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 as the file store backend.

Software

Start by installing syncthing

apt-get install syncthing

Filesystem

Configure your system as a 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.

   1 <gui enabled="true" tls="false" debugging="false">
   2     <address>127.0.0.1:8384</address>
   3     <apikey>apikey</apikey>
   4     <theme>default</theme>
   5 </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.

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.

   1 [Unit]
   2 Description=Syncthing - Open Source Continuous File Synchronization for %I
   3 Documentation=man:syncthing(1)
   4 After=network.target
   5 
   6 [Service]
   7 User=%i
   8 ExecStart=/usr/local/bin/syncthing -no-browser -no-restart -logflags=0
   9 Restart=on-failure
  10 SuccessExitStatus=3 4
  11 RestartForceExitStatus=3 4
  12 
  13 # Hardening
  14 ProtectSystem=full
  15 PrivateTmp=true
  16 SystemCallArchitectures=native
  17 MemoryDenyWriteExecute=true
  18 NoNewPrivileges=true
  19 
  20 [Install]
  21 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