http://drup.org/setting-syncthing-ubuntu-1604-server

https://docs.syncthing.net/intro/getting-started.html

https://apt.syncthing.net/

$ curl -s https://syncthing.net/release-key.txt | sudo apt-key add -

echo "deb http://apt.syncthing.net/ syncthing release" | sudo tee /etc/apt/sources.list.d/syncthing.list

$ sudo apt-get update
$ sudo apt-get install syncthing

$ syncthing

Ctrl-C to abort…

$ sudo nano ~/.config/syncthing/config.xml

change:

<address>127.0.0.1:8080</address>

to:

<address>0.0.0.0:8080</address>

USER=vagrant #or whatever

$ sudo systemctl enable syncthing@$USER.service

$ sudo systemctl start syncthing@$USER.service

Open Virtualbox, right-click on the running virtual machine, click ‘Settings', select ‘Network', click ‘Advanced', click ‘Port Forwarding', add new port forwarding rule by clicking the ‘+' icon in top right of menu, the enter:

‘Host IP': 127.0.0.1
‘Host Port': 8384
‘Guest Port': 8384

Click ‘OK' save and exit.

go to http://127.0.0.1:8384 and set up GUI Authentication User and Password

Syncthing Getting Started
https://docs.syncthing.net/intro/getting-started.html