.. _faq:

FAQ
===

General
-------

What is Syncthing?
~~~~~~~~~~~~~~~~~~

Syncthing is an application that lets you synchronize your files across
multiple devices. This means the creation, modification or deletion of
files on one machine will automatically be replicated to your other
devices. We believe your data is your data alone and you deserve to
choose where it is stored. Therefore Syncthing does not upload your data
to the cloud but exchanges your data across your machines as soon as
they are online at the same time.

Is it "syncthing", "Syncthing" or "SyncThing"?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It's **Syncthing**, although the command and source repository is
spelled ``syncthing`` so it may be referred to in that way as well. It's
definitely not :strike:`SyncThing`, even though the abbreviation
``st`` is used in some circumstances and file names.

How does Syncthing differ from BitTorrent Sync?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The two are different and not related. Syncthing and BitTorrent Sync
accomplish some of the same things, namely syncing files between two or
more computers.

BitTorrent Sync by BitTorrent, Inc is a proprietary peer-to-peer file
synchronization tool available for Windows, Mac, Linux, Android, iOS,
Windows Phone, Amazon Kindle Fire and BSD.
`1 <http://en.wikipedia.org/wiki/BitTorrent_Sync>`__ Syncthing is an
open source file synchronization tool.

Syncthing uses an open and documented protocol, and likewise the
security mechanisms in use are well defined and visible in the source
code. BitTorrent Sync uses an undocumented, closed protocol with unknown
security properties.

Usage
-----

What things are synced?
~~~~~~~~~~~~~~~~~~~~~~~

The following things are *always* synchronized;

-  File Contents
-  File Modification Times

The following may be synchronized or not, depending;

-  File Permissions (When supported by file system. On Windows, only the
   read only bit is synchronized.)
-  Symbolic Links (When supported by the OS. On Windows Vista and up,
   requires administrator privileges. Links are synced as is and are not
   followed.)

The following is *not* synchronized;

-  File or Directory Owners and Groups (not preserved)
-  Directory Modification Times (not preserved)
-  Hard Links (followed, not preserved)
-  Extended Attributes, Resource Forks (not preserved)
-  Windows, POSIX or NFS ACLs (not preserved)
-  Devices, FIFOs, and Other Specials (ignored)
-  Sparse file sparseness (will become unsparse)

