Syncthing is a file synchronization tool. I decided to try it after seeing this post on hacker news. Many posts have been written about how awesome it is, and this is another one of those -- I'm really having fun with it.

Setup

I mainly run syncthing on three devices -- my Android phone, my server, and my laptop. I ended up switching to it because I upgraded my laptop to Ubuntu 20.04, and this broke Unison, which I had previously been using to synchronize a few folders between my server and laptop. After several hours wasted didn't solve the issue, I gave up on it altogether, and I'm glad I did.

Setup was straightforward on my Ubuntu laptop.

On the server, I had to do a few manual steps. After adding the apt rep and installation, I copied a systemd unit file from here. I wasn't familiar with the @.server and the User=%i syntax of unit files, and I still can't find it documented anywhere. This confused me for a bit, but eventually I got the file named properly, reloaded unit files with systemctl daemon-reload, and got the service running with systemctl enable and systemctl start syncthing@igor47.service.

Next, I wanted to get into the configuration web GUI. I used a local tunnel:

$ ssh -L 4567:localhost:8384

I was then able to visit localhost:4567 in my local browser and configure syncthing on the server. I picked a custom port for the syncthing protocol, and punched a firewall hole for incoming connections on that port. Also, I picked a custom port for the web GUI server, so I wouldn't conflict with other users who might want to enable their own syncthing. I set the web GUI to only listen on localhost, and then added a reverse proxy to this port from my web server config.

  ProxyPass /syncthing/ http://localhost:12345/
  ProxyPassReverse /syncthing/ http://localhost:12345/

On my phone, I wanted syncthing to be able to write stuff onto the SD card. Apparently, this is not currently possible. I worked around it by granting Syncthing root permissions, which works for me on my rooted Lineage android build. YMMV.

What I use syncthing for?

• removed google photos from my phone and allowed syncthing to sync photos directly to my laptop. This is especially handy when I use my phone as a scanner (to take photos of documents for archival), since I then immediately have them available for email. It's nice to be off Google photos -- one step closer to a google-free life!
• syncing my documents folder between laptop and server
• local cache of music. I prviously used dsub to play my music collection, and occasionally had to fight it's cache system to convince it that I really wanted it to cache my entire music library. Now, I just syncthing my music collection onto the SD card in my phone, and then play it with Pulsar
• i use a text-based email reader (mutt) which I access while SSHed into my server. Dealing with attachments can be annoying. Previously, I would save them to a web scratch folder and open them in a browser. Now, I simply keep a syncthinged scratch folder and throw them into there -- they're immediately accessible on my laptop.