Set Up Syncthing for Continuous Peer-to-Peer File Sync

Skip the Cloud, Sync Directly

Syncthing does something most sync tools won’t: it moves your files directly between your own devices, with no server in the middle, no subscription, and no company holding copies of your data. Getting it running takes about 20 minutes, and once it’s set up, it keeps folders in sync across as many devices as you want – continuously, automatically, and without touching the internet unless your devices happen to be on different networks.

What Syncthing Actually Does and Why It Matters

Syncthing is open-source software that uses the Block Exchange Protocol to detect file changes and push only the modified chunks of data between devices. Unlike Dropbox or Google Drive, there is no central server that stores your files in transit. Your data travels encrypted, peer-to-peer, from one machine directly to another. If both devices are on the same local network, the sync happens entirely on that network – no internet traffic at all.

The software runs as a background process on each device and exposes a local web interface, typically at http://127.0.0.1:8384, where you manage everything. There are no accounts to create, no email addresses required, and no cloud storage costs. Each device gets a unique cryptographic device ID – a long alphanumeric string – and you authorize connections by exchanging those IDs between devices manually. That manual step is what keeps the system private: no device can join your sync network without explicit approval from you.

Syncthing supports Windows, macOS, Linux, Android, and several BSD variants. There is no official iOS app, though a third-party app called Möbius Sync exists for that platform with some limitations. For most desktop and Android setups, the official clients work without issue. The project is actively maintained, has been around since 2013, and has a clean track record on security disclosures.

One detail worth understanding before you start: Syncthing syncs folders, not individual files. You designate a folder on each device as a shared folder, and everything inside it stays in sync across all devices that share that folder. You can have multiple shared folders with different devices – for example, a work folder shared between your laptop and desktop, and a photos folder shared between your desktop and Android phone. Each folder is configured independently.

Installing and Connecting Your First Two Devices

On Linux, Syncthing is available through most package managers. On Debian or Ubuntu, add the official Syncthing repository, then run sudo apt install syncthing. To make it run automatically on login, enable it as a systemd user service with systemctl –user enable syncthing and systemctl –user start syncthing. On Windows and macOS, download the installer from syncthing.net – Windows users can also install SyncTrayzor, a wrapper that puts Syncthing in the system tray and handles autostart more cleanly than the raw binary does.

Once Syncthing is running on your first device, open the web UI at http://127.0.0.1:8384. You will see your device ID in the top right corner under “This Device” – click it to copy the full string. Go to your second device, open its Syncthing web UI, and click “Add Remote Device.” Paste in the device ID from the first machine, give it a name you will recognize, and click Save. Within a few seconds, the first device should display a prompt asking whether to accept a connection from the second device. Confirm it, and the two devices are now paired.

With the devices connected, you can create your first shared folder. On either device, click “Add Folder” in the web UI. Give the folder a human-readable label, set the folder path to a directory on disk (Syncthing will create it if it does not exist), and note the auto-generated Folder ID – both devices will use this ID to recognize that they are syncing the same folder. Under the “Sharing” tab in the folder settings, check the box next to your paired device. Click Save. The other device will then receive a prompt asking whether to accept that folder – confirm it, choose where to store the folder locally, and sync begins automatically.

The first sync can take a while depending on how much data is in the folder. Syncthing shows progress in the web UI with a percentage and an estimated time. After the initial sync completes, subsequent changes sync quickly – typically within a few seconds of a file being saved. Syncthing watches for filesystem changes using OS-level notifications, so it does not need to poll the folder repeatedly; it responds to changes as they happen.

Folder types are worth configuring correctly from the start. By default, a folder is set to “Send and Receive,” meaning both devices can modify files and changes flow both ways. You can also set a folder to “Send Only” – useful for a source device that should push files out but never have its contents overwritten by another device. “Receive Only” is the opposite, useful for a backup target that should accept incoming files but never send changes back. For most two-way sync scenarios, the default is correct, but for backup-style workflows, changing the type prevents accidental overwrites.

Keeping It Running Reliably

Syncthing handles version conflicts by keeping a hidden .stversions folder inside each shared folder when versioning is enabled. Under folder settings, the “File Versioning” tab lets you choose between Simple (keeps a set number of old versions), Staggered (keeps more versions of recently changed files, fewer of older ones), and External (passes deleted or overwritten files to a script you define). For most users, Staggered versioning with a reasonable maximum age – 30 to 90 days – gives a useful safety net without consuming excessive disk space.

If you want to sync between devices that are not on the same local network, Syncthing uses a relay server infrastructure maintained by the Syncthing community when a direct connection cannot be established. This relay traffic is still end-to-end encrypted – the relay server cannot read your data – but it is slower than a direct connection. For more reliable remote sync without relying on community relays, you can run Syncthing on a small VPS and configure it as an always-on device that holds copies of your folders and stays reachable from anywhere. That machine does not need to be powerful; a single-core instance with 1GB of RAM handles several devices and folders without strain.