I've been a SyncApp user for some time, enjoying it immensely, although it has it's own flaws.

Question about transition from SyncApp to BitTorent Sync:

  • I've used SyncApp for some time, 3 folder with ~20GB of data across 2 machines (Win & Mac)
  • Installed new version called BitTorrent Sync & uninstalled SyncApp

Will I be safe with my files by creating new "secrets" on one machine and getting the files from/to exact same folders I used for SyncApp? My concern here is about overwriting and damaging files (and that's my work there), also 20GB of traffic may be too much.

So am I safe by doing so?


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theo, it's a shame you've uninstalled SyncApp, because (depending upon which version of SyncApp you were on), you could have just copied the settings across to BitTorrent Sync and carried on as it nothing had happened!

The way to do this is simply to exit BitTorrent Sync, copy across everything in the %AppData%\Roaming\SyncApp folder across to the %AppData%\Roaming\BitTorrent Sync folder and voila! when you restart BitTorrent Sync, all your previously sync'd folders should appear!

However, if you've indeed completely uninstalled SyncApp and all corresponding settings files, you may not still have your %AppData%/Roaming/SyncApp folder... in which case you will have to re-add each folder to BitTorrent Sync again!

This shouldn't be an issue, but it will mean that everything will be re-index, and BitTorrent Sync may prompt you when you add a folder to reset ownership on folder you're syncing - just accept these prompts if they appear, and all should be good!

If your folders were in sync in SyncApp, whilst re-adding them to BitTorrent Sync will re-index them, it won't transfer them all again if they haven't changed! (i.e. if they are already in sync)

Hope that helps! :)

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  • 2 weeks later...

Is there anyway to see the sync'ing progress when the webui is deactivated on linux ? I use the option shared_folders.

Hmm... not to my knowledge! ...unless there's something in the CLI (command line interface)? - The CLI is primarily for controlling/managing BitTorrent Sync, rather than reporting on current transfer status - but you could try running BitTorrent Sync with the --help argument anyhow to see a list of available commands, and see if there's anything there that may be of use!?

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  • 2 weeks later...

Great page. Could anyone please add an explanation for the Status column on the Devices tab? What do these mean?

U: (size)

D: (size)

Up/Down arrows

I.e. does "U" mean "Waiting to upload" or "Actually uploading", etc.? What's the diff between a U and an up arrow? Etc.


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An "up" arrow (↑) denotes the amount of data being sent from BitTorrent Sync to the device listed in the Devices tab

A "down" arrow (↓) denotes the amount of data being received by BitTorrent Sync from the device listed in the Devices tab

Not entirely sure about "U" and "D" - are you seeing these as well as up/down arrows? I have seen U: and D: in earlier builds, but assumed these had simply been replaced with up/down arrow icons?

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Thanks again, but this leaves more questions.

- I currently see an Up Arrow with a size of 3.2GB. But the sum of all current transfers ongoing is closer to 50 kBps. So the meaning of the Up Arrow is something nuanced, not simply "amount of data being sent/received." Any further details?

- What's the difference between a "U" and an Up Arrow? I see both at different times, on the same machine. The status changes back and forth between letters and arrows. Both of my machines are running version 1.0.134. Currently one machine shows U:1.2GB, D:3.2GB; the other machine shows UP Arrow 3.2GB, DOWN Arrow 1.1GB. Both machines show the same two files in the Transfers tab.

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- I currently see an Up Arrow with a size of 3.2GB. But the sum of all current transfers ongoing is closer to 50 kBps. So the meaning of the Up Arrow is something nuanced, not simply "amount of data being sent/received." Any further details?

Don't get confused between the amount of data being transferred and the speed that the data is being transferred. The "status" column of the Devices tab indicates the amount of date to be transferred/received, along with the corresponding up/down arrow

- What's the difference between a "U" and an Up Arrow? I see both at different times, on the same machine. The status changes back and forth between letters and arrows. Both of my machines are running version 1.0.134. Currently one machine shows U:1.2GB, D:3.2GB; the other machine shows UP Arrow 3.2GB, DOWN Arrow 1.1GB. Both machines show the same two files in the Transfers tab.

Ok, I've done a bit more digging - are both your devices running the same version of Windows?

If not, this will likely be the reason why one shows "U: 1.2GB, D: 3.2GB" and the other shows "↑ 3.2GB, ↓ 1.2GB". For instance, on Windows 7 and Server 2008, I see ↑/↓ arrows, whereas on Server 2003, I see U:/D: instead.

It's therefore safe to assume that the "up arrow" is the same as "U:" and the "down arrow" is the same as "D:" (i.e. earlier Windows OS versions are perhaps unable to display the graphical arrows, and so they are instead substituted with corresponding U/D letters)

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  • 2 weeks later...

jonnojohnson, there are all kinds of issues surrounding the idea of being able to sync a parent folder separately to a sub folder. There was quite a length discussion on "nested" shares a while ago, with the official word from the developers at the time being "We see a demand for this and will add it soon." (Source).

My advice would be to post your suggestion in the Wishlist thread, as the more popular certain ideas become, the greater the chance that the developers are likely to look at implementing them!

In the meantime, the workaround for your scenario would be to not sync the parent folder, and instead setup individual syncs on each of the sub-folders. That way you can precisely control which sub-folders sync where!

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Thanks for the info GM. Unfortunately I can't access this site from work so I haven't been able to get through the forum much.In fact one of the things I'm excited about with Sync is that it works from behind our firewall.

Anyway I really want to use Sync for both backup (RO Sync of almost everything) and selective sync of subfolders so "nested share" capability is huge for me.

The more I think about the possibilities of Sync - especially if the API is complete - the more I think the possibilities are endless.

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  • 1 month later...


I cant connect to devices when i am on different networks along with the "use tracker server" option not being used.

as soon as i enable that option.. devices on different networks immediately see each other.

so in a nutshell.. if i dont use tracker.. i cant have devices see each other on different networks. like wifi and 3g.

I have read the security details mentioned in the thread link under this heading "What data is collected/seen by BitTorrent Inc when I use Sync" in this post.. but i still dont understand what information does the tracker contains that allows the devices to see each other? this tracker seems to be equivalent to THAT small .torrent file which allows anyone to get access to the shared content in normal torrent sharing.

how is the tracker used in btsync different from these .torrent files? and what will stop from any hacker who might hack the server where this tracker information is, to get access to my information?

Thanks.. for the help.

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Well, yes. That's exactly what a tracker does - how did you expect the devices should find each other?

In my understanding the tracker has a hash of the secret plus the IP/Port of devices with folders for that secret, and that's it.

With that information alone you cannot access the shared data (but you do know where to reach the devices for additional attacks - which is why it's so important BTSync and its protocol become open source at some point...).

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  • 2 weeks later...

Hi, very valuable info this is.

I have an issue though with the BitTorrent Sync App. I recently installed it on Windows XP SP3 and connected it to my Windows 7 PC from where i wish to be synchronizing files from.

1. I successfully link both devices. BUT

2. synchronization does not take place...

The two PCs are on the same LAN, using a P2P wireless link for connectivity.

Your assistance will be highly appreciated.

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  • 3 weeks later...

Once you make a folder 'live' and people are connected to it, that entire folder acts as a 'group' folder correct?


So if one person deletes a file, its deleted for everyone?

Correct (but if you're using SyncArchive, the file will still be present in the SyncArchive folder if deleted by another user)

So if someone sends you files that you never intent to delete, it's best to make another copy that file and place somewhere else?

...or you could consider using read-only secrets, or even changing a folder's secret/removing it from Sync once you've received all the expected files

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