File sync¶

Syncthing keeps the same folders on every device that needs them. It works peer to peer, with no cloud in between, and it's open source. It's for getting files onto devices, not for keeping them safe: that's what Backups are for.

How it's set up¶

flowchart LR
    nas["NAS<br/>(always on)"]
    mac["Laptops"] <--> nas
    phone["Phones"] <--> nas
    other["Other devices"] <--> nas
    nas -- "SMB" --> apps["Apps on other machines<br/>(Immich, Photoview, ...)"]

• The NAS is the hub. It runs Syncthing in Docker and is always on, so devices that are rarely online at the same time still stay in sync through it. It's also the one place that has every folder, which makes it the natural thing to back up.

• Folders, not whole drives. Each folder is shared only with the devices that need it:

  Folder	What for
  Personal files	Documents I want on every laptop
  Shared family library	One library the whole family can read and add to
  Lightroom	Catalog and photos, so either laptop can edit
  Code	Projects that aren't in git, or not yet
  Emulator saves	Continue a game on a different device

• Send & receive everywhere. Every device can change files. For a folder that should only flow one way (a phone's camera roll, say), set that device to Send Only and the NAS to Receive Only.

• Apps read the synced folders over SMB. Immich and Photoview on the Docker host mount the photo folders from the NAS rather than syncing their own copy.

Install¶

brew install syncthing
brew services start syncthing   # starts at login; web UI on http://127.0.0.1:8384

syncthing:
  image: lscr.io/linuxserver/syncthing:latest
  container_name: syncthing
  environment:
    - PUID=1000
    - PGID=1000
  volumes:
    - ./syncthing/config:/config
    - /srv/<pool>:/data          # the folders to share
  ports:
    - 8384:8384                  # web UI
    - 22000:22000/tcp            # sync protocol
    - 22000:22000/udp
    - 21027:21027/udp            # local discovery
  restart: unless-stopped

Pair devices by device ID in the web UI, then share a folder from one side and accept it on the other.

Settings worth changing¶

• File versioning on the NAS. In each folder's settings on the NAS, set File Versioning to Simple or Staggered. Files deleted or replaced from another device are moved into .stversions/ instead of being removed. Only the hub needs it, so laptops don't fill up with old versions.

• .stignore: ignore everything, then include what you want. I don't list what to leave out. I list what to sync, and end the file with * so everything else is ignored:

  .stignore

  // Junk first, so it's dropped even inside included folders
  (?d).DS_Store
  (?d)Thumbs.db
  node_modules
  .venv
  
  // What to sync
  !/Documents
  !/Papers
  !/notes.md
  
  // Everything else
  *
  

  Patterns are read top to bottom and the first match wins, so the ! includes must come before the final *. The advantage is that nothing appears on every device by accident. A new folder, a big download or an app's cache stays local until you add it to the list.

  The (?d) prefix lets Syncthing delete those files when they're the only thing stopping a folder from being removed. .stignore itself isn't synced, so each device keeps its own. To share one list, put the patterns in a synced file and add #include .stglobalignore to each device's .stignore.

• Watch for changes (on by default) syncs within seconds of a save. The full rescan interval can then be long, such as an hour, which keeps the disks quiet.

• Over Tailscale, devices find each other on the tailnet without relays. Syncthing also encrypts everything itself, so nothing else is needed.