Is synchronization fast?
~~~~~~~~~~~~~~~~~~~~~~~~

Syncthing segments files into pieces, called blocks, to transfer data
from one device to another. Therefore, multiple devices can share the
synchronization load, in a similar way as the torrent protocol. The more
devices you have online (and synchronized), the faster an additional
device will receive the data because small blocks will be fetched from
all devices in parallel.

Syncthing handles renaming files and updating their metadata in an
efficient manner. This means that renaming a large file will not cause a
retransmission of that file. Additionally, appending data to existing
large files should be handled efficiently as well.

Temporary files are used to store partial data downloaded from other devices.
They are automatically removed whenever a file transfer has been completed or
after the configured amount of time which is set in the configuration file (24
hours by default).

Should I keep my device IDs secret?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

No. The IDs are not sensitive. Given a device ID it's possible to find
the IP address for that node, if global discovery is enabled on it.
Knowing the device ID doesn't help you actually establish a connection
to that node or get a list of files, etc.

For a connection to be established, both nodes need to know about the
other's device ID. It's not possible (in practice) to forge a device ID.
(To forge a device ID you need to create a TLS certificate with that
specific SHA-256 hash. If you can do that, you can spoof any TLS
certificate. The world is your oyster!)

See also `Understanding Device
IDs <http://docs.syncthing.net/dev/device-ids.html>`__.

What if there is a conflict?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Syncthing does recognize conflicts. When a file has been modified on two
devices simultaneously, one of the files will be renamed to
``<filename>.sync- conflict-<date>-<time>.<ext>``. The device which has
the larger value of the first 63 bits for his device ID will have his
file marked as the conflicting file. Note that we only create
``sync-conflict`` files when the actual content differs.

Beware that the ``<filename>.sync-conflict-<date>-<time>.<ext>`` files
are treated as normal files after they are created, so they are
propagated between devices. We do this because the conflict is detected
and resolved on one device, creating the ``sync-conflict`` file, but
it's just as much of a conflict everywhere else and we don't know which
of the conflicting files is the "best" from the user point of view.
Moreover, if there's something that automatically causes a conflict on
change you'll end up with
``sync-conflict-...sync-conflict -...-sync-conflict`` files.

How to configure multiple users on a single machine?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Each user should run their own Syncthing instance. Be aware that you
might need to configure ports such that they do not overlap (see the
config.xml).

Is Syncthing my ideal backup application?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

No, Syncthing is not a backup application because all changes to your
files (modification, deletion, etc) will be propagated to all your
devices. You can enable versioning, but we encourage the use of other
tools to keep your data safe from your (or our) mistakes.

Why is there no iOS client?
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Alternative implementation Syncthing (using the Syncthing protocol) are
being developed at this point in time to enable iOS support.
Additionally, it seems that the next version of Go will support the
darwin-arm architecture such that we can compile the mainstream code for
the iOS platform.

Why does it use so much CPU?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1. When new or changed files are detected, or Syncthing starts for the
   first time, your files are hashed using SHA-256.

2. Data that is sent over the network is first compressed and then
   encrypted using AES-128. When receiving data, it must be decrypted
   and decompressed.

Hashing, compression and encryption cost CPU time. Also, using the GUI
causes a certain amount of CPU usage. Note however that once things are
*in sync* CPU usage should be negligible.

How can I exclude files with brackets (``[]``) in the name?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The patterns in .stignore are glob patterns, where brackets are used to
denote character ranges. That is, the pattern ``q[abc]x`` will match the
files ``qax``, ``qbx`` and ``qcx``.

To match an actual file *called* ``q[abc]x`` the pattern needs to
"escape" the brackets, like so: ``q\[abc\]x``.

Why is the setup more complicated than BTSync?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Security over convenience. In Syncthing you have to setup both sides to
connect two nodes. An attacker can't do much with a stolen node ID,
because you have to add the node on the other side too. You have better
control where your files are transferred.

How do I access the web GUI from another computer?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The default listening address is 127.0.0.1:8384, so you can only access
the GUI from the same machine. Change the ``GUI listen address`` through
the web UI from ``127.0.0.1:8384`` to ``0.0.0.0:8384`` or change the
config.xml:

.. code:: xml

    <gui enabled="true" tls="false">
      <address>127.0.0.1:8384</address>

to

.. code:: xml

    <gui enabled="true" tls="false">
      <address>0.0.0.0:8384</address>

Then the GUI is accessible from everywhere. You should most likely set a
password and enable HTTPS now. You can do this from inside the GUI.

If both your computers are Unixy (Linux, Mac, etc) You can also leave
the GUI settings at default and use an ssh port forward to access it.
For example,

.. code:: bash

    $ ssh -L 9090:127.0.0.1:8384 user@othercomputer.example.com

will log you into othercomputer.example.com, and present the *remote*
Syncthing GUI on http://localhost:9090 on your *local* computer. You
should not open more than one Syncthing GUI in a single browser due to
conflicting X-CSRFTokens. Any modification will be rejected. See `Issue
720 <https://github.com/syncthing/syncthing/issues/720#issuecomment-58159631>`__
to work around this limitation.

The CSRF tokens are stored using cookies. Therefore, if you get the
message
``Syncthing seems to be experiencing a problem processing your request``,
you should verify the cookie settings of your browser.

Why do I see Syncthing twice in task manager?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

One process manages the other, to capture logs and manage restarts. This
makes it easier to handle upgrades from within Syncthing itself, and
also ensures that we get a nice log file to help us narrow down the
cause for crashes and other bugs.

Where do Syncthing logs go to?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Syncthing logs to stdout by default. On Windows Syncthing by default
also creates ``syncthing.log`` in Syncthing's home directory (check
``-help`` to see where that is).

How do I upgrade Syncthing?
~~~~~~~~~~~~~~~~~~~~~~~~~~~

- If automatic upgrades is enabled (which is the default), Syncthing will upgrade itself automatically within 24 hours of a new release.

- The upgrade button appears in the web GUI when a new version has been released. Pressing it will perform an upgrade.

- To force an upgrade from the command line, run ``syncthing -upgrade``.

Note that your system should have CA certificates installed which allow a secure connection to GitHub (e.g. FreeBSD requires `sudo pkg install ca_root_nss`). If ``curl`` or ``wget`` works with normal HTTPS sites, then so should Syncthing.

Where do I find the latest release?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We release new versions through GitHub. The latest release is always found `on
the release page <https://github.com/syncthing/syncthing/releases/latest>`_.
Unfortunately GitHub does not provide a single URL to automatically download
the latest version. We suggest to use the GitHub API at
https://api.github.com/repos/syncthing/syncthing/releases/latest and parsing
the JSON response.
