= Syncthing =
Syncthing is a modern file synchronization tool. It synchronizes files between various devices and operating systems. It is a great tool for automatic backup of personal files and smartphones. It has several usefull features:

 * Easy and simple configuration
 * File versioning
 * File ignore patterns

For this setup we will use [[GlusterFS|GlusterFS]] as the file store backend.

== Software ==

Start by installing syncthing

{{{
apt-get install syncthing
}}}

== Filesystem ==

Configure your system as a [[GlusterFS Client|GlusterFS client]], so you have the following in your fstab.
{{{
/etc/glusterfs/home.vol /srv/home glusterfs defaults,_netdev,rw 0 0
}}}

== Configuration ==

For each user that is going to synchronize against this system, create a directory for them in `/srv/home` and give it the correct ownership.

{{{
mkdir /srv/home/kale
chown -R kale:kale /srv/home/kale
}}}

For each user add the syncthing service to default runlevel and start it.

{{{
systemctl enable syncthing@kale.service
systemctl start syncthing@kale.service
}}}

When the syncthing service starts, it creates a set of config files in the users home directory. Edit `/home/kale/.config/syncthing/config.xml` and look for the section below. Change the address, so the service listens on all interfaces `<address>0.0.0.0:8384</address>`, instead of just localhost. Notice that when you make this change, your syncthing service is public. Everyone can change it.

{{{#!highlight xml
<gui enabled="true" tls="false" debugging="false">
    <address>127.0.0.1:8384</address>
    <apikey>apikey</apikey>
    <theme>default</theme>
</gui>
}}}

Restart the service for the specific user.
{{{
systemctl restart syncthing@kale.service
}}}

=== GUI ===

It should now be possible to connect to the syncthing GUI on https://syncthing:8384 and configure it.

=== Credentials ===

Start by setting up a username, a password and force https. This is done in the settings dialog in the GUI tab. Your installation should now be secure.

{{attachment:syncthing-settings-gui.png||align="top"}} 

== Transfer speed ==

When transferring files, the default behavior of syncthing is to flush for every file transferred. This makes transfer of many small files very slow. The version of syncthing provided in Debian Buster does not have an option to disable syncthings use of the fsync call. In newer versions of syncthing, this can be found in `~/.config/syncthing/config.xml` as `<disableFsync>false</disableFsync>`. Changing that option to `true` will make syncthing transfer files much faster, on the expense of risking data loss. Currently the version of syncthing in Debian Bullseye does have this functionality implemented.

=== Using syncthing from bullseye ===

On a side note, it looks like the modern version (1.18.1) of the syncthing application for android, does not work with the version (1.0.0) of syncthing in Buster. It was not possible to get the two to sync properly. Using the version (1.12.1) from Bullseye made the sync possible.

Set your default release in `/etc/apt/apt.conf.d/99defaultrelease` by adding.
{{{
APT::Default-Release "stable";
}}}

Add the bullseye repository to `/etc/apt/sources.list.d/bullseye.list`
{{{
deb http://deb.debian.org/debian/ bullseye main contrib non-free
}}}

Then setup pinning in `/etc/apt/preferences.d/buster.pref`
{{{
Package: *
Pin: release a=buster
Pin-Priority: 1000
}}}

And in `/etc/apt/preferences.d/bullseye.pref`
{{{
Package: syncthing
Pin: release a=bullseye
Pin-Priority: 500
}}}

Install syncthing from bullseye
{{{
apt-get update
apt-get -u install syncthing/bullseye
}}}
=== Using eat my data ===
A library called libeatmydata has been created to stop applications like syncthing from using fsync, by replacing the fsync library call.

{{{
apt-get install eatmydata
}}}

Link syncthing to eatmydata
{{{
ln -s /usr/bin/eatmydata /usr/local/bin/syncthing
}}}

Now change the init script for the syncthing service in `/lib/systemd/system/syncthing@.service` to use the version of syncthing in `/usr/local/bin`, and eatmydata will take care of the fsync call.
{{{#!highlight bash
[Unit]
Description=Syncthing - Open Source Continuous File Synchronization for %I
Documentation=man:syncthing(1)
After=network.target

[Service]
User=%i
ExecStart=/usr/local/bin/syncthing -no-browser -no-restart -logflags=0
Restart=on-failure
SuccessExitStatus=3 4
RestartForceExitStatus=3 4

# Hardening
ProtectSystem=full
PrivateTmp=true
SystemCallArchitectures=native
MemoryDenyWriteExecute=true
NoNewPrivileges=true

[Install]
WantedBy=multi-user.target
}}}

Let systemd know that you changed a service
{{{
systemctl daemon-reload
}}}

Finally restart the syncthing service
{{{
systemctl restart syncthing@kale.service
}}}

== Instances ==

 * Kalle https://syncthing:8384/
 * Sanne https://syncthing:8385/
 * Family https://syncthing:8386/
 * Viktor https://syncthing:8387/
 * Karla (8388)
 * Jonna (8489)

== References ==

 * https://theselfhostingblog.com/posts/how-to-set-up-a-headless-syncthing-network/
 * https://docs.syncthing.net/advanced/folder-disable-fsync.html
 * https://wiki.debian.org/SimpleBackportCreation