# BitTorrent Sync

BitTorrent Sync (BTSync) is a file sharing system that relies on the BitTorrent protocol, and differs from other file sharing software in the connection type between devices. Instead of uploading the files to an online server, and then each device fetching them from the server itself, the file transfer is done directly from peer to peer, and therefore there is no limit on data storage and/or transfer speed.

## Security

BitTorrent Sync encrypts the traffic between devices with AES cypher and a 256-bit key created on the base of the secret — a random string (20 bytes or more) that is unique for every folder to be synchronized.

## Secrets

BitTorrent Sync uses a specific method for folder sharing, the 'secret': a random 21-byte key Base32-encoded.

## Synchronization

When a device adds a folder for synchronization, a secret is generated. From now on, every device that wants to synchronize that folder must know the secret key.

The synchronization has no speed or size limits, as long as both devices have enough disk space.

## Installation

btsync can be installed from the AUR. The package includes systemd service definitions for managing the btsync daemon. This package creates a default /etc/btsync.conf for system/root operation. Before enabling with systemctl review this file and make desired changes, e.g. to the login id and password.

Alternatively, the bare 'tar.gz' packaged executable is downloadable from the official website. The rest of this guide assumes that you are using the btsync AUR package.

## Usage

The Linux client of BTSync does not use a typical GUI, instead it sets up a WebUI server accessible at `localhost:8888`. Shared folders can also be configured statically in a configuration file, but doing so disables the WebGUI.

Once installed, you'll first need to create a configuration file at `~/.config/btsync/btsync.conf`, see #Configuration. When that is done, start and (if you want it to start on boot) enable the service:

    # systemctl start btsync@user
    # systemctl enable btsync@user

replacing `user` by the desired username. The service will run as the named user.

You can also run it as the `btsync` system user, just leave the `@user` part out:

    # systemctl enable btsync
    # systemctl start btsync

Configuration for this user is located at `/etc/btsync.conf`, and metadata is saved in `/var/lib/btsync/` by default. You should review the configuration settings especially user and password, see below.

## Configuration

A sample configuration file can be created using `btsync --dump-sample-config`. You'll probably want to change some of the settings, including:

- device_name
- storage_path
- webui/login
- webui/password

Note: The storage_path setting defines where metadata will be saved, not the synced files themselves. Where synced files are saved is configured on a per-folder basis in the WebGUI.

### Automatic config file creation

The btsync-autoconfig package provides a systemd service (btsync-autoconfig@user.service) that, if enabled, triggers when btsync@user.service starts and creates a config file with default values if it does not already exist. The install script enables btsync-autoconfig@user.service by default.

btsync-autoconfig@user.service creates `~/.config/btsync/btsync.conf` if it does not exist, and guesses some default values of the settings:

- device_name: `$USER@$HOSTNAME`
- storage_path: `~/.btsync`
- webui/login: `$USER`/password

## Troubleshooting

### Missing storage path

If you start the service but can't reach the WebUI, check the status of the btsync by entering `systemctl status btsync@user`.

A common error is `Storage path specified in config file does not exist.`. btsync-autoconfig does generate a config file, but not the storage directory, do so by entering e.g. `mkdir ~/.btsync`.

### WebUI is not running on port 8888

If the config file was generated by btsync-autoconfig it will be configured with a different port. Rather than 8888, the port for the user's instance of `btsync` will be `7889 + $UID`. If your `$UID` is "1000", the port will be 8889.

### WebUI is not running on `7889 + $UID`

The btsync-autoconfig does not create $HOME/.btsync directory. This will cause the start up to fail.

### Ignore some files/folders syncronization

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:

- Remove the folder from sync on all the devices.
- Modify .SyncIgnore file on all of them so that it contains same info.
- Re-add the modified folders.

### ARM alignment error

Add the line `w /proc/cpu/alignment - - - - 2` to `/etc/tmpfiles.d/btsync.conf`. (You need to create the file).
Note that this may lead to performance degradation.

## See Also

Official BitTorrent Sync FAQ

Category:

- Internet applications