2016-07-21 EDIT: add screenshot of web ui

A quick tutorial on getting Syncthing up and running on Ubuntu Touch, without needing r/w on system.

1. Access the terminal on the device, using either SSH, the terminal app, or adb shell.

2. Download and extract the tarball for arm64 (or another arch, depending on your device - I set it up on the M10 which is 64bit). The following sequence of commands will be pretty much what needs doing:

   # I like a separate dir for storing downloaded programs
   mkdir apps
   
   # download (note: you could download through the browser - same result)
   cd Downloads
   VERSION="0.13.10" # set this to the version you want to install
   wget https://github.com/syncthing/syncthing/releases/download/v${VERSION}/syncthing-linux-arm64-v${VERSION}.tar.gz
   
   # extract to the apps dir
   tar xzf syncthing-linux-arm64-v${VERSION}.tar.gz -C ~/apps/
   
   # rename for neatness
   cd ~/apps
   mv syncthing-linux-arm64-v${VERSION} syncthing
   
   # now, the tarball is still in ~/Downloads,
   # and the syncthing files are in ~/apps/syncthing
   

3. Now you can run syncthing by executing ~/apps/syncthing/syncthing. (You can symlink it to somewhere on your path for easier access if you want.) You’ll probably want it to start automatically though - in that case create ~/.config/upstart/syncthing.conf with the following contents (ref. this askubuntu answer):

   description "run syncthing on startup"
   author "Your Name"
   
   start on started unity8-dash
   respawn
   exec /home/phablet/apps/syncthing/syncthing
   

4. It should now start automatically when you login to your device. You can now check the status of the upstart service with $ status syncthing, and control Syncthing through it’s web ui at http://localhost:8384.

Syncthing web ui running locally on the tablet

Beware that since this is a service that is running constantly and performing a lot of disk operations and using the network, it could chew through the battery quicker than expected…