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README-Docker.md

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Docker Container for Syncthing

Use the Dockerfile in this repo, or pull the syncthing/syncthing image from Docker Hub.

Use the /var/syncthing volume to have the synchronized files available on the host. You can add more folders and map them as you prefer.

Note that Syncthing runs as UID 1000 and GID 1000 by default. These may be altered with the PUID and PGID environment variables. In addition the name of the Syncthing instance can be optionally defined by using --hostname=syncthing parameter.

To grant Syncthing additional capabilities without running as root, use the PCAP environment variable with the same syntax as that for setcap(8). For example, PCAP=cap_chown,cap_fowner+ep.

To set a different umask value, use the UMASK environment variable. For example UMASK=002.

Example Usage

Docker cli

$ docker pull syncthing/syncthing
$ docker run -p 8384:8384 -p 22000:22000/tcp -p 22000:22000/udp -p 21027:21027/udp \
    -v /wherever/st-sync:/var/syncthing \
    --hostname=my-syncthing \
    syncthing/syncthing:latest

Docker compose

---
version: "3"
services:
  syncthing:
    image: syncthing/syncthing
    container_name: syncthing
    hostname: my-syncthing
    environment:
      - PUID=1000
      - PGID=1000
    volumes:
      - /wherever/st-sync:/var/syncthing
    ports:
      - 8384:8384 # Web UI
      - 22000:22000/tcp # TCP file transfers
      - 22000:22000/udp # QUIC file transfers
      - 21027:21027/udp # Receive local discovery broadcasts
    restart: unless-stopped
    healthcheck:
      test: curl -fkLsS -m 2 127.0.0.1:8384/rest/noauth/health | grep -o --color=never OK || exit 1
      interval: 1m
      timeout: 10s
      retries: 3

Discovery

Note that Docker's default network mode prevents local IP addresses from being discovered, as Syncthing is only able to see the internal IP of the container on the 172.17.0.0/16 subnet. This will result in poor transfer rates if local device addresses are not manually configured.

It is therefore advisable to use the host network mode instead:

Docker cli

$ docker pull syncthing/syncthing
$ docker run --network=host \
    -v /wherever/st-sync:/var/syncthing \
    syncthing/syncthing:latest

Docker compose

---
version: "3"
services:
  syncthing:
    image: syncthing/syncthing
    container_name: syncthing
    hostname: my-syncthing
    environment:
      - PUID=1000
      - PGID=1000
    volumes:
      - /wherever/st-sync:/var/syncthing
    network_mode: host
    restart: unless-stopped
    healthcheck:
      test: curl -fkLsS -m 2 127.0.0.1:8384/rest/noauth/health | grep -o --color=never OK || exit 1
      interval: 1m
      timeout: 10s
      retries: 3

Be aware that syncthing alone is now in control of what interfaces and ports it listens on. You can edit the syncthing configuration to change the defaults if there are conflicts.

GUI Security

By default Syncthing inside the Docker image listens on 0.0.0.0:8384 to allow GUI connections via the Docker proxy. This is set by the STGUIADDRESS environment variable in the Dockerfile, as it differs from what Syncthing would otherwise use by default. This means you should set up authentication in the GUI, like for any other externally reachable Syncthing instance. If you do not require the GUI, or you use host networking, you can unset the STGUIADDRESS variable to have Syncthing fall back to listening on 127.0.0.1:

$ docker pull syncthing/syncthing
$ docker run -e STGUIADDRESS= \
    -v /wherever/st-sync:/var/syncthing \
    syncthing/syncthing:latest

With the environment variable unset Syncthing will follow what is set in the configuration file / GUI settings dialog.